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.
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.
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
----- Original Message -----
From: Jim Lux
To: Larry Phipps ; towertalk@contesting.com
Sent: Monday, June 28, 2004 12:40 AM
Subject: Re: [TowerTalk] Actual LP Performance vs Tribanders
I see that our posts crossed in the mail, as it were. I was at FD for the
last couple days so I was working of the 200 or so emails.
the 20 minute averaging interval could be done with the beacons, it would
just take longer (and during that longer time, there's a higher chance that
propagation would change.
Here's some ideas... on 40m, you could use broadcast stations, of course.
Maybe you could use the max level recorded, rather than the average. The
idea (poorly thought through, I grant you) is that propagation tends to be
either good enough or somewhat less than good (more ionization doesn't get
you more reflection). (although, more ionization would imply more lower
level ionization which would increase absorption.... )
Maybe you could reference against signals from ionosondes?
----- Original Message -----
From: "Larry Phipps" <larry@telepostinc.com>
To: <towertalk@contesting.com>
Sent: Sunday, June 27, 2004 6:17 PM
Subject: Re: [TowerTalk] Actual LP Performance vs Tribanders
I posted a message a couple of days ago in this thread regarding a similar
thing I did using
a software utility I wrote to automatically rotate and integrate multiple
passes of S-Meter
readings and plot the results. My method requires a 20-minute or longer
transmission from
the reference station, so beacons could not be used. I average 10 readings
at each 10-degree
heading, then rotate to the next heading. I then repeat the process several
times, average the
results and plot them.
As long as the band is open (stable), it works pretty well. I'm not saying
it is a rigorous test,
or statiscally accurate to any particular degree, but it does give a
reasonable indication of
the skywave pattern... at least for the conditions at the time of the test.
It's also fun to do.
You can see some plots on my website at www.telepostinc.com/n8lp.html under
the
E-Beam link.
Larry N8LP
----- Original Message -----
From: Jim Lux
To: Tom Rauch ; w3frg ; towertalk@contesting.com ; Pete Smith
Sent: Sunday, June 27, 2004 8:39 PM
Subject: Re: [TowerTalk] Actual LP Performance vs Tribanders
Perhaps an inexpensive approach (instead of something like SRI's RELEDOP),
albeit time consuming, would be to hook up something that monitors the NCDXF
beacons around the world. Monitor for quite some time (a week?)
continuously, with the antenna in various positions. One would want to
think about the sequence for rotating the antenna. You might want to rotate
to a position, get a complete cycle or two of the beacons, rotate to the
next, get a few cycles, etc. In the long run, you might get something with
statistical validity (i.e. averaging out the short term variations in
ionosphere)
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "w3frg" <w3frg@comcast.net>; <towertalk@contesting.com>; "Pete Smith"
<n4zr@contesting.com>
Sent: Friday, June 25, 2004 8:06 PM
Subject: Re: [TowerTalk] Actual LP Performance vs Tribanders
> > But let's ask a practical question. If you are trying to
> evaluate a
> > horizontally polarized antenna, either versus another or
> more generally,
> > won't the relative signal to a station a mile or two away.
> as you rotate
> > the antenna, give you some indication?
>
> Ground effects are attenuating or nulling ANY horizontal
> signal following the earth. The worse possible way to
> measure anything is in the null, because small changes in
> the system which includes everything between and around the
> antennas can cause big changes in FS.
>
> The slightest amount of feedline radiation or polarization
> tilt of a horizontal wave caused by reflections from other
> structures can cause huge changes in FS over groundwave,
> because path attenuation is significantly less for vertical
> polarization at HF frequencies and lower.
>
> With that in mind, what would a groundwave measurement tell
> us?
>
> This is exactly what mislead a certain fellow into thinking
> his stub-matched all band dipole was several S-units louder
> than a tuner matched but otherwise *identical* dipole. Poor
> measurement methods are at the root of much misinformation
> we see. Measuring a horizontally polarized antenna over a
> large distance (more than a few wavelengths) is definitely a
> very poor method.
>
> It would be much more reliable to measure skywave in an A/B
> test than groundwave of a horizontal antenna.
>
> 73 Tom
>
>
> _______________________________________________
>
> 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.
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
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and ask for Sherman, W2FLA.
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