To: PUBtech Public Radio Tech Talk Subject: PRSS Dish Alignment Necessity is the mother of invention. Saturday I was setting up a new PRSS installation for a client. Spectrum Anaylzer went belly up. And of course this all happend after I explained to the client how impossible this job would be with out a spectrum analyzer. Normally I look for the nice notch at around 70 mHz on the Downconvertor front panel output. The signals are on both sides of the notch, and you align AZ and EL by peaking those. The LNB is typically set to about 11 o'clock and then tweaked. Looking at the notch, you null out any cross-pol interference from the adjacent. Typically TSP 3 has more Video intereference coming in on the notch, so we use TSP 3 ("B"). SCPC Channels on G4R are between 56.9 and 69.05 and from 76.90 to 78.80 MRN feeds with nice tone found at 77.7 Also Michigan Radio Network 77.2 is weak but usually there. More action on Saturday afternoons in fall- college football. Sometimes Rush Limbaugh (when remote). Anyhow, using a potomac FIM, you can tune in these channels and the rotate the LNB. You will hear the white noise go away easier than you can see it on a meter, but the meter will show a dip as the sideband interference nulls. That's right- a dip when tuned to the desired analog signal. If you off-tune a bit you can also null the hetrodyne, anybody who has ever used a Heath Q-Multiplier knows the routine. On the spectrum Analyzer you can see the noise floor on both sides of the analog signal go down dramatically. Today I reveiwed the alignment with both Spectrum Anaylzer and FIM. Although initial identification of the bird (AZ and EL) is easier with the spectrum analyzer, you can actually "see' the notch by tuning up and down with the FIM. For the Cross-Pol alignment, the process I just described using the FIM actually WORKS BETTER than the analyzer (and my FIM is also more portable and easier to use in bright sunlight). You learn something new everyday. Note: Religious networks SRN, Moody, FOTF etc are on Americom-3 (87 deg) Tsp 17, YOu might be able to find some analog video on C-pol TSP 20 which you can null out.