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Using one of the cheap chinese VHF 100 watt amps https://www.ebay.co.uk/itm/100W-FM-VHF- ... 1776288254.
Driving it with Portsdown at 0% attenuation, one of these 'amps' (https://www.ebay.co.uk/itm/50-1200MHz-1 ... ctupt=true which are a single device on a reworked board - 2 watts dissapation maybe but not RF!) 125KS and tweaking the bias for power and symmetry, I get the attached waveforms and 44 dBm = 25 watts.
It looks 'good to go' to me or am I being hopeful? Gareth
Time to fix a fan, box and add coaxial switching.
Planning the box/switching so SA off and portable batteries charging. Will check later. Note to self, WRITE STUFF DOWN!!
We did not manage DATV though, neither with 125SR nor 333SR. Martin is using a decent RTL dongle on a Portsdown, I'm using a MT V2 straight in. We can both see the beginnings of signals but not enough to lock. More signal required, but how much more?
I'm guessing that some form of preamp for my MT would be a good idea, given it was designed to operate with a BIG LNB signal, maybe the same for the RTL, or is that at its limit anyway perhaps ie more gain may not improve matters unless well-filtered?
Suggestions welcome, other than 'move house'
You will definetely need a pre-amp and filtering in front of a MiniTiouner - the normal LNB that it was designed to work with has ~55dB of gain and a low noise front end.
There are a number of solutions but the best I found was the GM3SEK design DG8 pre-amp which has a decent NF plus on board filtering but the source of kits is no longer available.
An alternative could be this unit made by Anthony M0UPU for the HA balloning market - it has a low noise device followed by a SAW filter which should give protection from paging / band 2 but not from packet and local repeaters https://store.uputronics.com/index.php? ... duct_id=89
Alternativly there are loads of low noise pre-amps on ebay but you MUST MUST use a filter - they will appear to work on the bench but not on the aerial- I know, I've been there - see https://wiki.batc.org.uk/Filters and https://wiki.batc.org.uk/146_MHz_filters
Re G4FKK - if he is using the leanDVB in the Portsdown he will instantly be 8 dB down as there is no FEC implmented and the above about filtering also applies. He maybe be better off trying the s/w decoder developed by Marko92 on the Oscar 100 chat - apparantly it's got a challenging UI and not sure anyone has used it for anything other than Oscar100 but reports say it would be better than LeanDVB. Available from here: http://v.1337team.tk/dvb-s_gui_amsat.zip
Hope this helps...
Noel - G8GTZ