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G8MNY > TECH 23.01.26 20:03l 94 Lines 4066 Bytes #4 (0) @ WW
BID : 50265_GB7CIP
Subj: DYMAR Mod Meter Type 1785
Path: JH4XSY<N3HYM<GB7YEW<GB7CIP
Sent: 260123/1102Z @:GB7CIP.#32.GBR.EURO #:50265 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Mar 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have one of these old VHF-UHF AM/FM Modulation meters it is similar to the
Marconi TF2300 type. It has a blue grey metal case plastic case 42 x 17 x 20cm
& has a large 13cm mirror scaled meter on the left & slow motion Rx converter
tuning knob & dial on the right.
Large Meter Mode Fine Band
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ｳ .-~~~-. ｳ
ｳ ｳ ｳ ｳ /\ _ ﾚｿ | .-. | ｳ
ｳ ｳ'�. ｳ ｳ ( ) (_) ﾃｴ | | | | ｳ
ｳ ｳ '�. ｳ ｳ || ﾀﾙ | '-' | ｳTuning
ｳ ｳ~~~~~~~~~~~~~~~ｳ ｳ "-___-" ｳ
ｳ ｳ 0 ｳ ｳ /\ ｳ
ｳ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳ O _ ( ) ｳ
ｳ [][][] ｳ O o (_) || o O O ｳAF
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
On Bat Chk IN Attn Set Range Comms IF
SCHEMATIC
o)ﾄ20dB Atten ______ ______ Batt testﾄo
ｳ ﾚﾄﾄﾄｿ o20dBo Level ﾚｴ>ｴFilterﾃｴAM Detﾃﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄo<ﾄMeter
o)ﾄﾄﾁﾄｴMixﾃ>oﾄﾄﾄﾄo<ﾄPotﾄｴ>ｴ ﾀﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾙｳ ﾚﾄﾄﾄﾄﾄﾄｿ Set level o
Inputsﾀﾄﾂﾄﾙ _______ ｳ AFﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳ HiFi ｳ Range ｳMeasure
ｳ oｴ 30 -60ｳ ｳ ampﾀｴ>ﾄﾄﾄo<ﾄﾄ>oｴFilterﾃo<ﾄAtten Mean ｳ
ﾀﾄ>oｴ120-240ｳ ｳ AM o oﾀﾄﾄﾄﾄﾄﾄﾙo oooo _ｳ__ ｳ
ｳMHz VFOｳ ｳ Lim _______ ｳFM ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳ ｳPeakｳ ｳ
ﾀﾄﾄﾄﾄﾄﾄﾄﾙ ﾃｴ>ｴ>ｴFM Discﾃﾄﾙ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁｴ>ﾂﾄｴ Detﾃｴ>ﾙ
ｳ | ﾀﾄﾄﾄﾄﾄﾄﾄﾙ| ｳ ______ NFB ｳ ﾀﾄﾄﾄﾄﾙ
ﾚﾄﾄﾄｿ ｳ ﾀRF Squelchﾙ ｳ o ｳComms ｳ ｳ
ｳPSUｳ ｳ ﾀ>oﾄｴfilterﾃﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄ(o AF output
ﾀﾄﾄﾄﾙ ｳbuffer ﾀﾄﾄﾄﾄﾄﾄﾙ
ﾀﾄｴ>ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ(o IF output
I have now reverse engineered the whole thing & have all the circuits. I have
done lots of modifications, so it now fully calibrated with much improved spec.
MODS
1/ Modulation detector rebuilt, now true very fast peak & mean reading.
2/ FM squelch (fast shut, slow open).
3/ Internal monitor amp & LS added.
4/ Rebuilt PSU, it now copes with external 12V operation as well.
5/ Broadband mode added, FM & AM detectors widened.
6/ HiFi filter set to 30Hz-15kHz @-3dB (sharp M derived HF cut off)
7/ Comms filter set to 300Hz-3KHz @-3dB
8/ Used it for FM deviation up to 900MHz (e.g. UHF radio mics) OK.
NEW SPECIFICATION
Power : 180 - 250V AC, 50 - 100Hz (90 - 125V internal straps)
12 - 24V DC @ 200mA
Internal battery option (not fitted).
With external/internal battery charging & battery check.
RF Inputs 50� : 1 - 100mV, or attenuated 10mV - 1V MAX.
Frequency range : 27 - 480MHz (2 x 2 BANDS) (900MHz possible on harmonics)
IF Frequency : 600kHz, Scope output � 100mV.
IF Bandwidth : AM � 135kHz @ -3dB
FM � 435kHz @ -3dB
Modulation Detector
Peak Hang time: > 1 Sec to -10%
Peak Rise time: < 50uS to -10%
AF Bandwidths: Wide Mode 10Hz - 50kHz @ -3dB
HiFi Mode 30Hz - 15kHz @ -3dB
Comms Switch 300Hz - 3kHz @ -3dB
AF Scope output follows detector bandwidth & range levels.
Monitor LS " " " " " " " &
has volume control & 50uS de-emphasis. Output Power 500mW.
Meter Scales
Set Level MODE : dB scale -12dB to +2dB, cal to 100%
AM Modulation RANGE : 3 - 10 - 30 - 100% Modulation depth.
FM Modulation RANGE : 3 - 10 - 30 - 100 Hz Deviation.
Anyone want further information on it?
See my buls on "RTT Mod Meter (100)", "Simple Carrier Squelch", "Low Voltage
Drop PS", "FM Deviation Calibration", "FM Stereo Radio Principles",
"AM Broadcast Radio Principles", & "Meter Damping & Speed Up".
Why don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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