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G8MNY > TECH 26.08.09 17:59l 91 Lines 3921 Bytes #999 (0) @ WW
BID : 35543_GB7CIP
Read: GUEST DG9NBR OE7FMI
Subj: Recording whole LF + MF bands
Path: DB0FHN<DB0MRW<DB0FOR<DB0SIF<HB9EAS<OE9XPI<OE7XLR<OE5XBL<OE6XPE<UA6ADV<
GB7CIP
Sent: 090826/0941Z @:GB7CIP.#32.GBR.EU #:35543 [Caterham] $:35543_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Update Mar 08)
(8 Bit ASCII Graphics use code page 437 or 850)
Here is an untested idea for recording 100kHz - 3MHz on an old VCR. In theory
a VHS VCR can record 40dB S/N over that whole DC - 3MHz bandwidth, or 70dB S/N
in each 3kHz. Old VCRs would be the best to try this on as they do less cleaver
signal processing to much up the RF.
SUGGESTED CIRCUIT
Wire
Aerial ÚÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄ +12V
\³/ 100k ³/Any === u1
ÀÄÄÄÄ´ÃÄÄÁÄÄ´BF NPN _³_
n1 ³\e
³ 10n
1k<ÄÄÄÄÄÄÄ´ÃÄÄÄÄÄ¿
pot ³
0VÄÄÄÄÄÄÄÄÁÄÄÄ¿ u22 ³ ____________
=== ³ | VCR | 10n
TV Camera >ÄÄÄ(((()ÄÄÄÁÄÄÄ(((()ÄÄÄÁÄÄ| In Out |ÄÄ´ÃÄÄÄ> LF/MW Rx
With lens 1mH 1mH ------------
cap on.
FILTER
0dB´ÄÄÄÄÄÄÄÄÄÄ-. _.--ÄÄÄÄ
-3dB´ Video ³ / HF
³ Syncs ³ / Filter
³ Filter ³ /
ÀÄÄÂÄÄÄÄÄÂÄÄÁÄÄÂÄÄÄÄÄÂÄÄÄÄÄÂÄ
30 3k 30k 300k 3M
The VCR is designed to lock up to 50Hz video syncs & the best way to get these
is from a camera. Here the camera's HF is filtered off to not cause QRM. The RF
signals need to peak to 700mV p-p to add to the 300mV of frame syncs.
_
Black Cam signal Filtered Cam RF ± ±±±±±±±±±± ±
¿Ú¿ڠ- 300mV Ä¿ÚÄÄÄÄÄÄÄÄ¿Ú Added ±±±±±±±±±±±±±± 1V P-P
ÀÙ312linesÀÙ - P-P ÀÙ ÀÙ ± ± _
\ 50Hz / VCR sees this as video
To get the right RF level into the 75ê VCR input, an MF amplifier will be
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 & patterning as bright
as a normal picture, the VCR will have a few dB of AGC as well to keep the
levels approximatly right.
MF Rx
If your MF aerial supplies enough signals, without a too strong predominant
one, it may be possible to tune into recorded LW & MW AM/DRM broadcast stations
as well as 160M SSB/CW stations, but with some FM due to the normal VCR head
drum-tape instability! 80M will not be possible due to the 3MHz video wall
filter.
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
carriers could cause QRM in this application. The complex 4.4MHz PAL colour
signal is down converted to 600KHz & 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
³ Luminance Colour HiFi Colour FM Video
³---------------- _______ ³ _ _ _______ ----------------
³ || | ³| || || ||Sync Black White|
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÂÄÄÄÄ ÀÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄ
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 the only save a few % of the
picture information per frame is encoded, they rely on picture storage of up to
15 frames to complete the task!!
===========================================================================
Comment:
> Hans PA0CX has done some experimenting, & he has published his findings in
> the Dutch magazine Electron Feb 1998 p59-63 De Luistermachine by pa0cx/f2zi
73 - Andre, PE1HWO @ PI8HGL
Why Don't U send an interesting bul?
73 De John G8MNY @ GB7CIP
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