"Bruce in Alaska" wrote in message
...
In article ,
"David G. Nagel" wrote:

The satellite tv systems
use this to tune the block down converters out at the dish antenna.

Well not quite, Block DownConverters are not "Tuned". They take a
Fixed Bandwidth from the Input Frequency, and DownConvert it to
an equal Fixed Bandwidth at a lower IF Frequency. Back in the LONG
Past era, there were First Generation SAT Receivers that did have
the Frequency Selecting Mixer out at the dish, and used an IF of 70Mhz
to bring a Single Channel of Wideband FM Tv to the DeModulator in
the SetTop Box. This system was universally designed out of the
Consumer SAT systems due to Temperature Insability and other problems.
The system used today, which is basically Standardized now, have a Low
Noise Preamp, feeding a Block Downconverter, (LNB) and feed the total
Fixed Bandwidth of the SAT Segment, (500 Mhz) to the SetTop Box at a
lower IF Frequency. (900 Mhz - 1400 Mhz approx) They still use DC Bias
on Coax Feeds to the LNB's, and these both power the LNB's, and also
select the Polarization of the FeedHorn.

Bruce in alaska
--
add a 2 before @


Some satellite dish sets also use a 22 kHz signal to switch between 2 local
oscillators in a "dual band" LNB.