National Products Receiver NC-300 User's Manual
Contents
1. Lie xe ACCESSORY SOCKET va ACCESSORY SOCKET CALIBRATOR v8 SOCKET 6BE6 642 1 o 0 32 2 5 o 6 0 2 0 CONDITIONS im er AC LINE VOLTAGE 15 VOLTS 6ALS HIGH IMPEDANCE VACUUM TUBE VOLTMETER USED sac 0 CONTROL SETTINGS BAND 1 8 2 a m MODE EXCEPT WHEN MEAS 2 5 URING VB WHEN IT IS AT cw yg RFG MAXIMUM CLOCKWISE POSITION 6846 26 SELECT OFF A AFG MAXIMUM CLOCKWISE POSITION 1e POSITION 1 4 150 TONE OFF 06 150 ANL OFF CAL OFF 6846 2 ALL VOLTAGES MEASURED FROM SOCKET PIN TO CHASSIS ALL VOLTAGES DC EXCEPT AS NOTED TOLERANCE 10 FRONT Figure 5 Tube Socket Voltages ANT TRIMMER xi CALIBRATOR SOCKET vis 128 IST MIXER TUNING T4 CRYSTAL FILTER TUNING RYSTAL FILTER TUNING Rag METER ADJUST MAIN TUNING X DO NOT DISTURB THE SETTING OF THE SCREWS AT THE TOP OF THESE CANS Figure 6 Component Locations Top View of Receiver EA C690 Figure 7 Capacitor and Alignment Adjustment Locations Bottom View 16 Figure 8 Resistor and Miscellaneous Component Locations Bottom View 17 CD ser swircw AT 20 METER BAND WITH CAL SET HAIRLINE AT CENTER OF CUTOUT TUNE IN KNOWN SIGNAL OF 14 2 Mc MAKE SUR2. TION FOR PROPER GAIN ie aren lh rone CONTROL 150 MITER Sw DETECTOR NOISE LIMITER p ON Limit ER CONTROL x2 ACCESSORY SOCKET vac Figure 10 Schematic Diogram 23 amp 24 INSTRUCTIONS FOR THE NATIONAL XCU 300 CRYSTAL CALIBRATOR UNIT GENERAL The type XCU 300 Crystal Calibrator Unit is designed expressly for use within NC 300 receivers It utilizes electron coupled crystal oscillator circuit The calibrator provides crystal controlled marker frequencies of 100 kilocycles When plugged iam the Crystal Calibrator Socket Xl the XCU output is coupled to the RF amplifier input circuit Selection of the 100 kilocycte crystal controlled signal is made possible by the front panel mounted OFF CAL switch on the receiver INSTALLATION The XCU 300 Crystal Calibrator is installed in the NC 300 receiver by plugging the unit into the Crystal Calibrator Socket X1 on top of the chassis OPERATION The XCU 300 Crystal Calibrator provides a means of checking the accuracy of the frequency calibration of the receiver The front panel mounted Calibrate switch marked OFF CAL connects B plus to the To check calibration accuracy tune in the desited marker Calibrator for instantaneous service signal with the MODE switch set at CW and zero beat the receiver with the harmonic marker
3. 3 50 mmf A12502 4 Mica 1 000 mmf 2 7666 69 C3 Ceramic 100 mmf D825C 304 300 vdcw 4 Ceramic 0 01 mfd 100 0 K946 2 Mica 2 700 mmf 5 666 28 C5 Ceramic 0 01 mfd 100 0 K946 2 500 vdew C6 Ceramic 100 mmf D825C 304 C47 Ceramic 240 mmf 2 A14157 Ceramic 0 01 mfd 100 0 K946 2 300 vdew C8 Mica 470 mmf J665 56 C48 Ceramic 12 mmf 15 CC20UJ 120 C9 Ceramic 0 01 mld 100 0 K946 2 Ceramic 15 mmf D825 D 467 C10 Ceramic 0 01 mfd 100 0 946 2 50 Mica 470 mmf 1665 56 Ceramic 39 mmf D825D 455 C51 Ceramic 0 01 mfd 100 0 K946 2 C12 Ceramic 62 mmf D825D 472 CS2 Air Variable 12 100 mmf A12501 C13 Ceramic 1 mmf 20 D825D 470 CS3 Mica 470 mmf 1665 56 14 Ceramic 59 mmf D825D 455 C54 Ceramic 100 mmf D825C 304 C1S Ceramic 6 8 mmf 5 D825D 475 C55 Ceramic 5 mmf D825D 401 16 Mica Variable 5 20 mmf 12312 CS6 Paper 0 01 mfd 4208 Q693 19 part of 400 vdew 17 Ceramic 5 mmf 120 D825D 401 57 Ceramic 47 mmt D825D 466 C18 Ceramic 01 mfd 100 0 K946 2 58 Paper 0 01 mfd 209 Q693 19 C19 Differential Air 25 mmf 12510 400 vdew part of CF1 C59 Paper 0 001 mfd 2205 Q693 1 C20 Ceramic 3 mmf 40 25 mmf D825D 499 400 vdew C21 Ceramic 39 mmf D825D 455 C60 Paper 0 01 mfd 420 Q693 19 C22 Mica 120 mmf 557 1665 34 400 vdew C23 Mica 150 mmf 5 1665 37 C61 Paper 0 47 mfd 120 0693 89 C24 Ceramic 5
4. 330 ohms 1569 19 Fixed 270 000 ohms 1569 54 Fixed 100 ohms 1569 13 Fixed 470 000 ohms 1569 57 Fixed 47 000 ohms J569 45 Fixed 470 000 ohms J569 57 Fixed 220 000 ohms 1569 53 Variable 1 megohm with 11697 Fixed 470 ohms J569 21 SPDT switch S3 Fixed 68 000 ohms J569 47 Fixed 220 ohms 2 watts J572 17 Fixed 100 ohms 569 13 Fixed 100 ohms 1569 13 Fixed 100 000 ohms 569 49 Fixed 10 000 ohms 1569 37 Fixed 22 000 ohms 1569 41 Fixed 470 000 ohms 1569 57 Fixed 2 200 ohms 1569 29 Fixed 10 000 ohms 1569 37 Fixed 220 ohms 5 569 108 Fixed 4 3ohms 5 watt K098 48 Fixed 1 500 ohms 5 1569 87 Fixed 4 7 megohms 1569 69 Fixed 12 000 ohms 1569 38 Fixed 10 000 ohms 1569 37 Fixed 1 megohm 569 61 Fixed 10 ohms 569 1 Fixed 330 1200 ohms 10 1 2 watt value individually chosen to meet requirements 1569 Resistors 10 tolerance 1 2 watt except as noted of each receiver Fixed 1 megohm 1569 61 Crystal Filter Assembly C12721 Fixed 1 megohm 1569 61 ANL 811800 Fixed 1 000 ohms 5 569 139 Knob Tone BI1801 Fixed 330 ohms 5 1569 140 Knob IF B11802 Fixed 560 ohms J569 22 Knob Zero A11969 Fixed 2 200 ohms 1569 29 CWO B11804 Fixed 1 megohm 1569 61 Knob AFG 811805 Fixed 1 200 ohms 5 1569 79 Knob Antenna Trimmer B11803 Fixed 56 ohms 55 1569 141 Knob OFF CAL 11969 Var 100 000 ohms inc1 56 13597 Knob Band
5. 9 A potentiometer is pro vided on the chassis co zero set the meter 1 11 TUBE FUNCTIONS The following table lists the types and functions of al tubes used in che NC 300 IUBE TYPE FUNCTION 6826 R F Amplifier 6 6 Oscillator 6 7 First Mixer 6 6 Second Converter 68 6 First LF Amplifier 6BJ6 Second I F Amplifier GALS Detector and Noise Limiter 6BEG C W Oscillator Heterodyne Detector 12AT7 S Meter Amplifier and A F Amplifier GAQS Audio Output Amplifier SY3GT High Voltage Rectifier Voltage Regulator Current Stabilizer s KC OFF RESONANCE 16 SELECTIVITY CHARACTERISTIC SELECT SWITCH AT OFF 2519 79 42 Ke OFF RESONANCE CRYSTAL FILTER SELECTIVITY IF SWITCH AT 3 5XC 2 Figure 1 I F and Crystal Filter Selectivity Characteristics 3 1 12 POWER REQUIREMENTS The NC 300 requires 105 130 vole 50 60 cycle AC source of supply Power consumption is approx imately 60 watts 1 13 CALIBRATOR SOCKET A socket is provided on the chassis to permit in sertion of the National type XCU 300 crystal cali brator unit The OFF CAL switch on the front panel of the NC 300 provides the
6. keyed the NC 300 will automatically mute Since the muting circuit is well filtered no key clicks should be heard The receiver now 2 5 ANTENNA A two terminal strip 15 provided for connection of antennas fed by unbalanced transmission line sys tems Usually the most efficient antenna is the one which has been tuned and adjusted for optimum transmitting results For the 40 80 and 160 meter bands a single wire antenna of between 15 and 40 feet is recommended This should provide ample signal pickup and reduce the likelihood of inter ference from strong undesired signals outside the IF passband Switching the antenna from the transmitter to the receiver is most easily accomplished by means of a relay actuated by the RELAY terminals of the NC 300 Any of the popular dipoles beams etc which are fed with 50 to 70 ohm coaxial cable will be ideal In installations where it is desired to use an already DRE gt FINAL AMPLIFIER 100K To TRANSMITTER CONTROL CIRCUITS BLOCK METHOD RELAY METHOD RECOMMENDEO MUTING INSTALLATIONS DIPOLE NORMALLY CLOSED EXTERNAL OK CONTACTS ON ANY RF GAIN CONVENIENT RELAY CONTROL IN THE TRANSMITTER CONTROL SYSTEM E LEADS MUST BE SHORT TP XMTR CIRCUITS MUTE RECOMMENDED ANTENNA CHANGEOVER AND SHORTING RELAY INSTALLATION METHOD OF WIRING EXTERNAL RF GAIN CONTROL CONNE
7. mc 10 28 0 29 7 mc 6 49 5 54 5 mc with converter 2 143 5 148 5 mc with converter 11 4 220 225 mc with converter 1 3 CONTROLS The following controls appear on the front panel of the NC 300 Tuning Phasing A F Gain Antenna R F Gain Cal Set Tone 1 2 3 ANL C W O Mode ACC AM CW SSB Xmr Rec Selectivity Off 1 2 3 Band 1 4 IF SELECTIVITY The IF pass band may be set at 500 cycles 3 5 ke or 8 kc at the operatot s discretion Figure 1 shows the IF selectivity characteristics With the ever incte sing amount of activity on the amateur bands 2 variable selectivity is a must on any modern com munications receiver For copying CW signals in the midst of heavy QRM the 500 cycle bandwidth is invaluable The 3 5 kc position is provided to im prove the readability for phone operation when inter ference is heavy and the widest range 8 kc makes it possible to copy net stations or roundtables with a minimum of retuning The bandwidth is also important when using the converters in the VHF ranges The operator will find many varied combina tions of crystal and IF selectivity adjustments that will best suit his particular receiving requirements 1 5 CRYSTAL FILTER Exhaustive tests have proved that the crystal filter is a necessary adjunct to communications re ceivers Three degrees of crystal selectivity are provided The Phasing control inserts the notch in the sele
8. means for turning the SECTION 2 2 I GENERAL All installation procedures are described in this section Figure 2 locates connection points on the receiver and depicts typical installations Before proceeding with installation raise the hinged cover of the receiver and make sure that all cubes are seated firmly in their sockets 2 2 LOUDSPEAKER A National cype NC 300TS speaker or any permanent magnet dynamic speaker with an 8 ohm voice coil may be connected to the speaker terminals No polar ity need be observed 2 3 CHANGEOVER RELAY A terminal marked Relay is mounted at the rear of the receiver When the Xmt Rec switch is set at Xmt the two Relay terminals are shorted Thus they may be used to complete any external relay circuit whether it be AC or DC so long as the circuit requirements do not exceed 5 amps at 125 volts AC A typical circuit might consist of a 110 volt AC antenna change over relay in parallel with the transmitter plate supply relay with one side of the AC line broken by the NC 300 Relay connector strip When connected in this manner the Xmt Rec switch on the receiver front panel performs all the required change over operations for the entire station 2 4 MUTING A Stdby Mute terminal strip is mounted at the rear of the receiver These three terminals provide for two entirely different methods of receiver muting during transmitting periods With no external con nections made to the strip the receiver
9. mmf 20 D825D 401 150 vdew C25 Ceramic 3 mmt 10 25 mmf D825D 449 C62 Electrolytic 40 40 20 mfd A13183 C26 Ceramic 0 01 mfd 100 0 K946 2 250 vdcw C27 Ceramic 100 mmf 5 D825C 342 C63 Mica 0 001 mfd 1 000 vdew J667 50 C28 Paper 0 047 mfd 207 Q693 28 64 Ceramic 5 mmf D825D 401 C29 Mica 910 mmf 12 300 vdew 1666 67 C65 Mica 0 001 m d 1 000 vdew 667 50 C30 Mica 3 600 mmf 2275 1666 66 C66 Mica 0 001 mfd 1 000 vdew 1667 50 300 vdcw C67 Ceramic 0 01 mfd 100 0 K946 2 C31 Ceramic 0 01 mfd 100 04 K946 2 C68 Mica Variable 4 sections A12493 C32 Paper 0 047 mfd 202 Q693 28 cach 5 80 mmf 400 vdcw Part of C68 C33 Ceramic 5 mmf 20 D825D 401 COBB Part of C68 C34 Mica 150 mmf 5 1665 37 C68C Part of C68 C35 Mica 150 mmf 5 1665 37 C68D Part of C68 C36 Mica 1 000 mmf 22 1666 69 C69 Mica Variable 4 sections 12493 300 vdcw each 2 2 40 mmf C37 Mica 3 600 2 1666 66 C69A Part of C69 300 vdcw C69B Part of C38 Paper 0 047 mfd 320 9693 28 C69C Part o C69 400 vdew C69D Part of C69 C39 Paper 0 047 mfd 20 0693 28 C70 Air Variable 2 8 19 7 mm 12744 400 vdcw 71 Variable 2 8 19 7 mmf 12744 C40 Paper 0 1 mfd 400 vdew Q693 34 C72 Air Variable 2 8 19 7 mmf A12744 PARTS LIST CONT D RESISTORS CONT D Description Natco Type CAPAC
10. oscillator plug ia headphones or connect a loudspeaker set the MODE switch at CV and the CWO kaob 3 4 of a division knob marking clockwise from center 10 Adjust L16 for zero beat 4 3 SECOND CONVERSION AND CRYSTAL FILTER ALIGNMENT The first IF frequency of the NC 300 is 2215 kc 3 kc The exact frequency is determined by the tolerance of the crystal in the crystal filter For this reason the exact setting of the signal generator will be determined by the crystal peak frequency The following alignment procedure must be used 1 Set the BAND switch at 80 meters 2 Move the output lead of the signal generator to connect to the stator of the first mixer tuning capacitor center section of the main tuning capaci tor The ground lead may be connected to the capacitor frame 3 Set the IF control at position 1 4 Set the SELECT control at position 3 5 Set the PHASING control at its center 6 Tune the signal generator slowly from 2212 to 2218 kc observing the S Meter closely The crystal peak will be evidenced by a sharp upward swing of the S Meter pointer Carefully set the signal generator at the exact peak of the crystal frequency and leave it at chat setting 7 Set the SELECT control at OFF and the IF con trol at position 2 8 Align the 2215 kc IF stage and crystal filter by first adjusting 1 6 This is the second conversion oscillator tuned circuit and must be tuned very slowly and carefully The oscillato
11. that the switch is actuated removes the RF gain control from the RF stage and allows the RF amplifier to run at full gain This affords better reception of weak signals It should be noted that regardless of the switch posi tion the gain of the second 1 amplifier is always adjustable by means of the RFG control The AFG control may then be returned to the desired position To place the RFG control into the RF amplifier cir cuit rotate the AFG control to its full counterclock wise position so that the switch is thrown then the AFG control may be reset This setting affords an improvement in reception when strong interfering Turning the control clockwise increases turning it counterclockwise decreases The second function is the switching signals are encountered BAND CHANGE SWITCH This control is used to select the desired frequency band to be tuned Gear reduction is employed in the NC 300 to assure smooth working control and positive locking switch positions For this reason the BAND control makes more than one revolution in switching through all 10 bands The band to which the receiver is set is identified by the scale visible on the slide rule dial since the dial and the BAND switch are mechan ically coupled Positive stops are provided at both ends of che BAND control travel PHONES JACK Headphones of the high impedance type may be plugged into the PHONES jack using a standard two circuit phones plug There is no DC v
12. the XMT REC switch must be left at the REC position at all times 3 4 SINGLE SIDEBAND OPERATION Provision has been made in the NC 300 for the reception of single sideband transmissions The low 1 frequency 80 kc involved and the oscillator circuit design provide an extremely stable oscil lator with a high equivalent level of injection Make the initial adjustments as in paragraph 3 3 of this section While tuning set the MODE switch at AM until the SSB signal is located then switch to SSB Set the CWO control to receive the SSB signal Posi tion Lis used for lower sideband reception on the 160 80 and 40 meter bands position 2 for upper sideband signals on these bands The sidebands are reversed on the 20 15 11 and 10 meter bands Optimum reception is obtained by careful adjustment of the CWO control about this previous setting The selec tivity controls may be set at the positions which provide the maximum readability under a particular set of receiving conditions For single sideband reception the widest bandpass offers no particular advantage and interference elimination will probably be the criterion for choice of bandwidth settings Normally IF switch position 2 would be used Reduc tion in background noise is best effected by adjust ment of the RFG contol 3 5 MEASUREMENT OF SIGNAL STRENGTH The strength of a received signal as indicated by the S Meter will be correct only when the receiver is properly adju
13. to the other side of zero beat so that the pitch is the same as before and observe the marked reduction in output This latter dial setting is not recommended for use other than to demonstrate the single signal properties of the receiver With the receiver tuned to crystal peak an interfering signal may be attenuated by proper setting of the PHASING control since this control has little effect on the desired signal As in phone operation combinations of control settings may be selected to suit varying requirements except that it must be remembered that the crystal filter cannot be used with IF switch at position 3 It is possible by means of judicious manipulation of these controls to copy signals which would be com pletely unreadable on receivers which do not incor porate these features important aid to CW operation of the amateur station has been included in the NC 300 It is fre quently desirable for the operator to monitor his own transmitted signal while sending CW To accomplish this two gain conmols adjusted for two different signal levels are necessary The additional control may be mounted on the station control panel adjacent to the transmitter controls or at any other convenient location Connect the control as shown on Figure 2 Adjust the external control to receive the incoming signal at the desired level and adjust the RFG control of the NC 300 for comfortable monitoring level When using an external RF gain control
14. to utilize these features to full advantage For com plete appreciation of your NC 300 READ THESE INSTRUCTIONS CAREFULLY 3 1 CONTROLS Complete utilization of the operating instructions is not possible without a thorough understanding of all front panel devices See Figure 3 for the location of all controls The control designations used cor respond to the markings on the receiver ANL Automatic Noise Limiter The ANL control is used only for phone reception This control incor porates a switch which turns the limiter off when the control is rotated to its maximum counterclockwise position Turning the control clockwise just enough to throw the switch places the limiter in operation Further rotation of the control increases the limiting action Noise clipping is obtained at the expense of audio quality so a position should be chosen to provide maximum noise clipping consistent with intelligibility Noise conditions will vary with localities so the limiting level is a matter satisfactory of personal choice To provide noise limiting for CW reception the IF amplifier of the NC 300 is designed to limit on pulse interference The time constants incorporated in the grid circuits are very short to permit following fast pulses To achieve limiting action the RFG control should be advanced until overload is approached The AFG control should then be adjusied for best listening level Then the RFG control can be used to adjust f
15. will be muted whenever the Xmt Rec switch is placed in the position If muting is not desired for trans calibrator On or Off 1 14 ACCESSORY SOCKET The accessory socket provided at the left rear corner of the chassis is designed to accept suitable external accessories within the power limitations of 1 5 amperes 6 3 volts A C and 25 milliamperes at 150 volts D C See the schematic diagram for pin connections etc Refer to Section 3 for instructions on the use of external accessories INSTALLATION miter monitoring etc a jumper wire may be con nected between STBY and GND operates regardless of the Xmt Rec switch position For remote switching of the receiver connect leads to Stdby and Gnd leaving the switch in the Xmt position If CW break in operation is desired the MUTE and GND terminals may be used to mute the receiver To accomplish this it is necessary to find a point in the transmitter circuitry that will provide a source of negative 22 to 50 volts when the trans mitter is A 100 000 ohm resistor connected to the grid of a keyed stage which develops at least minus 22 volts with the key down will suffice Since grid blocking is employed in the receiver no current will be drawn from the transmitter Connect the minus 22 vole lead to the terminal marked MUTE and the transmitter chassis to the terminal marked GND Leave the Xmt Rec switch in the Receive position When the transmitter is turned on or
16. 66 2 OG Dial Drum Cord Assembly B13000 T13 Antenna Transformer B15297 Pi Power Cord and Plug A12612 AG aicut bind 21 Description PARTS LIST CONT D Natco Type Description Natco Type Iz T14 115 T17 TIB T22 123 T24 T25 T26 T27 T28 T29 T30 TBI TB2 TB3 TB 121 v2 v3 4 v5 v6 v7 v8 v9 VIO vil MISCELLANEOUS CONT D MISCELLANEOUS CONT D lst Mixer Transformer 40 meter band 1st Oscillator Transformer 40 meter band Antenna Transformer 20 meter band Ist Mixer Transformer 20 meter band 1st Oscillator Transformer 20 meter band Antenna Transformer 15 meter band Ist Mixer Transformer 15 meter band 1st Oscillator Transformer 15 meter band Antenna Transformer 11 meter band 151 Mixer Transformer 11 meter band tse Oscillator Transformer meter baad Antenna Transformer 10 meter band lst Mixer Transformer 10 meter band lst Oscillator Transformer 10 meter band Antenna Transformer X band 1st Mixer Transformer X band 1st Oscillator Transformer X band Antenna Terminal Board Speaker Tetminal Board Relay Terminal Board Standby Mute Terminal Board Tube type 6BZ6 Tube type 6BA7 Tube type 6BE6 Tube type 6 6 Tube type 6BJ6 Tube type 6AL5 Tube type 6 Tube type 6BEG Tube type 12AT7 Tube type 6A
17. CT RF OUTPUT PLUG IN CONNECT EXTERNAL FROM 14 2 OR METER XCU 300 RF GAIN CRYSTAL CONVERTER CRYSTAL CALIBRATOR CONTROL MUTE GND CONNECT GOOD EXTERNAL GROUND REMOVE LINK AND CON CONNECT SHIELD BRAID OF COAX NECT TERMINALS TO TRANSMITTER MUTING VOLTAGE 22VDC CONNECT IN SERIES WITH RELAY ACTUATING VOLTAGE TO CONTROL ON OFF OF TRANSMITTER BY MEANS OF NC 300 XMT REC SWITCH FUSE SPEAKER ZAMP NATIONAL NC 300TS CONNECT SINGLE WIRE CONNECT TO NORMALLY OPEN CONTACTS ANTENNA OR CENTER T R RELAY TO DISABLE RECEIVER CONDUCTOR OF COAX TRANSMIT Figure 2 Typical Installation Plan 5 existing antenna with a 300 ohm balanced feedline an antenna coupler such as a balun can be used to match this antenna to the 70 ohm unbalanced input of the NC 300 The balun may be either a quarter wave section of coax or a pair of balun coils NOTE If the receiver is used in close proximity to the transmitting equipment some provision must be made to short the antenna terminals to ground during transmitting periods to pre vent damage to the antenna coils This is most easily accomplished by means of a relay con nected to the antenna terminals and ground The relay should be located within six inches of the antenna terminal strip to prevent exces sive pick up Connect the shield braid of the coax to terminal G and the inner conductor to the A terminal A good electrical ground shoul
18. E CAPACITOR REMAND AT THiS Oise eco scion rewove orat ev wiTHORAMING SCREW menr sioe TO PREVENT SLIPPING ome RECEIVER AND RETAINING RING FROM LEFT ENG OF NOTE PONTOON PL ENDS OF COND OF SPRING WASHER AND DAUM IAL CORD 10 PER UNT POWTER ONE TO PREVENT CORD FROM SLIPPING OFF PULLEYS MAINTAIN ax Timu POWTER MN arercace onum ser poire EXACTLY 14 2 BY SLIDING DIAL CORD AROUND PULLE LOOP comu AROUND PULLEYS CORD SHOWN EXPOSED FOR CLARITY CORD LENGTH 4 250 FEET FOR FINE ADJUSTMENT LOOSEN SCREWS RETIGHTEN 68 FOR COARSE ADJUSTMENT OF DIAL SCALE JUMP BEAD CHAIN ON SPROCKET TIGHTEN CHAIN GUIDE _ POSITION so THAT 160 METER SCALE 15 CENTERED IN DIAL WINDOW SET BANO SWITCH AT EXTREME COUNTERCLOCKWISE G POSITION CHAIN 4 CORD LENGTHS 20 EACH Figure 9 Cord Stringing Guide PARTS LIST CAPACITORS CAPACITORS CONT D cl Air Variable 3 sections 11779 Ceramic 0 01 41007 0 K946 2 CIA 7 4 40 3 mmf part of C42 Mica 220 mmf 20 J665 44 CIB 7 4 40 5 mmf part of CI C43 Mica 150 mmf 45 J665 37 CIC 14 4 80 7 mmf part of C44 Mica 150 mmf 15 J665 37 C2 Air Variable
19. F Set the XMT REC switch at REC Set the IF control at position 2 Turn the AFG control fully counterclockwise until the switch dicks then advance it approximately to mid position 9 Set the BAND switch to the desired frequency range as indicated by the slide rule dial scale 10 By means of the CAL SET knob center the hairline in the diamond shaped cutout directly above 9 the knob 11 Turn RFG control fully clockwise Power is now applied to the receiver Allow at least two minutes for the tubes to reach operating temperature before proceeding Set the AFG control to provide the desired audio level 12 Rotate the TUNING control until the desired signal is located Adjust the TUNING control very carefully for maximum S Meter reading 13 Turn the ANT TRIM and PHASING controls to obtain maximum S Meter reading These controls may be set in the absence of a signal by adjusting them to obtain a peak in the background noise 14 Set the AFG control to produce the desired listening level 15 the desired audio response Turn the contro to a position giving 16 To shut down the receiver turn the RFG control fully counterclockwise The AFG control should be used in all cases to adjust the audio output level The RFG control setting may require readjustment for true S Meter readings Refer to paragraph 3 5 Various types of interference which may be encoun tered due to adverse receiving conditions ca
20. FOR COMPLETE APPRECIATION OF YOUR NC 300 READ THE 800 IMPORTAN tuned lo tomorrow INSTRUCTION BOOK FOR THE NATIONAL MODEL NC 300 RADIO RECEIVER SECTION 1 DESCRIPTION 1 1 GENERAN 0 s dhe sensitivity and excelent NATIONAL COMPANY INC MALDEN amp MELROSE MASS ducing any trace of backlash The outward appearance of the receiver is com pletely modern and functional Cabinet and panel construction permits the receiver to be removed from the cabinet and rack mounted wirhout modification or the addition of any parts other than mounting hardware Adequate ventilation is provided by the use of convection cooling through holes in the chas sis and a perforated cabinet lid 1 2 FREQUENCY COVERAGE The NC 300 tunes all amateur bands from 160 through 10 meters plus a 30 35 mc band designated as the X band for use with external converters for the 6 2 and 1 1 4 meter bands Each dial scale is calibrated for only one band Each scale has band limit marking plus underscoring to indicate the phone portion of the band The dial drum rotates with the band switch so that only the dial scale associated with the band being tuned is visible The following table gives the frequency of each band tuned by the NC 300 BAND FREQUENCY RANGE 160 18 2 0 mc 80 3 5 4 0 me 40 7 0 7 3 mc 20 14 0 14 4 mc 15 21 0 21 5 mc 11 26 5 27 5
21. ITORS CON Ti Air Variable 2 8 19 7 A12744 Fixed 1 megohrs j 569 61 Air Variable 2 8 19 7 12744 Fixed 1 megohm 1569 61 Variable 2 8 19 7 mmf A12744 Fixed 27 000 ohms 1569 42 Aic Variable 2 8 19 7 A12744 Fixed 100 000 ohms 569 49 Air Variable 2 8 19 7 mmf 12744 Fixed 100 ohms 1569 13 Paper 0 047 md 20 Q693 28 Fixed 10 000 ohms 569 37 400 vdew Fixed 10 000 ohms 569 37 Paper 0 022 mfd 400 vdew 0693 23 Fixed Wire Wound 1 800 1959 26 Paper 0 022 mfd 400 vdew 0693 25 ohms 555 5 watts Paper 0 022 mfd 400 vdcw 0693 23 Fixed 39 000 ohms 2 watts 572 44 Ceramic 100 mmf 5598 D825C 342 Variable Wire Wound 413598 10 000 ohms Fixed 68 000 ohms J569 47 Paper 0 001 mfd 20 400 vdew Q693 1 Ceramic 0 005 mfd 100 0 946 1 Fixed 100 000 ohms 569 49 Ceramic 15 mmf D825D 467 Fixed 68 000 ohms 1569 47 Mica Variable 3 5 35 mmf A12312 Fixed 500 olus 2122 1569 87 Fixed 270 000 ohms 1569 54 Fixed 33 000 ohms 1569 43 Variable Wice Wound A12166 1 000 ohms Fixed 3 300 ohms 569 31 Variable 500 000 ohmstwith 413596 Paper 22 mf 400 vdew 693 40 10 tolerance 500 volts working on all capacitors unless otherwise noted RESISTORS Fixed megohm 1569 61 SPST switch 57 Fixed 33 ohms J569 7 Fixed 1 megohm 1569 61 Fixed
22. If the slide rule dial does not read accurately correction should be made by adjusting the front panel mounted CAL SET control Only a slight adjustment of the CAL SET control should be necessary If calibration is far off the RF coils associated with the band being checked probably require realignment and teference should be made to Section 4 25 PARTS LIST Symbol Description Natco Type Ceramic variable 6 20 mmf E311 2 C2 Ceramic 10 mmf 500 vdcw 872 1 Ceramic 3 mmf 500 vdew 1695 4 C4 Ceramic 220 mmf 500 vdcw K946 24 L1 5 mh type R 100 SA 2608 P1 Octal 783 1 R1 Fixed 4 7 megohms 1 2 W 1569 69 R2 Fixed 470 000 ohms 1 W 1571 57 VI GAKG Y1 Quartz 100 Kc A16126 c2 NOTE CAPACITOR VALUES MICROFARADS EXCEPT AS NOTED RESISTOR VALUES OHMS K 1 000 MEG 1 000 000 Figure 11 XCU 300 Schematic Diagram SM 3000 ER481 9 56 R F MIXER OSCILLATOR METERS 80 40 TIG 20 119 15 T22 I T25 10 T28 2 8 19 7
23. Q5 Tube type 2 15298 B14908 B15300 B15299 814910 815302 815301 B14905 B15304 15303 14907 B15305 B15306 B14812 B15307 B15308 B14911 A12617 A12616 A12615 22 Tube type 5Y3 Tube type 4 4 Crystal Calibrator Socket A12831 Accessory Socket 12831 S Meter Lamp Socket A12284 Dial Light Socket A11721 Dial Light Socket A11721 Dial Light Socket A11721 Fuseholder A12013 Ceystal Unit 2215 kc A12704 part of CF1 RESISTORS CONT D Fixed 100 000 ohms 110 569 49 1 2 watt Fixed Vire Wound 330 ohms 17436 1 109 10 watts Fixed 2 2 ohms 11026 1 watt 098 24 x CALIBRATOR SOCKET ax RF GAIN B CONTROL E ces GREEN SY3GT 6 3 B CURRENT Prec STABILIZER li mare iss vac 62 RE GAIN LH BA iu VOLTAGE 4 REGULATOR 082 nare CAPACITOR VALUES MICROMICROFARADS EXCEPT AS NOTE RESISTOR VALUES OWNS x Ipo M 10 0000 Y VALUE SELFCTEC IN PROCUCTION FOR PROPER GAIN 14 3 ni M RE GAN MICROFARADS EXCEPT AS NOTED
24. Switch A11917 Resistors see Page 22 PARTS LIST CONT D Symbol Description Te Type Description Natco Type 4 MISCELLANEOUS CONT D MISCELLANEOUS CONT D E10 Knob Main Tuning B13599 51 Band Switch 8 wafers Ell Knob Mode 11916 13 poles 6 positons knob Selectiviey Hibbs SIA Wafer 2 poles 8 positions 0212376 Pis 111807 SiB Wafer 2 poles 8 positions 12373 113 11606 SIC Wafer 1 pole 8 positions 812372 SID Wafer 1 pole 8 positions D12372 m Lamp S Meter type 47 A12285 SIE wee 1 pole 8 positions E 12 Lamp Dial type 47 A12285 d san 5 b B Lamp Dial type 47 A12285 MO 5 B positions BU Lamp Dial type 47 12285 3 mele 2 poles 8 posicions 2375 SE 52 Svcs 1 wafer 126 sitions J2 Converter Input Jack 1199 5 porre L1 Choke 41 miceohenties 14904 99 Swatch SEDIS Md mounted on R51 L2A Inductor Variable iron core RS T 54 Selectivity Switch 1 wafer 1312511 T3 primary part of T3 2 L2B Inductor variable iron core 2 poles positions 5 5 55 LE Selectivity Switch 3 T3 secondary part of T3 T TOM onec wafers 12 poles 3 positions v L4 inductor variable iron core 12588 Si eee jrostions 18 35 2215 ke part of CFL 28 522 3 positions ei L5 Inductor variable iron core 12415 594 a
25. ator when receiving CW signals During single sideband operation the control is set at 1to receive lower sideband signals on the 160 80 and 40 meter bands at 2 to receive the upper sideband on these bands The converse settings are used for the 20 15 11 and 10 bands OFF CAL Calibrate Switch the XCU 300 Crystal Calibrator is plugged into the receiver the CAL switch is used to turn the calibrator Off and On The test signal every 100 kilocycles so that dial calibra calibrator provides a crystal controlled tion may be checked and if necessary corrected by means of the CAL SET control TUNING The tuning knob provides a 40 to 1 KILOCYCLES Figure 4 Audio Response ratio for ease in selecting the desired signal as indicated on the slide rule dial Frequency increases with clockwise rotation of the knob XMT REC This is a two position toggle switch which may be set at XMT to mute the receiver during standby and or transmitting periods In addition it will turn the transmitter on and off if the relay terminals at the rear of the receiver have been con nected to provide this function Since the XMT REC switch performs its muting function in the audio and IF stages normal operating voltages are main tained on the oscillators and all other frequency critical circuits to ensure that no frequency drift will occur during standby periods PHASING Crystal Filter Phasing Control Maximum selectiv
26. ctivity curve so necessary to interference free reception The filter used in the NC 300 has been specifically designed ro work with the receiver IF circuitry There is but one limitation During CW operation the crystal filter cannot be used with the IF switch at the sharp position 3 1 6 TWO WAY RF GAIN CONTROL A special switch is made an integral part of the audio frequency gain AFG control so that the switch may be operated at either extreme of control rotation By means of this switch the RF gain control may be removed from the RF amplifier stage permitting the stage to operate at maximum gain regardless of the setting of the RF gain control Thus when maximum front end gain is desirable with reduced overall gain the action of the control can be restricted to the IF stages only In the presence of strong local signals the control should be switched into the RF amplifier cathode circuit to prevent overloading by retarding the RF gain control as necessary 1 7 MUTING CIRCUIT A built in muting circuit silences the NC 300 when desired without resorting to the use of relays Any point in the transmitter which supplies approximately minus 22 volts with the mansmitter on may be con nected to the muting terminals at the rear of the receiver When the transmitter is energized the audio amplifier in the receiver is cutoff to prevent feedback key clicks etc 1 8 SINGLE SIDEBAND DETECTION To receive single sideband signa
27. d be used This may be a convenient cold water pipe scraped clean of paint and oxidation or a suitable ground rod driven into the earth as close as possible to the receiver location The outstanding and characteristics of the NC 300 cannot be fully appreci ated unless every effort is made to provide proper sensitivity signal to noise antenna and ground facilities 2 6 CALIBRATOR SOCKET The Calibrator socket at the rear of the receiver chassis is factory wired so that it is only necessary to plug in the National type XCU 300 Crystal brator unit The OF F CAL switch on the front panel will then energize the calibrator when desired 2 7 ACCESSORY SOCKET This socket permits a variety of accessories to be used with the NC 300 Audio devices such as a crystal phono pickup may be connected to pins 5 and 6 Heater B AVC and ground connections are available for external converters etc IF output is connected to pin 4 for use with SSB devices and the RF Gain bus is brought to pin 1 for external control of RF Gain see paragraph 3 3 The receiver SECTION 3 OPERATION The purpose of this section is to provide the opera tor with a clear and concise understanding of the operating techniques of the NC 300 to assist him in securing maximum satisfaction from the receiver The design of the receiver circuitry provides every feature necessary for outstanding performance but a thorough knowledge of correct operation is required
28. ed in FM receivers For CW reception the IF control may also be used in its sharpest position 3 It js important to remem ber however that the IF passband in this posi is only 500 cycles wide so that the receiver tuning and CWO tuning must be adjusted very slowly and carefully The crystal filter must be off when this sharpest setting is used For the reception of CW signals the action of the crystal filter is similar to that for phone reception except that full use of the sharp selectivity position may be used without the loss of intelligibility ex perienced in phone reception When maximum selec tivity is used SELECT switch at pos must be used in tuning When the receiver is slowly ion 3 care tuned across the carrier of the received signal the beat note produced will be very sharply peaked in output at a particular audio pitch This peak in response indicates the correct receiver dial setting The setting of the CWO control must be such that the beat note peak is well within the audible range so that the receiver peak response may be readily observed After the receiver has been correctly tuned the pitch of the beat note peak may be adjusted by means of the CWO control to provide an audio tone which is pleasing to copy or coincides with any response peaks in the speaker or headphones Under these conditions the receiver will exhibit pro nounced single signal properties which may be demonstrated by tuning the receiver
29. fer d poles 3 positions vic S6 Limiter Switch SPDT mounted on R27 L6 inductor variable iron core 57 Tone Switch SPST 2295 kc part of T5 L7 Inductor variable icon 12414 R46 masa 800 Mode Switch 1 wafer B12371 S9 A C Switch SPST 82 Netised mounted on R37 e L9 oe variable core 12414 510 Xmit Rec Switch DPDT 13663 toggle 110 Inductor variable iron core 12414 mri Baer nasqa pussy 80 kc viis aa need 115 volts 50 60 cycles m ina RS T2 Audio Output Transformer 13615 x ES i 3 LF Transformer 2215 kc B12465 L13 Inductor variable iron core 12414 14 Transformer 51812302 80 k 143 aae IS 2ndOscillator Transformer 18120649 s 3 LIS RE Choke 750 microhenries 5 2868 WO Transformer 812650 17 Antenna Transformer 160 B15294 L16 Inductor variable iron core ER suco TE meter band T8 Ist Mixer Transformer 160 815294 LI7 Nor Used meter band Ist Oscillator Transformer Inductor B16653 PAARE 914906 M1 5 Meter 0 1 ma illuminated 12325 iio waaka Tran 812584 Oi Assembly C12713 QUAE meter band 93 T11 Ist Mixer Transformer 15296 O3 Dial Mounting Drum C11756 04 Dial Pointer A11814 Oscillator Transformer B1490 05 Dial Cord Assembly 119
30. generator must be adjusted to produce an S Meter reading of approximately 5 S Units When the XCU 300 is used the RFG control can be used to regulate the signal strength Make all adjustments in the order set forth in the following Alignment Chart The trimmer capacitors and inductance trimmers are located on Figures 6 and 7 The inductance adjustments are made by moving the small loop of wire inside the oscillator coil forms using an insulated alignment tool or a small diameter bakelite rod Because of the 2215 kc first IF frequency and the limited range of the trim mers images will not be readable on the NC 300 so no special precautions need be taken in this regard 4 5 SME ADJUSTMENT The S Meter balancing resistor R44 is used to obtain a zero meter reading in the absence of signal input to the receiver To make this adjustment set the controls as follows Set the RFG control just far enough in the clockwise direction to trip the AC switch Set the MODE switch at AM Set the AFG control fully counterclockwise so that the RF gain switch is actuated Ground both A terminals of the Antenna terminal strip to the chassis Adjust the S Meter balancing resistor R44 to produce a zero read ing on the S Meter This is a screwdriver adjustment located on top of the chassis 4 6 MIXER IMAGE TRAP ADJUSTMENT he mixer image trap should ordinarily not require readjustment readjustment does become necessary due to replaceme
31. he second intermediate frequency of the NC 300 must be aligned at exactly 80 kc The signal genera tor used must be capable of being set at this fre quency with precise accuracy The IF transformers are tuned by means of adjustable Fertite cores These adjustments are located on Figure 7 The IF alignment procedure is as follows 1 Disregard the Band switch setting 2 Connect the output lead of the signal generator to pin 7 of V3 the 6BE6 2nd converter tube and connect the ground lead to chassis Use a generator output connection which may be attenuated 3 Set the MODE switch at AM 4 Set the IF switch at position 3 5 Set the RFG control at 15 maximum clockwise position 6 Set the XMT REC switch at REC 7 Turn the modulation of the signal generator off and set the frequency of the generator at EXACTLY 80 kc Increase or decrease the generator output until the S Meter of the receiver indicates S 5 8 Adjust L13 1 12 1 10 L9 L7 and 1 5 in that sequence to produce maximum S Meter reading Each time a maximum is tained for any one adjustment reduce the generator output to regain the S 5 reading Failure to reduce the generator output may result in an overload condition and subsequent incorrect alignment When the above procedure is followed it is not necessary to disable the second oscillator oc AVC Spurious signals from this source will only appear if the input from the generator is too high 9 To set the CW
32. is the condition set the control on center and adjust T4 for maximum background noise 14 The following two checks may be performed to prove that the second conversion oscillator is in correct alignment 15 Set the MODE switch at CW the SELECT switch at OFF the PHASING contro at center position and the IF switch at position 3 Rotate the CWO knob about its center and listen to the back ground noise Two peaks in noise with a null between will be heard The null should occur with the CWO knob set 3 4of a knob division clockwise from center this is not the case place the CWO knob this setting and adjust 1 16 to obtain the null 16 5 the IF switch at position 2 and the SELECT switch at 3 The null should occur with che CWO knob at its center setting Set the SELECT switch at OFF The null should again appear at the CWO knob center setting If this is not the case set the CWO knob at center and adjust L6 to obtain the null 4 4 RF AMPLIFIER One of the outstanding features of the NC 300 is its accuracy of calibration In ordet to maintain this precision the signal source used for front end alignment must have the accuracy of precision crys tals A secondary standard crystal controlled will suffice or the XCU 300 Crystal Calibrator may be used Either of these last mentioned units may be used in conjunction with a standard signal generator to insure calibration accuracy Owing to the restricted f
33. ity is obtained when the crystal filter circuits are balanced at the crystal frequency The Phasing control is used to accomplish this balance In addi tion a characteristic of crystal filters is their ability to provide a pronounced null at any particular fre quency This feature is extremely useful tuning out an unwanted signal very close to the desired signal This control is operative only when the SELECT switch is at position 1 2 or 3 When the SELECT switch is at off it is important that the PHASING knob be set at mid position in order to peak the preceding IF stage IF F Selectivity Switch In order to provide the wide range of selectivity characteristics neces sary to cope with the variety of amateur operating requirements the IF switch permits the operator to select one of three different IF bandwidths Position number 1 is 8 kc wide position 2 is 3 5 kc and position 3 is 500 cps In normal phone operation the 3 5 kc position would usually be used position 3 affords the sharpest selectivity and is normally desirable for CW operation Position 1 places the IF passband at its broadest AFG Audio Frequency Gain Control Two func tions are performed by this control The first is the customary adjustment of audio output level to suit the listener the volume the volume of the RF gain control out of the RF amplifier circuit for optimum performance during CW operation Turning the AFG control fully clockwise so
34. ls satisfactorily the CW frequency oscillator CWO must supply stable output of sufficient amplitude to maintain adequate carrier re insertion voltage The single sideband detector used in the NC 300 utilizes the heterodyne detection principle 1 9 CONVERTERS AND CABINET The National types NC 300Ci NC 300C2 and NC 300C6 are broad band crystal controlled converters to tune the 11 4 2 and G meter Amateur bands respectively The slide cule dial of the NC 300 incorporates three separate dial scales to provide direct teading frequency calibration when the con verters are used with the receiver All opcrating voltages required by the converters are available at the accessory socket of the 300 The National NC 300 Converter Cabinct is designed to provide a convenient and attractive means of mount ing the converters From one to three converters may be mounted in the cabinet which matches the receiver cabinet and is identicalin size and appearance to the NC 300 speaker cabinet A four position switch is mounted on the front panel to permit operation of the ceceiver any one of the three converters without changing connections to the receiver or antenna 1 10 S METER The S Meter gives the operator a true indication of relative strength of incoming signals The meter is calibrated in S units from 0 to 9 and in decibels from S 9 to 40 db over S
35. n be minimized by adjusting the following controls in the manner described NOISE LIMITER When an AM signal is accom panied by static peaks or noise pulses of high inten sity and short duration the best signal to noise ratio will be obtained by turning On the ANL control In general it will be found that turning this control just far enough to actuate the switch will effectively minimize interference caused by external noise pulses In cases where the noise pulses are ex tremely pronounced a higher degree of noise sup pression will be realized by advancing the ANL control Advancing the control fully clockwise will introduce some audio clipping This is an inherent characteristic of all noise limiters and the operator must choose the setting which under severe con ditions will produce best readability TONE CONTROL The TONE control can be used to adjust the upper and lower cut off frequencies of the audio amplifier IF SELECTIVITY The NC 300 incorporates two separate means of adjusting its selectivity char acteristics IF and SELECT controls This para graph deals with the IF control For normal phone reception the IF switch will satisfy narrow band width requirements in position 1 8 kc or position 2 3 5 kc The 500 cycle position 3 is too narrow and should not be used for phone signals CRYSTAL FILTER SELECTIVITY AND PHASING The increased selectivity afforded by the crystal filter vill frequently prove
36. nt of L18 or C86 or inadvertent maladjustment of these components proceed as follows 1 Set the Band switch at the 20 meter band and the dial at 14 1 mes 2 Connect signal generator as outlined in par 4 4 Tune the generator to 9670 kc and adjust the output to produce an audible audio output 3 Tune C86 for minimum output 4 7 VOLTAGE DATA The voltage measurements on Figure 5 will facili tate any setvicing which might be required on the NC 300 4 8 DIAL CORD STRINGING In the event of breakage of the dial scale actuating cord or the dial pointer cord the instructions shown on Figure 9 should be studied with care before attempting replacement Failure to carry out these instructions correctly will result in incorrect indica tions of band setting and frequency The dial scale in view at the front panel MUST correspond to the frequency range being tuned 4 9 TUBE REPLACEMENT Tubes which become weak or defective should be replaced In the case of the 4 current regulator a type 6V6 may be used as a temporary substitute This substitution will sacrifice the current regu lating qualities provided by the 4H4C but will keep the receiver operative Type 4H4C regulators arc not generally available most supply houses A replace ment can be obtained from National Co or any National authorized service station A type 4H4 will not provide the required regulating action 14
37. oltage associated with the headphone circuit The loudspeaker is automatically silenced when the phones plug is inserted RFG RF Gain Control The sensitivity of the receiver is adjusted by means of this control lt may control the gain of the RF amplifier and second IF stages or the second IF stages only depending upon the position of the RF gain switch mounted on the AF gain control This two way feature may be used at the discretion of the operator and generally the gain control will be restricted to the IF ampli fiers when maximum CW sensitivity is desired to provide better ceception of weak signals very strong local signals tend to cause overloading the RF gain control should be switched into the RF amplifier circuit to permit reducing the RF amplifier gain The AC switch which turns the NC 300 ON and OFF is mounted on the RF gain control When this control is rotated to its maximum counterclockwise position the AC power is shut off Rotating the con trol slightly in the clockwise position will actuate the switch and turn the receiver on Further rotation increases the receiver sensitivity until maximum is reached at the full clockwise position 3 2 PHONE RECEPTION The instructions in Steps 1 through 16 adjust the teceiver for the normal reception of Phone signals 1 Set the ANL control at OFF 2 Set the MODE switch at AM Set the SELECT control at OFF Set the TONE control at OFF Set che OF F CAL switch at OF
38. or best limiting action Experience with the receiver will dictate the proper settings df the RF and AF gain controls to achieve the desired point of IF limiting CAL SET Dial Pointer Adjustment Used in conjunction with the XCU 300 Crystal Calibrator this control provides calibration correction for each band With the CW oscillator and the crysral cali brator switched on and the receiver tuned to zero S METER CAL SET CAL SET TUNING MODE ZERO SET INDICATOR CONTROL DIAL INDICATOR 58 ANT MODE CONTROL SWITCH R27 54 ANL SELECT CONTROL SWITCH 052 PHASING CONTROL CONTROL R46 510 XMT REC CONTROL SWITCH 55 52 851 St TUNING R37 SELECTIVITY OFF CAL AFG BAND CONTROL RFG CONTROL SWITCH CONTROL SWITCH CONTROL Figure 3 Front Panel Control Locations beat at any 100 point of the band any slight acteristics The crystal filter cannot be used in etror in dial reading may be corrected by turning the combination with che sharpest IF selectivity posi CAL SET contro to position the pointer on signal tion This is a mechanical adjustment of the dial pointer and in no way affects the receiver s oscillator fre quency ANT Antenna Trimmer This control is included to provide a means of matching the RF tuned circuits to varying antenna impedances After the desired sig nal is selected the antenna trimmer should be ad justed to produce maximum S Metet reading MODE The Mode switch selects
39. r must operate 80kc above the first incermediate frequency If two peaks are noted use the peak which occurs with the adjusting screw most nearly withdrawn The peak will be evidenced by a pronounced increase in the S Meter reading 9 Set the signal generator 2 kc either side of the crystal frequency noted in step 6 Set the SELECT switch at position 1 and adjust 1 4 for maximum output To check this adjustment move the SELECT Switch to 2 and then to 3 the bandpass should increase in sharpness at each position as noted by listening to background noise 10 Return the signal generator to the exact crystal frequency and set the SELECT switch at OFF Adjust C16 for maximum output 11 Adjust T4 and L2A for maximum S Meter deflec tion Keep the output of the generator low enough to give maximum readings of approximately S 5 12 Set the signal generator exactly 160 kc higher than the setting determined in step 6 Increase the generator output to obtain an S Meter reading of S5 Tune L2B for minimum meter reading Return the generator frequency and output to their previous settings Tune L2A for maximum Repeat adjustment of L2B and 1 2 as described above until true maxi mum and minimum arc achieved 13 Disconnect the signal generator and keep SELECT control at off Rotate the PHASING control to obtain maximum background noise The control should now be at its exact center position or 180 degrees diametrically opposite this
40. requency coverage of the receiver and the limits of the various alignment adjusoments it is not necessary to move the signal generator from point to point Connect the signal generator to the antenna terminals using a 1 2 watt resistor of approximately 300 ohms between hot lead and the antenna terminal The generator may remain conaected to this point for the remaining alignment adjustments Leave the modulation of the generator shut off and proceed as follows 1 Set the CAL SET control to position the hairline the center of the diamond shaped cutout 2 Set the BAND switch according to the Alignment 12 ALIGNMENT CHART SET ADJUST TO RECEIVE TEST SIGNAL ADJUST FOR MAXIMUM OUTPUT C68A Repeat steps 1 3 and 4 if necessaty C68B Repeat steps 1 3 and 4 if necessary 14 4 mc 14 2 mc 14 0 mc 14 4 mc 68 Repeat steps 1 3 and 4 if necessary C 8D Repeat steps 1 3 and 4 if necessa C694 Repeat steps 1 3 and 4 if necessar C69B Repeat steps 1 3 and if necessary C69C Repeat steps 1 3 and 4 if necessary 13 C69D Repeat steps 1 3 and 4 if necessary Chart 3 Set che MODE switch at AM 4 Set the SELECT switch at OF F 5 Set che IF control at position 3 6 Set the REG control fully clockwise The S Meter of the receiver will be used as the indicating instrument for the ensuing procedures and at all times the output of the signal
41. sted Atmospheric noise levels will differ in different localities An S Meter does not have the ability to recognize the difference between this noise level and an actual signal By adhering to the following instructions this problem is overcome and accurate S Meter readings will result 1 Set the RFG control fully clockwise and the MODE switch at AM 2 Set the SELECT switch at OFF 3 Tune the receiver to a band setting where no signal is heard so that the S Meter is reading back ground noise 4 Ser the control so that the meter reads half way between 0 and 5 1 5 Tune in the desired signal The S Meter will indicate the strength of the received signal in S Units from 1 to 9 or in decibels above the 5 9 level from zero to 40 db These readings will remain accurate until the RFG control is moved or the receiver is switched to a different band The S Meter circuit compensator requires adjust ment only when it is impossible to obtain a zero read ing with no antenna connected and the RFG control turned fully counterclockwise See Section 4 5 for adjustment procedure Design of the S Meter actuating circuit is such that a signal stronger than 60 db above S 9 cannot cause the meter pointer to come into violent contact with its stop pin thus preventing possible bending of the meter pointer Measurements of the signal strength of CW signals cannot be made with the MODE switch in the CW the AC switch on the RFG control se
42. t at OFF or when the MODE switch is on CW the S Meter pointer will return to its mechanical zero located on the right hand or 60 45 end of the meter SECTION 4 MAINTENANCE DATA 4 1 GENERAL All circuits in the NC 300 receiver are carefully aligned before shipment using high precision lab oratory equipment to insure high accuracy The quality of components used together with careful design makes any realignment unnecessary unless the receiver is tampered with or certain part or tube replacements have been made In no case should realignment be attempted unless conclusive tests indicate that such realignment is required Even then it must be remembered that the NC 300 is a highly specialized instrument and should not be serviced or realigned by any individual who does not have a complete understanding of the functioning of the equipment and who has not had previous experience adjusting receivers of this type In addi tion because of the calibration accuracy and extreme bandspread of NC 300 it is mandatory that ade quate test equipment be used Complete alignment of the receiver can be divided into three steps as follows a IF Amplifier and CWO Alignment b Second Conversion and Crystal Filter Alignment c RF Amplifier All circuits must be tuned in the above order when complete alignment is required All alignment adjust ments and controls are shown on Figures 6 and 7 4 2 IF AMPLIFIER AND CWO ALIGNMENT T
43. the mode of operation i e ACC AM CW or SSB The mode selected appears in the small round opening at the left of the switch knob The AM position is used for all forms of amplitude modulated transmissions In the ACC position the audio amplifier is connected to the accessory socket to permit use of the receiver as an amplifier for a phono pick up or similar audio device In the CW position the CW oscillator is energized and the AVC and S Meter circuits are disabled In the SSB position the heterodyne detector is used for carrier reinsertion and the AVC and S Meter circuits are active SELECT Crystal Filter Selectivity Three de grees of crystal selectivity plus an Off position are provided by the SELECT knob When used in con junction with position 2 of the IF switch tbe Select contro affords the desired range of selectivity char J TONE The adjustment of the characteristics of the audio circuitry is permitted by the Tone control Rotated in a clockwise direction it increases atten the higher At counterclockwise position it actuates a switch which uation of frequencies its extreme effectively attenuates frequencies below the voice This Characteristic range feature is provided to equalize the roll off the filter Figure 4 illustrates che audio characteristics of the receiver CWO CW Oscillator Pitch This control varies the pitch of the generated audio tone to suit the introduced by crystal oper
44. useful for phone reception n 1 of the SELECT control will probably Posi prove most useful In this position che PHASING control becomes operative By careful adjustment of the PHASING control the unwanted signal can usually be reduced sufficiently to permit copying the desired signal Experience in the use of the IF SELECT and PHASING controls will ultimately indicate various combinations of settings that best suit the varying operating conditions encountered 3 3 CW RECEPTION The initial adjustment of the receiver controls for CW reception is the same as given in Section 3 2 with the following exceptions Set the MODE switch at CW Set the CWO control at its mid scale position Rotate the AFG control clockwise until the switch is actuated Then rotate clockwise approximately to mid position The audio level of the receiver should be adjusted by means of the RFG control Strong CW signals cannot block the IF circuits but will result in an unnecessarily high background noise level Always keep RFG control below the point where this condition occurs short duration pulse interference ignition etc is encountered the noise reduction feature of the IF limiter circuits may be utilized to good advantage Advance the RFG control and retard the AFG control until limiting occurs This limiting takes place in the last IF stage and because of the extcemely fast time constants the limiting action is similar to that encounter
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