[aprssig] weak signal ISS packet

Bill wa7nwp at gmail.com
Mon Jan 12 09:33:42 CST 2015


I bet the folks on the ISS could make an audio recording of the packets they hear on a busy pass across the continental US.   That would make for some interesting analysis.

Bill

> On Jan 9, 2015, at 8:06 AM, Robert Bruninga <bruninga at usna.edu> wrote:
> 
> Yes, again, "best packet"  all depends on the settings of the transmitting
> station (and matching it on receive).
> 
> When the ISS used a kenwood, then another kenwood would always work the
> best. Because both are built at the factory for optimum performance (to each
> other) and they use direct modulation and demodulation to the same levels.
> My kenwoods can decode another kenwood (direct) with only 3 bars.    BUT
> similarly, I can see many signals that appear to have full scale signals and
> then barely deocde because so many signals on the air were never adjusted
> properly.  AND there are two standards.
> 
> Do the sending and receiving radios use pre- and de-emphasis (speaker and
> Mic connections)? Or do they operate flat with direct modulation and
> demodulation.  Is the receiver an FM demodulator or Phase demodulator?
> 
> BUT on ISS, I believe they are currently using another radio, not a kenwood.
> SO now you need a receiving system best matched to this radios transmitted
> waveform.
> 
> Maybe someone on the AMSAT-BB has captured the existing ISS waveform and we
> can see what kind of receiver is best.  But then again, the captured
> waveform MUST indicate exactly what kind of receiver (with or without
> de-emphasis) was used in capturing the waveform!
> 
> Two manufactured APRS radios work BEST between them because they were
> factory adjusted for BALANCED tone levels and NO preemphasis or de-emphasis.
> But other stations may just use the Mic connections and  speaker connections
> and get over 6 dB of performance loss if they are not accounted for.
> 
> The use of speaker/mic connections(with pre- and de-emphasis) and direct
> modulation and discriminator demodulation can each have optimum performance.
> But there are always problems when crossing between the two.  BUT, it IS
> possible to adjust on the transmit side for a compromise between the two and
> then receivers of each type can decode pretty good.
> 
> Though maybe 1% of hams go to this trouble.  Packet radio is NOT
> Plug-N-play.  The transmitter must be adjusted for optimum waveform!
> 
> I should be able to tell everyone what the RIGHT way to do it is, but I
> never trust my memory anymore, and don’t have time today to go do all the
> research again...  But I'm going to recall from memory, that I think the
> WORST situation of most TNC's is if the LOW tone is higher than the HIGH
> tone, that decoding always suffers.  And suffers FAR WORSE than the other
> way around.  So that is why the compromise is to make the high tone about 3
> dB higher (30% on an OO scope)  so that it doesn’t get completely lost when
> it goes through a speaker connected receiver and gets de-emphasized.
> 
> OR, If  I remember wrong and it is the other way around!
> 
> Good luck.
> 
> Bob
> 
> -----Original Message-----
> 
> I was hoping for some ideas to better my station and am very pleased you
> have responded. I want to better utilize my station and increase my
> throughput with the ISS in particular. I have available 10 element crossed
> Yagi antennas and Yaesu az el rotor and several radios with TNC's built in
> including Yaesu FTM-350 and FTM-400 and Kenwood
> TM-D700 and TS-2000. MFJ and Kantronics TNC's as well as products from
> Byonics and Argent Data are found on my bench. I am currently running a
> Kenwood TM-D700 to a M2 Eggbeater as a 24/7 ISS station with UISS software
> and modules to upload to the internet.
>         I want to increase my capabilities with respect to the ISS and
> APRS. I have found that the Kenwood TM-D700 requires that you get about
> almost a half scale reading to effect good packet reception. I don't want to
> use the fully automated  station (FT-847) that I have when I'm not home
> because in the past a failure caused my rotor to jam and I had to lower my
> tower to remove and repair the az-el rotor. I suspect that the best way
> might be to use a sound card software and computer to give the best
> decoding. Thanks for the response Steve KB1CHU
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