[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: AO40 user population



Well there have been a lot of good points made about the reasons why
activity seems so light but yesterday I put up one of RUH's wok dishes and
patchfeeds on my tower to replace the old X9 2 metre antenna that was there.

Observations:

With a DB6NT preamp I can hear the noise floor of the transponder and lots
of earth noise. Unless you want to hear the nosie floor at very high squint
angles there is no purpose in making it bigger. The received S/N of
transponded signals will be NOT be increased. It is a shame that we will
never be able to have S9+ SSB signals without any apparent backgound noise
through this transponder however much gain we have in our receive antenna.

The dish is much smaller than the 2 metre antenna it replaces and seems ok
on my kenpro elevation rotor.

The argument that an HF rig will always work with a piece of wire is right
in theory but a somewhat flawed in practice. Yes it can work but then so can
an unmodifed downconvertor with a helix antenna. Many HF operators use beams
and linears to achieve satisfaction! The S band equivalent is a good, but
not larger than say 36" dish, with a good matching circular polarised feed
and a preampor low noise converter directly connected to the back of it.

At an amateur radio show last weekend in North London, we were "advertising"
AO40 as the new DX band thats 250KHz wide, predictable, needs only small
antennae and where big linears are "banned". There was lots of interest in
this concept and in the three different dishes (RUH, a "sky" dish and
Howard's portable umbrella one) we had on display at the back of the booth.

Yes 2400MHz is/will become more and more congested with non amateur signals
but using very directional antennae that are generally pointing at least a
few degrees up will help us co-exist and if we dont use it we will certainly
lose it!

Reading the AMSAT 2002 Convention Proceedings last night, it suggests that
the S2 transmitter, being a late addition to the bird had to share some of
the matrix switching with other bands and, if I understand the text
correctly, as a result the S2 TX can only transmit the Middle Beacon not the
GB or EB. If so, I guess we are stuck with it.

I think the jury is still out an what makes the best antenna farm for Mode U
or L for both portable/temporay installations and for permanent ones that
won't need us to stik our arm out the shack window.... Lots of work remains
to be done by our many expert friends.

73

Graham G3VZV

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home