Message 24680 in ATV.WW
From: G8MNY
Date: Thu, 25 Jun 26 08:34:00 Z
Newsgroups: ATV.WW
Subject: 23cm ATV Repeater GB3HV System
Message-ID: <63325_GB7CIP>
Path: N2NOV|VE2PKT|VE3CGR|CX2SA|OK2PEN|GB7CIP
R:260625/0846z @:N2NOV.#RICH.NY.USA.NOAM $:63325_GB7CIP
R:260625/0846Z 11685@VE2PKT.#TRV.QC.CAN.NOAM LinBPQ6.0.25
R:260625/0845Z 82825@VE3CGR.#SCON.ON.CAN.NOAM LinBPQ6.0.25
R:260625/0841Z @:CX2SA.SAL.URY.SOAM #:1128 [Salto] FBB7.00e $:63325_GB7CIP
R:260625/0838Z 27862@OK2PEN.SP.BRA.SOAM [Sao Jose dos Campos] $:63325_GB7CIP
R:260625/0834Z @:GB7CIP.#32.GBR.EURO #:63325 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : ATV@WW
By G8MNY (Updated Jun 12)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a run down of what the old closed down repeater was like (site rental
rocketed). A new one exists as a much simplified Rx only internet streaming
device near Reading.
The old one was very complex repeater, it was sited on the hill @ High Wycombe
IO91OO, that has grown & grown over many years, 1985 proposed 1987 on air.
It had ATV Rx on 3 bands, 2 with intercarrier sound & 1 band with a digital Rx.
It also has 2 comms Rx channels as well. All of these control the repeater or
output on the Analogue or Digital ATV Tx. As well as RF it had an expensive
internet side with 1 way video steaming @ www.gb3hv.com
(http::gb3vh.camstreams.com) where a few broadband visitors could see & hear
live ATV.
RX SIDE
24cm Aerials @ 20m
~~~~~~~~~~~
The four 24cm (6 loop & reflector) aerials are searched one at a time for the
best picture by measuring the picture noise during the frame sync, this took
several seconds if the radar is strong, as frame lock can be difficult. If you
selected all 4 aerials or use an omni Rx aerial you are RF worse off by 6dB S/N
+ reflections!
The 1248MHz FM ATV Rx, had a radar video clipper in it and the video feeds a
PAL conditioner that can handle very weak signals of just a few dB S/N. Software
in the controlling old VIC20 also allows for DX signals by holding in repeat
mode for up to 30 seconds if the signal is persistantly fading.
Milton keynes
GB3TG 10GHz
LUTON / GB3AD 23cm
GB3TV 23cms QRP
|
GB3BH 13cms
/ GB3EN 23cms Isle of Sheppy
NEWBURY GB3HV 23cm GB3KT 23cms
_ _ .- -'~~
GB3FT 13cm
(test only) L O N D O N
GB3AT 23cm
SOUTHAMPTON GB3VR 23cm GB3VX 23cm
BRIGHTON
The 13cm Rx system pointed at GB3BH, that can see 23cms ATV repeater GB3TV etc.
So manually controlled forward linking was possible, but active onward link
control was not possible.
The 2m & 70cm comms Rx could both be QSYed a few channels from DTMF menu.
____________________
Parallel I/F VCR TX Rx Test AE
Timeout Sync card info
The very old but highly reliable VIC20 runs things (PCs crash, VIC 20 not!),
and provides a carousel of 12 pages when in beacon mode, including control of
the seperate the testcard generator. The DTMF menus were all in hardware and
menus seen were from the testcard generator multiple EPROM system. DTMF menu
options have sound confirmation was by G8MNY's voice recorded in EPROMs.
An old V2000 format VCR had been wire up to record the 1st 10 mins of ATV
activity, unless it is a SUNDAY RSGB news time, when the 10 min limit was
suppressed.
All video sources were DTMF controlled from hardware menus. The video switcher
had all inputs DC clamped so there was no DC thumps & Tx PLL off lock when
switching sources.
VIDEO SOURCES MATCHING AF1 SOUND SOURCE AF2
" " (13BH) -o o- VIC20 ID + 13 AF Rx 2m AF
" " (13FT) -o o- " " " " " " "
" " (70) -o o- VIC20 ID + 70cm AF 2m AF
Digital 23cm Rx -o o- VIC20 ID + Dig Rx AF 2m AF
V2000 VCR Replay -o o- VIC20 ID + VCR AF 2m AF
Shack Camera -o o- VIC20 ID + Shack Mic 2m AF
Security " " -o o- VIC20 BERP + Shack Mic Shack Mic
Mast Camera @ 20m -o o- VIC20 ID + 70cm AF 2m AF
Internet Video PC -o o- VIC20 ID + Internet PC AF 2m AF
TX SIDE
This was on 1308MHz which was the only frequency available 27km away fro
London Heathrow 530MW ERP 4 channel Radar (Primary User).
Aerials @ 22m
~~~~~~~~
Two FET PAs were used, and were linear enough to handle QPSK digital Tx at only
a couple of dB down on the satuated FM output. As the MPEG coder can only
encode full spec video a Time Base Corrector is used to clean up all the Tx
sources to full TV spec. The encoder generates P & Q data streams that drove
the 70MHz QPSK modulator, its output was transverted to 1308MHz. As the main
mode is FM, users had to DTMF to digital mode, which lasts until 1 or 2 of 15
min testcard idents were done.
Only the analog Tx system could handle the 7Mb/s 100 page Teletext signal so
that is inserted into that path only. Two sound carriers were used, a HiFi one
@ 6MHz @ -17dBc and a comms quality one @ 5.5MHz @ -20dBc (not Sat Rx freq). As
there was potential with a 1308MHz FM Tx with 6MHz sub-carrier to generate
significant -12MHz (1296MHz) noise, a cleaver 2nd harmonic subcarrier (both for
5.5 & 6MHz) phasing system is introduced to null out much of the 1296MHz
products, this was in addition to the 3 pole Tx filters.
________ __________
~~~~~~~~~~~
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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