Short spaced TV stations...
 

A quote from Wikipedia about WESH TV channel 2 Orlando... "The stations signal was short spaced to prevent interference with WTHS channel 2 in Miami."... I'm trying to work out what 'short spacing' means & how it prevents co-channel interference?

I think this article was poorly worded. If you look up the definition of "short-spaced" it means to reduce the power or increase directivity to protect another station on the same channel at less than normal distance.

The article says:
"On that day, the station activated a new 1,000-foot (305 m) transmitter tower in Orange City. The tower was located farther north than the other major Orlando stations' transmitters because of Federal Communications Commission (FCC) rules at the time that required a station's transmitter to be located within 15 miles (24 km) of its city of license. The station's signal was short-spaced to prevent interference with non-commercial educational station WTHS-TV (channel 2, now PBS member station WPBT) in Miami."

I think it should say:
"On that day, the station activated a new 1,000-foot (305 m) transmitter tower in Orange City. The tower was located farther north than the other major Orlando stations' transmitters to prevent interference with non-commercial educational station WTHS-TV (channel 2, now PBS member station WPBT) in Miami. The tower had previously been located closer to Orlando because Federal Communications Commission (FCC) rules at the time that required a station's transmitter to be located within 15 miles (24 km) of its city of license. The shorter distance to Miami had required the signal to be short-spaced."

see:
https://en.wikipedia.org/wiki/City_of_license

http://rogersimmons.com/wesh-channel-2/

this site says the first transmitter was furhther north, in Holly Hill (near Daytona Beach), so maybe it was short-spaced from the time it moved to Orange City, and the location in Orange City rather than even further south was part of the short-spacing.

"On that day, the station activated a new 1,000-foot (305 m) transmitter tower in Orange City. The tower was located farther north than the other major Orlando stations' transmitters because of Federal Communications Commission (FCC) rules at the time that required a station's transmitter to be located within 15 miles (24 km) of its city of license." Still doesn't make sense, because Orange City is 22 miles from Daytona Beach.

Also, any of the locations are more than 200 miles from Miami.

In UK when they reused a low band channel that was near'ish to a high power vertically polarised transmitter (all high power low band TX's were vertically polarised) they'd use horizontal polarisation to try & cut down co-channel interference, then the next co-channel TX would use vertical & so on. AFAIK all american TX's use/used horizontal polarisation...

In the good old NTSC days WESH was the most common DX station
to be picked up in New England. Always in there with the slightest
sporatic-E. No other did this, it would be random from certain areas.

73 Zeno:smoke:
LFOD !

You are correct. Either pure horizontal or elliptical.

In the Boston area we had 2 OTA pay TV stations in the late 70's
Ch 27 in Worcester ( Wistah in NE speak) used the Zenith system &
Ch 68 from Boston ( B-T system ??). IIRC Ch 68 used circular polarization. On
the biggest UHF antennas it was always very snowy even at +- 30 miles.
Both installed cut to freq antenna & the signal from CH 68 was rock solid.
Just before OTA pay died "someone" sold off boxes for a few hundred $$ each.
It lasted about a year then back to unscrambled NTSC. Gee I wonder who
was selling them :scratch2:

73 Zeno:smoke:
LFOD !

I've actually experienced 'short spacing.' When Channel Five (Channel Five is the station name, it doesn't actually transmit on channel 5) started in 1997 in UK the only spare channel in the UHF (the VHF band was de facto not used since the 1970's) in most parts of the country was 37, so most high power stations used 37. I lived about half way between two Channel Five channel 37 TX's (Lichfield near Birmingham & Emely Moor near Leeds) when I lived in Kirkby-in-Ashfield near Mansfield, my antenna was pointed at Lichfield but was wiped out by interference from Emley Moor with severe patterning & beating effects making it unwatchable. I moved to Hucknall near Nottingham & received a good picture when the local'ish Waltham TX started TXing Channel Five on channel 35. I now get perfect Channel Five pictures from Waltham via over the air Freeview & Virgin free cable. (If you use Virgin media for broadband & landline phone you get free cable TV.)

I know back in 1948/49, WDTV of the Dumont TV network went on the air on channel 3. They were later shunted down to channel 2 in the early 1950's because Cleveland, OH had WEWS in channel 3 and there was concern that in the middle of the two cities, you would have co-channel interference. Later on, WDTV became KDKA-TV when Dumont went under and Westinghouse bought the station. There was a channel 6 in Beckley, WV that ran at halff maximum power because there was WJAC in Johnstown, PA on channel 6 also. Maybe not exactly co-channel interference, but when WTAE-TV, channel 4 in Pittsburgh signed off at night, there were times WRC-TV from Washington DC came in.

And to add to this, co channel interference in that era was a very real problem, especially for viewers in between the two affected station signal. Those viewers had more interference issues than people living closer to either station. Short spacing is not good band planning, the recent years FM band debacle is a major reason why. Stations on a frequency need 50-100 miles or even a bit more depending on ERP, and also there needs to be reasonable interference protection. I think directional antennas are going to be a reality in practical terms for the FM broadcast band to have a chance at being usable. Especially for listeners who live between the two signals equally apart.

I know, I live 8 miles north of Wheeling, WV on the Ohio side of the Ohio River and one station that plays a lot of 70's and 80's music, I love the 80's, is on 105.5 Mc, WUKL Bethlehem, WV, but when I drive to work in the Pittsburgh area, I get about 4 or 5 miles into PA and the translator they have on 105.5 Mc in Pittsburgh takes over and it is from 104.3 Mc, a Froggy country music station.

When Mom and I went to California in 1987 and drove from Frisco to LA on I-5 in the San Jouquin Valley, there were many FM stations going back and forth on the capture effect, the FM band was a pain in the butt to listen to.

In Britain a sort of solution to co-channel interference was frequency offsetting, but this only worked well when the interfering signal used the same system i.e. 405 lines. Problem was a lot of the interference was from foreign stations using 625 or 819 lines which used varying bandwidths, most European 625 systems used negative video modulation & FM sound, but Belgium had some TX's that used positive video & AM sound, French 819 used positive video & AM sound. The British TV set working on 405 lines, positive video & AM sound was totally confused when these signals came in & you'd get a horrible broken up picture & a warbling distorted sound. European viewers I presume had the same sort of problems when 405 line signals came bounding in..

In the UK precision offset was used on the UHF 625 analogue TV network to minimise co-channel interference: https://en.wikipedia.org/wiki/Frequency_offset The UK UHF network was meticulously planned to allow for 4 national channels covering 98%+ of the population. Channel 5 was shoehorned in much later and was always a bodge.

I'm not convinced we used precision offset on VHF in the days of 405 transmissions. I could easily be proven wrong if somebody finds a BBC or other document saying that it was tried.

Frequency planning in the UK has always had to be co-ordinated with France, Belgium and Holland. Again back in the says of 405 lines on VHF, viewers on the south coast of England were often troubled by interference from French stations. Usually in periods of settled weather when the troposphere would happily propagate Band I frequencies further than usual. Because the French 819 system used almost exactly twice the line scan rate of 405 you could resolve them on a 405 set but with 2 pictures side by side.

I assume other countries used similar offset methods. All now irrelevant in this age of digital TV.

PS: Searched BBC R&D reports and found these:
https://www.bbc.co.uk/rd/publications/rdreport_1962_19
https://www.bbc.co.uk/rd/publications/rdreport_1968_21
Pluse several more possibly relevant papers.
So the method was defninitely known in 405 days but I'm still not certain it was used in practice.

There is still band planning in digital transmission systems. Sometime back I was reading about the band planning around ATSC 3.0 and how channels had to be spaced and how close cellular data channels could be placed to prevent interference.

During the phase-in of ATSC, there were precise offsets applied to minimize interference into analog stations. This was needed because of ATSC's use of a pilot carrier near the lower edge of the 6 Mhz channel. Offsets were controlled not only for co-channel, but anylowe r adjacent NTSC channel as well. ATSC 3.0, like DVB, uses COFDM, with multiple pilots at the same level as data scattered over the band, so the signal is very noise-like and no visible pilot beats would appear in an analog set. Of course, precision lock between ATSC transmitters is required if they are part of a single-frequency network (use of multiple transmitters to cover an area with a single broadcast on the same frequency), just as it is/would be with DVB.

Analog NTSC co-channel stations were offset by 10 kHz, which turned the interference from a wavering picture into horizontal sine wave "venetian blinds."

At least one company sold a filter that plugged into the back of a monochrome TV CRT (and the socket then plugged into the filter), which contained 10 kHz traps for the grid and/or cathode leads.

I don't know the electrical details, but I have seen pictures of one. Thought I might have a picture, but can't find one.

Band planning for digital TV systems is very different to analogue. As others have said, a COFDM signal is very much like white noise over the entire channel. Single frequency networks are possible though not always used. There is no particular need to worry about adjacent channels.

If you're using analogue TV RF signals in your system (vintage or otherwise) then try to avoid any local digital channels. They look like white noise to an analogue set and a strong local digital signal can give you a very noisy picture. We suffered this problem at the Vintage Wireless Museum, London, when a new COFDM multiplex started up from the main high power TX at Crystal Palace little more than a mile away. We had to change to a different channel at the museum.

To be effective, it would also need a 20kHz trap for when a plus offset and a minus offset station collide.

I wonder if you lived in Hartford or Philly.

WEDU (Tampa, channel 3) was ultra-common, too, but WFSB or KYW have have drowned WEDU out.

Sporadic-E propagation in the VHF-Low TV band strongly favors paths of 1,000 miles (1,600 km), not much further, and not much shorter. If a TV DXer gets a station 350 miles distant, he/she will brag about it.

I remember watching a snowy French ORTF side by side picture on channel 3 or 5 in the 1960's, of course there was no sound just a loud buzzing noise.Where I lived in Nottingham I used to often pick up BBC London on channel 1, BBC Scotland or BBC South on channel 3, BBC South West on channel 5 & BBC Wales on channel 6...

I sometimes pick up distant stations on FM, but the band round here is crammed full of high power national stations & lower power local stations. The bit lower than 88.3 is free & I often pick up European stations down there. I now usually use internet radio in the living room, digital+ radio in the car, also have a digital+ radio clock for the bedroom...

Tampa Bay, Florida had two ABC affiliate stations in one market. Channel 10 for North Tampa and Channel 40 for South Tampa. People bought special Antenna Kits with two antennas, called "Tampa Bay Special". That would be for one antenna pointed North and the other pointed East. Orlando had a Special too. Big Yagi cut to channel 2, regular pointed at Christmas...

Read somewhere that they had a 'mid Florida special' antenna setup. When I rented an apt in Miami in the late 1980's I had a rabbit ears on top of the TV that got near perfect (just a bit of ghosting) pictures on channels 2,4,6,7 & 10, all UHF stations were very noisy...

FM stations have also this issue here I live (Brazilian triple border with Argentina and Paraguay; Foz do Iguaçu). Besides some pirate station playing havoc with my 70's-80's-90's preferred station, some legal stations are crowded one adjacent or almost to each other (bad planning and communications between countries). Well, for poor stations, it's favorite sport is to change frequency from time to time. And, the radio comms cannot use VHF band due to harmonic interference from poor stations; where I work, the private radio comm network needed to be UHF.
Also from TV analogue era, was common to have some TV channels adjacent being used (4-5, 8-9, 12-13 for example). For this, the solution of rotating the antenna applies, due to different country station location.

True, that is a big problem in border area, radio signal travel across the border no problem and sometimes there can be interference with both or all nations if they do not share the same or similar band plans. I know if I past Mercer County, PA ( Mercer County, on Mom's side, my ancestors was among the first settlers there after fighting the American Revolution) and north, as an amateur I can to be careful since I would be above "Line A" and prohibited from transmitting on 420 - 430 Mc because in Canada that is used for different purposes than amateur radio. I was also above Line A when I was eclipse chasing in April and ended in Ashtabula County, Ohio.

BTW, WTAE-TV, channel 4 in the analogue days was one of those Class B (IIRC) low power VHF stations in Pittsburgh. VHF-Lo TV stations from channels 2 to 6 can transmit up to 100 kW but WTAE-TV was restricted to 50 kW because there was a Channel 4 in Washington DC (When WTAE-TV went off the air, many a night, I could get the Washington, DC station, WRC) O the other side, there was a channel 4 in Columbus, Ohio so Pittsburgh was in between. I lived in the West Hills of Pittsburgh and WTAE-TV had their transmitter East of Pittsburgh so there were times it was hard to get over the air, it was a true challenge plus I also lived near the airport, a busy flight pattern. There was an adjacent Channel 5 too, WDTV to the south in Bridgeport, West Virginia.

WTAE-TV went on the air in 1958, until then, except for a brief time with a weak UHF station, Pittsburgh only had KDKA-TV which was WDTV (until the West Virginian TV station took those call letter later on, but Pittsburgh was on the Dumont Network and was said to be the belt buckle. There were people who tried to pull in TV stations from adjacent TV markets such as Steubenville, Ohio, Wheeling, West Virginia and Johnstown, PA too.

One of WTAE-TV first shows, a huge part of Pittsburgh history, was called Top Banana, Second Banana and the Musician that was al ocal variety show. The musician was named Joe Negri who was also the first musical director on WTAE-TV. He is a jazz guitarist and a local legend, he played the Handyman in Mr. Roger's neighborhood. He turns 98 in two days, he got his first start in radio at the age of 3 (been performing on radio since 1929), still performs, still teaches music. Married to the same wife for 70 years too.

Another Pittsburgh TV oddity was we had two NET/PBS stations, WQED on channel 13 and WQEX of channel 16. Joe Negri performed on them too. Pittsburgh was the last US city to still have an all black and white TV station and WQEX was it. It was low budget, using al old 1953 vintage UHF TV transmitter up till it died in 1986. A lot of them ore far our programs ended up there plus a lot of British TV shows too. I was like Brit Box before Brit Box, albeit in black and white. I remember watching Dr. Who and Black Adder on it.In 1986 when they got s new transmitter, they went to color.

Sorry I went long but I love history and Pittsburgh does have a vivid TV/radio history like most places in the world. I also like to go to Youtube to see what TV is like in other nations too, it is fascinating.

In SE PA, 100+ miles from both NYC metro and Wash DC, with decent regular reception from Baltimore's 2-11-13 at 75 miles to SW, either set of big-city channels 2-4-5-7-9-11-13 could be received on summer mornings/after sunsets during heatwaves.

A fast-moving thunderstorm rolling through brought out some incredible mid-Atlantic reception, but not anything from west and rarely from north. The rotor was very helpful in nulling out the co-channel using a JFD medium sized LP VHF only 10 feet above the roof.

Once while testing a smaller VHF antenna in the yard, WPBT-2 Miami over 1000 miles away, wiped out WMAR-2 one muggy summer morning in '78, later WPTV-5 in West palm beach showed up as I was afraid to turn the 19" GE BW off. No great reception equipment employed so it was deemed miracle it was then. What made it really odd was the usual co-channel "venetian blinds" and audible beat frequencies were absent.

Most cable companies in Eastern PA had issues with WTNH New Haven and WTIC Hartford messing with Philly's KYW-3, WPVI-6, WCAU-10. WHYY-12 had some areas N of Allentown receive its duplicate WBNG-12 Binghamton, received normally in most of NE PA.

WGAL-8 near my location, the only VHF channel between Philadelphia's quad and Altoona (10)-Johnstown (6 and 8)-State College (3). Those "upstate" Pa channels never interfered or were received in areas east of the Appalachians.