I believe DCI specs their filters on their website. I have a 6-pole 144-MHz cavity filter that runs about 0.1 dB insertion loss, though I believe they spec it as 0.2 dB. There are several models so one would need the model number. I use mine between my 1st preamp and 2nd preamp in my 2m-eme station to help isolate out of band RF overload of the receiver. It is rated for 200w so can be used for Tx filtering.
73, Ed - KL7UW
At 09:57 PM 3/16/2009, Nate Duehr wrote:
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@natetech.com
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