[Milsurplus] Fw: NVIS vs Ground Wave again

[Hue Miller]

[ FWD from Armyradios group ]

-----Original Message----- 
From: Hue Miller
Sent: Sunday, May 13, 2012 12:45 PM
To: armyradios at yahoogroups.com
Subject: NVIS vs Ground Wave again

A discussion group for those who collect>> Gang,
>>
>> Subject header says it all. I'd really like to understand why 
>> transmitters
>> chirp when they send code, and if anybody has ever been successful in
>> modifying an AN/GRC-9 to make it legal.
>>
>> Thanks in advance.
>>
>> By the way, I know this has been said on the group before, but I'm pretty
>> sure these radios were not used to send NVIS signals. I think it was
>> sometime after our involvement in the Vietnam War that the concept came
>> into vogue. I do know that the division operating area was much smaller
>> during the Korean War and I suspect they just used groundwave propagation
>> with the long wire antenna and counterpoise set. (Dennis, care to correct
>> the self-appointed "expert"?)
>>
>> Sean

Sean, you didn't really mean to use "legal", did you, unless for humor and I
missed
it?

A tidbit for you: a former military user of the SCR-131 told me that on
field
maneuvers they would sometimes use a wire dipole with the SCR-131 to
gain more distance. The wires were tapped onto the SCR-131 loop antenna
using something like battery jumper clamps, on one side of the loop, and
spacing adjusted for best impedance match. I think he said something like
35 miles range, day, with this.

An anecdote re NVIS and ground wave: on a recent walk around the bayfront
of Newport, Oregon, I discovered the city had installed new sidewalks where
there had previously only been a dirt trail next to a road by the the USCG
station. ( U.S. Coast Guard ). At quite a bit of expense I imagine, the city
had
made part of the sidewalk wheelchair accessible, via ramps beside the
stairs,
even on part of the walkway that just seemed to deadhead to a beach walkway
that is really too rocky for wheechair travel - but maybe I'm wrong on that.
Anyway the new walkway is higher on the hillside, and you can see better
down into the parking lot area of the CG station. And the small building
on whose roof is the USCG information radio on 1610 kHz.  The antenna is
about a 15 foot mast. The transmitter apparently is contained in a box about
12 x 12 x 6 inches - my guess. ( This story DOES have a point. ) Now with
the
raised walkway, you can better see what's going on with the antenna, and
how it's grounded - you can see the ground network on the roof, and it's an
'umbrella' pattern of wires radiating out from the transmitter box over the
roof.
The roof is not that large, I think maybe 20 x 20 ft. At the transmitter
end,
the wires all attach to a hoop wire about the diameter of a basketball hoop.
I'd guess maybe 20-30 of those rather short ground radials. I think I'm
going
to try to later get a photo for Popular Communications magazine because
it's rarely that you get to see what's going on with the ground system of
such an operation.
I don't think these stations run much more than about 10 watts, but I don't
know whether that's in or out.
Anyway, I found on my work truck radio, I can copy this broadcast out to
about 8 miles, and that includes over the coastal hill range. It's not
broadcast quality for the usual civilian but DX-able level for a radio
fanatic.
CW of course would increase that range and make copy at this distance
100%. The terrain is hilly and rocky and very thickly forested.
Now the payload.  As I was DXing this, seeing how far I could hear it, I
was reminded of German WW2 vehicular communications in the 1 - 3
MHz range. I had read this was to exploit ground wave coverage in
typical rolling European country. I also recalled reading in QST
antenna book a comparison of signal strengths of mobile 160 and 80
meter transmitters. The article said 160 actually gave better range,
due to ground wave coverage, even with the substantially greater
antenna inefficiency at 160 meters. I do NOT at all believe my
experience had anything to do with NVIS propagation - if it did,
I believe the signal strength would not obviously fluctuate with
the lay of the land. I was quite impressed with the distance range
I heard the USCG station at, especially as it's at sea level and
the landward route is all uphill, shaded by steep uphill grade.
-Hue Miller