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G8MNY  > TECHNI   20.11.21 10:50l 529 Lines 29928 Bytes #999 (0) @ WW
BID : 53574_GB7CIP
Subj: RTT Comms Test Set
Sent: 211120/0933Z @:GB7CIP.#32.GBR.EURO #:53574 [Caterham Surrey GBR]

By G8MNY                              (Updated Nov 21)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
At a club sale, 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 & would have
cost > 10K UKP back then!

Some of my repairs & modification information may be useful for other kit too.
      /                                                          /|
     /                                                          / |
 Þ /__________________________________________________________/Ý  |
 Þ³³³ \ AF  ³³ \SINAD³³ 5 3 9.9 9 9 9 0 0 ³³ \MOD  ³³ \POWER³³³Ý  |
 Þ³³³__\____³³__\____³³___________________³³__\____³³__\ ___³³³Ý  |
ÚÁ³³.   _         _           _   _                    _     ³³Á¿ |
³_³³   (_)_______(_)         (ú) (_)    o   ù ! ! !   (_)    ³³_³ |
AF³³'  _ ³________³    _          _      _     _        .-.  ³³   |
in³³o (_)  o  o  (_)  (_) ! !   =(_)   =(_)   (_)   o  ( o ) ³³RF /
  ³³CTCSS SELCAL MOD     _      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 of this in one box...
Dummy Load & Attenuator
Power meter 6 ranges (Peak reading)
Frequency Counter (9 decimal places, very accurate)
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) & 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)
AM/FM/PM Automatic wide band scanning Rx, tunes in & locks up in 5 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          N socket 50ê 20dB Load atten. 1kW peak, 50W continuous
Power Meter       1-300W, 6 ranges (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 reference
Signal Generator  PLL 100Hz steps from 10 - 539.9999MHz, O/P -13dBm (50mV)
Sig Gen Harmonics >-20dBc, Typically >-30dBc
Gen Attenuator    10x1dB & 8x10dB for 1.7uV-50mV & via 40dB splitter & Load
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)
AF Modulation     Internal AF osc or ext, Mod Level Pot & 20dB Atten.
AF Osc            2 Dig Thumb wheel Wayne bridge, 100Hz-9.9kHz (Now to 15.9kHz)
Ext Mod/AF out    Needs >1V in, or gives 0-4V RMS AF out, 600ê BNC
Xtal/IF           455kHz & 10.7MHz in built & ext Xtal socket & osc O/P BNC
AF Meter          Bal/floating 3mV-10V & dBs 8 ranges, 11Hz-27kHz -3dB
SINAD meter       Auto level, 1kHz Notch, 0 to -20dB/100-0% Noise & Distortion 
Automatic Rx      Scans 2MHz->1GHz, 100mW-300W Load input, up to 60dB S/N
RF & IF O/Ps      Rear BNCs for 450-470kHz & RF in/out
Rx AF Filters     Comms -3dB 300Hz-3kHz, or HiFi -3dB 50Hz-15kHz
Modulation meter  Auto Rx. +/- peak, AM 50/100%, FM 5/100kHz, PM 2/5 Rad
Power             AC IEC Mains input 230V/115 @ 60W, or XLR for 12V DC @ 5A
Weight            24kg in flight case

SCHEMAIIC (reverse engineered)
      _______      ________   ________              ________________________
AF:ÄÄ´Bal AmpÃÄÂ>Ä´Range SWÃÄ´AF Meter³      MainsÄ´PSU +26,15,8.5,5,-12,-20³
     _______   ³   _______   ________   ___________
  :ijIF Xtal³  À>Ä´AGC AmpÃÄ´Rej 1kHzÃÄ´Sinad Meter³         Ext Mod/AF out
    __________    _________ link   ___________    _________ Mod AM/ ³   ___
RF ³Dummy Load³  ³AttnRelayÃo--oÄ<´ Switched  Ã<Ä´ PLL Sig ³FM/PM   ³  ³ AF³
INo´AttenuatorÃÄ>´Splitter ÃÄÄÄÄ¿ ³Attenuators³  ³GeneratorÃÄ<ÄÄÄÄÄÄÁ/Ä´Gen³
                 RF³ rly³    ³  ³        _________³_ ³  _³_         ³
   ___________    _³____³_  _³_ ÀÄÄ>ÄÄÄÄ´1/ö10 FreqÃ<)Ä´Ref³  _____ ³ _ _ _ _ 
  ³Power MeterÃÄ<´   RF   ³³Pre³     Exo´ Counter  ³ ³ ³OscÃ>´CTCSSÃÁ|Selcall|
  ³ & Range SW³  ³Detector³³amp³      inÀÄÄÄÄÄÄÂÄÄÄÙ ³ ÀÄÄÄÙ ÀÄÄÄÄÄÙ |ÄÄÄÄÄÄÄ|
  ÀÄÄÄÄÄÄÄÄÄÄÄÙ  ÀÄÄÄÄÄÄÄÄÙÀÄÂÄÙ          ctcss³     ³ ÚÄ>ÄoIF Out   |Display|
   _________       _______   ÀÄÄÄÄÄ>ÄÄÄÄÄÄÄ¿  _³_____³_³_            À--Â----Ù
  ³Mod MeterÃÂÄ<ÄÄ´  AF   ³   ____________ ÀÄ´ Automatic ³              ³
  ³+/-Switch³ÀoRx ³FiltersÃÄ<´Range & ModeÃ<Ä´Scanning RxÃÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÙ

Auto RF switching changes the Rx & Counter over & disconnects the Signal Gen,
when the Power Meter detector sees 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 |               |³        ³           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 PCB³³ ³³ ³³   Rx   ³  ³& Atten ³
³³ FOR 6 PLL³³  Ý FÝ  Ý  : ³ ßßßßßßßßßßßßßßßßß³        ÃÄÄÙ        ³
³³          ³ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÙ                  ³ SCREEN ³    ÚÁÁ¿   ³
³³ HF - UHF ³         ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿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   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            Xtal  Mod  Gen ÀÄÙ RF³
                  /AF out  in               IF/Osc  out  out  N  Sample
Going through the maze of functions, I found several faults....

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

2/ Tx Load 20dB atten, presented 147ê not 50ê! It looked clean & not smelling,
so not burnt out? I stripped it down (front & side panel off), to find it was
all quite loose. It had screw on ends that held large ally washers with spring
washers in the tube surrounding the RF resistors.

     3 Small rod type Rs              Þ Þ Þ Þ Þ Þ Þ Þ Þ Þ
     /       |       \                Þ Þ Þ Þ Þ Þ Þ Þ Þ Þ
(o)Ä8êÄÂÄ ÄÄ47êÄÄÄÄÂÄ39êÄ<SMA      __Úßßßßßßßßßßßßßßßßßßßß¿
 N³    ³  \loose   ³     ³       N³  ³Ü._____±_____±_____.³Ä¿SMA
  ³   139ê  here  14ê    ³        ³__³ß'~~~~~±~~~~~±~~~~~'³ÄÙ
        \         /                   Þ Þ Þ Þ Þ Þ Þ Þ Þ Þ
       2 Disc type Rs                 Þ Þ Þ Þ Þ Þ Þ Þ Þ Þ

There were no open circuit Rs or burnt bits. Putting it all back together
tightly, I now see 50ê. (previous owner been playing?) And on an analyser &
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! Access was by removing top, bottom & a side panel, then strip
down the Rx Box's side panel with the Rx bolted on it. I found a broken 10K FM
Adj preset. Replaced, but needed to be 15K to calibrate the 5kHz range! Rough
holes had been drilled for calibration adjustment! The inner PCB is only
soldered in place. The 3 nuts are just stand offs under the PCB, (used before
soldering), & I soldered in the 2 loose captured screws for ease of assembly!
³( )         FM       PM           AM          /~~\      ³ INSIDE
³( )         Adj      Adj          Adj         \__/      ³ AUTO SCAN 
³         Signal conditioning & AF meter PCB             ³ Rx Box is
³³ in  Mixer     IF[o]    AGC IC    AM [o]           ³   ³ With 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
Also the 20kHz range needed a series preset on the range switch to get that
right too. (See D/ Mod) Inside the Rx box there are AM AGC & FM discriminator
adjustments that affects calibration & the scanning STOP ability! (previous
owner playing?)

4/ PM un-calibratable. (PM = 6dB/Octave treble lifted FM). 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....
"1 Radian (57ø) of PM occurs when the FM AF Mod Freq = the Deviation."

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

5/ 12V DC input, uses a 2 transistor inverter on dedicated windings on the
mains tranformer, but there was a NPN collector framing (OK on an isolated
battery). Only 6 screw 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, & the mains is disconnected on 12V mode!

 NÄÄÄÄoÄoÄÄÄÄÄÄÄ/oÄÄÄÄÄÄÄÄÄÄÄÄÄ¿           ³Transformer
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.

6/ Later in an attempt to reduce 12V hum & other rail interference, I lifted of
centre (ct) tap's high current earth pulses off the transformer chassis, & now
wired it directly to isolated (2 nylon screws & insulation kit) PSU PCB's 0V.
So now the PSU DC earths only come from the PSU-module connector & no more hum
loops via the chassis!

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

7/ AF osc & SINAD circuits are on a plug in 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. I adjusted one of the Wayne bridge osc C values (room
for 4 caps on PCB for this). Each of the 2 thumb wheels actually operates 4
relays, to control the 8 pairs of Wayne bridge Rs, that determine the 100
frequencies. I also put a CR (220 & n82 in series) across the 150R (Thermistor
to earth R) to frequency calibrate the extended upper frequencies after my mod.
(See H/ mod).

8/ CTCSS pilot tone had poor shape @ LF. In the PCB card 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 in to 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.

9/ The 1dB RF sig gen's stepped attenuator was doggy. Leaning on the knob gave
different levels! Access to remove the atten unit was very difficult, front
panel & 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¿        It was these weakened SMA gold plated springs,
      ³ ÝßßßßßßßßßÞ ù³        needed a slight bend to fix. But also a
 Shaft³ \[ atten ]/ |³Click   sliding to the SMA 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.

10/ A recent fault was hummy FM RF when cold, affecting all 6 RF osc & not an
external signal. This was not mains locked hum, as I first thought, but from
the 100Hz PLL RF osc system. Access was by removing top, bottom & a 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  ÃÄ<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        ÚÄÄÄÄÄÄÄÄÄÄ¿        ³
  FM >ÄÄÄÄÄÄÄÄÄÄÄÄÄÙ   AFC     ³  Filter  ³
With the help of freeze spray's long stalk & a hair dryer, it eventually turned
out to be on the PLL active filter, where an FET was not able to fully turn off
a 2N2481 NPN AFC amp, on the plug in PLL control PCB inside oc box.
Changing it for another NPN cured it, after a lot of testing.

     === ³    ³                        2K2  Pull up   ³
  33u Á  ³    ³                         ³   Current   ³    In this unusual
         ³   22K                        e\³ Mirror   2K7   circuit, the filter
         ³    ³           Low Level    PNPÃÄÄÄÄÄÄÄÄÄÄÄ´    Cs are only active
    AFC   \³  ³   s  g  Active Filter    /³           ³    when the FET is in
    AMP NPNÃÄÄÁÄÄÄÄ´>ÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÄÄ´             ³    class A & amplifying
         e/³   P ch³FET   22K ===1u      \³ 47u     ³/     input DC pulses.
         ³       ÚÄ´       ÃÄÄÄ´       NPNÃÄÄÂÄÄÄÂÄÄ´NPN
    OSC  ³       ³d    2u2=== ===       e/³ === 2K2 ³\e
 R   DC                                2K2     Á     2K2
 Á          FET only sees 0.6V      Down³             ³Up
                                         100Hz Pulses
                                       Phase Detector IC

Later after reducing the 12V hum (see 6/), I reduced some of the RF osc wobble
for a better UHF CW note, by reducing the 1u to u47 & removing 1 of the 2u2.
Osc lock up time also reduced. But further C value reduction left unstable non
lock up!

11/ A recent crackly Rx noise fault in the very wide-band 2MHz->1GHz automatic
Rx. (see 3/) On testing I blew up its 78L05, & 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                             ÀÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄ<ÄÄÄÄ)ÄÄÄÄÄÁÄÄ>Lock LED
   ³Harmonic Ã<´1-2MHzôRampÃ<´256 RampÃ<´10HzÃ<ÄÙStop  ³FM ôFM  ôAF ÃÄ>FM
   ³Generator³ ³ Osc  ³³Amp 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 gets 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, if it was the wrong side image.

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

A/ Set of usefull trimming tools & 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 opearated thumbwheels). Large leads stored between feet.

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> Banana plugs & clips for AF testing

BNC to double banana plug adapter, for Sinad input testing.

BNC T, to enable monitoring of signals.
B/ Inside the counter box, 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 sheet, usable with the top cover just slid off.

Unregulated           Ú-----------¿      This permitted the finest of tweaks
  +8.5V >ÄÄÄÄÄÄÄÄÄÄÄÄÄoOVEN HEATER|      when hot, when calibrated with an
                      |           |      external off air reference.
    +5V >ÄÄÄÄÂÄÄÄÄÄÄÄÄo+5V        |
Local reg    ³        |  REF OSC  |      I also made a polystyrene cover for 
            10K  +10u |   MODULE  |  __  the protruding hot oscillator box,
            PreÃÄÄÂÄÄÄoAGE     RF>oÄ)__  to reduce oven power & make the
            set  ===  |           | ³    temp more stable (& hence frequency)
        ÄÄÄÄÄÁÄÄÄÄÁÄÄÄo0V      GNDoÄÙ    more quickly.
Tracking down FM hum & drift, I found thgnal 6.8V reference zener & 1K8
were a poor regulator of the hummy 8.5V, & gave a lot of long term thermal
drift. The fine tuning AGE voltage, only needed around 2.5V, so I used the
nearby 5V regulated rail with a 10uF on the pot slider. This was much better
for hum & much lower drift now too.

Also I added 6mm dia ferrite beads to the +5V rails feeding the 3 items in the
counter box, & 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/ Inside the counter box, I also added an "OVEN" LED, to show when the oven is
warming & freq not accurate.

Unregulated ³          ³
            ÃÄÄÄÄÄ´>ÃÄÄ´1N4001       The circuit & LED are placed inside
            ³   +      ³             counter box & soldered to the +8.5V &
            ÃÄÄÄÄÂÄ4k7ÄÙ             0V pins of the oven PCB for support,
            e\³ === Â preset         making sure they missed the lid's
          PNP ÃÄÄÁÄÄÙ                counter display & LED is visible.
             /³ 100u    OVEN
            ³           //           Adjust the preset so the LED lights
            ÀÄÄ180ÄÄÄÂÄ´>ÃÄÂÄo 0V    & just goes out, once the oven is
                     ÀÄ1K8ÄÙ         fully warmed up (5-10 mins).

D/ 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 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!

E/ After removing the front panel, I added meter LEDs. I ground down 4 normal
white LEDs, to a thin square sliver 4x4x2mm to fit.

            __       Smaller             \\   \\   \\   \\
  Original (__³==    Ground []==      ÚÄÄ´<ÃÄÄ´<ÃÄÄ´<ÃÄÄ´<ÃÄÄÄ220RÄ<+15V
  Lensed LED         Down LED         Á     4 white LEDS

Wired up all in series & glued 1 on top of each meter, making sure the top
fascia bezel did not foul, & feed them via a 220R from 15V in nearby Rx relay
box plug. Then for good measure I taped silver plastic foil (sweet packet)
around outside edge of the meters, to help even out the light.

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

Rx mode>ÄÂÄÄÄ¿
        ÚÁ¿ 470             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/ Also after removing the front panel, I stripped out the Selcall thumb wheel
bank from front panel, & replaced it with a small LS (bent metal to fit), Amp,
Vol control, & a source switch.

                         +15V>ÄÄ47ÄÂÄÄÄ¿+               Loud Volume clipped
                SOURCE             ³  ===2m2            when Volts drops.
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   10    ³      can all be heard.
                        Pot  ³ 3³  /  ³+    ³    ³_/³8
Rx Mod BNCÄÄÄÄÄÄÄÄo      ³   ³  ³/ ³ ===   ===   |_ ³LS
                         ³   ³    4³  ³10u  ³u1  ³ \³

H/ Also after removing the front panel, I changed AF modulation BCD controlled
Wayne Osc's "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. But 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 @ HF frequency & gain were trimmed on the AF PCB,
so the AF osc is now accurate in level & frequency to ñ1% see /7.

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

The PSU has only a -20V preset, & test points for all other voltages.

For AM FM PM calibration of the Rx module & for the for AF volts meter, I use a
"calibrated by design" source a "FeelTeck Dual DDS Oscillator FY6600-60M".
(This is despite it having an AM depth "number" issue, & P-P values needed.)
Underside of Rx box has presets for FM PM & AM calibrations.

Auto tune Rx box has internal presets inside the inner RF box as sketched
earlier. Set STOP preset for reliable action, then tune IF coils for narrow
bandwidth (scope IF O/P with wide dev sweep) & constant level from AGC for AM,
centred AFC action with FM discriminator for FM & PM mode giving identical +/-

Rx Splitter atten preset (small hole to bias DC into diodes in Tx mode)
adjustment needs to be enough so, no Rx overload occurs on an AM signal @ 300W
carrier (3W after load), & still leaves good Rx sensitivity @ 500mW (5mW after

Once the Rx is calibrated, it is easy to check the sig gen is working correctly
against it & the counter is functionaling correctly. Internal RF oscillator box
has a preset for the RF AGC, 6 AM bias pots for each osc are adjusted for best
modulation shape over each osc range, checked with a scope from Rx IF. 4 lower
PLL tuned circuit centring. FM deviation modulation sensitivity varies
depending on the varicap voltage needed for the frequency, so 100kHz deviation
is not possible at all frequencies.

SINAD meter cal with its AGC, is done with the AF osc patched from the AF Osc/
Rx mod O/P, & for the 100% level set frequency to 2-3 kHz, then @ 1kHz the 2
null pots adjusted, for lowest 0% reading (listen Sinad O/P). The AGC range can
cause some slight distortion, so calibrate over the AF level range needed.

CTCSS Frequencies are accurately clocked from the 4 dig thumbwheel data, so
should be accurately seen on the counter with the CTCSS measure button. For
lowest distortion, set @ 300Hz & scope (distortion analyse) the Rx wave shape &
adjust the + & - clippers for best shape. Adjust the set square @ 800Hz, LF
correction 8/ pot @ 50Hz & redo for best results again. Distortion was < 2% 50-

AF Osc, the 160 dial up frequencies were trimmed with added Wayne bridge caps
for the LF end, & gain setting caps around the op amp for the 15.9kHz. All are
now within 1%. Distortion is < 0.3% (-50dB) @ 1kHz.

RF Frequencies are clocked from the 7 dig thumbwheel data & PLL so should be
accurate if reference is OK. For calibrating the reference oven, I use a scope
& view a 1MHz locked from 198kHz off air standard, with the sig gen's 10MHz &
adjust for no drift when it is properly warmed up (10mins). This calibrates the
9 digit counter too.

RF Level should be -13dBm measured with atten set to max level at the pre-load
BNC link. Adjustment is the ALC present inside the nested Osc box. Level
flatness (+/-0.5dB 10MHz-539.9MHz). Each Osc coil is tuned for good PLL lock
voltages on band edeges.
RF harmonics & sig gen's 90dB atten checked @ all frequencies on spectrum
analyser. And the 300W dummy 20dB atten load & Splitter box 20dB with analyser
tracking gen.

RF Power has 6 presets for the 6 power ranges. These have only been compared
with other meters occasionally & itself on range steps.

See my tech Buls on "RTT Comms Test Set 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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