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G8MNY  > ATV      15.06.18 11:30l 155 Lines 8311 Bytes #7 (0) @ WW
BID : 25328_GB7CIP
Subj: 23cm ATV Repeater GB3HV System
Sent: 180615/0917Z @:GB7CIP.#32.GBR.EURO #:25328 [Caterham Surrey GBR]
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 @
( where a few broadband visitors could see & hear
live ATV.

4 Switched 90°
24cm Aerials @ 20m
\│/ ___ \│/                          _______
 └─┤Pre├─┘                __________│Digital├─>Rx Dig Vid
   └─┬─┘    ___   ____   │          │24cm Rx├─>Rx Dig AF
mast └─────┤amp│_│Filt│_┌┴┐splitter │_______├─>Rx Dig   ____________
     ┌─────┤___│ │____│ └┬┘  _________                 │WEAK SIGNAL │
\│/┌─┴─┐\│/       5 pole │__│Narrow   ├─>24 AF Rx      │PAL TIMEBASE│   Good
 └─┤___├─┘ ________         │Analog Rx├───┬───>────o   │RESTORER &  ├──>Analog
Preamp│   │LOGIC AE├>VIC20   ~~~~~~~~~ ┌──┴────┐ ┌o <──┤CONDITIONER │   Rx Vid
  DC  └───┤selector├─────┬──────<──────┤RxSyncs│ │ o    ~~~~~~~~~~~~
           ~~~~~~~~      └<Rx Dig       ~~~~~~~  │ │ DTMF
13cm Yagi @19m       ______                      │ │ Controlled
 \│/           ___  │ 13cms├──────────────────>──┘ │ Switch
  └───────────┤Pre├─┤ATV Rx├─>13cms RX AF          │
70cm Yagi @19m ~~~   ~~~~~~______                  │
 \│/ Cam Pan  ___         │ 70cm ├────────────>────┘
  └──────────┤Pre├────────┤ATV Rx│  _______            _______   _____
2m & 70cm     ~~~____      ~~~~~~  │Comms  │ 24 AF Rx>┤DTMF   │_│MENU │­Options
 \│/ Colinear   │Dupl├─────────────┤70cm Rx├─┬───>────┤Decoder│ │LOGIC│­
  └─────────────┤exer├┐ ___________ ~~~~~~~  └>70cm AF ~~~~~~~   ~~~~~
@ 19m            ~~~~ └┤Comms 2m Rx├─>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

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  >─┤        VIC20       ├─>Vic Vid
Joystick input (Pmeter)>─┤      Computer      ├─>Vic AF
           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

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    ─o          o- VIC20 ID + Rx Sync Tones       2m AF
  Test card gen     ─o <──Tx──> o- VIC20 ID + Rx Sync Tones       2m AF
  Analog Rx (23)    ─o          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

This was on 1308MHz which was the only frequency available 27km away fro
London Heathrow 530MW ERP 4 channel Radar (Primary User).

4 90° 23cms
Aerials @ 22m
\│/ \│/ ______  ___             1308      _____  70 ___ PQ _____
 └──[]─┤Filter├┤PA1├┐   ______   MHz    ┌┤Xvert├───┤ModĂ══ÁMPEG ├─<AF1
        ~~~~~~  ~~~┌┴┐_│Driver│Digital o┘ ~~~~~  MHz~~~   │CODER├─<AF2
\│/ \│/ ______  ___└┬┘ │ PA   ├───────/o┐│~~~~~├─<AF1     │_____├┐ ______
 └──[]─┤Filter├┤PA2├┘   ~~~~~~  Analog  └┤FM Tx├─<AF2  ________  ├┤T.B.C.├<VID
   mast ~~~~~~  ~~~           DTMF MENU  │_____├───<──┤TELETEXT├─┤ ~~~~~~
splitters                               ________       ~~~~~~~~  │
                      Broadband link <─┤Internet├──<─────────────┘
                                       │  PC    ├─<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 /_│ UHF FM │_______________________┌────────────────┬┤ 6MHz Mod ├─<AF1
Buffer\ │Modultor│   │   _│____________  │   ___________  │ ~~~~~~~~~~ 
         ~~~~~~~~  DC^  │Video Filter &│ ├<─┤12MHz Phase├─┘
               from PLL │ Pre emphisis │ │   ~~~~~~~~~~~    __________
                         ~│~~~~~~~~~~~~  ├────────────────┬┤5.5MHz Mod├─<AF2
                          └<Video        │   ___________  │ ~~~~~~~~~~
                                         └<─┤11MHz Phase├─┘
Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP

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