Comag SL30/12 question

[G4WIM]

Hi guys,

I think I've done something silly (all part of the learning curve I guess!)

Just bought a Comag SL30/12 and it was working great, managed to set it up with no problem for 24cms, great picture good sensitivity etc, then I thought let's clear out all the broadcast stuff and re-enter just the DATV channels.

So I did just that, now while it finds the DATV signals ok (using TP scan) and reports good strength even at a low level of input (indicating the tuner is good) and allows me to save them as planned. When I come back to them in the channel list it reports weak signal and won't display anything.

All pids vids etc look ok.

Tried it as a freesat tuner again and works perfectly - just doesn't seem to like my signals anymore

Any ideas as to where i've screwed up ?

Tried doing a reset to default and most of the obvious stuff.

73 Tim

PS this is the tuner I hope to use for GB3FT

[G4WIM]

Seems when the SL30/12 says weak signal it means it can't decode due to FEC mismatch rather than weak signal ?

Anyway after fiddling around with the FEC setting on the tx the comag now decodes again (the SL30/12 does not have a setting for FEC), phew !

[G4EWJ]

It sounds very strange. The 'No signal', 'Weak signal' and teardrop screens probably all mean 'I could not find a signal'.

Which FEC were you using and have you tried going back to that one? Most domestic receivers will automatically determine the FEC without being told.

I have an SL30 on the way, so I'll be doing exactly the same as you shortly

Brian

[G4WIM]

Hi Brian,
maybe I was mistaken with my conclusion, but there was definitely something odd going on and it was caused by wiping all the stored channels.

One thing for sure was that it was correctly tuned with right symbol rate but absolutely no decode until a changed FEC on the tx at which time the rx seemed to recover and has been fine since.

Hence why I assumed it was FEC related - but could have been coincidence.

Must say though the rx even without an external pre-amp is pretty sensitive.

Now looking for another rx which has a signal good output for use in a repeater I'm assembling.

Might get another SL30/12 - might I ask where you got yours from ? Just checked ebay and nothing showing on there.

73 Tim

[G1LPS Terry]

Hi Tim I use Comag SL25 on GB3KM believe its the same but with internal psu
hope that helps
Terry

[G4EWJ]

I bought a couple of SL30s off Ebay yesterday. I should have them to try tomorrow.

Brian

[G4WIM]

Hi Terry, Brian

just ordered another sl30/12 on Amazon from Germany - I will likely RFI proof it in a diecast box and use it as the rx on GB3FT.

Brian, not sure where you are on the Wirral but you might just be within range and I maybe able to work you direct.

I have DATV for 70cms and 24cms.

73 Tim

[G4EWJ]

You were a huge signal when we worked you from G3NWR on 23 and 70. I'm a couple of miles to the east and lower down, but still worth a try.

Brian

[G4WIM]

Hi Brian,

maybe we should conduct some tests on 24cms or 70cms ? Your choice.

BTW just made a rather alarming discovery about the Comag SL30/12, this might be known to others but not to me.

When you turn off the LNB power the output voltage drops to about 0.75V as you might expect, however if you have a DC short to ground from say an inter-digital filter, the unit still tries to provide about 350mA of current.

The end result is the excess power is dissipated in the control transistor and series mounted resistor.

However I notice on the later units they have re-designed the LNB PSU using a switcher - don't know if this suffers from the same issue.

73 Tim

[M0SKM]

They also produce a voltage on switch on; which can cause the PSU to go into trip mode if presented with a short. I'm using F type DC blocks on mine to eliminate the problem.

One very useful mod for repeater use is the digital lock indicator which can be found in CQ TV 240.