The repeater uses a dual RA18H PA running ultra-linear into a Alford slot offering 360 degrees radiation.This provides an ERP of 25Watts. The signal occupies a 5Mhz bandwidth containing digital video and two audio channels. These are MPEG2 encoded in the same format as DVB-S (Satellite) signals, thus allowing commercial FTA satellite boxes to be used for reception. More details on the 'Seeing SQ' page.
- The dual slot Alford/JVL pole is now weather-proofed with a white down-pipe cover.The Alford slot design uses dimensions supplied by Roy G8CKN. There is a single slot being used for both transmit and receive simulataneously. This requires careful filtering and we have employed a Duplexer to accomplish this separation.
- The Digital output is centered on 1304 MHz.
- Various data rates were tried during tests. Whilst 6Ms/s gave a visibly better (sharper color resolution and better dynamic range especially on fast changing scenes) colour picture but caused a small drop in received signal strength, future bandplan space only allows for 4Ms/s per station so we will be using 4Ms/s in and 4Ms/s out from now on. With MP4 compression becoming more commonplace it should be possible to give an 'analog quality' picture using less than 4Ms/s in the future. Testing with 1/2 FEC and 3/4 FEC gave no discernable problems over several days of tests and means we are staying with 1/2 as a satisfactory option.
- The original main repeater control boards prior to wiring up and installing in die-cast boxes. Designed and built using smd by G8AJN.
On the left the audio-video switcher containing the local/IV signal detector and to the right the digital control board,containing the PIC controller, dtmf decoder,character generator, real time clock, rs232 interface.The board on the left has been revamped since this photo.
- This is the new replacement board containing all circuits on the above boards and also a number of sub-circuits such as audio amp, LED arrray drivers and attenuators.
The new repeater front panel....
- THE REPEATER has now been set to be off-line from Midnight to 10AM each day.It will not transmit continuously, rather it will be in standby awaiting a digital signal input and as soon as it receives a valid digital tv signal it will come out of standby and operate normally. BATC stream will also start then. For one hour each evening (7pm to 8pm) the repeater will transmit testcards and slides (unless in use repeating a signal). Outside these hours, when the current user drops their carrier, the repeater will go to standby again at the next Ident. The Ident will be shown every ten minutes.
- DTMF is available on the 2mtr talkback channel (144.725 MHz) but not needed normally as all regular functions are fully automatic. It can be used to display signal strength readings on 23cms signals. The DTMF menu is available with *01 on the 2m talkback sound channel. # can be used to clear errors or screens.
- THANKS to the many local Amateurs who have contributed to the financing, design and building of the repeater. Particular thanks to those who are not actually club members but who have been important in helping overcome technical issues. A few are listed here (in alphabetic order) G0DQH G3NZL G3PYB G8CKN G8GTZ G8LES .
- MAIN specifications:
REGION: CENTRAL SOUTH ENGLAND
SITE : POKESDOWN, BOSCOMBE, BOURNEMOUTH EAST
LOCATION: Nr POKESDOWN STATION IO90 CR16CH SZ125
INPUT : DIGITAL: 1249MHz. Symbol rate: 4000 FEC: 1/2*
* Any common FEC setting will work on the input.
INPUTS : AUDIO MAIN SPEECH CHANNEL (LEFT: Channel 1 or A)
INPUTS : AUDIO RIGHT(Channel 2 or B)was reserved for DTMF control of repeater extra functions. Currently DTMF is on 2m talkback channel, so both audio channels can be strapped to mono.
OUTPUT: DIGITAL: 1304MHz. Symbol rate: 4000. FEC: 1/2
VPID:256(=hex 0100) APID:257(=hex 0101) PMTPID:4095(=hex 0FFF)
OUTPUTS : AUDIO MAIN SPEECH CHANNEL LEFT (Channel 1or A) Usually White Phono.
OUTPUTS : AUDIO RIGHT(Channel 2 or B) RELAY OF 144.725MHz TALKBACK CHANNEL.Usually Red Phono.
ANTENNA : ALFORD SLOT
TALKBACK: on 144.525MHz V FM
Repeater will be on standby from 10AM to midnight each day and will auto start (<5s)when a digital tv signal is detected. Test sequence will transmit 7pm to 8pm each evening. Ident every 10 minutes. Out of these hours, if being used, it will remain on until after the input signal drops, the repeater will then give an on-screen countdown to the next Ident then return to standby automatically.This ensures maximum availability with minimum power waste.
DTMF CODES: Ensure the entry buffer is clear, a # will clear it. Please dial at 'hand' speed as there is an amount of error checking involved which can slow down response to the next character entered.
*01 MENU (use # to exit)
There is no requirement to use any DTMF codes when using the repeater normally. It comes out of standby as soon as it detects your digital signal and then goes to standby at the next Ident after you have dropped carrier. If you try to access the repeater using 70cm whilst it is receiving a signal on 23cm input you will not be able to get in until 23cm carrier is dropped.
Conversely, please ensure that the repeater is not currently in use on 70cm before sending signals on 23cms as they will get priority over 70cms.
When sending the obligatory on-screen Ident every 10 mins the system will not be able to deal quickly with other requests, such as new signal detect and DTMF codes, due to the limited processor power so please be patient.
Built by G8AJN and financed by Bournemouth Amateur TV Group