[amsat-bb] Re: 10m band kibitzing
bill at hsmicrowave.com
Sun Sep 10 13:40:14 PDT 2006
I am tried to get 10 metres looked at again by the AMSAT team but my
comments have gone unanswered. I have also tried to query Peter to get an
understanding why 29 MHz was dropped on P3E but no answer there either.
I can assume that antenna size is the big negative but I have been
researching and doing some preliminary experimentation on ferrite loaded
loops and dipoles for 28 MHz with some encouraging results so far. It
appears that a ferrite loaded receiving dipole can have a gain of -12 to -8
dBi (yes a loss!) but given the frequency (lower path loss) and the
availability of high power on the ground (almost all HF transceivers have
100+ watts Pout) my calculations show a nice link can be established.
Perhaps the biggest plus is that a satellite receiver at 29 Mhz looks down
on a world wide frequency allocation void of those pesky WiFi's, cordless
phones, CCTV's etc. and no one is predicting it will be taken away from us.
Speaking of allocations being taken away, I just can't fathom the AMSAT
decision to drop L-Band up because of the "Galileo Affair." Now that's a
decision based on "crystal ball engineering" and not fact. I've even read
that if Galileo ever was launched - and that appears in the latest press to
be questionable" the US "would has threatened to shoot them down!"
Regards...Bill - N6GHz
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org]On
Behalf Of Robert Bruninga
Sent: Sunday, September 10, 2006 9:18 AM
To: Amsat-bb at amsat.org
Subject: [amsat-bb] 10m band kibitzing
> In the San Diego meeting, there was discussion about using
> the V, U, L, S, C and X bands. The spacecaft is too small
> for a decent HF antenna...
I hate to suggest this low tech approach, but we do have plenty
of uplink bandwidth in the 10 meter band if we could find a way
to use it. I know that most of the future thinking AMSAT
engineers abhor this idea.... But it is still something to think
While an HF -gain- antenna cannot fit on a HEO satellite, a
simple 10m dipole could be deployed... The main advantage is
the users can use high power on the uplink.
Lets assume users with a 500W transmitter and the link equation:
PR = PT + GT + GR -LI - LS
PT - power transmitted on the ground is say 500W = 57 dBm
GT - Gain of transmitter Ant is say 6 dB? (3 element beam)
GR - Gain of satellite receive antenna is 0 dB?
LI - is say 3 dB to cover all losses in the system
LS - is (4Pi*R/wavelength) squared = -154 dB
PR - is then 57+6+0-3-154 = -94 dBm
That is a pretty strong signal, but it is the Signal to Noise
ratio that counts. And the problem is the GALACTIC AND other
NOISE... It's just as high up there as it is here, and That
can be as high as 20 dB ??? Over the noise floor of the
satellite receiver? (someone more knowledgible here please fill
this in.). If it is 20 dB of galactic noise, then the receiver
noise floor might be more like -105dbM and now we just barely
have a 10 dB margin over noise.
I just don't know whether it is worth doing. We had hopped that
the HF uplink on PCSAT2 would have given us good info. But the
transponder failed and so we still have no experience with 10m
uplinks. It would be nice to do some more expermeintating with
the 10m uplink receiver on AO-51 some time...
But one thing is certain, NO ONE is targeting the 10m band for
consumer electroncis devices other than all the ILLEGAL CB
operations. I just don't know how bad that is. In the solar
max, it will probably be a ZOO!!! But maybe they will stay down
at 27 MHz and leave 10m alone. Especially if we go after the
10m interlopers with a vengence...
Maybe just like HAM radio, the "HF-ers" are finding it easier to
just play on the internet than mess with all that "RF" stuff...
Just babbling and thinking out loud.
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