# I saw the Cat Detector van! **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [October 13, 2018, 11:23pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917 "2018-10-13T23:23:09Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 13, 2018, 11:23pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/1 "2018-10-13T23:23:09Z")
[Driving down my street.](https://cl.ly/bb20b9b3f240) I’ve never seen so many bleedin’ aerials (I counted at least 6, although the photo doesn’t show them all). ---
**Author:** ![CairoCarol](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cairocarol/32/3825_2.png) [@CairoCarol](https://boards.straightdope.com/u/CairoCarol)\ **Post date:** [October 13, 2018, 11:29pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/2 "2018-10-13T23:29:30Z")
Where are the cats? I want cats. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [October 14, 2018, 12:01am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/3 "2018-10-14T00:01:45Z")
Huh? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 14, 2018, 12:07am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/4 "2018-10-14T00:07:36Z")
> [@Just\_Asking\_Questions](#): > > Huh? [![](https://img.youtube.com/vi/M5MnyRZLd8A/hqdefault.jpg "Fish License") ](https://www.youtube.com/watch?v=M5MnyRZLd8A) ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [October 14, 2018, 12:20am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/5 "2018-10-14T00:20:57Z")
Did Eric escape detection? ---
**Author:** ![nightshadea](https://avatars.discourse-cdn.com/v4/letter/n/7ba0ec/32.png) [@nightshadea](https://boards.straightdope.com/u/nightshadea)\ **Post date:** [October 14, 2018, 12:29am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/6 "2018-10-14T00:29:55Z")
its a van that they use in the uk to make sure your not avoiding the infamous tv tax by tracing the cable /antenna signals cause the BBC needs its loot for all the gorgeous nature shows sir Attenborough makes ……. (and other than dr who there the only British thing on BBC America) ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [October 14, 2018, 1:26am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/7 "2018-10-14T01:26:39Z")
I’ve never understood how they can detect that a tv is _receiving_. Signals go through the air, bounce off objects, go through walls. Some even escape into space. How can they tell a signal wandered into your tv’s rabbit ears? Do tv’s in the UK have a special chip that transmits a signal authorities can detect? A transmitters location can easily be tracked. I know they’ve been detecting unlicensed tv’s for decades. Whatever they’re doing works. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [October 14, 2018, 1:35am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/8 "2018-10-14T01:35:03Z")
Looney detector van, you mean. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [October 14, 2018, 1:35am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/9 "2018-10-14T01:35:10Z")
Whatever they are doing seems to be a well kept secret. Only a few details here. > **[TV detector van](https://en.m.wikipedia.org/wiki/TV_detector_van)** > > TV detector vans are vans which contain equipment that can detect the presence of television sets in use. These vans have been used by the General Post Office and later by contractors working for the BBC to enforce the television licensing system in the UK, the Channel Islands and on the Isle of Man. > When television broadcasts in the UK were resumed after a break due to World War 2, it was decided to introduce a television licence fee to finance the service. When first introduced on 1 June 19... This sounds like the technobabble they say on Star Trek. > [@](#): > > The warrant revealed that a BBC contractor had used an “optical detector” to reveal the possible presence of a TV.[10] The warrant stated that: “the optical detector in the detector van uses a large lens to collect that light and focus it on to an especially sensitive device, which converts fluctuating light signals into electrical signals, which can be electronically analysed. If a receiver is being used to watch broadcast programmes then a positive reading is returned.” [10] The BBC stated that this was strong evidence that a set was “receiving a possible broadcast”. ---
**Author:** ![burpo\_the\_wonder\_mutt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/burpo_the_wonder_mutt/32/365_2.png) [@burpo\_the\_wonder\_mutt](https://boards.straightdope.com/u/burpo_the_wonder_mutt)\ **Post date:** [October 14, 2018, 1:56am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/10 "2018-10-14T01:56:33Z")
> [@eschereal](#): > > Looney detector van, you mean. It’s people like you what cause unrest. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [October 14, 2018, 2:44am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/11 "2018-10-14T02:44:42Z")
> [@burpo\_the\_wonder\_mutt](#): > > It’s people like you what cause unrest. Now, _LOOK!_ ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [October 14, 2018, 3:06am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/12 "2018-10-14T03:06:00Z")
Many (most?) receivers are super heterodyne ([Superheterodyne receiver - Wikipedia](https://en.wikipedia.org/wiki/Superheterodyne_receiver)). If you are tuned to (analog) channel 27 (picture carrier 549.25 MHz) it is mixed with 595\* MHz to produce a 454.75 MHZ (For a different channel it is mixed with freq + 45.75 MHz) then the 45.75 MHz signal is amplified. I’m not sure if they go for the mixer frequency or the intermediate frequency, in any case your TV does produce RF that can be detected Digital TV is a bit different, but I believe you will still get RF out of it Brian - It could be carrier freq - 45,75 ---
**Author:** ![burpo\_the\_wonder\_mutt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/burpo_the_wonder_mutt/32/365_2.png) [@burpo\_the\_wonder\_mutt](https://boards.straightdope.com/u/burpo_the_wonder_mutt)\ **Post date:** [October 14, 2018, 3:11am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/13 "2018-10-14T03:11:41Z")
Housinge? ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [October 14, 2018, 4:14am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/14 "2018-10-14T04:14:09Z")
That’s the way it was spelled on the van! ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [October 14, 2018, 4:21am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/15 "2018-10-14T04:21:19Z")
> [@Sunspace](#): > > That’s the way it was spelled on the van! You’re very observant. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [October 14, 2018, 2:10pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/16 "2018-10-14T14:10:54Z")
> [@N9IWP](#): > > Many (most?) receivers are super heterodyne ([Superheterodyne receiver - Wikipedia](https://en.wikipedia.org/wiki/Superheterodyne_receiver)). If you are tuned to (analog) channel 27 (picture carrier 549.25 MHz) it is mixed with 595\* MHz to produce a 454.75 MHZ > (For a different channel it is mixed with freq + 45.75 MHz) then the 45.75 MHz signal is amplified. > I’m not sure if they go for the mixer frequency or the intermediate frequency, in any case your TV does produce RF that can be detected > > Digital TV is a bit different, but I believe you will still get RF out of it > > Brian > > - It could be carrier freq - 45,75 I hadn’t considered that possibility. I agree it could be the oscillator in the circuit. Or a stage in the IF circuit. ---
**Author:** ![voltaire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voltaire/32/313_2.png) [@voltaire](https://boards.straightdope.com/u/voltaire)\ **Post date:** [October 14, 2018, 2:25pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/17 "2018-10-14T14:25:01Z")
> [@aceplace57](#): > > Whatever they are doing seems to be a well kept secret. Only a few details here. > > [TV detector van - Wikipedia](https://en.m.wikipedia.org/wiki/TV_detector_van) > > This sounds like the technobabble they say on Star Trek. > > > [@](#): > > > > The warrant revealed that a BBC contractor had used an “optical detector” to reveal the possible presence of a TV.[10] The warrant stated that: “the optical detector in the detector van uses a large lens to collect that light and focus it on to an especially sensitive device, which converts fluctuating light signals into electrical signals, which can be electronically analysed. If a receiver is being used to watch broadcast programmes then a positive reading is returned.” [10] The BBC stated that this was strong evidence that a set was “receiving a possible broadcast”. That’s just a fancy way of saying they saw (and probably recorded for evidence) a tell-tale variable glow emanating from their window. Doesn’t sound very high tech. ---
**Author:** ![Filbert](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/filbert/32/3433_2.png) [@Filbert](https://boards.straightdope.com/u/Filbert)\ **Post date:** [October 14, 2018, 2:44pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/18 "2018-10-14T14:44:05Z")
> [@aceplace57](#): > > I’ve never understood how they can detect that a tv is _receiving_. > > Signals go through the air, bounce off objects, go through walls. Some even escape into space. How can they tell a signal wandered into your tv’s rabbit ears? > > Do tv’s in the UK have a special chip that transmits a signal authorities can detect? A transmitters location can easily be tracked. > > I know they’ve been detecting unlicensed tv’s for decades. Whatever they’re doing works. You know how it works? They drive the vans down the street to scare people into paying (actually it’s been years since I’ve seen one). To actually find TVs, they look through windows, send letters to anyone who hasn’t paid for a license, and occasionally send people round to check. The only way anyone gets fined is 'cos an enforcement guy actually sees a TV. All else is theatre. I’ve known a few people get caught because the TV was visible from the doorway, or in a shared house because someone didn’t realise their housemate had one and let the inspector in (they don’t show up with a warrant). I’ve also known people who just hid it in a cupboard and did not get caught or fined. They showed up at my old house, I just said I didn’t have a TV, which was true, but I did not give them permission to come and search. They went away and didn’t come back. Incidentally, technically, until the internet made it more complicated to define, you needed a license if you had equipment capable of receiving a signal, it wasn’t necessary to have it in operation. ---
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [October 14, 2018, 4:19pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/19 "2018-10-14T16:19:41Z")
NHK in Japan has people going around knocking on doors. I never paid because I didn’t own a TV. Since I’m a foreigner they gave up really quickly. For years, I was waiting for my brother in Utah to show up and claim the TV I had bought for him. . . It was rather kind of him to allow me to use it in the meantime. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [October 14, 2018, 4:36pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/20 "2018-10-14T16:36:55Z")
> [@](#): > > The warrant stated that: "the optical detector in the detector van uses a large lens to collect that light and focus it on to an especially sensitive device, which converts fluctuating light signals into electrical signals, which can be electronically analysed. Sounds like they’re describing what is commonly called a “camera”. [Next page](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917.md?page=2)