Author Topic: For the countries which need Radio and TV licenses. How TV Detector Vans work...  (Read 11878 times)

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Online Monkeh

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Alright; but what explains the large discrepancy between what I'm told is ~90% of UK viewers still receiving signals over the air vs. a much lower fraction in the US? (Don't know the number but it's a lot less than 90%.)

I don't think of the UK as a technologically backward place, so I'm assuming that isn't the reason.

Why would you think of it as technologically backward?

What, are you baiting me? Please reread my comment: I said I don't think of the UK as being technologically backward.

*sigh*

Why do you equate terrestrial broadcast with being technologically backwards?
 

Online Analog Kid

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OK, maybe not backwards, but my prejudice, if I have one here, is that it seems like an inferior method in some ways (multipath, interference, weak signal strength, etc.), compared to cable or satellite. Of course it does have its advantages too, certainly less and simpler infrastructure for one.

I will say that this whole thread has been an eye-opener for me, as I knew practically nothing about how people receive TV in the UK.
 

Online coppice

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OK, maybe not backwards, but my prejudice, if I have one here, is that it seems like an inferior method in some ways (multipath, interference, weak signal strength, etc.), compared to cable or satellite. Of course it does have its advantages too, certainly less and simpler infrastructure for one.
The UK is smaller than the US, so most people are not a crazy distance from a transmitter. Most houses with the modest sized aerial on the roof get a very clear signal. My parent's house had an issue with a tower at the end of the road blocking enough direct signal to a rooftop antenna, leaving them with the ghosty picture made up mostly of reflections. We put an aerial on a pole at the end of the garden, where it saw past the tower. With a cheap amp at the aerial, to boost the signal to overcome losses in the extra 50m of cable down the garden, they got a very clean signal with no visible ghosting. Of course, now we have all digital broadcast TV none of the degradation issues matter.
 

Online coppercone2

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also that makes me wonder for this van, would it not need to have a tall antenna to receive emissions from the high up antennas? near the ground things suck
 

Online TimFox

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Online Analog Kid

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For some reason that looks so veddy veddy British to me:

 

Online coppercone2

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lmfao the driver of that thing has nerves of steel

also where is the video footage of them chasing it down the street in the wind
 

Online Analog Kid

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This whole thread puts me in mind of a song from long ago:
Quote
Let me tell you how it will be
There's one for you, nineteen for me
'Cause I'm the taxman
Yeah, I'm the taxman.

Should five percent appear too small
Be thankful I don't take it all
'Cause I'm the taxman
Yeah, I'm the taxman.

I'll tax the street
(If you try to sit) I'll tax your seat
(If you get too cold) I'll tax the heat
(If you take a walk) I'll tax your feet
(Taxman)

'Cause I'm the taxman
Yeah, I'm the taxman.

Don't ask me what I want it for
(Taxman Mr. Wilson)
If you don't want to pay some more
(Taxman Mr. Heath)
'Cause I'm the taxman
Yeah, I'm the taxman.

Now my advice for those who die (taxman)
Declare the pennies on your eyes (taxman)
'Cause I'm the taxman
Yeah, I'm the taxman
And you're working for no one but me (taxman)
« Last Edit: January 09, 2025, 11:12:59 pm by Analog Kid »
 

Online coppice

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This whole thread puts me in mind of a song from long ago:
A Laffer minute.
 

Offline Canis Dirus Leidy

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What amazing stories I learned from you, in the Soviet Union there were never any licenses for radio and television.
Not quite. Since the mid-twenties, a subscription fee[1] has been charged 'per receiver' (official justification: broadcasting network maintenance), so they had to be registered on time to avoid a fine. In 1961, this fee was dropped, and, "to reimburse the costs of broadcasting", prices for radio equipment were raised by 15-20% instead.

1. The value of which depended on the type of receiver. In the thirties, the simplest crystal set receiver cost three rubles per year, and a mains-powered tube radio cost 24/year.
 

Offline Xena E

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Was early BBC television transmitted on only one channel (per locality) for very long?
A TRF set is practicable for a single preset frequency, but superheterodyne with LO is much better for selecting between multiple frequencies.
Yes. The UK had only one BBC channel until 1955. Then regional commercial channels began, one in each region, referred to as ITV.

The potted history of UK television standards...

1928 to 1936 several competing mechanical and electronic scanned systems were trialed.

The first regular "EMI electronic" 405 line system BBC television transmissions (1936 onward), were all on channels within the low VHF band 1.

What was common as the setmakers were exclusively domestic, was that the sets would be manufactured to cater for the individual channels, so sets were dispatched to dealers with the relevant tuning already carried out for the local reception, regardless of whether TRF or Superhet.

With the start of commercial TV, (ITV) in 1955, that was transmitted all on band 3. Dual band antennas were works of art.

Both used positive going video and AM sound, .

With the advent of the 625 UHF BBC 2 television service in the early 1960s, the proneness of the VHF system to picture and sound disturbance by poorly suppressed interference was addressed by the use of negative going picture luminance modulation, (so interference spikes would not be displayed as peak white), and the sound was transmitted as FM. As a concequence, the production of dual standard television receivers was complex for manufacturers.

Within a few years all channels were moved to the 625 UHF service and were transmitted with the compatible PAL Colour system.

The VHF transmitters of the old two band VHF 405 system being finally shut down in 1984.
« Last Edit: January 10, 2025, 01:16:24 am by Xena E »
 

Online BrianHGTopic starter

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With the advent of the 625 UHF BBC 2 television service in the early 1960s, the proneness of the VHF system to picture and sound disturbance by poorly suppressed interference was addressed by the use of negative going picture luminance modulation, (so interference spikes would not be displayed as peak white), and the sound was transmitted as FM. As a concequence, the production of dual standard television receivers was complex for manufacturers.
Thank you.  I never considered that aspect of using a negative going picture modulation scheme.
 

Offline Ranayna

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For those who didn't realize, older TV and radios LO oscillator was mixed with the antenna signal coming in and it also literally leaked and radiated out through the same antenna the TVs and radios used to receive their broadcasts.

Yes, you can see each LO on these TV prior to the mid 90s with ease by a few houses in each direction.

When sniffing with a directional antenna and spectrum analyzer, you can easily narrow down to every 1 to 2 houses.

Everyone who says this is impossible never played with this equipment in the 70s and 80s.  The signals are there visualized in spikes on the cheap analog RF spectrum analyzers of the time and the changes in their amplitude is easily seen on said spectrum analyzers of the time just by rotating your directional antenna.

Importantly, there was far less "crud" polluting the spectrum in earlier years as switch mode supplies were virtually unknown & there weren't the other incidental radiators to contend with.

I do think that the vans were probably more useful for obtaining statistics, rather than chasing down individuals.
If a building showed strong LO signals on the standard channels used by the BBC, say, that building might be of interest for "follow up" activity.

Still, I read about things like simple refrigerator compressors blocking microwave wifi. I am almost sure that there could have been poorly maintained motors that do all kinds of havok to measurements. Like elevator, appliance, alternators on the street from cars, etc. I still think you must have had a fair bit of crap to deal with, even back then. Now I would think its basically impossible lol

Apparently simple electromechanial street lights could make up to 10Ghz interference! Especially with how shoddy some switches on lower cost things used to be before they come up with good platings, not to mention good brushes. And this was before everyone replaced everything (coins in the fuse box).

While there is less guaranteed RF sources, I think you had enough shoddy electrical engineering and maintenance practices that must have made it at least difficult or temperamental.  And poor knowledge of ground bonding techniques outside of advanced places like radio stations, bad weathering on shield infrastructure, poor electrical jointery. I noticed unless its something expensive, things looked mega shoddy

and crappy insulating arcing.
That reminds me...
This report made it even into german tech media:
https://www.bbc.com/news/uk-wales-54239180

An old TV caused an ongoing internet outage in a village. A lot of stuff was done in vain before the TV was found out to be the culprit.
 

Online Analog Kid

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This report made it even into german tech media:
https://www.bbc.com/news/uk-wales-54239180

An old TV caused an ongoing internet outage in a village. A lot of stuff was done in vain before the TV was found out to be the culprit.

So they tell us that the old TV was the source of the RFI emission that caused the outage, but what internet device was knocked out by it? A broadband repeater? Sounds like it must not have been very well protected for that to have happened.
 

Offline m k

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OK, maybe not backwards, but my prejudice, if I have one here, is that it seems like an inferior method in some ways (multipath, interference, weak signal strength, etc.), compared to cable or satellite. Of course it does have its advantages too, certainly less and simpler infrastructure for one.
The UK is smaller than the US, so most people are not a crazy distance from a transmitter. Most houses with the modest sized aerial on the roof get a very clear signal.

I had a 2m 11GHz satellite system with polar mount through the '90s and on, never upgraded it to 12GHz and digital though.
It was very practical, raw feeds and stuff.

Few transmitters were also dedicated to our local feeds, so cable was not needed, not available either, too far.
Later came pay TV and sort of a mini disc receiver, for some time few aerial feeds through satellite continued to be free.

Currently satellite TV is probably all gone, aerial digital feeds are still there and updating, DVB-T is changing to DVB-T2 in few months.
Some may wonder why not directly to DVB-T2, it's only few years ago when the whole thing started.
I guess old analog transmitters were not accurate enough.

For spooks,
spying secure fax using acoustic noise and skipping the whole encrypted part was pretty clever, and it actually worked.
Early "RFID" by the Great Seal bug wasn't dumb either.
Advance-Aneng-Appa-AVO-Beckman-Danbridge-Data Tech-Fluke-General Radio-H. W. Sullivan-Heathkit-HP-Kaise-Kyoritsu-Leeds & Northrup-Mastech-OR-X-REO-Simpson-Sinclair-Tektronix-Tokyo Rikosha-Topward-Triplett-Tritron-YFE
(plus lesser brands from the work shop of the world)
 

Online TimFox

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The "Great Seal Bug" in the US embassy in Moscow, was apparently designed by Lev Terman, the inventor of the theremin (from the French spelling of his name).
It was very clever:  a microwave cavity with one face forming an acoustic diaphragm, was excited from a narrow microwave beam from outside the building, and the reflected beam was modulated due to the resonant frequency changing with local sound pressure.  It was totally passive, so not detected when external microwaves were not present.
The US ambassador to the UN, Henry Cabot Lodge, showed this device to the General Assembly in 1960 when the US government was scrambling to account for their U2 espionage flights over the Soviet Union;  it had been discovered earlier (1951).  It was embedded in a carved wooden Great Seal of the United States, presented in 1945 when the US and USSR were still allies.  I was only 10 at the time, but I remember TV news coverage of that UN meeting.
The Wikipedia article has technical details:  apparently the fundamental frequency was 330 MHz, but operated at overtones.
I built a theremin for myself years ago, after reading a good biography of Terman.  He spent a long time in the US, but returned to the USSR just in time to get in trouble with Stalin and sent to the Gulag.  He was yanked back when the Soviet government needed his expertise during the war.  He did make a short return to the US before his death in 1993.
« Last Edit: January 10, 2025, 07:40:14 pm by TimFox »
 
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Offline Stray Electron

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Nearly everyone has access to terrestrial transmissions.

Yeah, I got that; same sitch here in the US. Everyone (for the most part, except those way out in the boonies) has access to over-the-air signals; few use that, though, compared to cable/satellite users.



     That is absolutely not true.  There are still large parts of the rural US where cable TV (or cable internet) is not available and those people still rely entirely on over the air TV.  Also there are huge numbers of consumers in the US that are "cutting the cable" due to the huge monthly costs of cable TV and they're going back to over the air TV.  I just changed the connections of my TV literally two days ago so that I now receive all of the local stations over the air instead of via the cable and the reception is better and I don't get the lags due to cable companies crappy software AND I now receive 99 different local stations instead of just the FOUR that my cable company rebroadcast. 
 

Online Analog Kid

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Well, then I stand (sit, actually) corrected.

I'd be curious to see what the actual figures are for different transmission methods in the US. Have to look that up, I guess.
 

Online vk6zgo

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With the advent of the 625 UHF BBC 2 television service in the early 1960s, the proneness of the VHF system to picture and sound disturbance by poorly suppressed interference was addressed by the use of negative going picture luminance modulation, (so interference spikes would not be displayed as peak white), and the sound was transmitted as FM. As a concequence, the production of dual standard television receivers was complex for manufacturers.
Thank you.  I never considered that aspect of using a negative going picture modulation scheme.

It isn't the only reason, an equally important one is that as signal strengths fall, picture sync is the last thing to fail.
In the early days of TV in Australia, when country transmitter sites were rare, it was not unusual to see a fully locked, but very noisy picture at places well outside even the "fringe area" of the city station.
 

Online BrianHGTopic starter

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It isn't the only reason, an equally important one is that as signal strengths fall, picture sync is the last thing to fail.
In the early days of TV in Australia, when country transmitter sites were rare, it was not unusual to see a fully locked, but very noisy picture at places well outside even the "fringe area" of the city station.
I guess I could imagine that with poorly designed sync separator circuitry with very wide PLL locking circuitry due to age/temperature drift in old tube TV circuit designs.

Sync locking onto the snowiest most garbage source video signals appeared to not be a problem at all with TV receivers in the mid 70s here in North America.  I guess a gated pll locking scheme sifted out the 15.7khz and 60hz syncs and just didn't care much about the noise.  Just passing the source video from the tuner through a very low pass filter, like below ~500khz, left you with a clearly visible visible video sync even on the noisiest junk imaginable directly coming from the tuner unfiltered.
« Last Edit: January 11, 2025, 05:28:04 am by BrianHG »
 

Offline special_K

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OK, maybe not backwards, but my prejudice, if I have one here, is that it seems like an inferior method in some ways (multipath, interference, weak signal strength, etc.), compared to cable or satellite. Of course it does have its advantages too, certainly less and simpler infrastructure for one.

I will say that this whole thread has been an eye-opener for me, as I knew practically nothing about how people receive TV in the UK.

Terrestrial UHF broadcast is very popular in the UK for a very simple reason: it is free, and everyone knows about it.

Unlike in the USA, every TV Station serving a region will all share one transmission tower. These are extremely high power (In the analogue days, Winter Hill put out 2 megawatts across four channels), and serve about a 40 mile radius depending on geography. There is no tradition of indoor antennas, instead everyone has a rooftop yagi-uda, if not several - one for each room of the house!

There was no commercial TV stations until the very late 1980s, at which time all-europe satellite stations began to exist on the C band with the giant dishes. So until that time, there was no point to having Cable TV unless there was a mountain between your house and the transmitter tower. For those unfortunate people there was "rediffusion", which was a service which used special stripped down TV sets with no tuner or IF section, and you changed channel by turning a control knob mounted near the window frame. The TV was of course rented from the rediffusion company. This system was just a bunch of distribution amplifiers and wires zigzagging from rooftop to rooftop, it had no provision for commercial TV features like pay-per-view or even to cut off service if you stop paying - because if you stopped paying they just came to your house and took the tv.

In 1990 BSB and Sky, both satellite TV providers started their service. You got only 4 new stations, neither had anything good, mostly just old movies or cartoons, or news. But it had the advantage that you just had a man come and fit a dish to the wall of your house. A little later, "American style" cable TV services carrying commercial stations begin but took a very long time to roll out and only become significant in the 2000s, and are not nationwide.

In the 2000s satellite dishes was everywhere, and there was much more stations. I think 100 or so? All the impressive American sounding ones like disney channel, MTV, Cartoon Network etc. Pay per view features like sky box office.

Despite this, every house which has a satellite dish is also basically guaranteed to also be using terrestrial TV, because installing a satellite receiver box in each room is expensive. Satellite becomes less and less attractive as the attractive American style commercial stations are all closing down and replaced with streaming services. It's common for people in their 20s and early 30s to have a TV connected to the internet for netflix but not pay for satellite or cable.

Terrestrial got a strong second wind as the digital transition allows 100ish stations to exist on it, all funded by advertising. These stations are mostly showing cheap low budget shows and 60s/70s/80s/90s reruns, which is very attractive and comforting to the remaining - frankly elderly - TV watching audience. So terrestrial is probably going to outlive the expensive subscription services.

What I think is interesting, and a little backwards, is how uncommon Terrestrial is in the USA. A lot of people have no idea that you can still pick up TV with an Antenna, and are paying for "basic cable", which is just the free channels but for money. This seems to be a failure to communicate the Digital transition, with people becoming misinformed into thinking that over-the-air just vanished.


As far as TV Detector vans go, the principle of operation is very simple. They have a list of every residential address in the UK. They also have an address of every house which bought a TV License. subtract one from the other.

There are no court records of any TV Detector equipment being used in prosecution. There are a few of the vans from different eras surviving into preservation, but all are entirely empty inside with no witness marks from equipment having been installed in the past. The stuff on the roof is faked, it's fibreglass and stuff from hardware stores glued together and painted. The only people claiming that they worked were the TV Licensing people themselves, who refused to demonstrate it. Make of that what you will.
« Last Edit: January 11, 2025, 06:21:37 am by special_K »
 
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Offline AVGresponding

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There was no commercial TV stations [in the UK] until the very late 1980s

This is incorrect, commercial broadcasting started in 1955 in the UK
nuqDaq yuch Dapol?
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Online tom66

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The big issue with terrestial is it uses a lot of bandwidth for relatively little content.  RF bandwidth is precious.  Freeview DVB-T2 only supports at most 13 FHD channels in 1080i60 with the current multiplex arrangement.  Forget about 4K, HDR or anything like that.  Very easy to do that over the internet, and then the terrestrial bands can be freed up for future phone connectivity or long range wireless applications (there's a shortage of bandwidth in the sub-800MHz band that Freeview uses.)  Bring on the death of terrestrial television, I welcome it.
 

Online vk6zgo

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It isn't the only reason, an equally important one is that as signal strengths fall, picture sync is the last thing to fail.
In the early days of TV in Australia, when country transmitter sites were rare, it was not unusual to see a fully locked, but very noisy picture at places well outside even the "fringe area" of the city station.
I guess I could imagine that with poorly designed sync separator circuitry with very wide PLL locking circuitry due to age/temperature drift in old tube TV circuit designs.

Sync locking onto the snowiest most garbage source video signals appeared to not be a problem at all with TV receivers in the mid 70s here in North America.  I guess a gated pll locking scheme sifted out the 15.7khz and 60hz syncs and just didn't care much about the noise.  Just passing the source video from the tuner through a very low pass filter, like below ~500khz, left you with a clearly visible visible video sync even on the noisiest junk imaginable directly coming from the tuner unfiltered.

The only TV systems which used positive modulation  were the UK 405 line system & the old French 819 line system.
Both the North American 525 line & the European originated 625 line systems used negative modulation from the start.

Anything you saw in NA would benefit from the advantages of that modulation system, just as the Australian ones around 20 years earlier did, as I pointed out.

Another advantage of negative modulation was that the horizontal sync pulses & their associated black/ blanking level signals offered a standard DC level in the video waveform, which allowed automatic level control of the transmitted RF signal.

In 1971, on a visit to the UK, I had the opportunity to watch a dual standard BW TV.
Conveniently, there was a Commercial (ITV) station with a both a 405 & 625 line outlet, so I could switch back & forth.

I expected to see a noticeable difference in resolution between the two systems, but that was barely discernible.
What I did notice was that on some ads, the screen suddenly went from a relatively normal grey to bright white with text upon it.
With those, the 625 line system had no problems, but with the 405 line positive modulation system, the TV would momentarily lose vertical sync.
 

Offline Xena E

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There was no commercial TV stations [in the UK] until the very late 1980s

This is incorrect, commercial broadcasting started in 1955 in the UK

I think special_k post looks like it was AI generated, it is mostly bollocks.

The commercial TV companies were started in 1955 as you said, the first commercial radio station in late 1973.

There were no 2MW UHF television transmitters operating within the UK, the most powerful were Sutton Coldfield, Crystal Palace and Sandy Heath all at 1MW.

And... functioning detector vans did exist! At least during the days of analogue television, there were however very few of them. They were operated by the GPO but their main mode of operation was to be sent to areas where there was a high  proportion of households that had sales of receivers credited to them, but who did not have licences, the vans were more of an encouragement for people to go get the licence than be an effective tool in catching unlicenced viewing.

The vans were effective in pinpointing when the unlicenced housholds were viewing their sets so that the agent could call and catch the owner in the act. Very few "prosecution cases" were successful but it was not down to the vans equipment being fake or not working... it was a tool in the investigation but AFAIK was in itself inadmissible as evidence in court as the unlicenced set had to be positively identified as installed and being used.

https://www.britishtelephones.com/vehicles/lightvans/023.htm


« Last Edit: January 11, 2025, 10:52:43 pm by Xena E »
 


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