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G8MNY > TECH 04.02.23 12:52l 168 Lines 8346 Bytes #999 (0) @ WW
BID : 39866_GB7CIP
Read: GUEST
Subj: Systron Donner 1702 Sig Gen
Path: IW8PGT<I3XTY<GB7COW<KE0GB<W0ARP<LU9DCE<EA2RCF<SR1BSZ<IW0QNL<ON0AR<
GB7CIP
Sent: 230204/1043Z @:GB7CIP.#32.GBR.EURO #:39866 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Nov 17)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
In 1998 I bought this large digital signal generator & not regretted it. It is
a deep 19" 3U rack unit with side handles, & weighs 25kg!
Mod Frequency Lever Wheels AM LED 0-120dB
____________________________________________________________________
³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³Off ref
³ ³ ÚÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ | o ___ (_)³ ³Tune
³ ³ ³ 18.10 ³ ³9 Ý9 Ý9.Ý9 Ý9 Ý9 Ý9 ݳ | / \ /~~\ ³ ³
³ ³ ³________³ ³ Ý Ý Ý Ý Ý Ý Ý³ | ³ /~\ ³ ³ ³ ³ ³Atten
³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ | ³ \_/ ³ ³ ³ ³ ³1-10dB
³ ³~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~³ \___/ \../ ³ ³& Zo
³ ³ (_) (_) __ __ __ __ ³ ³ ³
³ ³o [Û ] [__] [__][__][__] ³ o (o) o o ³ ³Trip
³ ³' (ú) Äo (ú) ³ ' ³ ³LED
³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
AF osc mod ext Power FM CW AM On/Off N o/p Reset
It was made in the USA by Thorn EMI that owned the SYSTRON DONNER Co. in 1983
at around $10,000!
It uses several PLL oscillators & mixers, all locked to an internal temperature
compensated or external reference. It has a calibrated 4 digit display of peak
AM & FM modulation from the built in locked 400Hz & 1kHz sine wave sources as
well as external modulation.
FAULTS
It was not all working (e.g. no 144MHz), & later a main smoothing cap O/C. But
I have managed to repair all the faults, without a diagram! Which was very time
consuming, working out how it all worked, (internal silvered brass sectioned RF
unit & 16 gold plated PCBs).
The lever gear operated frequency wheels have very strong home clicker spings.
So strong that their internal arc & pinion gears are at risk of stripping. I
had to take one apart to repare the gear (heat treatment of the plastic teeth).
So I weakened all 7 wheels home spings, so they would last longer. But the
partly striped gear arc did not last & I eventually replaced it with a glued on
toothed wheel (from VHS deck) to make it a conventional thumb wheel.
I have done several mods to it now, eg. FM deviation increased to ñ100kHz,
improved modulation bandwidth > 30kHz, off reference fine tune, & external 625
line TV timebase ref lock (obsolete now with digital TV!)
MY SPECIFICATION
AC Mains input 240V 40-100Hz @ 50W on rear IEC connector
Mains voltage links on plug inside.. 250, 220, 125, 110V
RF Output N socket 50ohm. 0.1uV to 1V RMS Max.
Attenuator 120dB 20dB/step & 10dB 1dB/Step attenuator (& 50ohm Term)
Frequency Range 100Hz to 999.9999MHz in 100Hz steps,
using 7 large lever operated wheels.
Accuracy 1/10^7 internal temperature compensated Xtal reference,
Off Calibration Fine Tuning ñ70 PPM (added by me),
Frequency accuracy compromised on FM mode with ñ5Hz jitter!
Rear 1 MHz BNC O/P Reference TTL level
Rear 1 MHz BNC External input Reference TTL level/TV
Harmonics & spuri > -30dBc, typical -55dBc. 400MHz up/down mix system.
Accidental Tx RF trip relay @ >500mW in, but the 10dB atten is unprotected!
PLL lock indicator & Level correct indicator (AGC OK eg. not in AM)
Modulation FM Indicated 0-19.99 or 100.0kHz, AM 0.0-100.0% (clips @ 95%)
Internal Locked 400Hz & 1kHz (FM offset @1kHz!) BNC O/P
External BNC I/P into 5K 10Hz-30kHz
USES
As well a very low carrier freSB HIFI @ WW
Technics Rx ST-RT550
By G8MNY (Updated Jan 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ÚÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³
³ÀÄÄÄÙ o O O O ³Quartz lock Stereo RDS ch TUNE³() /~~~\ ³
³ ³ ÚÄ¿ .. 3 | ÚÄ¿ ÚÄ¿ ÚÄ¿ ÚÄ¿26 MODE³ | | ³
³ [_][_][_] [__]³ ³³³ .... 2 ³ ³ ³ ³ ÃÄ´ ³ ³ Auto³ Þ Ý³
³ ³ ³³³³³ ......1 | ÀÄÙ |*ÀÄÙ ÀÄÙ Man ³ | | ³
³ ³ signal FM MHz Lock³ \___/ ³
³ ÚÄÄÄÂÄÄÄ¿ÚÄÄÄ¿ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ[ ] ³
³ ÀÄÄÄÁÄÄÄÙÀÄÄÄÙ<][ 1][ 2][ 3][ 4][ 5][ 6][ 7][ 8][ 9][ 0][10][> ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
I was given a faulty one of these tuners, it covers LW, MW & Band 2 with RDS, &
its has 39 memories. I have now got it all going OK.
CLEVER AUTO IF WIDTH
It has an unusual feature regarding the automatic FM IF filter width selection
I have not seen before. If the station is strong enough, it uses the wider low
distortion IF (300kHz), unless there is a nearby carrier. It decides this by
tuning ñ100kHz first with the narrow filter (180kHz) & if there is a signal
marking the spectrum graphic display with a bar ³ to the left or right of the
main carrier & then it uses the narrow filter.
PSEUDO SPECTRUM GRAPHIC
The Spectrum Graphics shows the IF bandwidth selected....
IDEAL BAD BAD BAD IDEAL
STRONG LF HF ñ LF HF ñ BUT WEAK
NO QRM Sig QRM QRM QRM QRM QRM QRM NO QRM Sig
ÚÄÄÄ¿ .. 3 ÚÄÄÄ¿ ÚÄÄÄ¿ ÚÄÄÄ¿ ÚÄ¿ ÚÄ¿ ÚÄ¿ ÚÄ¿
³ ³ ³ .... 2 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³³³ ³³³ ³³³ ³³³
³ ³ ³......1 ³³³ ³ ³ ³³³ ³³³³³ ³³³³ ³³³³ ³³³³³ ³³³......1
WIDE MANUALLY FORCED INTO WIDE NARROW FILTER MODE SELECTED
I wonder if anyone has any information, tips, do's & don'ts etc. for this Rx?
AM ÅÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
It had no AM pickup Å´ VHF TUNER ³
loop aerial, so I am ³ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
using a large loop from ³ ÚÄÄÄÄÄÄÄ¿
6m of wire, (about 10uH) ³hf³( ) ( )³hf
& I tracked the series ³MW³ ³LW
LW & MW aerial & Osc coils ³lf³( ) ( )³lf
coils to best match this. ³ ÀÄÄÄÄÄÄÄÙ
³
³ ÚÄÄ¿
³ ³()³
³ AF ÀÄÄÙ
³ Notch ÚÄÄ¿
³Filters³()³
³______ ÀÄÄÙ_______
NO MAINS SWITCH!
As with many modern items there is NO MAINS SWITCH, the standby switch only
really powers off the display.
Much of the power consumption on my UK mains @ 245V 50Hz is due to the large
over run mains transformer (for 2x 110V 60Hz?) & gets hot even on standby with
little load, as does the plastic power supply regulator transistors when on.
POWER MODIFICATION
I modified the mains circuit (the large empty PCB with the transformer was
ideal) with a 2W 1k resistor in series with the mains neutral, & mounted it
well above PCB, I also tuned the mains transformer to 50Hz with a mains 0u15
X type Cap for minimum mains current (PF=1.0).
___________
LiveÄÄÄÄÄÄÄÄÂÄÄ¿ ... ³ Cooler ³_____Rx
³ )³³( ³ Regulator ³
245V 0u15=== )³³( ³Transistors³
³ )³³(... ~~~~~~~~~~~
NeutralÄÄ1kÄÄÄÁÄÄÙ Cooler
2W Transformer
The result was a much cooler transformer all the time & cooler power supply
regulators, & hence less power wastage despite adding the 2W resistor. The
transformer voltage now has 230V on standby (2W consumed) & 220V when on (5W),
there is enough power supply headroom for the cooler running regulators OK, but
the display is very slightly dimmer due to the directly heated fillements.
(longer lifetime?)
HUM
I have done this sort of thing before on another FM Rx, but that case is was
due to acoustic & strong stray magnetic flux leakage hum from the super
saturated transformer causing problems. Again adding an series R reduced both
these completely.
Any feedback would be greatly appreciated.
Y don't U send an interesting bul?
73 de John G8MNY @ GB7CIP.
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