[amsat-bb] Re: Photos From ISS via Twitter

MM ka1rrw at yahoo.com
Fri Feb 5 13:54:56 PST 2010

Hi Luc:
Your question was:
Why they don't put the ISS cross band repeater on?

I assume you are referring to the Kenwood TM-D700 radio, when it is in "Cross-Band" mode.
The TM-D700 is a good radio, but it was never designed to support the duty cycle required by a full time "Cross-Band" repeater on Earth or in Zero Gravity.

Even though the radio does have the Cross-band option and the ISS crew has on several occasions placed the radio in Cross band mode, they only do so for short periods of time, when the crew can monitor the radio.

One of the primary reasons for only running the TM-D700 in "Cross-Band" for short times slots is because of the potential for overheating.  All electronics on ISS run hotter, because there is NO convection cooling.  Earth based Electronics must be modified to compensate for Zero gravity and the loss of convection cooling.  The TM-D700 is not immune to overheating.  

In August 2006 ISS commander Pavel Vinogradov reported the D700 over heated and locked-up when it was left running SSTV all night long.  It was during his mission we discovered the problem with the ARISS Vox box was getting stuck transmitting, possibly because of RF getting into the Vox box.  During an ARISS telecomm , Sergej Samburov, RV3DR, relayed the gist of the conversation he had with Pavel Vinogradov to myself and the ARISS team in the teleconference.  Pavel had to unplug the power cables to the radio and then reconnect the radio, in order to clear the non functioning buttons.

We do not know what power setting was used on the D700 during that part of the mission (special modifications limit this radio to 5,10 or 25 watts).  What we do know, is that it did over heat and the radio was never quite the same afterwards.  A backup TM-D700 was sent to ISS for Richard Garotts Mission.

The duty cycle for Cross-Band modes is much higher than those required for unattended packet modes..  While passing over the USA, it is possible for the Cross Band repeater to be active for 20 consecutive minutes with a duty cycle over 50%.

In my professional opinion, placing the TM-D700 in unattended Cross Band repeater mode on ISS would not be safe.

Marex did propose in 2006 and 2008 ARISS International meetings a Heat sink / Fan upgrade for the TM-D700.  ARISS rejected the proposals, stating they did not see any need.


--- On Fri, 2/5/10, Luc Leblanc <lucleblanc6 at videotron.ca> wrote:

> From: Luc Leblanc <lucleblanc6 at videotron.ca>
> Subject: [amsat-bb] Re: Photos From ISS via Twitter
> To: amsat-bb at amsat.org
> Cc: sarex at amsat-bb.mail03.videotron.ca, eu-amsat at yahoogroups.com
> Date: Friday, February 5, 2010, 1:10 PM
> On 5 Feb 2010 at 9:35, Clint Bradford
> wrote:
> Date sent:          Fri, 05
> Feb 2010 09:35:39 -0800
> From:       
>        Clint Bradford <clintbradford at mac.com>
> Subject:           
> [amsat-bb]  Photos From ISS via Twitter
> To:         
>        AMSAT BB <amsat-bb at amsat..org>
> > Last month we received the first Twit from space. Now,
> Astronaut Soichi is sending some spectacular photos via his
> Twitter account ...
> > 
> > http://tinyurl.com/space-twitter
> > 
> > Clint Bradford
> What is the difference between these pictures and those
> sent by SSTV?
> Only serious business instead of amateur stuff... Again
> amateur radio apparatus is left on the extreme right lane
> and probably soon in the 
> ditch if the ISS amateur radio apparatus is not put back in
> service soon! I asked this question about an hundred times:
> why they don't put 
> the ISS cross band repeater on? It can run unattended and
> there is no risk the batteries get down as those in the
> camera. It will also send 
> the QRP'er away off the other sat as the ISS repeater is
> very very easy to hear and work too.
> Great promoting asset collecting floating dust in space.
> "-"
> Luc Leblanc VE2DWE
> Skype VE2DWE
> www.qsl.net/ve2dwe
> DSTAR urcall VE2DWE
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