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 Post subject: Long distance reception of analog TV channels
PostPosted: Dec Fri 29, 2017 12:03 am 
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Joined: May Sun 07, 2017 11:35 am
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Since it seems there are still some about in the US, I recalled what some enterprising farmers used to do in Australia in the '50s before TV became available in regional areas.

www.wtfda.org/mem/rhombic.pdf

How about a VHF antenna with 27dB gain?


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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Dec Fri 29, 2017 1:09 am 
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Joined: Jun Mon 24, 2013 3:00 pm
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Location: Champaign IL 61822
The analogs are all low power and low antennas.

Digitals are a different matter. In my old location I regularly got
Indianapolis, St. Louis, Nashville, and Memphis on UHF with
a 16 dB gain antenna and importantly a 0.5 dB NF GaAsFet preamp.


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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Dec Fri 29, 2017 1:41 am 
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I recall doing a TV service call at a high location on Sydney's northern beaches on a hot summer's day in 1975. After fixing the TV here's a list of what I was able to receive - VHF:

Ch 0 - NZBC, New Zealand (freak skip reception, watched the NZ evening news at 3 in the afternoon!)
That's 2155km across the Tasman sea!
Ch 1 - NRN 1 - Taree I think That;s about 320km north.
Ch 2 - ABN 2 Sydney
Ch 3 - NBN 3 Newcastle. About 150km north.
Ch 4 - WIN 4 Wollongong. About 120km south.
Ch 5 - ABC Newcastle
Ch 5A - ABC Newcastle
Ch 6 - ABC Taree
Ch 7 - ATN 7 Sydney
Ch 8 - unknown TV signal, very weak
Ch 9 - TCN 9 Sydney
Ch 10 - TEN 10 Sydney
Ch 11 - no signal

No special antenna, just a band 1 - 3 yagi pointed south-west. I had to point out to the customer that this situation would not last!

I've seen NZBC TV from New Zealand several times over the years, always in hot weather!


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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Dec Fri 29, 2017 11:41 am 
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I don't think skip really cares about what kinda skyhook is used. My best distance was about 1200 miles using just the whip antenna on my Sharp 12" B&W TV, in 1970.

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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Dec Sat 30, 2017 12:30 am 
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My first sighting of NZBC was also in 1970. In Seven Hills, a western suburb of Sydney.

After fixing the TV I flipped through the channels and saw a test pattern on Ch 0, way down in the snow.
I thought it was captioned "NZBC" so I asked the child sitting on the lounge (he had been left home from school to let the TV Man in - more innocent times back then) what the letters were. "NZBC" he said. I tried to explain the significance to the child but he was quite unimpressed.

At around the same time there were some strange voices on the 2 way radios in the service vans (VHF low band 77.90MHz) that turned out to be an electricity utility dispatcher from Wellington in New Zealand. I seem to recall that there was some unusual ionospheric conditions happening in 1970.

So you are right about skyhooks. You also don't need a lot of power. 1/4 wavelength whip on the roof of the van and, 3000km east, 50 watts ERP into an omnidirectional ground plane dipole (probably).

The story about how the only extant recording of pre-war TV happened (16mm fil actually) is similarly interesting.


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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Dec Sat 30, 2017 3:26 am 
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irob2345 wrote:
<snip>
The story about how the only extant recording of pre-war TV happened (16mm film actually) is similarly interesting.


Oh, do tell!

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A collector of TV signal boosters and UHF converters -- God help me!
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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Dec Sat 30, 2017 9:08 am 
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Here's a link:
https://archive.org/details/BbcTelevisi ... wYork-1938
and here's a paste of part of the story:

The four-minute compilation from 1938 exists only because of a technological fluke and the enthusiasm of two television buffs, one in Britain and the other in America where, thanks to freak atmospheric conditions, it was picked up and recorded on a cine camera placed in front of a television screen as the images came in.

Andrew Emmerson, the British enthusiast, spent five years tracking down the recording and believes it is the only surviving example of pre-war live high-definition British television. The flickering black-and-white footage includes Jasmine Bligh, one of the original BBC announcers, and a brief shot of Elizabeth Cowell, who also shared announcing duties with Jasmine, an excerpt from an unknown period costume drama and the BBC's station identity transmitted at the beginning and end of the day's output.


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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Jan Tue 02, 2018 8:35 am 
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Trans-Atlantic reception of the BBC's 405-line Alexandra Palace television transmitter was described in an article in the New York Herald Tribune, Sunday, February 26, 1939 -- "In the Realm of Science: Phenomena of Radio Bring Television Pictures Across the Atlantic" by John J. O'Neill.

The accompanying photo shows Dr. Dewitt R. Goddard, RCA engineer filming at Riverhead, L.I., television broadcast from London. The 16-mm camera faces an early version of RCA's mirror-in-the-lid receiver. Some excerpts.

"Dr. Dewitt R. Goddard of the Radio Corporation of America laboratories at Riverhead, L.I. has been studying the propagation of radio waves. He made continuous observations of the wave used by the television station of the British Broadcasting Commission [sic] in London and found that by using particularly sensitive receivers available in his laboratory it was possible to pick up this station. He has done this on many occasions since last fall (1938) and this week was able to make public the pictures obtained of the television program he received. He thus received pictures 150 times farther than the range of the station sending them out, the great circle distance from London to New York being 3,400 miles...

His first tests were made in January 1937 when the sunspot cycle was at its maximum and on January 21 of that year succeeded in picking up a faint broadcast on a frequency of 45,000,000 cycles [45.0 mc] and the voice on 41,500,000 cycles [41.5 mc], both of which correspond to seven meters.

Until March of that year, the voice wave was picked up with a great deal of clarity on several occasions but no recognizable pictures could be obtained. During the summer all reception on this channel was blotted out. In the fall (1937) signals were picked up again. A tuned, diamond-shaped antenna (rhombic) with directional properties was installed. This made it possible to get occasional glimpses of the pictures.

"Ghosts" interfered seriously with the success of the experiments... The reflecting area in the skies reappeared in the fall of 1938 and Dr. Goddard was again able to pick up the London television transmitter. In October he was picking up both voice and picture signals. He then set up a motion picture camera which he synchronized with his television receiver and was able to make a motion picture film of the program...

Lt. Com. Lawrence Cockaday U.S.N. Reserve and director of radio research at New York University, who has been investigating radio wave propagation for years warned the Federal Radio Commission [sic] two years ago that the seven meter band was not a satisfactory one for television transmission principally because of reflections from the upper ionosphere which made it possible for him to receive the London broadcasts during the spring and fall..."

The BBC opened the Alexandra Palace station on November 2, 1936. The Victorian edifice on Muswell Hill, 300 ft. above sea level on one of the highest points in Greater London was remodeled extensively to accommodate the facility from which the BBC pioneered with the world's first regularly scheduled television service. A 220 ft. tapered lattice mast was erected on one corner of the building to support separate vision (top) and aural (just below) antennae both of which were vertically polarized. The Palace included two studios 70 ft. x 30 ft. with an interior height of 25 ft. The all-electronic EMI system had prevailed over Baird's more cumbersome intermediate film process though Baird had obtained the rights to use Farnsworth's all-electronic image dissector system though at a lower definition level.

The mode of propagation was F-2 scatter as opposed to lower-level but far stronger sporadic-e which on a single hop generally ranges only out to 1500 miles. NBC via its corporate connection to RCA attempted to replicate the earlier reception during the "Wide Wide World" Sunday afternoon program through1956/7 but without success at least during the all-live "spectacular." The Alexandra Palace facility closed down on March 18, 1956 and was succeeded by the more powerful, taller tower Crystal Palace transmitter about ten miles away.

Trans Atlantic reception should have come as no surprise. Amateurs on both sides of the Atlantic were experimenting with VHF during the 1930s and activity on 56 megacycles was widely reported and discussed in "ham" publications. "World Radio," the BBC's weekly technical journal devoted to transmission and reception topics often reported reception by UK-based listeners of police radio transmitters in this country operating above 30 megacycles. A listener in South Africa picked up the Alexandra Palace sound channel while a number of viewers beyond the normal coverage area reported reception from time to time.

During the Fifties and into the Sixties, hobby magazines published VHF receiver construction plans -- simple, superregerative circuits -- noting the possibility of receiving the BBC's 41.5 mc TV sound channel. By then, the original BBC-1 chain of stations had been expanded to cover the entire country with transmitters identified by their location, viz Sutton Coldfield, Wenvoe, Kirk o'Shotts, etc.

F-2 propagation got noted propagation expert Dr. Kenneth Norton into a stew versus Major Armstrong during the headed post World War II controversy about moving FM "upstairs" from 42-50 mc to the present 88-108 mc band. Dr. Norton made a big deal about F-2 scatter during periods of sunspot maxima when as things turned out, it was never more than a minor nuisance. In the ensuing confusion, while FCC didn't buy into Dr. Norton's claims about F-2, the Commission was well aware of the chaos that would have been caused within the 42-50 mc FM band filled with hundreds and hundreds of powerful stations tangling with more spectacular sporadic e outbursts and that's why FM broadcasting was wisely moved "upstairs."

Something else to ponder. If signals from the BBC's TV station could be coaxed across the Atlantic, one wonders if any of this country's TV or FM transmitters was ever received overseas. One potential source of information, the BBC's "World Radio" magazine shut down when was was declared in September 1939.

On FM, the TPO of Armstrong's W2XMN was said to range up to 40,000 watts which fed into the seven element Lingo turnstile antenna on the iconic Alpine, N.J. tower would have -- accounting for transmission line losses -- an ERP of more than 200,000 watts. The Yankee Network's W43B was listed in one FCC document as having an ERP of 340,000 watts (50 kW transmitter+12-bay turnstile antenna at Mt. Asnebumskit, Mass.).

And then.... some of the radio equipment used by our forces around the world was FM, operating somewhat proximate to the old 42-50 mc band. Such a wild though possible thought: In a foxhole somewhere in the theatre of war, a receiver -- altered of course -- is retuned to receive W2XMN, W43B or any number of the more powerful FM transmitters. Radio reception from home with out the squawks and whistles of short wave!


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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Jan Fri 12, 2018 11:51 pm 
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According to the Old CATV Museum (http://theoldcatvequipmentmuseum.org/), some early CATV systems used rhombic antennas to receive distant stations. These were very simple systems in which an RF amplifier was placed close to the antenna (but hopefully not so close that RF leakage caused feedback), and additional amplifiers were placed inline to make up for cable losses. The channel(s) offered were on the low end of the band (typically channel 2 or 3).


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 Post subject: Re: Long distance reception of analog TV channels
PostPosted: Jan Sat 13, 2018 5:43 am 
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Joined: May Sun 07, 2017 11:35 am
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There used to be a most ingenious passive repeater system installed on a mountaintop to supply Thredbo Village (ski resort in Australia) with TV. On one side of the mountain top were the pickup antennas on wooden poles. Cables ran from here to the Top Station of the skilift on the other side of the mountain, conveniently shrouded in the metal nacelle that formed the weatherproof covering over Top Station. Of course, the nacelle was open on the end facing the village, in the valley below. There was no frequency shifting needed, just CATV-style amplifiers feeding yagis that pointed to the village below, all installed inside the roof of the nacelle. At the village, antennas pointed to the top of the ski lift. The nacelle, and the mountain in between, allowed enough gain to be used without feedback. As I recall there were 3 antennas, Band 1, Band 3 and UHF.

It's possible this system is still in place, it's been nearly 40 years since I was there.


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