Thread: Calculating LNB Output Frequency (Project Part II)

Originally Posted by Tron

Radar, bandstacking is great because it allows the LNB(F) to send both polarities down the same cable at the same time. No polarity switching is required. The LNB(F) just sends the vertical transponders normally and "stacks" the horizontal transponders at a higher frequency. Therefore, both polarities are always there, and the cable may be split or looped through with both polarities intact. Of course, the added complication is that the signal path must be capable of passing about 2.2 ghz instead of about 1.5, and the horizontal transponders will be at unexpected frequencies (above the normal range). A blind scan receiver will usually take care of finding them.

TRON,

I do understand the theory and its uses/applications, but what eludes me is how they are doing this inside the LNBF. The internal circuitry to get the H TPs on the higher frequency. Is there a separate internal oscillator? I have brushed into several explanations of this before, but so many descriptions were vague and incomplete or they contradicted the others. So, I never found a really accurate explanation.

RADAR

Originally Posted by Tron

Radar, bandstacking is great because it allows the LNB(F) to send both polarities down the same cable at the same time. .....

I can see the utility of bandstacking for the DBS band, where there isn't anything in that upper band, but it seems to me that it wouldn't be as useful for other bands. Ie it seems like you'd at least lose the capability of receiving out band, ie such as locking some transponders in the DBS band with a regular linear lnb {this could be good or bad}. But the existance of signals in the upper band would also seem to be an issue relative to interferrence, although I haven't thought that topic through. But what I was thinking, was that say you had an 11700-12200 lnb that was putting one polarity up at 12200-12700, it seems to me that if you have strong signals in that upper band, that they will leak through and interfere with the polarity that is now sharing that band. Ie, I'm skeptical that they could have a sharp enough bandpass filter to keep the upper band out of what is sent as the lower band.
I'm sure that they probably made a serious effort to avoid such problems, but I just wonder how well it can work in practice.

I'm not sure, but I believe that there are two oscillators at work in these LNBs. There are two L.O. frequencies, i.e., 5150 lower L.O. and 5750 upper L.O. on the Eagle Aspen B1SAT C-Band LNBF. Many receivers don't have a provision for bandstacked LNBs, but I've found that using either of the two L.O.s will get you the channels that are there.

interesting read. ive seen cband freqs on lyngsat in the 3400 range (circular @ 40.5w) and ku freqs in the 10 000 range. from reading this i can see a wideband circular would be needed for the cband but what kinda lnb would translate the ku fraqs to usable IF.

crackt out,.