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Re: AMSAT has a SECRET: why not 10m instead of V band



My 2 cents worth:

I can recall operations on the early satellites with mode A (2M up & 10M
down) and on those with mode B (70cm Up & 2M down).  Mode A was never as
satisfactory as mode B, mainly because I never could hear the mode A 10M
downlink until it was well above the horizon, sometimes as much as 25
degrees above.  I could always hear my own mode B downlink signals within
20-30 seconds after AOS.  I assume the mode A 2M uplink was able to access
the satellite very shortly after AOS similarly.  The 10M downlink however
was poor or non-existent at my receiver.  The 10M antenna was a vertical
which had most of its gain near the horizon with very little gain
vertically.  However, I could hear the satellite on this antenna when the
angle of approach of the signal was high but not when the satellite was
below that elevation

I think the reason for this was that the satellite was above the ionosphere
layers and that the angle of incidence of the arriving signal was low
enough that the ionosphere absorbed or reflected the signal back out into
space.  When the angle of incidence became high enough, the signal began to
penetrate the ionosphere and reach my 10M vertical.  This was born out here
by the fact that this effect was more noticable during daylight hours and
less so at night.  It also varied with the sunspot cycle.  In other words,
when 10M was open to the world for terresterial DX, the mode A downlink
access was pretty limited.  When the old 10M band folded up, the 10M
downlink was much improved.

Another effect of this situation was that the 10M downlink might be poor at
one station when the satellite was in range.  However, other stations well
outside of the acquisition circle could often hear the 10M downlink due to
multiple refraction paths in the ionosphere.  This was of no use to them
because their uplink signals could not be heard by the satellite.

When mode B came along on AO-7, I jumped at the chance to build something
to make use of it.  I cobbled together an old Motorola 2C39 final box as an
amplifier and drove it with a transverter kit and 18 watt intermediate
amplifier kit, using my Heathkit HF rig.  The difference was remarkable.  I
could work stations horizon to horizon.  It was with this arrangement I got
my satellite WAS.

As a result I have never gone back to operating on mode A.  In my opinion
it is not a very satisfactory arrangement, probably for more reasons than I
have listed here.

-- 
73, Roy

Internet: w0sl@amsat.org
Home Page: http://home.swbell.net/rdwelch



sco@sco-inc.com wrote:

> I do not see what is so hard about putting a 10m downlink on "Project JJ".
> Then using a V band uplink with it. That combination (would it be called
> "V/A"?) I assume would work great at and near perigee (if an AO-40 type
> orbit is used for Project JJ). It would certainly help to attract new hams
> and current non-satellite hams to our hobby and to AMSAT. Anyone with a
> general coverage receiver and long wire antenna could hear the satellite at
> perigee.
----
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