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Tremetrics 900A Operating And Service Manual

Vlf/lf receiver
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OPERATING AND SERVICE AND MANUAL
TREMETRICS
MODEL 900A
VLF/LF RECEIVER
TREMETRICS

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Summary of Contents for Tremetrics 900A

  • Page 1 OPERATING AND SERVICE AND MANUAL TREMETRICS MODEL 900A VLF/LF RECEIVER TREMETRICS...
  • Page 2 Tracor Model 900A VLF/LF Receiver Picture courtesy of G. Kerber GLK INSTRUMENTS www.glkinst.com May 2008...
  • Page 3 TREMETRICS MODEL 900A VLF/LF RECEIVER OPERATION and SERVICE MANUAL 79611 G...
  • Page 4 The Model 900 Receiver is modified for MSK reception by addition of a circuit card shown in schematic diagram Figure 900- ADD-l . On the large circuit card c409 is removed and U402 pin 5 supplies the i-f input to the MSK card, while R444 receives the i-f output from the MSK card.
  • Page 5 were received. Thus if the result of figure page 13 were NAA, achieved using MSK reception from the conversion from centicycles to microseconds would be 0.28 (using figure 1, page 8, for 35.5 KHz). The change of 2943 CEC (page 16) would be multiplied by 0.28 to give microseconds The corresponding...
  • Page 6 205K 330K DISC 51011 I.~" r" 330K 100HZ 5 N7490 MSK OPTION SCHEMATIC DIAGRAM flGUR E 900 ADD I...
  • Page 7 ADDENDUM 900A MANUAL Listed below are currently available (1986) VLF/LF stations with stab;l ized carrier frequencies suitable for reception using the 900A receiver. RADIATED TRANSMISSION POWER STATION FREQUENCY LOCATION Norway CW Pulse 10 KW Omega 12.1 KHz Liberia CW Pulse...
  • Page 8 Installation and Operation Chart Recorder Adjustments Choice of a Transmitter Interpretation of Chart Records Calculation of Frequency Switch Setting Detailed Circuit Theory Antenna Coupler R-F/I-F Circuits Divider Circuit Group Synthesizer Circuit Group Synchronous Detector Circuit Group Ordering Information Parts Lists...
  • Page 9 Switch Settings for Various Transformers Conversion from Centicyles Microseconds Fractional Frequency Error Chart WWVB (60 kHz) as Received at Austin, Texas Oscillator Offset Approximately 10- 11 -2.3 NLK (18.6 kHz) as Received at Austin, Texas Osci~lator Offset Approximately NAA (17.8 kHz) as Received at Austin, Texas Osci~lator Offset Approximately -1.9 x 10- Block Diagram, VLF Receiver, Model 900...
  • Page 10 MODEL 9DDA VLF /LF RECEIVER Reception is, therefore, not limited to one or two trans- missions as has previously been the case with "economy" model VLF or LF receivers. FREQUENCY 100 Hz steps from 9.9 kHz to 25.6 kHz COVERAGE: 100 Hz steps from 59.9 kHz to 75.6 kHz...
  • Page 11 The Model 900 VLF/LF Receiver is used to keep track of the offset of a precision local frequency standard with respect to the accurately stabilized carrier frequency of one of the VLF or LF transmitters operated by NBS or by the United States Navy. VLF carriers are typically synthesized from Cesium Beam Frequency Standards located at the transmitters;...

  • Page 12: Unpacking And Inspection

    Special attention should be given to any areas where the outside shipping package was damaged. the frequency standard is damaged in any way, immediately notify the carrier. Also notify TREMETRICS Inc., 6500 Tracor Lane, Austin, Texas 78725-2100, 512/929-2051 Attention: Product Service.
  • Page 13 SECTION III INSTALLATION AND OPERATION Installation and Operation Use of the receiver is quite simple. Mount the antenna in a clear outdoor area, such as a rooftop. Other con- ducting objects should be kept at least four feet away from the antenna, and there should be no conductors (such as power lines) at a high elevation angle as viewed from the antenna position.
  • Page 14 TABLE 1 SWITCH SETTINGS FOR VARIOUS TRANSMITTERS XMTR SYNTH VLF/LF Frequency Switch Transmitter Location Freg. Freg. Switches OMEGA Trinidad England 16.0 U D D U U U U U 15.9 Maine 17.8 17.7 U D U U D D D U Wash State 18.6 18.5...
  • Page 15 For a strong signal the indicator light should corne on well below the maximum GAIN position. At maximum gain the lamp may flicker as a result of atmospheric noise reception. When reception is normal, and the GAIN setting proper, switching the third FREQUENCY switch from the right away from the correct position should usually cause the indicator lamp to go out.
  • Page 16 particular short range may give erratic cases a transmitter at a each of several strong transmitters results at sunrise. and select one with a stable diurnal days a period of several shift pattern. Interpretation of Chart Records Frequency offset of the local frequency standard with respect to the VLF carrier is determined from the chart record produced by the receiver.
  • Page 17 to noon, the phase reading increases by 7 CEC. period from noon This corresponds to 7 x 0.562 3.9 us. Twenty-four hours is So the fractional frequency offset is 86,400 seconds. 4.5 x 10- 11 (10)"6 8.64(10)4 An increasing pha~~ reading indicates that the local fre- quency is high.
  • Page 18 ~(;;) ~<v~~ ~~<v <vq:. <v~ .:$:'~ ~'i-~ ~<:::)~~ ~~~.::s ~':l ~ <0 <o~ ~~~~~ I I I I • • "- I I I ..•..• I'--- : I : • CARRIER FREQUENCY...
  • Page 19 "" ~Y\~ +-'" I X 10- 8 •... ~ ~~ "'~ ">~ f-q" I X 10- " ",y " •... 1 X 10- 10 1/ ./ " I X 10- 1 I 1000 10,000 O. I ACCUMULATED TIME ERROR, MICROSECONDS...
  • Page 20 random fluctuation of five to ten microseconds or more often occur. Thus the best results are obtained by taking readings at the same time each day; the time selected should be one during hich the transmission path is entirely in daylight. The entire chart should be examined in the neighborhood of the selected time...
  • Page 21 " ": fF-" ..'" " .": ==. ~- •. ". >- " •... i=:= t=== •... ·1 " · " ...• l-=..e _. "0 ~.!.= " _______ ._._"!!!!!~!~~t,k.._=_:.z=.._=_-.--1tU..l.A,--~::._:.!~!!!_.__ NOON . .. · ••..RU$TRAK ..• " · I"':'" ·F - .- I:::::: "...
  • Page 22 r.:::=._ ""' ,...,.-FfIIA --f',. 1== -~.: _:~,~r== __ I-.. _"I~':=~::'-~ '_~~' __ : __ : -~-~-~.I~ ---.-- _..__ ::- - _" .. _ _.~ 0:"-'" =-.l' -:::=:;= ~[~._. ._'. ~ - ,. _ - "t=I, .=: -- t::=.:E:'::r_. 0 "70,=- "...
  • Page 23 --Qj-.--®---l _~_ _ _reo. ,. _ ,. -L=~f-~.~=_'f- -·-f i ,. _./ E .. : _ .-: IF:: l- '. _ -J.. _. _ -;= =-.: .=/-.. - ·,'11 J:=-"'., .. -=-IE ".f==. . ,"'"If' '1 -,', "i ~ 50==="':"E: ."...
  • Page 24 Note also the apparent sudden jump from 100 CEC to 0 CEC at 6 PM near the left of the center strip. The total range of the phase detector is 100 CEC, or one full cycle of phase, When one extreme is reached the record reverts to the other extreme. If the phase just before 6 PM is 99 CEC, the phase just after 6 PM is obviously not 1 GEC, but 101 centicycles.
  • Page 25 Referring to figure 1, at 60 kHz the number of microseconds per centicycle is 0.167. The change expressed in microseconds then Referring to figure 2, 1.837 ~s in 24 hours is an offset of 2.3 parts in (10)~1 Since the change is negative the local frequency standard was low by 2.3 parts in (10)~1 Figure 2 shows reception of NLK, Jim Creek, Washington, at 18.6 kl~.
  • Page 26 An approximation could have been obtained over a shorter period of time. At 2 PM the first day the reading is 38 C ECa The change since noon is then CEe, 38 - 17 (21)(0.54) 11.3 ~s 11.3 1.7 X 10- 9 (2)(3600) This last result could, of course, be obtained from Figure 2 instead of making the calculation.
  • Page 27 Calculation of Frequency Switch Settings The most frequently used frequency settings have been given in Table 1. It is relatively easy to calculate any desired setting. The switches select the frequency in binary form as follows: S208 S207 S206 S205 S204 S203 S202...
  • Page 28 (UP) 8208 XO (DOWN) 8207 (UP) 8206 (UP) 8205 (UP) 8204 XO (DOWN) 8203 XO (DOWN) 8202 (UP) 8201 TarAL...

  • Page 29: Theory Of Operation

    SECTION IV THEORY OF OPERATION A block diagram of the Model 900 LF/VLF Receiver is given in figure 6. The signal is received by a vertical whip antenna mounted on the antenna coupler unit. A pre-amplifier in the coupler provides approximately unity voltage gain while converting impedance to a level which can drive the 50-ohm cable feeding the main receiver unit.
  • Page 30 T'U'." ..••. ..•. Figure 6. Block Diagram, VLF Receiver Model 900...
  • Page 31 reference signal is maintained constant. If the phase difference is temporarily less than 90°, retard pulses are repeatedly generated until the phase difference is 90°. If the phase difference is temporarily greater than 90°, r~peated advance pulses are generated. Thus closed loop action phase locks the coherent 100 Hz signal 90°...
  • Page 32 cable feeding the main receiver. DC voltage is supplied via the center conductor of the coxial cable. Figure is a schematic diagram of the receiver proper. For convenience the circuits are subdivided into s~ctions as follows: Divider R10l Synthesizer R20l Synchronous Detector R30l R-F/I-F...
  • Page 33 The next section of U403(C) feeds a limiter (CR1, CR2, etc.) which insures constant level I-F signal at the synchronous de- tector. The limited signal is amplified in the final section of U403(B) and applied to the synchronous detector section via emitter follower Q403.
  • Page 34 The 100 kHz signal from UIOI is frequency divided by 2 to 50 kHz by J-K flip flop Ul07B. The 50 kHz output is used as the local oscillator signal for mixing LF signals (such as 60 kHz) down to the VLF band. Ul02 receives 100 kHz at pin 1 and frequency divides by 5, producing 20 kHz at pin 11.
  • Page 35 positive pulse is produceu at pin b wnich feeds Ul13B. A negative pulse at pin 1 feeds Ul12A. If a positive signal exists on the advance enable input at Ul13, the occurrence of the positive pulse at pin 5 results in a negative pulse at Ul13, pin 6. This is applied as the advance gate at UI06, pin 5.
  • Page 36 from the 100 Hz output of U104 clears the flip flop to the positive state. If the clear pulse follows very quickly after the clock pulse is zero only a small fraction of one cycle at 100 Hz, and is positive the rest of the time. If there is a delay of nearly a full cycle between clock and clear, is zero nearly all...
  • Page 37 1 kHz fos c fos c N x 1 kHz The oscillator signal is frequency divided by 10 in decade divider U204. The output frequency fos c is thus N x 100 Hz. fos c Clearly then the synthesizer will produce any integral multiple N x 100 Hz which can be selected in U205 and U206.
  • Page 38 The synchronous detector circuit group receives the I-F signal from the receiver circuit group and the shifted 100 Hz signal from the divider section. The I-F signal is shorted out via Q302 during one half-cycle of the 100 Hz reference. During the other half cycle the I-F signal is passed through to integrator circuit U302.
  • Page 39 If the 1 CEC phase shift is inadequate to bring the reference signal to quadrature with the I-F so that a positive polarity exists as before at the integrator input, the entire cycle just described is repeated. When successive phase retardations finally bring the reference to the other side of quadrature, negative input to the integrator results, and the integrator output...
  • Page 40 SECTION REPLACEABLE PARTS Address orders or inquiries to either an authorized TREMETRICS Inc., Sales Representative or to: TREMETRICS Inc. Industrial Instruments Customer Service 6500 Tracor Lane Austin, Texas 78721 Name, model, and serial number of the instrument. TREtlliTRICS stock number Full description of the part.
  • Page 41 " -40X5/11> 5 " ftft ft" •• TI> "0 "6 ..lq~IC ••••• •• ".)Z ( III Llt5 CIOb CIC,) (l0: (20~ C2C •• '15-0 ••• ]]ZI-qI02 ()U~ l4n~ •• Z151)-010Z C~O~ r.~C5 ••• 11ZI-qIOZ C"!q '15-0121 t:4t;'O tAl' ~XD ceR .1 ~FD CbC'...
  • Page 42 .ol>a L~ 11 ("11 (u•• ..Z1~\l-02f1 •••• bl0-009'l £101 ••• )422-0221 lbOZ ••• 3422-0b81 ••• 3422-0222 1113'1010 •••• 900-52 ••b 9010 11152410 •••• lOlo-0]~4 •••• 212-Z053 •••• 20 ••-0105 •••• 10lo-0~1 •• •••• 1.;10-010] MIl''' ..•• .zO't-"" "1 •••• 20lo-01n 1<10)
  • Page 43 PARr :; •••• ZO ••·03"Z ~t'S •••• ZO ••-,) 10Z •••• JO •• -OII>Z •••• ZO •• -0162 Rzr"~ ~.ZIO •••• ZO"-O" •••• l04-0 1\)] o'oq •••• ZJ ••.• O•• 72 •••• ZO ••.•.05 •••• ZO"-0IC6 •••• ZC ••·OIOZ •••• ZO ••...
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  • Page 46 ••• 1411>-0012 •• , 31>1 •• 1]91>'1-057.9 of> C50l •••• ~00-4001 • • " • ~q91>115 I/~ZI) lI~lLt...
  • Page 47 .rlf • .13451,-0001,...
  • Page 48 ..•.. ~~ ~ ..•. I - - - - - '-_J '-------------, TO TP404 L __ Diagram Schematic, Chassis, Drawing No. 19356E...
  • Page 50 TP 10' • "'02 ~D II:HZ II". A6I7 1051( C614 J.!MH A61, IOjl C401 +12V 11442 ••.• 47 ].!It 1f40Z '" '421 A415 634' e· C20T "204 "210 5WlrcHfS TIS-51 ZMSZU 'tit'lU Iht'lll "UISTOIltS 'RE: 1/4.' TOI. WITH VALUES IN oHIlI5; CAPACITOR VAUJ£! ARE .1...
  • Page 51 IMHZ fROM FRED srD £101 (106 TP404 RSOZ C30. C304 AlaI "'~ DDZ~ _llY Rll' UllflLTUED ADVANCE ENUU • SV 100H/ -fZY RIIQ V CC2 ClllyCIIO Diagram Schematic, Receiver PCB, Drawing No. 19357~...
  • Page 52 §' 3.9MEG 2.2K IOpt 1000pl 4.7K 2N2270 IN914 2N2270 220K 150K 4.7K IN 914 2 .7WE~J 4.7K lOOp' 3.3K 1.5k .j::> '" " 1000pl I. ALL RESISTORS ARE 1/4 W 5% TOL WITH VALUES IN oHMSj CAPACITOR VALUES ARE IN MICROFARAOS NOTES: UNLESS OTHERWISE SPECIFIED Diagcam Schematic,...