Message 20778 in TECH.WW
From: G8MNY
Date: Tue, 14 Apr 26 06:48:00 Z
Newsgroups: TECH.WW
Subject: Recording whole LF + MF bands
Message-ID: <57213_GB7CIP>
Path: N2MH4|GB7BED|GB7YEW|GB7CIP
R:260414/0732Z 30187@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260414/0731Z 9767@GB7BED.#21.GBR.EU LinBPQ6.0.25
R:260414/0731Z 16878@GB7YEW.#79.GBR.EURO LinBPQ6.0.24
R:260414/0648Z @:GB7CIP.#32.GBR.EURO #:57213 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Feb 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a system for recording 100kHz - 3MHz on an old VCR. A VCR can record
40dB Signal to Noise over that whole DC - 3MHz bandwidth, or 70dB S/N in each
3kHz, and that equates to about 60dB S/N in each 9kHz AM channel!
Old VCRs (not HiFi) are best for this, provided the tape speed & head drum are
still good, as they do less cleaver video processing than later ones, so there
is less to corrupt the RF signal.
needed. Here a simple NPN follower to do that using any MF transistor. If you
look at the VCR signal on a monitor you should see noise and patterning as
bright as a normal picture, the VCR will have a few dB of AGC as well to keep
the levels approximately right.
CIRCUIT
///
FILTER
add to the 300mV of frame syncs. 30 3k 30k 300k 3M Hz
\ 50Hz / VCR sees this as video
MF Rx
If your MF aerial supplies enough signals, without a too strong predominant
one, it will be possible to tune into recorded LW & MW AM/DRM broadcast
stations as well as 160M SSB/CW stations, but with some 25Hz FM due to the
normal VCR head drum-tape instability! 80M will not be possible due to the 3MHz
video wall filter on record & playback.
VCR SPECTRUM
The VCR converts the video baseband DC-3MHz to higher frequencies by modulating
a FM carrier between 3.5-5MHz.
The AF is edge recorded or on hifi machines uses 2 lower FM carriers (around
100kHz) added into the head drum FM signal, these Hifi carriers could cause QRM
in this application.
The complex 4.4MHz PAL colour signal is down converted to 600kHz and also added
into the FM signal. All these added signals use the FM carrier as a record bias
(like an AF tape recorder), again these converted PAL frequencies could cause
QRM in a machine that can't drop to plain black & white mode.
VIDEO BASEBAND TAPE SIGNALS
DC 3 4.4 MHz 0.1 0.6 3.5 5 MHz
Have fun trying this one out.
N.B. It will NOT work with any digital recorder as they only save a few % of
the picture's information per frame is actually encoded & stored, they rely on
similar picture storage of up to 15 frames to complete the task!!
If you want more bands try a down converter with 5MHz xtal and aerial BPF for
5-8MHz, that would be quite interesting!
===========================================================================
Comments:
> Hans PA0CX has done some experimenting, and he has published his findings in
> the Dutch magazine Electron Feb 1998 p59-63 De Luistermachine by pa0cx/f2zi
73 - Andre, PE1HWO @ PI8HGL
-----------------------------------------------------------------------------
From : G6DTW
Date/Time : 15-Feb 2010
Title : mf video receive converter
IT WORKS!!!!!
wonderful circuit; so easy: a good aerial helps tremendously.
much better than i thought it wd be not hifi, but then it IS MF.
THANKS AGAIN FOR A WONDERFUL IDEA
ALVIN
Why Don't U send an interesting bul?
73 De John G8MNY @ GB7CIP
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