wmartin@Almsa-2 (Will Martin -- AMXAL-RI) (05/09/85)
The following discussion has recently arisen on the Videotech list;
I thought Info-Hams (& net.ham-radio) people might be interested in it:
Date: Mon, 06 May 85 09:34:28 CDT
From: mooremj@Eglin-Vax
Subject: What is the maximum range of VHF reception?
To: videotech@Sri-Csl
Questions about (gasp! how primitive) broadcast TV.
I live in an area where, due to local politics, we do not have cable TV
and probably won't for a few years. Realizing this, I bought a 30-foot
mast, the biggest antenna I could find, a rotator and a pre-amplifier;
I also live on top of a hill, so my configuration is pretty close to
optimum. After experimenting I find that my maximum range for a good
VHF picture is about 200 miles (New Orleans) on cloudy days, 150 miles
on clear days. Occasionally I get a picture from a Birmingham station
(230 miles), but it's not reliable. Now I thought that was pretty good;
but several of the old-timers in this area swear that one can sometimes
receive stations in the Yucatan, which is over 400 miles away across the
Gulf. Question #1: Is this possible? I know some Mexican stations are
much more powerful than American stations.
Question #2: My antenna has what is called an "FM filter", but I still
get blasted away by a station at 88.1 MHz when I try to watch Channel 6.
(The FM station is 50 miles away, channel 6 is 180 miles away, in opposite
directions.) Is there any way I can further reduce the FM signal without
affecting Channel 6?
Question #3: Is my 200-mile limit the best that can be done? What IS the
extreme range of VHF reception?
Thanks in advance,
Marty Moore (MOOREMJ@EGLIN-VAX.ARPA)
Date: Tue, 7 May 85 3:40:59 CDT
From: Will Martin -- AMXAL-RI <wmartin@Almsa-1>
To: mooremj@Eglin-Vax.arpa
cc: videotech@Sri-Csl.arpa
Subject: Re: What is the maximum range of VHF reception?
TV DXing (which is what you are really talking about) is a hobby in its
own right. I have never indulged, myself, but a friend, Glenn Hauser, is
one of the nation's top TV DXers (he once had an article on the subject
published in TV Guide, and also has had articles in various radio-related
publications, like the World Radio-TV Handbook).
There are several methods for long-distance propagation of high-frequency
(VHF and up) signals, such as "tropospheric ducting", "Sporadic E", and
"meteor scatter". (I don't know much more about these than the names,
though I know the last one involves catching the short-term reflections
of signals off the ionized trails of meteors -- that one always struck
me as fairly exotic...)
There is a club devoted to this hobby -- if I recall correctly, the
name is the Worldwide TV/FM DX Club, and their bulletin is The VHF/UHF Digest.
I don't have their address here at work; if you or others are interested,
I can look it up and post it. (You can find it in a back issue of Popular
Communications, if a local library gets that magazine...)
Anyway, Glenn and many other TV DXers have had quite long-range catches.
One I recall offhand, when he was in the USAF in Thailand, was when he
picked up Saudi Arabia. Of course, equatorial conditions are different
from those here in the temperate zone, but that can give you an idea.
I wouldn't be surprised if there was NO "theoretical" limit on the
distance you could pick up a signal -- it would all depend on the
propagation conditions, local electrical noise and interference,
transmitter power, and antenna configuration at both ends... So the
maximum would be 12,500 miles or so, on the opposite side of the globe.
And there are ways to receive signals via the "long path", which means
going the "wrong" way around the earth, which could increase that [and,
if you figure multi-circumferential paths, you can go up indefinitely!].
(This, of course, only refers to terrestrial transmission & reception;
we've seen TV pictures from Saturn, after all...)
Will Martin
ARPA/MILNET: wmartin@almsa-1.ARPA USENET: seismo!brl-bmd!wmartin
Date: Thu, 9 May 85 9:37:18 CDT
From: Will Martin -- AMXAL-RI <wmartin@almsa-2>
To: mooremj@eglin-vax, videotech@sri-csl
Subject: Re: What is the maximum range of VHF reception?
I looked up the data on the TV (and FM & public-service stuff, too)
DXing club. Here it is:
Worldwide TV/FM DX Association
PO Box 514
Buffalo, NY 14205
Their monthly bulletin is The VHF/UHF Digest. Sample copies were $1.25
as of the 1983 copy I happen to have (though the address was verified
as still being OK in the 1985 World Radio TV Handbook).
They also put out a pamphlet as an introduction to the hobby; if you
are at all interested in this (and the equipment investment mentioned
indicates a definite interest!), it would be worth sending them $2.00
(again, the price as of 1983, but probably still good) for a copy of
"Beyond Shortwave". This should answer any questions about modes of
propagation, expected distances of reception under typical conditions,
and general info on receivers and antennas.
The monthly bulletins consist mainly of reception reports and news about
new and changed stations, call letters, powers, etc. There are sometimes
equipment reviews; the issues I bought back in 1983 had some info on the
then-new Carver tuner. Equipment reviews in this sort of publication
can be quite useful; since they are informal, written by people who own
the gear, and often are printed after the equipment has been around a
while, they contain data on aspects like reliability, which is seldom
mentioned in just-released-product reviews in the "slick" magazines.
For example, years ago I bought a Pioneer TX-9100 tuner based on a review
which discussed using it for mobile FM DXing while travelling cross-country
by car (with an inverter power supply). It got much abuse but still
worked well. Based on that info, I picked one up when they were being
closed-out at discount from a local hi-fi emporium and was well pleased
with it thereafter. Now, seeing some references in the audio press to
this tuner, I find I have a "classic"! So I place some faith in this sort
of equipment review, whether it is positive or negative. Since there is
no advertising (or payment!), there can be no pressure on the reviewer.
Hope this info is of interest...
Regards,
ARPA/MILNET: wmartin@almsa-1.ARPA USENET: seismo!brl-bmd!wmartinstephany.WBST@Xerox.ARPA (05/11/85)
Re: TV DXing In reference to how far you can get on TV, here on the Great Lakes we regularly receive stations 200 miles away with a radio shack $25 antenna and an old rotar. The antenna is about 20 feet off the ground. During Summer, particularly, we get excellent reception, but almost never during the Winter. The duct formed is due to the humidity and temperature differentials. We can regularly pick up stations in Ottawa,Toronto, and Quebec. My son sent in a DX report and asked for QSL cards and he got a long distance phone call from the station manager in Quebec because he thought it was impossible and wanted to know how we did it. During World War II there was a guy in Boston that that picked up Rommels Afrika Corps regularly on about 150 MHz. The data was relayed to Washington and decoded, one of the factors leading to Rommels failure. (The "key to Rebecca" story about the same thing was pure fiction). Also, one night, my wife picked up a New Orleans FM station (about a 1000 miles away) on her radio in the kitchen with an internal antenna. We all verified that the station was one in New Orleans. Joe N2XS
jwb@ecsvax.UUCP (Jack Buchanan) (05/13/85)
In the early 50's, we fairly frequently received Cuban TV on channel 2 in
central Kentucky. We had a fairly elaborate antenna system since, at that time,
the closest stations were in Louisville and Cincinnati (about 100 miles away).
As a 7 or 8 year old kid, the only programming I remember was a Shell oil
commercial featuring scantilly clad dancing girls singing in Spanish (This was
before Castro).
Jack Buchanan
UNC-Chapel Hill
{decvax, akgua}!mcnc!ecsvax!jwb