TM Overhaul

Home Up GB3TM Digital TM Overhaul GB3TM History




 B3TM on the North Coast of Anglesey has recently been undergoing maintenance and minor upgrades .

 Digital Transmitter 1316MHz QPSK

 The AGAF DATV Encoder and Modulator board settings have been changed to provide improved picture resolution. New settings:


Elementary Stream      6MB/s

Symbol Rate               4.167 MS/s

FEC                             7/8

Video-PID                  33 (decimal)

Audio-PID                  49 (decimal)

A 2-metre receiver on 144.750 MHz has been installed and the audio output from this is taken to the B audio channel input on the Digital Transmitter to provide talk-back.


Analogue Transmitter 1316MHz FM

   The Analogue Transmitter has been in continuous operation for 16 years, since July 1994 and had been suffering some minor problems. These have now been corrected and the various transmission parameters checked and readjusted as necessary. After checks and maintenance, the Analogue Transmitting Aerial has been moved back from its temporary location to its original (higher) position which should resume normal coverage.

 The output can be switched between Analogue and Digital with DTMF tones on the incoming 6MHz FM audio channel. The default mode is Digital.

Present DTMF codes are:

 DTMF             1          Digital transmission                continuous

                        2          Analogue transmission            15 minutes

                        3          Test Card on                           1 minute

                        4          Test Card off

 Analogue Receive 1249MHz FM

 This is now powered from a UPS to prevent problems caused by intermittent brown-outs of the mains supply. The possibility of an additional Digital Receive facility is under review.

 Photograph of the GB3TM Technical Team at the Site: (Photo GW4KAZ)

Brian GW4KAZ, John GW3JGA and Repeater Keeper David GW8PBX

 Submitted by GW3JGA and GW8PBX 18.10.2010

Update October 2011.

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