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G8MNY  > TECH     12.11.23 09:31z 497 Lines 27906 Bytes #7 (0) @ WW
BID : 60179_GB7CIP
Subj: RTT Comms Test Set
Sent: 231112/0930Z @:GB7CIP.#32.GBR.EURO #:60179 [Caterham Surrey GBR]

By G8MNY                              (Updated Dec 22)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
At a club sale a few years ago, I bought this large, heavy & rare test set, in
its smart flight case. It should be able to do quite a lot, but not seen
working! The "Radio Telephony Test Systems" test set was made in Feltham UK in
1987-9 & it would have cost >10K UKP back then!

Some of my repairs and modification information, that were much revisited
during Covid lockdown, may be useful for other kit too.
      /                                                           /|
     /                                                           / |
 Þ /___________________________________________________________/Ý  |
 Þ³³³ \ AF  ³³ \SINAD³³ù 5 3 9.9 9 9 9 0 0 ³³ \MOD  ³³ \POWER³³³Ý  |
 Þ³³³__\____³³__\____³³____________________³³__\____³³__\ ___³³³Ý  |
ÚÁ³³.   _         _   Oven     _   _       Lock         _  Rx ³³Á¿ |
³_³³   (_)_______(_)          (ú) (_)    o   ù ! ! !   (_)  ù ³³_³ |
AF³³'  _ ³_______³_    _           _      _     _        .-.  ³³   |
in³³o (_)  o  o  (_)  (_)  ! !   =(_)   =(_)   (_)   o  ( o ) ³³RF /
  ³³CTCSS SELCAL MOD     _     SIG GEN FREQ    ú_ú  _   _'-'_ ³³in/
  ³³123ú4 123456 1ú2    (ú)    1 2 3ú4 5 6 7   (ú) (ú) (ú)=(ú)³³ /

It is a HF/VHF/UHF RF transceiver test set, with all this in one box...
Dummy Load & Attenuator
Power Meter 6 ranges (Peak reading)
Frequency Counter (9 digit, very accurate once warmed up)
PLL RF Signal Generator (7 Decimal Thumbwheels) with 90dB 1dB step Attenuator
Modulation modes CW, AM, FM, & PM
PLL CTCSS tone Generator (4 Decimal Thumbwheels) and CTCSS freq measure button
Selcall ID Generator & Decoder (6 Hex Thumbwheels, but no PCB, so removed this)
AF Oscillator (low distortion Wayne type, controlled by 2 decimal thumbwheels)
CW/AM/FM/PM Automatic wide band scanning Rx, tunes and locks up in 3 seconds
Modulation Meter, +/- Peak reading, 2 AF Bandwidth filters
SINAD Meter (AF AGC & 1kHz Notch, for Rx Sensitivity & Distortion measure/adj)
AF Volt & dB meter (Level, S/Noise & frequency response checks)
IF Xtal Oscillator. (Xtal tester & IF reference Output)

The RF generator uses 6 PLL oscillators & a PLL CTCSS generator. It came with a
brief Operating Guide, but no service information (nothing on net). So I had to
do a lot of reverse engineering.

RF Input          50ohm N socket 20dB Load atten. 1kW peak, 50W continuous
Power Meter       1,3,10,30,100,300W FSD, (RF detection for Counter & Rx mode)
Frequency Counter 9 digit 1Hz-540MHz in 3 gate times & 10s averaging to +/-1Hz
Freq Reference    Accuracy < 1/10^7/month, internal Xtal Oven & warming LED
Signal Generator  PLL 100Hz steps from 10 - 539.9999MHz, O/P -13dBm (50mV) BNC
Sig Gen Harmonics Better than -20dBc, Typically >-30dBc
Gen Attenuator    10x1dB & 8x10dB for 1.7uV-50mV, 40dB lower via Load Atten
Pilot tone(CTCSS) 4 Digit PLL 20-999.9Hz in 0.1Hz step, Mod Level, & Rx Counter
Selcall           6 char. Mod Level adjustable & Decoder. (No PCB, so removed)
Modulation modes  CW, AM, FM & PM
AF Modulation     Internal/External, Level Pot & 20dB Atten.
AF Osc            Wayne type 100Hz-15.9kHz in 100Hz steps, not PLL
Ext Mod/AF out    Needs >1V in, or 0-4V RMS AF out, 600ohm BNC
Xtal/IF           455kHz & 10.7MHz in built & ext Xtal socket & osc O/P BNC
AF Meter          Bal/floating 3mV-10V FSD, in 8 10dB ranges, 11Hz-27kHz @ -3dB
SINAD meter       Auto level, 1kHz Notch, 0 to -20dB/100-0% Noise & Distortion
Automatic Rx      Scans 2MHz->1GHz, <100mW to >300W Load input, up to 60dB S/N
RF & IF O/Ps      Rear BNCs for RF & 450-470kHz IF
Rx AF Filters     Comms 300Hz-3kHz @ -3dB, or HiFi 50Hz-15kHz @ -3dB
Modulation meter  Auto Rx. +/- peak, AM 50/100%, FM 5/100kHz, PM 2/5 Rad
Monitor Amp & LS  Vol & 1W for Listening to:- AF in, SINAD, AF Osc, & AF Rx
Power             AC IEC Mains input 230V/115 @ 60W, or XLR for 12V DC @ 5A
Weight            24kg in it's flight case

SCHEMAIIC I worked out.

    __________    _________ link   ___________   __________ Mod AM/ ³    ___
RF ³Dummy Load³  ³AttnRelayÃo--oÄ<´ Switched  Ã<´6 PLL Sig ³FM/PM   ³   ³ AF³
INo´AttenuatorÃÄ>´Splitter ÃÄÄÄÄ¿ ³Attenuators³ ³GeneratorsÃÄ<ÄÄÄÄÄÄÁ/Ä<´Gen³
                 RF³ rly³    ³  ³        ________³_  ³  _³_         ³
   ___________    _³____³_  _³_ ÀÄ>ÄÄÄÄÄ´1/ö10 FreqÃ<)Ä´Ref³  _____ ³ _ _ _ _ 
  ³Power MeterÃÄ<´   RF   ³³Pre³   Ext o´ Counter  ³ ³ ³OscÃ>´CTCSSÃÁ|Selcall|
  ³ & Range SW³  ³Detector³³amp³    in  ÀÄÄÄÄÄÄÄÄÂÄÙ ³ ÀÄÄÄÙ ÀÄÄÄÄÄÙ |ÄÄÄÄÄÄÄ|
  ÀÄÄÄÄÄÄÄÄÄÄÄÙ  ÀÄÄÄÄÄÄÄÄÙÀÄÂÄÙ            ctcss³   ³               |Display|
   _________        _______  ÀÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ¿  __³___³____           À Ä Â Ä Ù
  ³Mod MeterÃÄÄÄ<ÄÄ´  AF   ³   ____________ ÀÄ´ Automatic à - - - - -> - Ù
  ³+/-Switch³  Rx o´FiltersÃÄ<´Range & ModeÃ<Ä´Scanning RxÃÄ>-oIF Out
      _______      ________   ________        ________________________
AF:ÄÄ´Bal AmpÃÄÂ>Ä´Range SWÃ>´AF Meter³      ³PSU +26,15,8.5,5,-12,-20ÃÄMains
     _______   ³   _______   ________   ___________       _______________
  :ijIF Xtal³  À>Ä´AGC AmpÃ>´Rej 1kHzÃ>´Sinad Meter³   >Ä´AF Mon Amp & LS³

RF switching changes the Rx and Counter over, and disconnects the Signal Gen
when the Power Meter detects Tx RF, so only the Tx signal is measured. Useful,
but confusing when I was chasing faults! (see F/ mod)

INSIDE (top lid slid off)

                PCB NEST        DC INVERTER      RF & IF
³ÚÄÄÄÄÄÄÄÄÄÄ¿³ RÝ SÝ CÝ S: ³ |                |³WIDEBAND³           ³
³³  DOUBLE  ³³ FÝ IÝ TÝ E: ³ |      MAINS     |³        ³           ³
³³          ³³  Ý NÝ CÝ L: ³ |   TRANSFORMER  |³  AUTO  ³           ³
³³ SCREENED ³³ FÝ AÝ SÝ C: ³ |________________|³        ³           ³
³³          ³³ RÝ DÝ SÝ A: ³      ³     ³ _  _ ³  SCAN  ÃÄÄ¿4 Way RF³
³³ BRASS BOX³³ EÝ &Ý  Ý L: ³      ³     ³³ ³³ ³³        ³  ³splitter³
³³          ³³ QÝ AÝ  Ý L: ³ o  PSU PCB ³³ ³³ ³³ Rx IN  ³  ³& Atten ³
³³ FOR 6 PLL³³  Ý FÝ  Ý  : ³ ßßßßßßßßßßßßßßßÛßß³        ÃÄÄÙ        ³
³³          ³ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÙ                Ý  ³SCREENED³    ÚÁÁ¿   ³
³³ HF - UHF ³         ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿³        ³ ==========³
³³          ³         ³         5V reg        ³³  BOX & ³ ===LOAD===³
³³  OSCs &  ³     OÚÄÄ´    ö10 PRE SCALLER    ³³        ³ ==========³
³³          ³     v³  ³Ref                    ³³ PREAMP ³ ==========³
³³MODULATORs³     e³  ³OSC  TOP SCREENED BOX  ³³        ³ ===ATTEN==³
³ÀÄÄÄÄÄÄÄÄÄÄÙ     nÀÄÄ´                       ³ÀÄÄÄÄÄÄÄÄÙ ==========³
³ÜÜÜÜÜÜÜÜÜÜÜ  _____   ³      COUNTER PCB      ³   _____  ÜÜÜÜÜÜÜÜÜÜܳ
³  ³ AF  ³   ³SINAD³  ³      ON LID WITH      ³  ³ MOD ³  =³POWER³==³
³  ³METER³   ³METER³  ³    9 DIGIT DISPLAY    ³  ³METER³  =³METER³==³
³                 Ext Mod  Counter         On  Xtal  Mod  Gen ÀÄÙ RF³
                  /AF out  in                 IF/Osc out  out  N  Sample
Going through the many functions, I found several faults....

1/ Mains on/off push switch's rod had come off the PSU switch deep inside, and
the button's top had swollen and jammed in the front panel. I sanded the button
down, used a rubber sleeve behind the inner front panel to captured it, and
heat-glued the push rod to capture the PSU switch, so it won't fall out again.

2/ Tx Load 20dB atten, N input presented 147 not 50 ohms! I removed it (front &
side panel off) and I stripped it down, to find it was all quite loose, looked
clean, and not smelling inside, so not burnt out? Inside it had screw on ends
that held large ally washers with spring washers in the finned tube surrounding
the 5 special RF resistors, in this asymetric power distributied attenuator.

       3 rod type Rs                  Ý Ý Ý Ý Ý Ý Ý Ý Ý Ý Ý
     /       |       \               =Ý Ý Ý Ý Ý Ý Ý Ý Ý Ý Ý
(o)Ä8RÄÂÄ ÄÄ47RÄÄÄÄÂÄ39RÄ<SMA      __Úßßßßßßßßßßßßßßßßßßßß¿
 N³    ³  \loose   ³     ³       N³  ³Ü._____±_____±_____.³Ä¿SMA
  ³   139R  here  14R    ³        ³__³ß'~~~~~±~~~~~±~~~~~'³ÄÙ
        \         /                  =Ý Ý Ý Ý Ý Ý Ý Ý Ý Ý Ý
       2 Disc type Rs                 Ý Ý Ý Ý Ý Ý Ý Ý Ý Ý Ý

No open circuit or burnt bits found. Putting it all back together tightly, I
now see 50 ohms (previous owner been playing?) And on an analyser with tracking
generator, it showed a constant 20dB atten to > 1GHz.

3/ FM deviation measurement range (used for the sig gen cal too) was un-
calibratable! Rx box access is by removing top, bottom & RH side panel, then
strip down the Rx Box's side panel with the Rx box bolted to it. In it I found
a broken 10K FM Cal preset. Replaced, but needed to be 15K to calibrate the
5kHz range! Rough holes had been drilled to access the calibration adjustments!
The inner PCB is only soldered in place. The 3 nuts are just stand offs under
the PCB, (used before soldering in), and I soldered in the 2 loose captured
screw for ease of assembly!

³( )         Cal      Cal          Cal         /~~\      ³ INSIDE
³( )                                           \__/      ³ AUTO SCAN
³         Signal conditioning & mod meter PCB            ³ Rx Box is
³³ in  Mixer     IF[o]    AGC IC    AM [o]           ³   ³ a Relay, &
³³                 [o]IF     IF[o]   Detect     (o)  ³   ³ Preamp too.
³³                                             AM AGC³   ³
³³Harmonic                                           ³2nd³
³³Multiplier      (o)        R x  P C B     (o)      ³Screened
³³     Sweep amp  STOP                      AFC      ³Rx ³
³³                                                   ³Box³
³³                                                   ³   ³
³³1.5-2MHz                   Limitor[o] FM           ³   ³
³³   [o]Osc   rampIC  10HzOsc       [o] Discrim    5V³   ³
³³___________________________________________________³   ³

The 20kHz range also needed a series preset on the front panel range switch to
get that right too (See 5/ Fault & D/ Mod). Inside the Rx box there are AM AGC
and FM discriminator adjustments that affect calibration and the scanning STOP
ability! (previous owner playing?)

4/ PM un-calibratable. Something is wrong, I had to change op amp's gain R in
the Rx as a get around it. Same as FM for inside the Rx box. But I did learn
that PM has same spectrum shape at all mod frequencies & it is just 6dB/Octave
treble lifted FM so....

"1 Radian (57ø) of PM occurs when the FM AF Mod Freq = the Deviation."

So 2 Rad = 1kHz  tone @ 2kHz FM Dev, 
 & 5 Rad = 1kHz  tone @ 5kHz FM Dev, 
or 2 Rad = 300Hz tone @ 600Hz FM Dev,
 & 5 Rad = 300Hz tone @ 1.5kHz FM Dev.

5/ The single superhet wide-band 2MHz->1GHz automatic Rx had a crackly Rx noise
fault. (see 3/) On testing I blew up its 78L05 reg, and zapped a CMOS 10Hz osc
hex inverter IC! In the end the noise was mostly from scratchy AFC preset pot.

RxÄ´Ring Ã>´460kHzôIF Ã>´460kHz ôAGCÃ>´460kHzôIF Ã>´460kHzôAM ôAF ÃÄ>AM
in ³Mixer³ ³  LPF ³³Amp³ ³Filters³³ IC³ ³Filter³³Amp³ ³Filter³³Det³³Buf³
      ³                             ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄ<ÄÄÄ)ÄÄÄÄÄÁÄÄ>Lock LED
   ³Harmonic Ã<´1-2MHzÃ<´RampÃ<´256 RampÃ<´10HzÃ<ÄÙStop ³FM ôFM  ôAF ÃÄ>FM
   ³Generator³ ³ Osc  ³ ³Amp ³ ³ Counter³ ³Osc ³        ³Lim³³Disc³³Buf³

The Rx has a wide LC tuned 460kHz IF, feeding AM & FM detectors. The front end
is just a ring mixer, fed with highly harmonic rich 1.5-2MHz oscillator. This
is tuned with a varicap in 256 steps, from a ramp gen/8 bit counter/analogue
out IC. It counts a 10Hz osc, that is stopped when a good enough IF signal is
detected by the AM (with AGC) detector. Then the FM discriminator's AFC takes
over for fine frequency control, or unlocks it to scan again if it is the wrong
sideband image.

The Rx is fed from a wide band preamp box, fed from the 4 way 20dB splitter
that feeds the power meter, sig gen, frequency counter, and a diode switched
preset Rx atten, all fed from the large 20dB load attenuator from transceiver
under test.

6/ 12V DC Power input option had a DC framing fault, The inverter has 2 NPN Tab
transistors on dedicated windings on the mains transformer, and 1 of the
collectors was framing to ground (OK on isolated battery). Only 6 screws to
remove PSU. The way the On/Off switch is wired it stops inverter, but leaves
bias load on the battery! The mains switch is cross-wired so when mains is off,
the DC power option is on, this ensures there is no inverter bias when the
mains is on, and the mains is disconnected when on 12V!

              on off
 NÄÄÄÄoÄoÄÄÄÄÄÄÄ/oÄÄÄÄÄÄÄÄÄÄÄÄÄ¿  115³  230³Transformer
IEC 2x 0.25A  ÚÄ\oÄÄÄÄÄÄÄÄÄÄÄ¿ (((((((((((() ______ÚÄÄÄÄÄÄÄÄÄÄÄÂÄÄmains earth
              ³  ============³====================== Shield   _³_
    ÚÄo-oÄ´>ÃÄ´  ()))))) ()))))))) ()))))))))))))))))         ///
    ³ 5A     120R³  ³  ³ ³ 8-0-8V³ ³  ³   ³ ³ ³  ³  ³Secondaries
+12VÙ         ÃÄÄ(ÄÄÙ  ³ ³       ³ 26 17  7 0 7  17 26V
XLR   INVERTOR³  ³1-0-1ÀÄ)ÄÄÄ¿   ³          Áct
  0V¿    BIAS ³  ³       ³   ³   ³   The cure was to file some metal case away.
    ³        22R ³     ³/    ³ ³/    This may have been from a bad upgraded
    ³FLOATING ³  ÀÄÄÄÄÄ´NPN  ÀÄ´NPN  from small to large 15A Tab transistors.
    ³DC       ³        ³\e     ³\e
    ÀÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÙ   I also added 4m7 Cap across the 12V input.

7/ Trying to reduce 12V hum & other rail interference, I lifted of centre tap's
(ct) high current 100Hz earth pulses off the transformer chassis, and re-wired
it directly to a newly isolated (2 nylon screws & insulation kit) PSU PCB's 0V.
So now the PSU DC earths only come from the PSU-module connector plug & no more
rectifier hum loops via the chassis!

Eventually to get the power rail interaction on the +12V rail right down, and
stop affecting the RF osc, I swapped the PSU's 7812 reg for a 7815. Then added
12V regs to both the RF osc box & the AF meter PCB, for a proper job. This gave
no power rail interaction (seen as FM noise on 70cms internal or external FM /
SSB Rx). Then I re-calibrated the Rx AM, FM, & PM on the new +15V!

8/ AF osc and SINAD circuits are on the 2nd card in the nest. The AF osc uses 2
push button BCD thumbwheels, to select the AF modulator frequencies, but they
are not very accurate, as measured on the counter with patch lead. I adjusted
one of the Wayne bridge osc C values (room for 4 caps on PCB for this). Each of
the 2 thumb wheels operates 4 relays, to control the 8 pairs of Wayne bridge Rs
that determine the 100 frequencies. I also put a CR (220R and n82 in series)
across the 150R (Thermistor to earth R) to frequency calibrate the extended
upper frequencies after my mod.(See H/ mod)

9/ CTCSS pilot tone had poor shape @ LF. It is 3rd card in PCB nest, the sine
wave osc device is a clock triggered ICL 8038BC function gen IC. So I added
some LF frequency correction bias to the set square 1:1 preset (sets balance of
+/- currents into the ramp Cap).

          Preset                    Set Preset for best @50Hz & set SQ @500Hz.
  ÚÄR21ÄÂÄÄ470KÄÂÄ100KÄ  R1-7       I used this on these AF osc ICs before,
  ³     4ÚÄÄÄÄ¿ ÃÄÄ47KÄ  Resistor   but this time the correction DC had to
 VR1     ³8038³ ÃÄÄ47KÄ  Pack       come from set of Rs decoding some of
 SetÃÄÄÄ6³ BC ³ ÃÄÄ47KÄ  CTCSS      the BCD data lines. (not in BCD order!)
  SQ     ³    ³ ÃÄÄ82KÄ  Freq
  ÀÄR15Ä5³ IC6³ ÃÄ390KÄ  Data       It now gives fairly good sine wave from
         ³    ³ ÀÄ180KÄ  Lines      20.0Hz to 999.9Hz.

10/ The 1dB RF sig gen's stepped attenuator was dodgy. Leaning on the knob gave
different levels! Access to remove the atten unit was very difficult, the front
panel and PSU had to be removed. Tiny atten screws removed, showed it had 10
"fuse like" T atten in a cage turret construction, with sliding contacted at
each end with the in & out SMAs spring contacts & spring earthing contacts too.

     SMA²         ²SMA
      ÚIJÂÄÄÄÒÄÄIJÄÄ¿        The fault was these weakened SMA gold plated
      ³ ÝßßßßßßßßßÞ ù³        springs, needed a slight bend to fix. But also
 Shaft³ \[ atten ]/ |³Click   sliding SMA earths each end of the cage too.
      ³  [ atten ]  |³mech
      ³  ÜÜÜÜÜÜÜÜÜ  ù³        The middle of the cage is earthed with
      ÀÄÄÄÄÄÄÐÄÄÄÄÄÄÄÙ        greased silver braid wrapped around it
      Cage with braid         to mate with the outer cylinder case.

11/ A recent fault was hummy FM RF osc when cold, affecting all 6 osc and not
an external signal. This was not mains locked hum, as first thought, but from
the 100Hz phase locked loop RF osc system. Access was by removing top, bottom &
LH side panel, then strip down the 2 brass pairs of nested covers that make the
dual RF Faraday cage.
                          ÚÄÄÄÄÄÄÄ¿         ÚÄÄÄÄÄÄÄÄÄÄÄ¿   ÚÄÄÄÄÄÄÄÄÄÄÄÄ¿
               SelectÚÄ<ÄÄ´ControlÃÄÄÄÄÄÂÄ<Ä´Control 1stÃÄ<Ä´7 Frequency ³
                Osc  ³    ³ EPROM ³ Freq³   ³PCB in nest³BCD³Thumb wheels³
                     ³    ÀÄÄÄÄÄÄÄÙ Data³   ÀÄÄÄÄÄÄÄÄÄÄÄÙ   ÀÄÄÄÄÄÄÄÄÄÄÄÄÙ
 Rx<Ä´ AM Mod &Ã<´6 Osc Ã>´  ö100   Ã>´ö N Ã>´100Hz PhaseÃÄ<100Hz from
 To<Ä´Level AGC³ ³HF-UHF³ ³Prescaler³ ³Freq³ ³Comparitor ³  Ref Osc
          ³        ³  ³    ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿   ³
  AM >ÄÄÄÄÙ        ³  ÀÄÄ<Ä´Buffered PLL FilterÃÄ<ÄÙ

Using freeze spray's long stalk & a hair dryer, it eventually turned out to be
on the PLL Filter Buffer, where an FET was not able to fully turn off a 2N2481
NPN AFC amp, on the plug in PLL control PCB inside the osc box. Changing it for
another NPN cured it, after a lot of testing.

     === ³   ³                         2K2  Pull up   ³
  33u Á  ³  22K                         ³   Current   ³
         ³   ³                          e\³ Mirror   2K7
          \³ ³   s        PLL Loop     PNPÃÄÄÄÄÄÄÄÄÄÄÄ´
    AFC NPNÃÄÁÄÄÄ>´ g      Filter        /³           ³
         e/³  P chÃÄÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÄÄ´             ³
         ³   FETÚÄ´       22K ===1u      \³ 47u     ³/
         ³      ³d         ÃÄÄÄ´       NPNÃÄÄÂÄÄÄÂÄÄ´NPN
    OSC  ³      ³      2u2=== ===       e/³ === 2K2 ³\e
    DC                Á                2K2     Á     2K2
  The P type FET source follower        ³Down         ³Up
  drives the NPN emitter follower.      -ve 100Hz Pulses
                                       Phase Detector IC

Later after reducing the 12V hum (see 7/), I reduced some of the RF osc wobble
for a better UHF CW note, by reducing the 1u to u47 and removing 1 of the 2u2,
Osc lock up time also reduced. But further C value reduction left unstable non
lock up!

A/ ADDED LEADS & BITS BOX. Set of useful trimming tools and test leads made up,
that fit in the flight case (small bits in a plastic box, so not to scratch the
4 meter fascia bezel or damage the lever-operated thumbwheels). Large leads
stored between the feet & manual above in the flight case.

13A Plugð===================> IEC right angle Mains (left in, in Flight case)

DC + >ÄfuseÂ================> XLR 12V @ 5A
   - >ÄÄÄÄÄÙ
3.5mm   5T on             ÚÄ> Balanced AF & SINAD
Rig LSú-(()===============ÁÄ> Meters. 4mm plugs
PL259 -]===================N> N Plug RF Dummy Load
         Both low loss coax
N Plug <N==================N> N Plug RF Dummy Load

BNC <======================N> N Plug RF Dummy Load

BNC <=======================> BNC general patch lead
BNC <=====================ÁÄ> 4mm plugs & clips for AF testing

BNC to double banana plug adapter, for Sinad input testing

BNC T adaptor, to enable monitoring of signals

B/ FINE REF CAL TRIM. Inside the counter box, access remove top slide cover and
front strip then remove brass top sheet. I changed the ovened 10MHz reference
osc's fine tune "AGE" 10K preset (hidden), for a fine multi-turn version. And
drilled an access hole in the brass cover sheet, usable with the top cover just
slid off.

Unregulated          Ú-----------¿      This permitted the finest of tweaks
  +8.5V >ÄÄÄÄÄÄÄÄÄÄÄÄoOVEN HEATER|      when hot, when calibrated with an
                     |           |      external off air reference.
    +5V >ÄÄÄÂÄÄÄÄÄÄÄÄo+5V        |
Local reg   ³        | 10MHz REF |      I also made a foam polystyrene cover
           10K  +10u | OSC MODULE|  __  for the protruding hot oscillator box,
           PreÃÄÄÂÄÄÄoAGE     RF>oÄ)__  to reduce oven power and make the temp
           set  ===  |           | ³    more stable (and hence frequency) more
        ÄÄÄÄÁÄÄÄÄÁÄÄÄo0V      GNDoÄÙ    quickly.

Tracking down FM hum & drift, I found the original 6.8V reference zener and 1K8
were a poor regulator of the hummy 8.5V, and that gave a lot of long term
thermal drift. The fine tuning AGE voltage, only needed to be around 2.5V, so I
used the nearby 5V regulated rail with a 10uF on the pot slider. This was much
better for hum and much lower drift now too.

Also I added 6mm dia ferrite beads to the +5V rails feeding the 3 RF noisy
items in the counter box, and a 100uF 16V on +8.5V @ regulator, as it was now
an "osc" after I added the ferrites!

Warm up time is now a lot better..
Counter's error of an air locked 10MHz reference.
Time min  0         1         3         5       10
Hz off  -41.9     +159      -2.6       +1       +1
Error  -42/10^7  +16/10^7  -3/10^7  +1/10^7  +1/10^7

C/ REF OVEN LED. Inside the counter box, I also added an "OVEN" LED, to show
when the thermally controlled oven is still warming and freq not yet accurate.

Unregulated ³          ³
            ÃÄÄÄÄÄ´>ÃÄÄ´1N4001       The circuit and LED are placed inside
            ³   +      ³             counter box and soldered to the +8.5V and
            ÃÄÄÄÄÂÄ4K7ÄÙ             0V pins of the oven PCB for support,
            e\³ === Â preset         making sure they missed the lid's
          PNP ÃÄÄÁÄÄÙ                counter display and the LED is visible.
             /³ 100u    OVEN
            ³           //           Adjust the preset so the LED lights,
            ÀÄÄ180RÄÄÂÄ´>ÃÄÂÄo 0V    and just goes out once the oven is
                     ÀÄ1K8ÄÙ         fully warmed up (5-10 mins).

D/ DEV 100kHz RANGE. Max deviation measuring range I changed from 20kHz to
100kHz. (E.g. now does 5kHz & 100kHz FSD). I put in a 10K series preset on the
3 pole (mode) range switch. But the Rx AF symmetry (+/- readings) needs setting
up with a scope for full 100kHz dev with low distortion, with careful tuning up
of the Rx discriminator & AFC pot! (see CAL procedure in next bul)

E/ METER ILLUMINATION. After removing the top strip & front panel, I added 4
meter LEDs & ground down normal white LEDs, to a thin square sliver 4x4x2mm to
            __       Smaller             \\   \\   \\   \\
  Original (__³==    Ground []==      ÚÄÄ´<ÃÄÄ´<ÃÄÄ´<ÃÄÄ´<ÃÄÄÄ220RÄ<+15V
  Lensed LED         Down LED         Á     4 white LEDS

Wired up all in series and glued each on top of a meter, making sure the top
fascia bezel/strip did not foul, and feed them via a 220R from 15V in nearby Rx
relay box plug. For good measure I taped silver plastic foil (sweet packet)
around outside edge of the meters, to help even out the light.

F/ Rx MODE LED. Also after removing the front panel, I drilled a hole in it and
added a Rx mode LED, near the "Zero power" pot, on the Tx/Rx relay's +8V via a
470R from the nearby Rx plug.

Rx mode>ÄÂÄÄÄ¿
        ÚÁ¿ 470R            So you know which mode the
      RF³ ³ _³_ Gn LED      test set is in, when switched
   RelayÀÂÙ \_/ Rx Mode     by the Power meter zero control!
         ³   ³\\

G/ AF MON LS. Also after removing the front panel, Stripped out the Selcall 6
push buttons thumb-wheel bank, and replaced it with a small LS (bent metal to
fit), Amp, Vol control, and a source switch.

                        +15V>ÄÄ47RÄÂÄÄÄ¿+               Loud Volume is clipped
                SOURCE             ³  ===2m2            when the Volts drop.
AF to SINAD PCBÄÄÄo<ÄÄ´ÃÄ¿      ³\ ³6  Á
                     10n ³     2³  \                    So now the "AF in",
SINAD Meter AFÄÄÄÄo      1M<ÄÄÄÄ´ LM \  5    +  220u    "Notched SINAD AF",
                        Log     ³ 386  >ÄÄÄÄÂÄ´ÃÄ¿      "Mod", or "Rx AF",
MOD Switch AFÄÄÄÄÄo     Vol  ÚÄÄ´    /¿7   10R   ³      can all be heard.
                        Pot  ³ 3³  /  ³+    ³    ³_/³8R
Rx Mod BNCÄÄÄÄÄÄÄÄo      ³   ³  ³/4³ ===   ===   |_ ³LS
                         ³   ³     ³  ³10u  ³u1  ³ \³

H/ AF OSC RANGE & LEVEL. Also after removing the front panel, I changed AF
modulation BCD controlled Wayne Osc's push button "kHz thumb wheel", from a
decade 0-9 type to a Hex 0-F type, recovered from the Selcall bank. This adds
6kHz more range (60 more) from 100Hz-15.9kHz. Unfortunately the thumb wheels
were not the same BCD data type! So 1 2 4 8 & C data lines had to be cross
wired with a ribbon to the wheel mounting PCB to make it work! The Wayne osc at
high frequency & gain were trimmed on the AF PCB, so the AF osc is now accurate
in level & frequency to +/- 1% see /8.

Also after the 15V PSU mod, I was able to greatly increased the AF osc level
(not clipping @ 4V RMS) to help the wide FM deviation I wanted, by replacing
the 56R with 680R in series with TH1 the regulating thermistor on the AF PCB in
the nest.

I/ OUT OF FREQ RANGE. The 100MHz frequency leaver operated thumb-wheel can be
set above 539MHz so I coloured RED the 6 7 8 9 thumb-wheel 100MHz number
options as a reminder!

See my tech Buls on "RTT Comms Test Set Cal & Use", "Analyser Takeda Riken
TR4122B", "AF Waveform Generator (RS)", "RTT Mod Meter (100)", "FeelTeck Dual
DDS Osc FY6600-60M", "Marconi Distortion Meter TF2337","Marconi 2019A Sig Gen"
"Systron Donner 1702 Sig Gen", "Marconi Counter Type 2432A", "198kHz Off Air
Standard", "Comparing Off Air Freq Standards", "Off Air Lock for Ref Osc", &
"Scope RF Trick".

Why don't U send an interesting bul?

73 de John, G8MNY @ GB7CIP

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