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G8MNY > TECH 19.12.24 09:34l 126 Lines 5361 Bytes #999 (0) @ WW
BID : 22226_GB7CIP
Subj: Marconi 2331A Distortion Factor
Path: IW8PGT<IZ3LSV<I0OJJ<LU4ECL<LU9DCE<GB7YEW<ZL2BAU<VK6HGR<GB7CIP
Sent: 241219/0825Z @:GB7CIP.#32.GBR.EURO #:22226 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Jan 21)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I bought this quite old large 19" 4U unit, made around 1975. It is an AF
Distortion meter, noise meter (weighting option) & an AF volt meter.
Frequency Freq Band Cal Power
_____________________________________________________
³ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿³
Input³³ /~~~~~\ . ( ) -~~~~- ( )³³
Level³³ ( ) / .-. \ ( ) / / \ ³³
³³ ³ ³ ³ ³ / / \ ³³Meter
³³ . \ '-' / o~--.__.--~ ³³
Input³³ ( ) \_____/ ³³
Range³³ ' . . ³³
³³ ( ) ( ) ( ) ( ) ³³
AF ³³ o o ß ' ß o o ³³Output
Input³ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ³
~ÜÜ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ÜÜ~
600R Fine Freq Phase Mode LF cut Range
Although with 20 germanium transistors & a -15V PSU, it works fine. Main issues
are large dirty switches & scratchy wire wound pescision pots.
SPECIFICATION
Volt Ranges: 1-3-10, 7 in all from 30V down to 1mV FSD or in dBm. 1M Input.
Built in voltage calibrator.
Input: 1-10 (10K) & 10-30V (10-100K) & 600R term (some models AM RF det option)
Notch Freq: 20Hz-20kHz in 6 bands, Fine trim for Freq & Phase to notch -80dB.
Bandwidths: 20Hz-100kHz, or 20Hz-20kHz @-3dB.
Weighting: one filter option for Comms, Broadcast, or other is fitted.
LF Cut: -3dB @ 400Hz steep roll off hum filter.
Power: 95-130V or 190-260V AC 40-500Hz 3VA, or -18 to -45V 25mA DC.
Output: up to 150mV @ 1K of what is being metered, for oscilloscope.
USES
AF Voltmeter measures a wide range on average reading meter.
Distortion measuring & seeing Oscillator's & Amplifier's figures, adjusting for
min distortion on FM discriminators.
Noise measurement, with filters as needed for accurate assessment of kit noise.
A modern way of doing this might be with a laptop soundcard & suitable (free)
AF spectrum analyser/scope program!
There are 3 main parameters to Audio quality....
FREQUENCY RANGE
Here is the approximate frequency plot for some audio sources. Note that the
old disk system was not really limited & special equipment can do Quad audio
with high frequency sub-carriers!
³Sub Sonic³<- - - - -Young Human ear response - - - - - - ->³Ultra Sonic >
³I BASS MID TREBLE
³N <- - - - - - - - - - -Disk H i F i- - - - - - - - - - - >
³F < - - - - - - - - -C.D. H i F i- - - - - - - - - - >
³R <- - - - - - - Broadcast HiFi - - - - - - - - >
³A < - - - - - Original Cassette- - - - - ->
³ <- - - - - Ä A.M. Radio - - - - - ->
³ F E E L I N G < - - COMMS - - -> B A T S
ÀÄÄÄÂÄÄÄÄÂÄÄÂÄÄÄÂÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÂÄÄÂÄÂÄÄÂ>Frequency
DC 10 20 30 50 100 300 500 1k 3 5 10 15 20 30kHz
CDs are the best source most people are familiar with, its frequency range is
limited by the 44kHz sampling rate & the requirement to filter off all the
frequencies higher than 22kHz to stop aliasing mixes caused by the sampling
rate.
SIGNAL TO NOISE RATIO
This is the measure of unwanted noises below the wanted sound..
e.g. Hiss & Hum, or windage/engine noise, Neighbours/street noises etc.
0dB´ Noisy Conversation
10 ´ Poor Comms, NORMAL CAR
20 ´ Fair Comms
30 ´ VERY QUIET CAR AM RADIO
40 ´ Typical Cassette Tape, Living rooms
50 ´ Reel-Reel tape, Dolby Cassette
60 ´ New Vinyl Record FM RADIO/TV SOUND
70 ´ Mini disk (unmasked noise)
80 ´ Dat tape. DAB
90 ´ Perfect Digital CD, apparent Minidisk
100 ´
110 ´
120 ´ Ear Threshold Signal : Silence to Pain ratio
With Digital sources there is also "Quantization Noise/Distortion", which is
due to the sample step size, & is a set No of dBs below any sound level for
logarithmic level sampling.
HARMONIC DISTORTION
This is the amount of unwanted signals generated in harmonics of the wanted
signal, in the audio pass band of interest. It is usually very dependent on
the level, except for digital systems where it is a mathematical design
feature. Note the ear generates these too!
It is measured as a % of the signal, so 10% = -20dB in harmonics.
% dB
10 Å -20 Cheap AM Radio at high Volume, Comms Audio
5 Å -26 Film Optical Sound
3 Å -30 Cassette & Reel Tapes (peak)
1 Å -40 Quality Valve Amps AM BROADCAST
.5 Å -46 High Quality Disk FM BROADCAST
.3 Å -50 Most Loudspeakers (not loud)
.1 Å -60 Most AF Amps, DAB
0.05Å -66 Good modern AF Amps.
0.03Å -70 Most Digital AF sources. CD ~MD ~Mpeg3?
Sometimes the above parameters are joined together in a "Signal In Noise And
Distortion" (SINAD) rating for measured RF signal level of a Rx.
See Tech bul "Marconi Distortion Meter TF2337", "AF Waveform Generator (RS)", &
"FeelTeck Dual DDS Osc FY6600-60M".
Why don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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