[amsat-bb] Re: Tranzit-B telemetry system on ISS

Nate Duehr nate at natetech.com
Mon Mar 16 22:57:15 PDT 2009

On Mar 16, 2009, at 6:27 PM, Nate Duehr wrote:

> How are the "American aircraft signals" which are all AM, being  
> rebroadcast
> in any intelligible way by an FM receiver?

You know, you didn't say (and probably can't) what kind of receiver  
it's using, actually.  I assumed FM in, FM out.

> I smell something wrong here with your information, or there's more  
> to the
> story.

I was careful to say this, but got one very professional and two nasty  
comments off-list who thought I was attacking the original poster.  I  
wasn't.  The professional comment came (not too surprisingly) from  
someone elected to AMSAT leadership, showing excellent taste and  
restraint.  Thanks, you know who you are.

Just saying it smelled fishy to me -- assuming an FM receiver.  No  
harm meant by it.  The typical FCC TSO'ed AM aircraft transmitter is  
5W PEP, some are 10W PEP.  5W PEP AM to an FM receiver to be well  
detected at ISS's range is certainly do-able, but it wouldn't sound  
very good, I'd think.  Don't know.  All depends on the receiver  
quality, of course... a bunch of stuff.

The MUCH more interesting tid-bit that was somewhat hidden in the rest  
of the non-AMSAT info in the message was that there's a DCI filter on  
the front-end of the Kenwood?  Did I read that correctly?

That made me wonder a new question:  What's the measured insertion  
loss on it?

It would make for more interesting data for accurate link-budget  
analysis/calculations for talking to the ARISS station.  Would be  
interesting to see if the rig meets the published Kenwood specs, minus  
the antenna "gain" and filtering by altering power from this end and  
seeing if the numbers match up in the real world.

Is the DCI filter being in-line widely known?  I've never seen it on  
any of the ARISS documentation I've read, but it might have been there  
somewhere.  Maybe I missed it.

That seemed to be the only AMSAT-related part of that original  
posting...  the fact that there's other "commercial" transmitters and  
receivers on board, seemed like a "given" to me.  It also seemed  
obvious that filtering and mitigation of effects from one system to  
another has to be done, like on all spacecraft or other multi- 
frequency RF systems crammed into a relatively small space.

Nate Duehr, WY0X
nate at natetech.com

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