[amsat-bb] Re: AO-16 & FM receiver thoughts (was: AO-16 report from Copenhagen)
ko6th_greg at hotmail.com
Sat Jan 26 10:44:27 PST 2008
The other thing you can do to lower your deviation is to lower your mike gain, or just not talk so loud.
> From: nate at natetech.com
> To: amsat-bb at amsat.org
> Date: Sat, 26 Jan 2008 03:06:20 -0700
> CC: K3IO at 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
>> 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 at natetech.com
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Climb to the top of the charts! Play the word scramble challenge with star power.
More information about the AMSAT-BB