>10 meter EME - interesting. If your 8/8/8/8 was 15 dB over the noise,
>then would a single 8 be 9 dB over? If so, could us mere mortals with
>a tribander be perhaps 5 dB over? Has anyone ever done this?
>
>73, Bill W7TI
Bill (and the others who have expressed interest in 10M EME)
Let me just give you a little better idea about signals on 10M EME
to illustrate what it takes. Yes, I have a tape with some echoes
that are 15 dB above the noise--but this is only about 10 seconds
out of a total of a few hours. Something else must have been
going on for this much enhancement of the returns--some sort of
ionospheric focusing possibly. And you must remember that if
you antenna is 6 dB down from my 8/8/8/8 it is 6 dB down on TX
and 6 dB down on receive.
For some statistics: I have probably run on 10M EME about a
dozen times and gotten echoes 9 or 10 times. But most of the
time during any run there are no echoes because of Farraday rotation
of the signal. So what one hears is usually up to about 10 or 12
seconds of echoes as the signal comes up out of the noise and
then drops back into the noise and then a couple of minutes of
nothing. On most occasions, during the approximately 15 minute
long window that is available, you usually hear less than a minute's
worth of echoes. And the signal rarely comes up more than just
a couple of dB above the noise. I am only working near the horizon
since I have no elevation control and utilize the ground reflection
gain as well.
With my 7/7/7/7 on 15M I have also gotten EME echoes but the
signasl are a lot weaker and the statistics are a lot worse. But a
2-way on 15M is also possible with someone with a similar
array (although my 15M array is not up at the moment).
The 10M array was down for a couple of years after I ran my original
tests. I ran a 2-way test with AA6TT and his 8/8/8/8 array and he
says he heard my echoes but I never heard him. We were handicapped
by lack of EME experience and lack of telephone communications
to coordinate things. We could hear each other's meteor bursts
quite well (all too well--a good meteor would blow your ears off
and then you had to recover for the the EME signal) His array is no
longer up, unfortunately. My 8/8/8/8 on 10M is back up but it is
now just fixed, although with an hour of preparation I can adjust the
direction by climbing the tower and re-aiming the beams. I have
replaced the main feedline with 1-5/8 hardline in an attempt to get more
of the 1.5 KW to the antennas. When I redo it again and make it
rotating once more I will replace the RG-213 subfeeds with 1/2
inch hardline.
I will be entertaining skeds in a few weeks, but the array is mounted on
a tower that is 1000 ft from the house and I will have to drive (or walk)
over to a shack at the tower, so it will take an effort on my part to be
on the air. I have found that the best times are at either moon rise
or moon set but only after the ionosphere has had a few hours to
quiet down. So I will only look at moonsets that are a few hours after
the sun has set--usually midnight or later in the summer, but the
array is currently pointed east. So for moon rise I usually wait
until after midnight until about 2 hours before sunrise.
What one needs is a very quiet location, with a smooth Fresnel zone,
and a big array. I think a 2-way QSO between my array and a
2-stack is so unlikely that I won't waste the time. But if you have
a good location and at least a 3-stack of big Yagis--6L or more
I may try to sked later this year. The other critical issue is that
we must share a common moon rise or moon set since ground reflection
gain is probably needed on both ends of the path to make this
work with even a 3 or 4 stack. I have not looked at any EME
programs to see how far in longitude on can stray from mine to
have this possible--and then it becomes possible only on a few
dates a year. I may be able to work someone as far east as
Houston or a similar distance to the west, but common moon rise
or moon set is only possible on a very limited basis. Of course
there is always a possibility to work a moon rise to a moon set but
that requires a big array on the opposide side of the world--and that
means something in VU.
And, of course, there are a lot of solutions to the problem from further
north due to the tilt of the Earth's axis and the tilt of the plane of
the moon's orbit. I will need to run W5UN's software again to get
familiar with it to see what areas the commonality of moon rise
and moon set cover. If you have a big 10M array--at least 18 elements
(6/6/6)-- I might do some tests starting in a month or so (time needed
to clean up some backlog of business and to get a rig and amp
moved over to the other shack. Rig would be an FT-1000D with
an Alpha 86. Previous runs were with a IC-781 and an Alpha 87A.
The 1000D is quiet but the filters are not as good as the 781's filters,
so I will run a few times to get my own echoes with the system before
I am confident enough to try and do a sked.
There is enough info here for anyone to try and receive their own echoes
and if you can't then your array may not be big enough. That 15 dB
S/N signal made for a great presentation at Dayton but was very unusual.
Hope this info helps and ultimately the 10M array will be back up
on a rotating tower again which will give me some more flexibility
as far as making skeds goes.
73 John W0UN
BTW The 8L Yagis are on 48 ft booms (3 inch x .125 wall) and are
somewhat similar to the design from DX Enginering, but I don't think
Bill is building any 10s anymore. The Yagis were mounted in the
center of the boom on a rotating Rohn 55 tower. They are now
on a non-rotating Rohn 55 tower. The window of echoes maps out
the predicited elevation pattern of the antennas quite well. The
antennas were originally at 40/80/120/160 ft on a bit of a rise. The
other tower is in more of a hole and the antennas were also mounted
at 40/80/120/160 ft when run with elevation beam steering to look
at Sprites. Now that that experiment is over I will probably move
the antennas to 60/100/140/180 to better duplicate the original
system.
--
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