| |
G8MNY > ATV 28.11.24 10:40z 155 Lines 8311 Bytes #91 (0) @ WW
BID : 20729_GB7CIP
Read: GUEST
Subj: 23cm ATV Repeater GB3HV System
Path: SR1BSZ<IW0QNL<JH4XSY<N3HYM<VE3CGR<PI8ZTM<I0OJJ<GB7CIP
Sent: 241128/1038Z @:GB7CIP.#32.GBR.EURO #:20729 [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
4 Switched 90ø
24cm Aerials @ 20m
\³/ ___ \³/ _______
ÀÄ´PreÃÄÙ __________³DigitalÃÄ>Rx Dig Vid
ÀÄÂÄÙ ___ ____ ³ ³24cm RxÃÄ>Rx Dig AF
mast ÀÄÄÄÄÄ´amp³_³Filt³_ÚÁ¿splitter ³_______ÃÄ>Rx Dig ____________
ÚÄÄÄÄÄ´___³ ³____³ ÀÂÙ _________ ³WEAK SIGNAL ³
\³/ÚÄÁÄ¿\³/ 5 pole ³__³Narrow ÃÄ>24 AF Rx ³PAL TIMEBASE³ Good
ÀÄ´___ÃÄÙ ________ ³Analog RxÃÄÄÄÂÄÄÄ>ÄÄÄÄo ³RESTORER & ÃÄÄ>Analog
Preamp³ ³LOGIC AEÃ>VIC20 ~~~~~~~~~ ÚÄÄÁÄÄÄÄ¿ Úo <ÄÄ´CONDITIONER ³ Rx Vid
DC ÀÄÄÄ´selectorÃÄÄÄÄÄÂÄÄÄÄÄÄ<ÄÄÄÄÄÄ´RxSyncs³ ³ o ~~~~~~~~~~~~
~~~~~~~~ À<Rx Dig ~~~~~~~ ³ ³ DTMF
13cm Yagi @19m ______ ³ ³ Controlled
\³/ ___ ³ 13cmsÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ>ÄÄÙ ³ Switch
ÀÄÄÄÄÄÄÄÄÄÄÄ´PreÃÄ´ATV RxÃÄ>13cms RX AF ³
70cm Yagi @19m ~~~ ~~~~~~______ ³
\³/ Cam Pan ___ ³ 70cm ÃÄÄÄÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÙ
ÀÄÄÄÄÄÄÄÄÄÄ´PreÃÄÄÄÄÄÄÄÄ´ATV Rx³ _______ _______ _____
2m & 70cm ~~~____ ~~~~~~ ³Comms ³ 24 AF Rx>´DTMF ³_³MENU ³ðOptions
\³/ Colinear ³DuplÃÄÄÄÄÄÄÄÄÄÄÄÄÄ´70cm RxÃÄÂÄÄÄ>ÄÄÄÄ´Decoder³ ³LOGIC³ð
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄ´exerÿ ___________ ~~~~~~~ À>70cm AF ~~~~~~~ ~~~~~
@ 19m ~~~~ À´Comms 2m RxÃÄ>2m AF
~~~~~~~~~~~
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 & 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.
____________________
DTMF > Keyboard wires >Ä´ VIC20 ÃÄ>Vic Vid
Joystick input (Pmeter)>Ä´ Computer ÃÄ>Vic AF
ÀÂÄÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÄÂÂÙ
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!), &
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 & 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
VIC20 Computer Äo o- VIC20 ID + Rx Sync Tones 2m AF
Test card gen Äo <ÄÄTxÄÄ> o- VIC20 ID + Rx Sync Tones 2m AF
Analog Rx (23) Äo o- VIC20 ID + 24 AF Rx 2m AF
" " (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).
4 90ø 23cms
Aerials @ 22m
\³/ \³/ ______ ___ 1308 _____ 70 ___ PQ _____
ÀÄÄ[]Ä´FilterôPA1ÿ ______ MHz Ú´XvertÃÄÄÄ´ModÆÍ͵MPEG ÃÄ<AF1
~~~~~~ ~~~ÚÁ¿_³Driver³Digital oÙ ~~~~~ MHz~~~ ³CODERÃÄ<AF2
\³/ \³/ ______ ___ÀÂÙ ³ PA ÃÄÄÄÄÄÄÄ/o¿³~~~~~ÃÄ<AF1 ³_____ÿ ______
ÀÄÄ[]Ä´FilterôPA2ÃÙ ~~~~~~ Analog À´FM TxÃÄ<AF2 ________ ôT.B.C.Ã<VID
mast ~~~~~~ ~~~ DTMF MENU ³_____ÃÄÄÄ<ÄÄ´TELETEXTÃÄ´ ~~~~~~
splitters ________ ~~~~~~~~ ³
Broadband link <Ä´InternetÃÄÄ<ÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
³ PC ÃÄ<AF1&2
~~~~~~~~
Two FET PAs were used, & 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 & 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.
________ __________
RF /_³ UHF FM ³_______________________ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´ 6MHz Mod ÃÄ<AF1
Buffer\ ³Modultor³ ³ _³____________ ³ ___________ ³ ~~~~~~~~~~
~~~~~~~~ DC^ ³Video Filter &³ Ã<Ä´12MHz PhaseÃÄÙ
from PLL ³ Pre emphisis ³ ³ ~~~~~~~~~~~ __________
~³~~~~~~~~~~~~ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´5.5MHz ModÃÄ<AF2
À<Video ³ ___________ ³ ~~~~~~~~~~
À<Ä´11MHz PhaseÃÄÙ
~~~~~~~~~~~
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
Read previous mail | Read next mail
| |