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]
To : TECH@WW
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 /
SO WHAT IS IT?
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
IN ÀÄÄÄÄÄÄÄÙ ³ ÀÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÙ 12V__/ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
_______ ³ _______ ________ ___________
:Ä³IF Xtal³ À>Ä´AGC AmpÃÄ´Rej 1kHzÃÄ´Sinad Meter³ Ext Mod/AF out
oÄÁÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÙ o
__________ _________ 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
OUTÀÄÄÄÄÄÄÄÄÄÄÙ ÀÄÂÄÄÄÄÂÄÄÁÄ¿ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÙ ÀÂÄÄÂÄÄÄÂÄÁÄ<ÄÄÄÄÄÄ¿ ÀÄÄÄÙ
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
ÀÄÄÄÄÄÄÄÄÄÙ Mod ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÙ
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 _____ ÜÜÜÜÜÜÜÜÜÜÜ³
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!
ÚÄÄÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³( ) FM PM AM /~~\ ³ INSIDE
³( ) Adj Adj Adj \__/ ³ AUTO SCAN
³ Signal conditioning & AF meter PCB ³ Rx Box is
³ÚÄÅÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ this PCB,
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
³³Multiplier (o) R x P C B (o) ³Screened
³³ Sweep amp STOP AFC ³Rx ³
³³ ³ ³
³³1.5-2MHz Limitor[o] FM ³ ³
³³ [o]Osc rampIC 10HzOsc [o] Discrim 5V³ 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
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!
LÄÄÄÄo-oÄÄÄÄÄÄÄ/oÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿Mains & Inverter
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.
ÚÄ²ÂÄÄÄÒÄÄÄÂ²ÄÄ¿ 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
To ÚÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÁÄÄ¿ ÚÄÄÄÄÄÄÄÄÄ¿ ÚÄÁÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄ¿
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
AttenÀÄÄÄÄÂÄÄÄÄÙ ÀÄÂÄÄÂÄÙ ÀÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÙ ÀÄÄÄÄÄÂÄÄÄÄÄÙ
³ ³ ³ ÚÄÄÄÄÄÄÄÄÄÄ¿ ³
AM >ÄÄÄÄÙ ³ ÀÄÄÄ<ÄÄÄÄ´Active PLLÃÄÄÄ<ÄÄÄÄÙ
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
Ú--AFC<ÄÁÄÄ10KÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÙ2u2 ³ ÀÄÂÄÙ ³
R DC 2K2 Á 2K2
Á FET only sees 0.6V Down³ ³Up
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
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.
ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄÄ¿ÚÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿ÚÄÄÄ¿ ÚÄÄÄÄÄÄ¿ÚÄÄÄ¿ ÚÄÄÄÄÁÄ¿ÚÄÄÄ¿ÚÄÄÄ¿
RxÄ´Ring Ã>´460kHzÃ´IF Ã>´460kHz Ã´AGCÃ>´460kHzÃ´IF Ã>´460kHzÃ´AM Ã´AF ÃÄ>AM
in ³Mixer³ ³ LPF ³³Amp³ ³Filters³³ IC³ ³Filter³³Amp³ ³Filter³³Det³³Buf³
ÀÄÄÂÄÄÙ ÀÄÄÄÄÄÄÙÀÄÄÄÙ ÀÄÄÄÄÄÄÄÙÀÄÂÄÙ ÀÄÄÄÄÄÄÙÀÄÄÄÙ ÀÄÄÄÂÄÄÙÀÄÂÄÙÀÄÄÄÙ
³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄ<ÄÄÄÄ)ÄÄÄÄÄÁÄÄ>Lock LED
ÚÄÄÁÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄ¿ÚÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄ¿ ³ ÚÄÁÄ¿ÚÄÄÄÄ¿ÚÄÄÄ¿
³Harmonic Ã<´1-2MHzÃ´RampÃ<´256 RampÃ<´10HzÃ<ÄÙStop ³FM Ã´FM Ã´AF ÃÄ>FM
³Generator³ ³ Osc ³³Amp ³ ³ Counter³ ³Osc ³ ³Lim³³Disc³³Buf³
ÀÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÙÀÄÄÂÄÙ ÀÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÙ AFC ÀÄÄÄÙÀÄÂÄÄÙÀÄÄÄÙ
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
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
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.
+8.5V >ÄÄÄÄÄÂÄÄÄÄ4R7ÄÄÄÂÄÄÄÄÄo Heater
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
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!
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
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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