[amsat-bb] Re: 10m band kibitzing

[Robert Bruninga]

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 at hsmicrowave.com] 
> Sent: Sunday, September 10, 2006 4:40 PM
> To: bruninga at usna.edu; Amsat-bb at 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 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
> 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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