Bill, The big question is the galactic noise floor. When I looked at this years, ago, I was very excited at the link budget for 10 meters to GEO, but I was assuming that the NOISE level at 10 m was all "atmospheric and ionospheric". Someone set me straight that most of the noise on 10m is not just atmospheric and does extend in the magnetosphere all the way out to LEO. But I wouild sure like to see a NOISE FLOOR plot of typical 10m band. Quiet and noisey sun...
Bob
-----Original Message----- From: Bill Ress [mailto:bill@hsmicrowave.com] Sent: Sunday, September 10, 2006 4:40 PM To: bruninga@usna.edu; Amsat-bb@amsat.org Subject: RE: [amsat-bb] 10m band kibitzing
Hi Bob,
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
-----Original Message----- From: amsat-bb-bounces@amsat.org
[mailto:amsat-bb-bounces@amsat.org]On
Behalf Of Robert Bruninga Sent: Sunday, September 10, 2006 9:18 AM To: Amsat-bb@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
about.
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. Bob, WB4APR
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