| |
G8MNY > TECH 07.02.21 11:21l 498 Lines 27283 Bytes #999 (0) @ WW
BID : 22683_GB7CIP
Read: GUEST
Subj: RTT Comms Test Set
Path: IW8PGT<IZ3LSV<I3XTY<I0OJJ<GB7CIP
Sent: 210207/0912Z @:GB7CIP.#32.GBR.EURO #:22683 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Feb 21)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
A few years ago at a club sale, I bought this large heavy test set in its smart
flight case. It could 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 many 1000s of UKP back then!
Some of the repairs & modifications info may be useful for other kit too.
___________________________________________________________
/ /|
/ / |
ÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜ/ |
Þ /__________________________________________________________/Ý |
Þ³ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿³Ý |
Þ³³ÚÄÄÄÄÄÄÄ¿ÚÄÄÄÄÄÄÄ¿ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ÚÄÄÄÄÄÄÄ¿ÚÄÄÄÄÄÄÄ¿³³Ý |
Þ³³³ \ AF ³³ \SINAD³³ 5 3 9.9 9 9 9 0 0 ³³ \MOD ³³ \POWER³³³Ý |
Þ³³³__\____³³__\____³³___________________³³__\____³³__\ ___³³³Ý |
ÚÁ³³o _ _ _ _ _ ³³Á¿ |
³_³³ (_)_______(_) (ú) (_) o ø ! ! ! (_) o ³³_³ |
AF³³o _ 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 /
³ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ³/
~~Þ²Ý~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Þ²Ý~~
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 CW AM FM & PM modulations
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 Rx (Automatic wide band scanning Rx)
Modulation Meter, (Auto Rx 2Mz-1HHz) +/- Peak reading, 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 the Internet
either). So I had to do a lot of reverse engineering.
SPECIFICATION
Power AC IEC Mains input 230V/115 @ 60W, or XLR for 12V DC @ 5A
RF Input N socket 50ê 40dB Load atten. 1kW peak, 50W continuous
Power meter 1 3 10 30 100 & 300W (RF detection for Counter & Rx)
Frequency Counter 9 digit 1Hz-540MHz in 3 gate times & 10 sec averaging to 1Hz
Freq Reference Accuracy < 1/10^7/month, internal Xtal Oven reference
Signal Generator 100Hz steps from 10-539.9999MHz, PLL type @ -13dBm (50mV)
Sig Gen Harmonics >-20dBc, Typically >-30dBc
Gen Attenuator 10x1dB & 8x10dB for 1.7uV-50mV via 20dB splitter & 20dB Load
Pilot tone(CTCSS) PLL 20.0Hz-999.9Hz Mod Level adjustable & Rx Counter readout
Selcall 6 char. Mod Level adjustable & Decoder.(No PCB, removed)
Modulation AF Osc 100Hz-9.9kHz or ext, Level adj.(Now goes to 15.9kHz)
Ext Mod/AF out Needs >1V in, or gives 0-4V AF out, 600ê.
Xtal/IF 455kHz & 10.7MHz in built & ext Xtal socket & osc O/P BNC
AF Meter Bal/floating 3,10,30,100,300mV,1,3,10V & dBs, 11Hz-27kHz -3dB
SINAD meter Auto level, 1kHz Notch, 0-20dB/0-100% Noise & Distortion
Automatic Rx Scans 2MHz >1GHz, 100mW-300W Load input, up to 60dB S/N.
Rx AF Filters Comms 300Hz-3kHz -3dB, or HiFi 50Hz-15kHz -3dB
Modulation meter Auto Rx. +/- peak, AM 50% 100%, FM 5kHz 100kHz, PM 2Rad 5Rad
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 _______ ________ ___________
:ijIF Xtal³ À>Ä´AGC AmpÃÄ´Rej 1kHzÃÄ´Sinad Meter³ Ext Mod/AF out
oÄÁÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÙ o
__________ ________ link ___________ _________ ³\ ____
RF ³Dummy Load³ ³ Relay Ão--oÄ<Ä´ Switched Ã<´ PLL Sig ³ / ÄÁÄÄÄÄ´ AF ³
IN o´AttenuatorÃÄ>´SplitterÃÄÄÄ¿ ³Attenuators³ ³GeneratorÃÄ<ÄÁÄÄÄÄ¿ ³Gen ³
OUT ÀÄÄÄÄÄÄÄÄÄÄÙ ÀÄÂÄÄÄÄÂÄÁÄ¿ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÙ ÀÂÄÄÂÄÄÄÂÄÙAM/FM/PM³ ÀÄÄÄÄÙ
RF³ rly³ ³ ³ _________³_ ³ _³_ ³
___________ _³____³_ ³ ÀÄÄ>ÄÄÄÄÄ´1/ö10 FreqÃ<)Ä´Ref³ _____ ³ _ _ _ _
³Power MeterÃÄ<´ RF ³ ³ Ex in o´ Counter ³ ³ ³OscÃ>´CTCSSÃÁ|Selcall|
³ & Range SW³ ³Detector³ ³ ÀÄÄÄÄÄÂÄÄÄÄÙ ³ ÀÄÄÄÙ ÀÄÄÄÄÄÙ |ÄÄÄÄÄÄÄ|
ÀÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÙ ³ ctcss³ ³ |Display|
_________ _______ ÀÄÄÄÄ>ÄÄÄÄÄÄ¿ ___³______³_ À--Â----Ù
³Mod MeterÃÄ<´ AF ³ ____________ À´ Automatic ÃÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄÙ
³+/-Switch³ ³FiltersÃÄ<´Range & ModeÃ<´Scanning RxÃ>ÄoRx Mod
ÀÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÂÄÄÄÄÄÄÄÂÄÙ
Ext RF In oÄ>Ù ÀÄÄ>ÄoIF Out
Auto RF switching changes the Rx & Counter over & disconnects the Signal
Generator, 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 (lid off)
PCB NEST DC INVERTER IF Out
ÚÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ÚÄÄÄÄÄÄÄÄÄÄ¿³ RÝ SÝ CÝ S: ³ | |ÚÄÄÄÄÄÄÄÄ¿ 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¿ RF ³
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 ÚÄÄ¿ 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 DIG DISPLAY ³ ³METER³ =³METER³==³
ÃÄÄÁÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÁÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÁÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÁÄÄ´
ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÂÄÄÄÂÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÂÄÄÄÂÂÄÄÄÄÂÂÄÂÄÂÄ´
³ Ext Counter Xtal Mod Gen ÀÄÙ ³
AF in IF/Osc out out N Sample
FAULTS
Going through the maze of functions, I found several faults....
1/ Mains switch's long push 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 onto the switch, & used a rubber sleeve behind the
front panel to captured it, so it won't fall out again.
2/ Tx Load 40dB attenuator, 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. There were no
open circuit Rs or burnt bits. Put backs all together & did up tight, all OK
now 50ê seen. (previous owner been playing?) And on an analyser & tracking
generator, showed it has a constant 20dB attenuation to > 1GHz.
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
ÀÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÙ ÀÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÙ
\ / Þ Þ Þ Þ Þ Þ Þ Þ Þ Þ
2 Disc type Rs Þ Þ Þ Þ Þ Þ Þ Þ Þ Þ
3/ FM deviation measurement range (used for the signal generator 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
preset. Replaced, but needed to be 15K to calibrate the 5kHz range! Rough holes
had been drilled for the Cal adjustments! 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 in captured screws!
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³( ) FM PM AM /~~\ ³ INSIDE
³( ) Adj Adj Adj \__/ ³ AUTO
³ Signal conditioning & AF meter PCB ³ SCAN
ÃÄÅÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ Rx
³ in Mixer IF[o] AGC IC AM [o] AM ³ ³ BOX
³ [o]IF IF[o] Detect AGC ³ ³
³Harmonic ³2nd³
³Multiplier R x P C B ³Screened
³ Sweep amp STOP AFC ³Rx ³
³ ³Box³
³1.5-2MHz Limitor[o] FM ³ ³
³ [o]Osc rampIC 10HzOsc [o] Discrim 5V³ ³
³___________________________________________________³ ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
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 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."
5/ 12V DC input, uses a 2 transistor inverter but had a NPN collector framing
(OK on an isolated battery). Simple 6 screw access to remove PSU.
LÄÄÄÄo-oÄÄÄÄÄÄÄ/oÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
NÄÄÄÄoÄoÄÄÄÄÄÄÄ/oÄÄÄÄÄÄÄÄÄÄÄÄ¿ Mains ³Transformer
IEC 2x 0.25A ÚÄ\oÄÄÄÄÄÄÄÄÄÄ¿ (((((((((((() ______ÚÄÄÄmains earth shield
³ ===========³======================
ÚÄo-oÄ´>ÃÄ´ ()))) ()))))))))) ()))))))))))))))
³ 5A 120R³ ³ ³ ³ 8-0-8v ³ ³ ³ ³ ³ ³ ³ ³Secondaries
+12VÙ ÃÄÄ(ÄÙ ³ ³ ³ 26 17 7 0 7 17 26V
XLR INVERTOR³ ³101ÀÄ)ÄÄÄÄÄ¿ ³ Á
0V¿ BIAS ³ ÀÄÄÄÄÄ)ÄÄÄ¿ 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 ÃÄÙ ÀÄ´ from small to large Tab transistors?
³DC ³ e/³ ³\e
ÀÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÙ I also added 4700uF across 12V input.
The way it is wired the On/Off switch stops inverter OK, but leaves bias load
on the battery! The mains switch is wired so when off, the DC is on.
6/ Later in an attempt to reduce 12V hum & other rail interference, I lifted of
centre tap's 0V high current pulses earth on the transformer chassis & isolated
it, so the humless PSU earth now come from the PSU DC connector & no hum loops!
Eventually to get the power rail interactions right down, I swapped the PSU's
12V 7812 reg for 15V 7815 one, & added 12V regs to both the Osc Box & AF meter
PCB for a proper job with no power rail interaction. Then I re-calibrated the
Rx on the new +15V!
7/ AF Osc is on a plug in card with SINAD circuit in the PCB card nest. It 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 it). The thumb wheels actualy operate 8 relays to control
the 8 pairs of Wayne bridge osc Rs that determine up to 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 modification.
(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 generator IC. So I added
some LF frequency correction bias to the set square 1:1 preset (sets balance of
+/- currents in to ramp C).
Preset
ÚÄR21ÄÂÄÄÄ470KÄÂÄ100kÄÄ R1-7 Set Preset for best 20Hz & set SQ @ 500Hz.
³ 4ÚÄÄÄÄ¿ ÃÄÄ47kÄÄ Resistor I used this on these AF osc ICs before,
VR1 ³8038³ ÃÄÄ47kÄÄ Pack but this time the correction DC had to
SetÄÄÄÄ6³ BC ³ ÃÄÄ47kÄÄ CTCSS come from set of Rs decoding some of
SQ ³ ³ ÃÄÄ82kÄÄ Freq the BCD data lines. (not in BCD order!)
ÀÄR15Ä5³ IC6³ ÃÄ390kÄÄ Data It now gives fairly good sign wave
³ ³ ÀÄ180kÄÄ Lines from 20.0Hz to 999.9Hz.
9/ 1dB stepped attenuator was doggy. Leaning on the knob gave differing levels.
Access to remove the attenuator unit was difficult, front panel & PSU had to be
removed. Tiny screws removed, showed it had 10 "fuse like" T attenuators in a
cage turret construction, with sliding contacted at each end by the in & out
SMAs spring contacts & 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.
±±±±±±±±±±±±±±±±±±±±±plate
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 a hummy RF osc when cold, affecting all 6 oscillators.
This was not mains locked hum as I first thought, but from 100Hz PLL system.
Access was by removing top, bottom & a side panel, then strip down the 2 brass
nested faraday cage RF covers.
ÚÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄÄ¿
SelectÚÄ<ÄÄ´ControlÃÄÄÄÄÄÂÄ<Ä´ 7 Freq ³
Osc ³ ³ EPROM ³ Freq³ ³Thumb wheels³
³ ÀÄÄÄÄÄÄÄÙ Data³ 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 ÚÄÄÄÄÄÄ¿ ³
AM >ÄÄÄÄÙ ³ ÀÄÄÄ<ÄÄÄÄÄ´ PLL ÃÄÄÄÄÄ<ÄÄÄÄÄÙ
FM >ÄÄÄÄÄÄÄÄÄÄÄÄÄÙ AFC ³Filter³
ÀÄÄÄÄÄÄÙ
With the help of freeze spray's long stalk, 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 the osc box. Changing it for
another NPN cured it, after a lot of testing.
+26V>ÂÄÄÂÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
=== 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 & amplying
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
100Hz Pulses
Phase Detector IC
Later after reducing 12V hum (see 6/) I reduce some of the osc wobble (better
UHF CW note) by reducing the 1u to u47 & removing 1 of the 2u2. Lock up time
also reduced. But further C value reduction left unstable non lock up!
11/ Recent noise fault in automatic very wideband 1MHz->1GHz Rx. On testing I
blew up its 78L05, & zapped a mosfet hex ineverter IC! Noise was mostly from
scratchy AFC preset pot.
The Rx has a wide 460kHz IF, feeding AM & FM detectors. The front end is just a
ring mixer, fed with highly harmonic rich 1.5-2MHz Osc. This is tunned with a
varicap in 256 steps from a ramp generator/8 bit counter/anolog out IC, from a
10Hz osc, that is stopped when a good enough IF signal is detected in the AM
(with AGC) detector, & then the FM discriminator AFC takes over for fine
frequency control.
The Rx itself is fed from a 4 way splitter attenuator unit, that feeds the
siggen & counter signal to & fed via the 20dB load attenutor from Tranceiver
under test, but attenuates the external signal when the Tx is enabled.
MODIFCATIONS
A/ Set of 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).
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
Ferrite
PL259 -]====================N> N Plug RF Dummy Load in
Both low loss coax
N Plug <N===================N> N Plug RF Dummy Load in
BNC <=======================N> N Plug RF Dummy Load in
BNC <========================> BNC general patch lead
ÚÄ>
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 oscillator's
fine tune 10kê preset (hidden), for a fine multi-turn version. And drilled
access hole usable with the top cover just slid off.
Unregulated Ú-----------¿ This permitted the finest of tweak
+8.5V >ÄÄÄÄÄÄÄÄÄÄÄÄÄoOVEN HEATER| when hot, to be comparable to 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)__ reduces the oven power & makes the
set === | | ³ temp more stable (& hence Frequency)
ÄÄÄÄÄÁÄÄÄÄÁÄÄÄo0V GNDoÄÙ more quickly.
À-----------Ù
Tracking down FM hum & drift, I found the original 6.8V ref zener & 1K8 was a
poor regulator of the hummy 8.5V, & gave a lot of long term thermal drift.
The fine tuning AGE voltage, only needed is around 2.5V, so I used the nearby
5V regulated rail with a 10uF on the slider. This was much better for hum &
lower drift now.
Also I added 3 large ferrite beads to the +5V rails feeding the 3 items in the
counter box & a 100uF 16V on +8.5V @ the 5V reg, as it was now oscillating
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/ Added an "OVEN" LED, to show when the oven is warming & Freq not accurate.
+8.5V >ÄÄÄÄÄÂÄÄÄÄ4R7ÄÄÄÂÄÄÄÄÄo Heater
Unregulated ³ ³
ÃÄÄÄÄ´>ÃÄÄÄ´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 miss the lid's
PNP ÃÄÄÁÄÄÙ counter display & LED is visible.
/³ 100u OVEN
³ // Adjust the preset so the LED lights
ÀÄÄ180ÄÄÄÂÄ´>ÃÄÂÄo 0V & goes out, once the oven is
ÀÄ1K8ÄÙ fully warmed up (5-10 mins).
D/ Max deviation measuring range changed from 20kHz to 100kHz. (E.g. now does
5kHz & 100kHz FSD). I put in a 10kê series preset on the range switch. But the
Rx AF symmetry needs setting up with a scope for full 100kHz dev with low
distortion, by careful tuning up of the discriminator & AFC!
E/ After removing the front panel, I added meter illumination 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 under run white LEDS
Wired up all in series & glued 1 on top of the meters, making sure the top
fascia bezel did not foul, & feed them via a 220ê from 15V in nearby Rx relay
box plug. Then for good measure I cellotaped silver plastic foil (sweet packet)
around outside edge of the meters, to help even out the illumination.
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 470ê on the nearby Rx
plug.
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\\
0VÄÄÄÁÄÄÄÙ
G/ 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
0VÁÄÄÄÁÄÄÄÄÄÁÄÄÁÄÄÄÄÄÁÄÄÄÄÁ
H/ 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 freq & 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) to help wide FM dev I wanted, by replacing the 56R with 680R in
series with TH1 the regulating thermistor on the AF PCB.
CALIBRATION
The PSU has only a -20V preset, & test points for all other voltages.
For AM FM PM cal of the Rx module & for the for AF volts meter, I use a
calibrated source "FeelTeck Dual DDS Osc FY6600-60M". (This is despite DDS
having an AM depth number issue, & P-P values needed.) Internal auto Rx box has
presets as sketched earlier.
Once the Rx is calibrated, it is easy to check the Siggen is working correctly
against it & the counter. Internal RF Osc box has a preset for the RF level, 6
presets for best AM bias on each Osc buffer & 4 tuneable Ls for the 4 lower PLL
tuned circuit centring.
SINAD meter cal with its AGC, is done with the test sets own AF osc patched
from the Rx AF O/P, & for the 100% level set freq to 2-3kHz, then @ 1kHz the
deepest 2 null pots, adjusted for 0% reading.
CTCSS Frequencies are clocked from the 4 dig thumbwheel data so should be
accurate as with CTCSS measure button. For lowest distortion, set to 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% 50-800Hz.
AF Osc, the 160 dual up frequenies were trimmed with added wayen 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% @ 1kHz.
RF Frequencies are clocked from the 7 dig thumbwheel data & PLL so should be
accurate if ref is OK. Calibrating the ref oven, I use a scope & view a 1MHz
locked from 198kHz off air standard, with the siggen's 10MHz & adjust for no
drift when it is properly warmed up (>10 mins). This calibrates Counter too.
RF Level should be -13dBm measured with the Atten set to 0dB from the pre-load
BNC link. Adjusment ALC present is done inside the Osc box. Level flatness,
harmonics & siggens 90dB atten checked @ all frequencies on spectrum analyser.
And the 300W dummy 40dB attenuator load with analyser's tracking generator.
The 6 ranges of power metering has only been compared with other meters
occasionally & itself on range steps.
IN USE...
With all my fixes, upgrade mods, & full calibration, it is now a very useful
lab or /P test set. A one stop shop for all rigs, when taken to my local club's
regular test & fixit evenings.
Sinad meter is used for best Rx S/N sensitivity (e.g. sig level for 12dB S/N)
& FM discriminator adjustments. For that, 5 turns on ferrite ring stops the LS
lead being a aerial on weak signals! RF leads may need the same!
The AF meter has >70dB range, so it is good for wide Signal to Noise
measurements.
With all the Osc Hum tracked down & fixed, the CW note is not too bad on 70cm
now, & 10x better than it was.
With an external spectrum analyser (can be connected to the rear RF socket) the
20dB high power attenuator & 20dB splitter one, works well too, but the power
meter's diode load does increase some of the even harmonics seen!
See my tech Buls on "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
Read previous mail | Read next mail
| |
