[amsat-bb] Re: doppler comp. for FT-736R

MM ka1rrw at yahoo.com
Thu Feb 4 06:05:37 PST 2010


That depends on the bird.

Let's start with a simple FM example.
Assume you want to work ISS FM packet .  Up on 145.990 FM, down on 145.800 FM.
Use the satellite TX/RX mode knob.
Set Stat VFO-A to RX on 145.800 FM
set Sat VFO-B to TX on 145.990 FM
Set your Meter to FM center tuning mode.
Push the button, "TX on B" button.  This will cause you to Hear on Vfo-A and TX on vfo-B.
When ISS comes in range Packet or voice, Look at your FM center tuning meeting.  When it sees a FM signal that is off frequency, the meter will deviate away from the center.  Turn the Sat knob to RX, and now tune the big knob to center the down links signal. Tune your receiver frequency on vfo-A to center the needle.  For ISS you can leave your TX on the published uplink for that mode,  the Doppler is small and not much need to compensate for Doppler.
The FM center tuning meter also works for all other FM birds.

Transponder FM Birds:
If you are working an FM transponder bird, the process is a little different.
Tune the Down link the same way as ISS.  Keep the needle centered.
On the Uplink side, select the vfo you are using for uplink with the Sat knob TX.
Pre set your uplink frequency and compensate to Doppler.
If uplink is on 2 meters, set the frequency to be 2-3 K below the published Uplink frequency for starters.
If uplink is on 440, set the frequency to be 5-8 k below the published uplink frequency.
(check your tracking program for the correct Doppler for that pass)
When the bird comes in Range, listen first.  Fine tune your down link by setting Sat knob to RX and tune for center meter.  Now turn the sat knob to TX and call.  If you hear your downlink on the FM bird, slowly adjust your TX uplink for best audio.  do not talk too  loud, you may over drive the fm birds.
Transponder SSB Birds:
LEO SSB satellites are the hardest satellites to work because the Doppler is changing very fast at two different rates on two different bands at the same time.  Do not try LEO SSB satellites until you have mastered FM satellites.
Do your homework and find the published transponder range.  Choose a matched uplink/down link set of frequencies.  Enter these 2 bands into the TX/RX VFO's (without Doppler correction at first).  Check your satellite program and find the Doppler for each band, for the beginning  of your upcoming selected pass.
let's assume Mode B,  440 up, 2-meters down.
at the beginning of the pass the 2-meter Doppler will be plus 2-3k.
at the beginning of the pass the 440 Doppler will be minus 6-10k (check your tracking program)
Now that you have your two Doppler numbers add/subtract  those from your tX/rx VFO's and you will be in the ball park for the beginning of the pass.   
The center tuning meter will not work in SSB.
for Inverted Transponders' set the Sat knob to Reverse
for Normal transponder, set the Sat knob to normal.
Now when you turn the knob, the two frequencies will follow each other.
now it gets harder.
When the bird comes in Range, listen first.  
Find someone else that is calling CQ. 
Tune to get best audio (sat knob must be in Reverse for V0-52)
once you have a good audio signal, then tune ONLY your TX, NOT the RX.
Turn the sat knob to RX and then call and tune at the same time.  While you are talking, you are listening to your voice and tuning your voice to match the Receiver frequency.  do not tune the receiver while you are transmitting.
Only tune your receiver while you are listening.
With VO-52, it moves so fast, you will need to tune for every other word that you speak.
When you are done talking.  Set the Sat knob back to Reverse.
When the other station starts talking, retune the locked VFO's to match his down link. On leo SSB satellites this process will repeat for every TX / RX session.

good luck wf1f

--- On Thu, 2/4/10, n4csitwo at bellsouth.net <n4csitwo at bellsouth.net> wrote:

> From: n4csitwo at bellsouth.net <n4csitwo at bellsouth.net>
> Subject: [amsat-bb]  doppler comp. for FT-736R
> To: amsat-bb at amsat.org
> Date: Thursday, February 4, 2010, 12:36 AM
> Can anyone suggest the best way to
> acquire doppler compensation for a Yaseu FT-736R?
> Dave, AA4KN
> _______________________________________________
> Sent via AMSAT-BB at amsat.org.
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