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Re: zero beat telemetry?



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     In case of Spoutnik 41 /RS18, the modulation on the TX side and 
     demodulation in RX side is FM.
     If there is dopller or if the tune of your receiver is not correct 
     this don't affect the frequency of the tone at your receiver. It 
     affect only the distorsion of the tone received. 
     So you can measure directly the tone frequency without the need of a 
     reference tone.
     
     This will not be right if you had to use a CW or SSB receiver.
     
     Now to measure the frequency, you can use:
     
     Frequency meter, but not easy because it's a burst
     use the sound blaster card on you PC to record the tone and analyse 
     the frequency by FFT
     
     Or the methode I prefere and more precise ( yes, more precise that 
     FFT) . Make a lissajou figure with an external AF frequency generator 
     and an oscilloscope.
     
     Good luck 
     
     F6FAO 


____________________________ Separateur Reponse 
________________________________
Objet : [amsat-bb] zero beat telemetry?
Auteur :  
/DDV=pellenzc@vax.cs.hscsyr.
edu/DDT=HPMEXT1/S=pellenzc/OU=BSFX1/O=ALCATEL/P=ALCA
NET/A=ATLAS/C=FR/ a x400
Date :    13/11/98 15:27


Hi All,
     
I am wondering how to capture accurate audio for telemetry (sputnik temp 
etc.).  (NOTE: I am a beginner, I have not transmitted to a satellite other 
than MIR yet.  I have been collecting info for over a year so far and have 
been a member of AMSAT for just a little less than that.  I have read the 
references available from amsat and participate and monitor this list daily 
so I know what I am doing before I do it.)
     
Being a biological scientist, I have a great appreciation for controls and 
standards.
     
I want to capture audio for decoding of telemetry.  My question is:
On a satellite where I cannot transmit a tone and find it on a downlink how 
do I know that the tone I recieve is actually accurate or if I am not 
capturing an audio tone that is erroneous.
     
I believe that possible sources of error can arise from:
     
1) My radio (FT-736R) frequency display not actually not what is injected 
into the mixer...(if this is the case I guess I am out of luck!!)
     
2) The doppler correction I make is not the actual that is necessary and I 
am tuning the rig improperly generating an audio tone that is not actually 
that which is transmitted.
     
It seems to me that error source #1 is just something that I would need to 
check and repair if necessary but, is error source #2 something that I can 
control for?  Is there a control or standard tone transmitted by satellites 
like sputnik 41 which does not change so I might use it as a "standard" for 
tuning?
     
Also, are there other sources of error I have not considered?
     
Any help is greatly appreciated!!!
     
Thanks
KC2BBU
Chris
     
     
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