LNB frequency qestion

[xtreme1]

Hi Y'all I'm new to this site. My question is how does the receiver auto adjust the TP frequency? The problem I'm having is sometime I have to manually adjust the TP frequency to receive a signal from a bird. Is it my receiver, switch, or LNB faulty???

[whoknows]

Each transponder has a bank of channels. When you change channels you change transponder. The receiver will not automatically switch to a working transponder when looking for signal or aligning a dish. You have to manually change.

[xtreme1]

Thanx for the reply, I've never had to manually adjust TP frequency for my other systems...guess I do now!

[jvvh5897]

I would suspect the LNB first. The LO in the LNB is usually set with a simple "puck" of a special material that can oscillate at 10's of Gigahertz, but it drifts with temperature and time. If the reciever can not lock in the frequency correctly at the setting it has, most boxes will do a fine tune search for the signal around the frequency it knows, but if the LO is off by a large amount it may not find it. Now, if you are setting the box's frequency to EXACTLY the same value as it had, then it may be that the diseqc switch is not getting set correctly or is having trouble changing to different output port. You should be able to take the diseqc sw out and see if the problem goes away.

[xtreme1]

I was thinking the switch too just because I have 3 LNB rolling. God knows switches don't fail lol

[Terryl]

A switch can't change the frequency of the IF signal from the LNB, and if 3 different LNB's are doing the same thing I would then suspect the receiver.

We have 3 to 4 stages in the signal frequency from the satellite, the main transponder frequecy (lets use 12224 MHz) for that satellite is in a list, 12224 MHz is the downlink frequency to the dish, this is way too high to run down most coax, so the LNB uses an LO (Local Oscillator) and a mixer to down convert it to some frequency that can be sent down a common coax. (like RG-6)

The LO for the Dish and BEV satellites is 11250 MHz, what the LNB does is inject this frequency into the mixing stage and this causes it to become a second lower frequency called an IF,(Intermediate Frequency) this IF is determined by the incoming frequency from the transponder, (selected from the list for that satellite) minus the LO frequency of 11250, thus giving you an IF of 974 MHz, well withing the range of the RG-6 coax.


Now inside the receiver, the satellite tuner has what is called an AFC circuit, (Automated Frequency Control) this AFC can compensate for most any drift in frequency of the LO in the LNB, but to a point, and it may be software controlled, if the AFC is not working, or somehow disabled in the software, ot the LO in the LNB has drifted too far then you have a problem like your talking about, having to manually adjust the transponders frequency.

But again having to do this for 3 LNB's I would then suspect the receiver to be at fault, ether it's AFC or the software (if any) controlling it.

Another possibility is that the receivers master oscillator for the tuner has drifted out of spec, or someone has put the wrong value in the software that calculates this frequency in the PLL circuit for the tuner.

You have several settings for the LNB's LO frequency, this is selected by the LNB type.

Dish and BEV LNB's use 11250, and 10750 for the 118 LNB
A standard LNB for the circular satellites uses 11250
A standard LNB for the linear satellites uses 10750
A universal LNB may use 10600 and 9750
A "C" band LNBF will use 5150

So you can see there are several settings, and you have to select the correct one for the LNB you are useing, or you will have problems.


Sorry too much coffee again......

[eramnauth]

I think the circular LNB for 118.8 /119W is 10750.

[xtreme1]

Thanks boys, I believe it was a software issue. last night the system was quick and working as it should without my intervention