I don't fully understand the real electrical/RF implications of circular
left/right vs linear horizontal/vertical other than to say that it's
related to how the signal is sent (polarised) from the satellite (it's
polarisation) and that you have to have a matching LNB of the same
polarisation. In some cases I've been able to receive circular right with a
H/V LNB but that was a rare exception, circular left never worked. I'd say
buy a linear H/V LNB if your goals are to tune to H/V feeds.
I'm not suggesting this is your only issue but it's certainly one of the
most important. If you have access to a spectrum analyzer when you could
see very quickly the L-band representation to see whether the LNB is
down-converting correctly, or whether you have a tuner related issue.
Steve
Thanks, Steve.
I was getting confused because it appears that even if you specify R or L in
channels.conf file, the response from szap still only shows V or H.
Other documentation that I found says that circular right is activated on
the LNB with 13 volts, the same as linear vertical would be activated.
Circular left is activated with 18 volts the same way linear horizontal
would be.
Does that sound correct?
Yes. dvbtune (via the standard linux API) really uses V/H to set 13/18.
R and L basically mean the same thing (13/18). The electronics on the
LNB however (triggered by 13/18) deal with the polarisations
differently. If you trying to receive a V/H signal on a R/L LNB this is
going to be a problem. You need to match a R/L LNB with a R/L polarised
satellite feed. It's an easy test, re-align your dish to 119deg where
you have regular DVB feeds running on R/L polarisations - matching your
DSS circular LNB.
(I did a whole bunch of tests with a spectrum anaylzer and rotating
circular lnbs, no effect what-so-ever on the downconverted carrier. V/H
on the other hand, well, it started to bleed energy from the opposite
polarisation).
In the end we bought a quad LNB for the lab in New York, able to put out
Linear and Circular polarisations on a pair of cables. The LNB
specifically handles polarisations for V/H, R/L.
I am now starting to think that possibly the signal I'm trying to tune to is
too weak. I am only using a small 18 inch DirecTV dish. Any insights on
this?
I used a 18 inch dish for DVB-S work at ome on 119 degress, I'd suggest
you give it a try.
Regards,
Steve
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