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RE: lower frequency downlinks



How long is it with the solar panels out?  I'm not sure of the dimensions of
P3E, either, but it might be big enough for a loop.

73s,
Eric KF4OTN FM15hn


-----Original Message-----
From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org] On Behalf
Of John B. Stephensen
Sent: Monday, 30 January, 2006 13:26
To: n2oeq@netzero.net; bod@amsat.org
Cc: amsat-bb@amsat.org
Subject: Re: [amsat-bb] lower frequency downlinks

Less doppler shift is an advantage for lower frequency downlinks, but path
loss isn't. The path loss decreases at 20 dB per decade but the galactic
noise level increases at 20 dB per decade so the two effects cancel out. HF
downlinks suffer even more loss when sunspot activity goes up.

HF is also a problem on small satellites because of antenna size. A
half-wavelength HF dipole is at least 16 feet long and Eagle is a 2 foot
cube. Shorter antennas are inefficient and waste power that is extremely
expensive to generate in space. Such a large antenna makes the satellite
difficult to control and deployment is a likely cause of failure. 2 meter
antennas push the limits on Eagle-class satellites.

73,

John
KD6OZH

----- Original Message -----
From: <n2oeq@netzero.net>
To: <bod@amsat.org>
Cc: <amsat-bb@amsat.org>
Sent: Monday, January 30, 2006 04:06 UTC
Subject: [amsat-bb] lower frequency downlinks


> greetings from patrick n2oeq 32323
>
> I'm in favor of low frequency downlinks for satellites because of the
lower signal or path loss, much less doppler, reception with standard or
readily available equipment, and possible use by many more individuals than
the super high frequencies.
>
> I enjoyed making contacts on rs-12/13, rs-15, and ao-7.
> I found HF downlinks to be much easier to use whereas I could concentrate
on the actual contact.
>
> Is it possible to incorporate an HF transponder into Eagle or is the
design etched in stone? Maybe the orbit is too high for such a downlink.
Then perhaps, could Amsat banter about the idea of a new satellite with this
in mind? I imagine the costs associated with a lower frequency satellite
would be less because of the components and designs which are already
proven.
>
> Anyway, this is a bulletin board so I thought I would raise the idea.
>
> Thanks and 73, pat
>
>
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