I was sure I'd seen some discussion on the Portsdown thread(s), but I can't (despite a lot of s arching) find anything.
So, is anyone using Portsdown on 6m? Any particular frequency/SR? Any tips for setting up - filters, PAs etc?
The specs for Portsdown are here https://wiki.batc.org.uk/Portsdown_Output_Levels
As you can see it does not cover 50 MHz natively but an external; converter can be used - here's one Mike is proposing for 71MHz rxr and could be used on 50 MHz tx and Rx. viewtopic.php?f=76&t=4108
One or two people are "thinking" about 50 MHz so maybe it's time for some experimentation...
73's Noel - G8GTZ
My receiver PCB (Noel has one now and is patiently waiting for me to send him the schematic) requires a 400MHz LO.
Plan is to use the spare output from the Portsdown in CW mode. It filters 50-70MHz, amplifies and converts it to 450 - 470MHz for input to the Minitiouner. There are many different ways you could use the board - no requirement to stick with it's intended use. For a TX converter for example. It can't make tea.
The problem with the Portsdown is that the QPSK modulator chip is only in-spec from 140 - 1000 MHz. It’s just about OK at 71 MHz, but gets worse quickly below that. The constellation becomes trapezoidal.
I see - so we either need a RX/TX frequency converter or another modulator. My current board will do that but only if the active device is bypassed to make it bi-directional. Then there would be a need for additional gain to overcome the ~10dB losses mostly important for the RX side. Maybe easier to use two boards one passive for TX, one active for RX. Or I could re-design I suppose but based on the level of interest so far I doubt there is any demand. The Pluto and Lime can do 50MHz and both are about to re breadily available again.