Some thoughts from the USA
-------- Original Message --------
Subject: Re: [Lf] Greetings! I have a modest proposal...
Date: Fri, 16 Nov 2001 17:53:12 -0500
From: Frank Gentges KØBRA <[email protected]>
To: [email protected]
CC: LF List <[email protected]>
Jake,
Like Bob, I am also intrigued by your proposal.
When wavelengths exceed 7000 feet, it is hard to construct directional
antennas inside a one tenth wavelength box except for a figure eight
pattern loop or a cardioid variant when a loop and efield probe are
combined.
For directional antenna patterns like we are more used to at HF we need
to
break out of the one tenth wavelength box. We could for example, place
several efield probes around the countryside and send the signal to a
central point for beam forming processing and other post beam forming
processing.
One way is to provide long cables to the connect the central point to
the
remote antenna sites. This would require a lot of cable and easements.
Another way is to transmit the individual remote antenna signals via
VHF,
UHF or microwave. If the system maintains phase integrity, the
individual
remote antenna signals can be combined in a beam former.
I think your idea is focused on the details of doing the translation and
transport process of getting the remote signals to the central beam
forming
site. Perhaps there are other approaches that could also be used.
In any event, with enough remote antennas spaced far enough apart, we
may
be able to form some narrow beams that would reject noise and
interference
off of the main lobe. I am not sure I would call this gain in the same
sense as a yagi beam antenna would exhibit. With LF, directivity is
much
more useful than raw gain.
Good thoughts and I am definitely not laughing. Your ideas are
stimulating.
A while back I was interested in building a remote LF receiver that
could
be tuned and listened to over an internet connection. Perhaps this
could
be a remote node for beamforming. We were looking at using dumpster
grade
computers and an RX320. I got some good ideas here on this list.
Keep us informed of your thinking and work.
Frank K0BRA
At 02:47 PM 11/16/01 -0500, you wrote:
I haven't seen any activity in a couple weeks since I signed up, so I
figure I'll introduce myself and hopefully you guys won't laugh too
hard...
Some of you may remember me. My call is AB3A.
Tony McConnell (N3JLI) and I were intrigued by K0BRA's antenna
article. We're building four of these things. Bear with me for a
minute, I have an idea and I'm wondering if anyone has considered
anything of this sort.
I'm curious if any of you have discussed the possibility of large
scale synchronous reception on LF.
The plan would be to use a set I and Q inputs from a quadrature
receiver, such as described by KK7B. We would use two or more
receivers, spaced at least several wavelengths apart. Suppose for a
minute that we manage to build an LO which we discipline to some
common reference, such as WWVB or GPS.
Knowing the precise position of each active antenna (using DGPS), one
might be able to construct a long base-line array if all the receivers
were tuned to the same frequency.
My initial thought was to have a local station (which both receivers
could hear) transmit an in-band signal with some sort of time mark on
it so that we could integrate the recordings from each site.
A carrier with a +/-90 degree phase shift each second would do nicely.
Using this time mark, one could take the recordings from each of the
two stations and sum them together making a long baseline phased
array.
I was thinking that if the station we were trying to receive were
maybe 1 kHz or so away from our reference transmitter, we ought to be
able to record the I and Q channels. Then, using a packages such as
Cool-Edit Pro, we ought to be able to sum them together with the
appropriate phases and time delays.
Has anyone considered this? Is anyone interested in trying it?
73,
Jake Brodsky, mailto:[email protected]
PP ASEL IA, Cessna Cardinal N30946, Based @ FME
Amateur Radio Station AB3A
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Frank Gentges KØBRA
<[email protected]>
LF web site at <http://www.amrad.org/projects/lf>
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