THIS IS NOW SHUT DOWN, NOV HAS BEEN RELINQUISED.
MB7TR is an SSTV repeater classed as a regenerative node operating on 432.525MHz NFM (narrow FM).
How To Use
MB7TR will repeat/regenerate your image in the following mode : the same as incoming
To have MB7TR repeat/regenerate your image, which you can transmit to it any SSTV mode, you need to do the following, all on 432.525MHz in NFM :
- TX your CW ident (good practice)
- TX a 1750Hz tone burst for around 2 seconds and key off
- Listen and wait for MB7TR to reply with its CW ident – this signifies it is ready to repeat
- TX your SSTV image within 10 seconds of the end of the CW ident
- Sit back and wait for your image to be repeated out
You can use your SSTV software of choice, MMSSTV being one often used.
Hardware
- PSU : 13.8v 25A linear
- Radio : Motorola GM340 UHF
- Time out timer (ToT) : 240 seconds
- Forward power at back of radio : 2.25w
- Antenna System gain (less other losses) : 5.27dB
- Maximum Deviation : +- 2.5KHz
- Emission code : 8K00G9W
- Max ERP permitted : 8.9 dBW ERP
- Diamond MX72N Duplexer – 0.1dB insertion loss
Aerial
- Diamond X300N
- Gain : 6.85dBd
- Height : 8m agl
- Elements : 5 x 5/8th on 70cm
- Max wind : 50m/s or 112mph
- Length : 2.9m
- Max Power : 200w
- Nominal Impedance : 50ohm
- SWR @ 432.525MHz : 1.27:1
Coax Feeder
- 18m of Ultraflex7 from Messi & Paoloni
- 2.23dB cable loss for the 12m feeder length (excluding connectors)
- 12.3dB loss for 100m at 430MHz
- 440watts at 430MHz handling
- 75pF/m +- 2
- 83% velocity factor
- 50ohm nominal +-3
- Terminated N-Type both ends (n-type to bnc adaptor at radio)
EMF Compliance
Compliance based on maximum power output defined by the NoV. Details Here
Logic
MMSSTV in repeater mode is used on a Windows10 PC.
The radio is in an outhouse and as such uses a USB audio dongle connected to a RaspberryPI 4. This PI4 runs VirtualHere which essentially brings that USB audio dongle device over the LAN to the PC in the house. The system also uses a homebrew Arduino Pro Mini emulating a Kenwood TS480 and associated CAT commands (code here). That Arduino is also connected to the PI4 and the ‘Kenwood TS480’ appears on the same Windows10 PC as a com port. MMSSTV issues CAT commands to that com port to PTT the Motorola GM340 UFH radio.
Supported SSTV Modes
MMSSTV supports the following SSTV modes.
- Robot B/W 8
- Robot B/W 12
- Robot 24
- Robot 36
- Robot 72
- AVT 90
- Scottie 1
- Scottie 2
- Scottie DX
- Martin 1
- Martin 2
- SC2-180
- SC2-120
- SC2-60
- PD50
- PD90
- PD120
- PD160
- PD180
- PD240
- PD290
- P3 203
- P5 305
- P7 406
Issues/Problems
If the are any issues please contact me via [mb7tr <at> grange-lane.co.uk]