[amsat-bb] 9600 baud packet- summary of responses

[<alan_bloom@xxxxxxxxxxx>]

Thanks to everyone for their replies.  Unfortunately there doesn't seem to be consensus on question #1 (What's the best equipment to send/receive 9600-baud packet to the satellites?).  In fact some of the data are contradictory.  For example, W0EEC has had good luck with the Kantronics KPC-9612, but the web page recommended by K8ZK (http://www.g1gyc.demon.co.uk/martin/9600.htm) says

   As far as we know the KPC-9612 does not use G3RUH technology
   but seems to work after a fashion. It is a definite no no
   for satellite and important links although across town it
   should be OK for offering a local cross-port gateway etc.

(!)

I have seen many web sites that imply that anything other than a "true-blue" G3RUH 9600-baud modem is not acceptable.  But an FIR filter is an FIR filter.  I would think that any modem that uses the same filter coefficients (and does a proper job of anti-alias filtering) should work pretty much the same, whether the FIR filter is done with discrete circuitry a la G3RUH or in software on a DSP or microprocessor.

Also I have heard in several places that sound cards typically high-pass filter above 30 or 40 Hz which degrades performance for 9600-baud packet.  But several replies to my message say that's not a problem.  I note that the known-to-be-working-on-Echo hardware list on the AMSAT web site http://www.amsat.org/amsat-new/echo/9600tnc.php does not include any soundcard solutions.  Also, WA4SXM had a good point that a disadvantage of many of the sound cards is that they have no convenient way to transfer the data to a telemetry decoding program.

The sound card program that several respondents recommended is MixW, but I know there are many others out there.  Is MixW the preferred choice for satellite work?

Hardware modems recommended for satellite work were: TNC2 clone with G3RUH or PacComm NB-9600 modem, Symek TNC2H, PacComm SPIRIT, Kantronics KPC-9612, Drake TNC-270, and Motorola DSP56002.

On question #2 (is the narrow IF in radios such as my FT-736 a problem?), most respondents said no, just make sure you connect to the discriminator output.  But N1JEZ pointed me to a web site http://www.mods.dk/view.php?ArticleId=1266 where postings by G3RUH, no less, mention that some 736s have a 12 kHz IF filter that should be changed to a 15 kHz filter, or even better, 20 kHz.  I believe this is also a problem with many FM radios that were designed primarily for voice operation.

On question #3, (9600-baud TNCs and radios suitable for use in space), a private communication from G0MRF recommended the TNC-7 http://www.nordlink.org/~tnc7/ (use Google to translate the German) as a low-power, compact unit that should work well in space.  I will probably buy one for my home station and we can also check it out for suitability for our space application.

Alan N1AL



> -----Original Message-----
> From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> Behalf Of alan_bloom@agilent.com
> Sent: Tuesday, October 19, 2004 3:58 PM
> To: amsat-bb@AMSAT.Org
> Subject: [amsat-bb] 9600 baud packet
> 
> 
> I have three questions.  The third might be the most interesting.
> 
> 1.  What are people using to send/receive 9600 baud packet to 
> the satellites?  I recall from times past that the standard 
> method was to modify a 1200-baud TNC-2 or compatible 
> (MFJ-1270 or whatever) by adding a G3RUH modem.  I know there 
> are programs to do the entire function using a PC with a 
> sound card.  How well do they work?  Do you have to modify 
> the sound card to pass DC (or at least get better 
> low-frequency response)?  Which is the best sound card 
> software for satellite operation?
> 
> Or do I need to buy a hardware 9600-baud TNC like the 
> Kantronics KPC-9612?
> 
> 2.  Do I need to modify the IF of my FT-736 to widen the 
> bandwidth to accomodate 9600 baud with doppler shift?  In my 
> web searches I found a little add-on IF filter/demod board 
> for the '736 to widen the bandwidth for 9600-baud packet: 
http://symek.com/g/index-g.html (click on "Satellite radio" then scroll down to the "F-ZFD").  The unit is out of production but they give the schematic so I suppose I could build one.  I'd prefer just to buy one if anyone still makes such a device.

3.  I am involved with a quick-turnaround project to take advantage of a possible opportunity to get an experiment into space on the cheap.  We'd have to provide our own telemetry and uplink/downlink radio, most likely on the 70 cm band.  Since we will likely be operating from a non-rechargeable battery, low power consumption is important.  In the interest of fastest possible development I'd prefer to buy as much as possible rather than build.

I found a German company that sells a little 430-440 MHz transceiver with built-in TNC.  http://www.wimo.com/packettrx_e.htm  (model PR-430)  There is no front panel - the user interface is on a PC via an RS-232 cable.  For that reason the unit is small and fairly low power.  TX power is 6W which is a little more than we need.  (2-3W should be about right.)

Is there a better transceiver/TNC choice?  Another alternative would be a stand-alone 9600-baud TNC plus Hamtronics RX/TX boards.  What is a good low-power 9600-baud TNC?

Al N1AL
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