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Re: Satellite Inquiry



At 11:08 PM 2/22/2005 -0500, Andrew Glasbrenner wrote:
>By Full Doppler Tuning I'm assuming you mean full computer control of both 
>uplink and downlink doppler tuning...

Not necessarily - manual FDT is possible, at least on the 910H.  I think 
the 847 and TS-2000 have similar schemes but I don't know for certain.

>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 totally agree that tuning in 5KHz steps is fine.  My observation has been 
only that it should be done.

While I used an FM repeater as an example my comments were really intended 
to indicate that would be the best situation and that FDT would certainly 
be required for SSB/CW operation.

It's interesting that you mention that AO-51's VHF receivers are 15K+ wide. 
While I know that the IF is that wide, I don't know if that correlates to 
the entire range of FM capture.  Perhaps someone can comment on that.

>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.

I haven't used it for some time, but I believe AFC on the 910H will track 
the receive frequency but doesn't compensate the transmit frequency in the 
same way that manual FDT (using the tuning knob) does.  I'll try it tonight 
on 27 to refresh my memory.

73,

Emily


---------------------------------
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