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Re: Satellite Inquiry

>Not everyone is using FDT on modes V/U and V/S and it isn't really required 
>for FM in those modes.  However, modes U/S, L/S or U/V (mode B) require it 
>even for an FM satellite.  

By Full Doppler Tuning I'm assuming you mean full computer control of both uplink and downlink doppler tuning...

Manually tuning in 5 khz steps works fine for UHF FM uplinks. With the exception of the ISS, most FM satellites have a very wide front end designed usually for 9k6 or higher reception. More like 15 khz wide than the 6 khz you assumed in your calculation. (quick reference, AO-51's 4 VHF receivers have 15 or 30 khz wide IFs, page 33 Echo book, first edition) The ISS is different in the fact that it is a terrestrial radio, and therefore is much more picky about being on frequency. For this exact same reason, narrow FM works MUCH better on the ISS repeater (instead of making the IF wider, you make the signal narrower). Still, 5 khz tuning is perfectly doable on ISS U/V repeat. In fact, I made several contacts on it while mobile, tuning in 5 khz steps. I'm sure the AFC feature in the Kenwood up there helps with this too. I also made dozens of contacts on SO-35 U/V FM (R.I.P.) with nothing more than an Alinco DR-605T and a dual band mag mount, again tuning the uplink in 5 khz steps. I don't mean to have a been there and done that attitude, but i _know_ it works because I have done it.

L is a different story and you may be right about needing full uplink tuning there, at least on AO-51. L uplink on 51 uses the SQRX receiver and it has either 4, 15, or 150 khz IF widths. Not sure which one is used on L repeat mode. SO-41 used (I heard) the same SQRX receiver for it's repeater and it was very picky with regard to VHF uplink frequency...but still a fine bird (please turn it back on someone!!!!!).

73, Drew KO4MA
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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