DiseqC Satellite switch problem

[ProDave]

Re setting up my satellite system. Previously I had a separate receiver for each satellite, but thought I would streamline things and have one receiver covering Aatra 1 and Hotbird with a DiseqC switch. Dish was alligned and working.

So tune in Astra 1 (connected to LNB1 on the Diseqc switch) all okay. Start tuning in Hotbird (connected to LNB2 on the DiseqC switch) and hang on, it's getting the same list of channels. Tried every DiseqC setting I could find on the receiver still just finding the Astra 1 channels.

Out of desparation I went to the dish and physically unplugged the Astra 1 LNB. Re scanned the receiver, and it found the Hotbird channels.

Go and plug the Astra LNB in again. Switch to an Astra 1 channel, okay, switch back to a Hotbird channel "no signal" Go and unplug the Astra 1 LNB and it switches over to the Hotbird LNB.

Out of desparation I swapped the Astra 1 LNB for a different one. Now it all works.

So what was going on, with the old Astra 1 LNB it would not "let go" of the DiseqC switch but the new LNB works fine. What would cause that? never seen anything like it before.

[Temp]

I read that DiseqC switches are normally backwards compatible with older LNB - but it suggests there can be compatibility issues.

[ProDave]

The DiseqC switch comes before the LNB so the LNB would know even know, let alone care, it was fed from a switch.

 

The only theory I can come up with is it's quite a long length of cable from the house to the dish about 30 metres, and I wonder if the old LNB consumed more power and was causing a volt drop issue stopping the switch from seeing it's signal and switching, and perhaps the replacement is lower power?  It was an OLD LNB it has been on that dish for 15 years, and it was by no means new when I got it then.  It's replacement is a modern one, no more than 10 years old.

[Declan52]

I used to make old analogue sat boxes over 20 years ago and from memory when we tested the lnb switching from horizontal to vertical we used as low a voltage as we could. It was around 14v for horizontal and 11v for vertical. If it worked on these it was deemed to be able to cope with a drop if the cable was long.