A model helicopter with a GPS receiver, a UHF link for the NMEA data,
and software for navigation and position/signal-strength recording --
what a cool idea! Are there off-the-shelf model helicopter controllers
with RS-232 or USB interfaces?
73,
Dave, AA6YQ
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Michael Tope
Sent: Monday, June 28, 2004 15:43
To: Larry Phipps; towertalk@contesting.com; Jim Lux
Subject: Re: [TowerTalk] Actual LP Performance vs Tribanders
One of my colleagues at work fly's model Helicopters. Seems like a model
helicopter with a small beacon transmitter might be the way to make a
poor man's HF antenna range. Alternatively, a tethered helium balloon
with a small beacon might be another way to build a cheap HF antenna
range.
Mike, W4EF........................
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "Larry Phipps" <larry@telepostinc.com>; <towertalk@contesting.com>
Sent: Monday, June 28, 2004 11:37 AM
Subject: Re: [TowerTalk] Actual LP Performance vs Tribanders
> At 02:08 AM 6/28/2004 -0400, Larry Phipps wrote:
>
> >Jim, I'm not that familiar with the beacons, but since your post I
> >did a little research. There are a couple of major problems.
> >
> >First, the transmissions are very short... there wouldn't be time for
more
> >than one sample per beam heading.. and it would take almost 2 hours
> >just to gather the samples for one rotation (36 samples). The signals
> >are
going
> >to be all over the place during that time frame... and that doesn't
> >take interference into account. Timing would also be critical... your
> >computer clock would have to be dead nuts on. There's also really no
> >accurate way to correlate the signal strength to anything else
> >minute-by-minute, so
the
> >levels would be more or less meaningless.
>
> Yes, I agree that you'd have a problem doing the measurement in one
> pass through. You'd have to do a statistical approach over many days
> and
hours.
>
>
> Timing you can get from the signals themselves, and the PC clock is
> good enough to sequence it. As long as you're within a few seconds of
> the
"real"
> time, it's fairly straightforward to track (programs like BeaconSee do
> it, for instance).
>
> You could correlate the signal strength on the antenna under test to a
very
> short monopole antenna or small non-resonant loop (which will be
> fairly consistent in azimuth and elevation response).
>
>
>
>
> >Even with a 20 minute continuous carrier at 100W, I doubt the
> >received strength of the beacons would be enough to be useful for
> >plotting the pattern of a beam with 30dB F/B ratio. You would need a
> >stable signal about 50dB above the noise floor... probably something
> >around S9... and you'd have to listen to make sure there is no
> >interference while the samples are being taken.
>
> Kind of depends on the accuracy you require. If you want tenth dB
accuracy
> on something that is 30 dB down, it would be a challenge (I doubt
> there
are
> many antenna ranges or network analyzers that can do that well). If
> you are willing to tolerate 1dB errors (out of 30), and, say, 0.5 dB
> out of 10dB, I think you could do it with, maybe, 10-15 dB SNR.
> Depending on the integration time. If the beacon is sufficiently
> narrow band (which the NCDXF beacons are, during the test tones), your
> measurement bandwidth (which sets the SNR) can be quite narrow
> (probably limited by ionospheric doppler spread). Maybe 5-10 Hz?
>
> Using the noise level in VOACAP for residential areas (-145 dBW/Hz),
> you're only going to be seeing something like -105 dBm noise floors.
> Running a quick VOACAP from a monopole in Tangier to a swwhip Los
> Angeles, (june SSN=100) it looks like you'll have SNR (in 1 Hz) of
> above
15
> dB for about 4 hours. That's going to be a bit marginal.
>
> However, as you point out, big broadcast stations would be a better
> bet.
>
>
>
>
> >My tests used commercial stations with BIG signals that transmit
> >continuously, like WWV. I was testing a very broadband beam, so
> >actual frequencies weren't that important. Testing a LPDA or SteppIR
> >should also work OK with my software. You could probably make it work
> >with a ham with a strong signal though, who would be willing to make
> >several 5 minute continuous transmissions while the data was
> >gathered.
> >
> >If you happened to have a neighbor within a few blocks, you could get
> >meaningful results, especially if your antennas are high. You could
> >use the TRX-Meter utility that comes with TRX-Manager since only one
> >pass,
and
> >one sample per 10 degree heading would be needed. I got the idea for
> >my program from trying TRX-Meter, but added the ability to integrate
multiple
> >samples over time to smooth out the effects of fading on skywave
> >signals. Further away than about 10 wavelengths would give you a nice
> >pattern, but I doubt that it would correlate into similar skywave
> >performance.
> >
> >Larry N8LP
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any questions and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
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http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
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