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Re: [aprssig] Differences between ISS and normal packet.



I caught an ISS packet on a scope and added it to my ISS-WEB page and show
the ISS downlink compared to the Kenwood D7.  It looks like the ISS is
using a compromise of about 3.5 dB premphasis and its deviation is lower
to allow some doppler.  (or my discriminator might not be flat either).
In either case, no complaints there..
Follow the links:

ISS-APRS FAQ's:  http://web.usna.navy.mil/~bruninga/iss-faq.html
DIFFERENCES:     http://web.usna.navy.mil/~bruninga/iss-aprs/issdelta.html
ISS Waveform:    http://web.usna.navy.mil/~bruninga/iss-aprs/iss3.jpg
D7  Waveform:    http://web.usna.navy.mil/~bruninga/iss-aprs/iss6.jpg

--------------------------------------------------------------------
> > BIG DIFFERENCES BETWEEN ISS and TERRESTRIAL PACKET              de WB4APR
> >
> > ... there are many factors that make this totally different from
> > Terrestrial packet...
> >
> > EQUALIZATION:    The age old controversy of FM pre/de-emphasis.
> > 1) TNC's connected to the Speaker/Mic produce a packet signal that is
> > pre-emphasized and similarly demphasized on receipt.  SEE PHOTO
> > 2) TNC's connected to the Discriminator and Modulator produce equal
> > level tones and the tones are independent of the speech processing
> > circuits.  SEE PHOTO
> >
> > LESSON:  Attempts to communicate between systems set up by #1 or #2 will
> > always suffer a 6 dB skew in their tones (and performance with noise
> > will be much worse.  I have not yet had a chance to look at my
> > discriminator output on a scope when ISS was in view, but I suspect it is
> > optimized for plug-n-play (spkr/mic) operation.

de WB4APR@amsat.org, Bob

ISS-APRS FAQ:       http://web.usna.navy.mil/~bruninga/iss-faq.html
PCsat Design        http://web.usna.navy.mil/~bruninga/pcsat.html
CUBESAT Designs     http://web.usna.navy.mil/~bruninga/cubesat.html
APRS SATELLITES     http://web.usna.navy.mil/~bruninga/astars.html

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