[amsat-bb] Re: Mode A antennas?

[Bruce Robertson]

On Sat, Sep 12, 2009 at 12:32 AM, John Geiger <aa5jg at yahoo.com> wrote:
> What is the minimal antenna you can use on 10m to hear the AO7 downlink in Mode A?  I have a homebrew G5RV type antenna up and can't hear AO7 on it at all.  What kind of antennas are others using on 10m for mode A?
>
> 73s John AA5JG
>

John --

I have had verticals of heights between 23' and 45' that could hear
the 10m downlink, even when connected to 100' of RG-8 and no preamp.

My guess is that your G5RV is highly directional at 10m. Such long
doublets develop flower petal lobes of high gain in the horizontal
dimension with very deep nulls between them. On HF this isn't such a
big issue, since the RF is going *somewhere*: you probably don't care
if you work NZ or Australia. (Ok, with the sunspots these days you'd
be overjoyed with either.) However, with satellite reception such
patterns make reception very difficult. Moreover, your G5RV is likely
to be up a good height at 10m, pushing its vertical pattern down to
the horizon. So now, to hear this bird, it has to be between, say 5
deg up and 15 deg. up and within the 'petals' of the horizonal
pattern.

Here's a situation where less truly might be more. A lowish dipole
will reduce the lobes, and crummy vertical will too, though in the
other dimension.

Let us know how things work!

73, Bruce
VE9QRP