Date: Wed, 18 Dec 1996 13:55:32 -0500 From: Bill Jones Subject: Re: SCPC >According to Keystone NASG: WGN-AM /Interstate Radio Network/Cubs >baseball, Bears football. Is located on Galaxy 6 and on Galaxy 3, Actual >Freq: 3756.60, 1st IF Freq: 1393.4, 2nd IF Freq: 66.6. All frequencies are >in Mhz. I hope this helps...Lenny >>>>>> > >This first IF frequency/ 2nd IF frequency business helps clear up a >question I posed to the SSSSC mailing list (no reply yet) and someone >else asked here yesterday, namely, how does the four digit frequency >(1st IF) translate to the two-digit (2nd IF)? This is important because the >Uniden (and presumable other) SCPC tuner only uses the latter. >....... >As of this moment, Robert Smathers South Scanner Satellite Services >Chart (SSSSC), Vol 6, No. 1, 12/16/96, is by far the most exhaustive and >up to date reference I know of. Unfortunately, it does not cover the >two-digit frequencies, though one could cross-reference to the ST chart. >As far as I can tell there is no simple pattern to the conversion. > The 2 digit numbers are somewhat IRD dependent, since some IRDs have a 70 MHz IF and others use 140 MHz. There are, however (perhaps not simple) conversion relationships: If A=your actual freq (3756.60), the first IF would be 5150 - A (ie 5150-3756.6=1393.4). ie the actual 3700-4200 MHz band translates to 950-1450 MHz. Translation to the 2 digit freqs is somewhat more complicated, since it is different for each channel. For example, the 1393.4 example is in channel 3. For example channel 3 goes from 3740 to 3780 MHz. The center of the channel is 3760 MHZ. This will correspond to 70 MHz on an IRD with 70 MHz IF. THus, to get the 2 digit freq for ch 3, subtract the actual freq from 3690, (ie 70 less than the center freq). Since the actual center freqs are 3700+(C*20) where C is the channel # (ie ch 3 is 3700+60=3760), then the 2 digit freq is: A-(3700+(C*20-70)) ie for the example, 3756.6-(3700+(3*20-70))= 66.6 . The only hard part then is figuring out what channel to use. This is complicated by the fact that the channels overlap, ie 3756.6 is not only part of channel 3, but is also within the channel 2 bandwidth (although your receiver won't cover the whole range). You would probably be safe chosing the channel with the center freq closest to the actual freq, but it is possible that you might end up with the wrong polarity. I'm curious how this Uniden thing works, ie I assume that in addition to the 2 digit freq you need to set your receiver on the proper channel ( and the channel info was not given in the above example). When I've done SCPC, I've usually done it off the LNB (1st IF) signal, which isn't so ambiguous. +---------------------------------+ | Bill Jones, N3JLQ,Sweden, Maine | | wejones@megalink.net | | http://www.megalink.net/~wejones| | N3JLQ@WA1WOK.FN43FE.NH.USA.NOAM | +---------------------------------+