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Re: AO-16 & FM receiver thoughts (was: AO-16 reportfrom Copenhagen)




The other thing you can do to lower your deviation is to lower your mike gain, or just not talk so loud.  

Greg  KO6TH


----------------------------------------
> From: nate@natetech.com
> To: amsat-bb@amsat.org
> Date: Sat, 26 Jan 2008 03:06:20 -0700
> CC: K3IO@verizon.net
> Subject: [amsat-bb] AO-16 & FM receiver thoughts (was: AO-16 report from	Copenhagen)
> 
> 
> On Jan 23, 2008, at 11:14 PM, Tom Clark, K3IO wrote:
> 
>> The receiver has a 15 kHz wide crystal filter with sharp skirts. So if
>> your NBFM xmtr is set with a ±5 kHz deviation, you may well find your
>> signal hitting the filter "walls". You may get better performance if  
>> you
>> crank the deviation back a bit.
> 
> Lots of folks who haven't worked on FM repeaters (or repeater  
> coordination) don't realize that a 5 KHz deviation signal actually  
> occupies 16 KHz, Tom.  This is a great reminder, and knowing there's a  
> sharp-skirted 15 KHz filter is great info for folks trying.
> 
> (Sadly, lots of repeater users don't know the difference between  
> "deviation" and "modulation" these days, either -- but that's a whole  
> different rant...)
> 
> This would also mean that if you're way off on correcting for doppler  
> on the uplink you could ram into the skirts of the filter too... on  
> modern rigs, go into those menus and set that FM step for as small a  
> number as it'll go, and play around folks... you might find that fine  
> tuning things a bit the correct direction for the doppler on the  
> uplink might help a bit too.
> 
> A little lower deviation and a little more tuning and fiddling as  
> needed with the uplink frequency, and voila!
> 
> Anyway this leads me to a thought, Tom -- for those who have modern FM  
> rigs that have so-called "narrowband" mode (usually max 2.5 KHz  
> deviation) would the satellite's FM receiver be fairly linear when fed  
> with low deviation levels?  I know it hurts on S/N ratio on the DSB  
> downlink, but would 2.5 KHz deviation yield 50% modulation of the DSB  
> transmitter, or is the FM receiver's audio output non-linear to some  
> extent (like most are) and 2.5 KHz deviation would really be down to  
> something like 30-40% modulated on the downlink?
> 
> It'd keep people from hitting the filter skirts as much, but if it  
> yields really low modulation levels of the DSB transmitter, it'd  
> probably hurt more than it would help.  What do you think from what  
> you know of the ol' girl's FM receiver audio setup?  Any thoughts?   
> Worth experimenting with the feature if folks rigs have that setting?
> 
> Neat stuff seeing the reports of those playing with the bird since she  
> came back to life, both the control stations folks who did their  
> magic, and now the end-users.  Cool to read along!
> 
> --
> Nate Duehr, WY0X
> nate@natetech.com
> 
> 
> 
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