Shortest FM TX time to not get caught ?

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Wireupwall
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Shortest FM TX time to not get caught ?

Post by Wireupwall » Sun Mar 17, 2019 6:24 pm

What is the shortest time that you can come on air on FM for to not get caught ? Let us say for a hypothetical fun broadcast to da necks on here, You know, let people know when a friend is coming on air and the likely reception area. Then he comes on air and stay on for 5mins/15mins/1 hour or whatever and see what necks on here can hear ? What TX time guarantees you won't get caught ?

The techy people must know how long you could safely be on without being triangulated.

For a fun Radionecks blast.

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Re: Shortest FM TX time to not get caught ?

Post by McDonalds » Sun Mar 17, 2019 6:42 pm

I have been running every other weekend for a a few years I think its only if another station Complains they do something.
Just do not interfere with peoples freeview

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Re: Shortest FM TX time to not get caught ?

Post by THE GOVERNOR » Sun Mar 17, 2019 7:47 pm

Wireupwall wrote:
Sun Mar 17, 2019 6:24 pm
What is the shortest time that you can come on air on FM for to not get caught ? Let us say for a hypothetical fun broadcast to da necks on here, You know, let people know when a friend is coming on air and the likely reception area. Then he comes on air and stay on for 5mins/15mins/1 hour or whatever and see what necks on here can hear ? What TX time guarantees you won't get caught ?

The techy people must know how long you could safely be on without being triangulated.

For a fun Radionecks blast.
Switch it on and off remotely and DONT do it from your home :idea:

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Re: Shortest FM TX time to not get caught ?

Post by THE GOVERNOR » Sun Mar 17, 2019 7:57 pm


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Re: Shortest FM TX time to not get caught ?

Post by McDonalds » Mon Mar 18, 2019 10:00 am

should add not in the city so maybe that helps to.

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Re: Shortest FM TX time to not get caught ?

Post by trancetechnic » Mon Mar 18, 2019 10:45 am

I can remember back in 2006 I tried a 150 watt TX @ home And an hour later I got a big knock on my front door And of course It was The 'DTI'. I never let them in!...Fortunately They eventually got fed up and left. :lol:

So, my advice is Don't broadcast with the transmitter from your house Especially If it's rented from a housing association As you will be evicted for 'illegal activity'. :tup

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Re: Shortest FM TX time to not get caught ?

Post by trancetechnic » Mon Mar 18, 2019 2:55 pm

The one that attracted attention: instantly! Only requires 1 watt ! And She Still works ! ;)
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Re: Shortest FM TX time to not get caught ?

Post by Albert H » Mon Mar 18, 2019 3:18 pm

Unfortunately, the lowpass output filter on that board is about as much use as an ashtray on a motorbike. Each coil needs to be screened from the other, and the whole filter needs to be screened from the rest of the PA. The copier who built this also didn't realise that he didn't need an expensive high voltage capacitor on the base of the '1407. It's also funny that there's a discoloured S18 coil in the output, with a slug inside it! That coil will melt into a little plastic puddle after a short time, and the PA will fail - fortunately. There's also insufficient base damping on the final, so the output will be very rich in harmonics, and there will probably be some amount of self-oscillation going on, giving rise to some huge spurs. There's also very little supply RF bypassing, so the supply leads will be RF live.....

I'll say it again: It's crap like this that gets pirate radio a bad name.
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Re: Shortest FM TX time to not get caught ?

Post by Albert H » Mon Mar 18, 2019 3:25 pm

If you're in a major UK city, your signal will be detected and triangulated within minutes of switch-on. The "Authorities" have automated monitoring stations all over the major cities and conurbations. If you're not causing interference, and there are no complaints, you can often get away with running for many hours at a time. However, if your station generates any significant audience or any interference to legal stations, you can bet that Global or Bauer will raise a complaint, and the RIS chaps will be sent out to take away your transmitter.

There are two ways to avoid this: operate well away from the big cities, or get on Medium Wave! OFCOM have said publicly that they can't "enforce MW", so as long as you don't cause interference, and you can find a nice second or third adjacent frequency, crack on!
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Re: Shortest FM TX time to not get caught ?

Post by trancetechnic » Mon Mar 18, 2019 3:51 pm

Albert H wrote:
Mon Mar 18, 2019 3:18 pm
Unfortunately, the lowpass output filter on that board is about as much use as an ashtray on a motorbike. Each coil needs to be screened from the other, and the whole filter needs to be screened from the rest of the PA. The copier who built this also didn't realise that he didn't need an expensive high voltage capacitor on the base of the '1407. It's also funny that there's a discoloured S18 coil in the output, with a slug inside it! That coil will melt into a little plastic puddle after a short time, and the PA will fail - fortunately. There's also insufficient base damping on the final, so the output will be very rich in harmonics, and there will probably be some amount of self-oscillation going on, giving rise to some huge spurs. There's also very little supply RF bypassing, so the supply leads will be RF live.....

I'll say it again: It's crap like this that gets pirate radio a bad name.
Hello Albert ! That's a professionally built amp for a licensed radio station. The amp is not a copy and It's certainly not Chinese crap.

The paper you see on the board is there to hide the company that built the amp. It's a superb piece of kit !
Shame It's only been on about 5 times in it's life.

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Re: Shortest FM TX time to not get caught ?

Post by Albert H » Tue Mar 19, 2019 12:38 am

Trancetechnic: I've seen those boards before - they're a very bad copy of an old Broadcast Warehouse board! At least Roger had a clue about screening and filtering and wouldn't use an S18 coil in the output of a 150Watt PA.

As I recall, JD and SM had a load of those boards etched by a PCB company in Wimbledon (I seem to remember). They had "simplified" the layout, without being aware of the ramifications and without the right test gear to detect and sort out the problems. They made loads of those PAs and sold them to lots of stations who couldn't understand why they kept getting raided......

There were two versions on the same PCB - the one you've got, and another with a BLF244 driver. Neither of them worked properly. I received two of the BLF244 boards in rigs from a station just north of London, who couldn't understand why they were causing interference to their local cab company..... I connected my signal generator, a dummy load and a regulated bench supply and spectrum analysed what was coming out of it:

The drive was on 94.2MHz, and there were two small spurs in the aircraft band, loads of second and third harmonic, a few other spurs in Band I and lots of "noise" around the carrier. By fitting screening in the right places, the 2nd and 3rd almost completely disappeared. Adding a bit of base damping to the final and correcting the match into the driver got rid of the spurs and close-in noise. I found that the output match was poor - they'd got a couple of capacitors wrong when they copied the original and Roger probably fitted the S18 to fool the copiers. Correcting the values, removing the S18 and fitting the correct coil, the current consumption decreased and the power output increased - the efficiency increased significantly, and the heatsink was much cooler.

I reassembled the whole rig, fixed the nasty synthesiser whine, and it was doing about 145 clean Watts and staying cool. Fixing the other one only took about 20 minutes!
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"Because it doesn't know the words!"
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Re: Shortest FM TX time to not get caught ?

Post by radionortheast » Mon May 13, 2019 9:37 am

Think this is more the answer you where looking for, I guess if you wanted to see if people where hearing it you come on announce the frequency leave it on for afew hours, then later on if you wanted to come back on change to a different frequency.

10 plus years ago I would leave my transmitter on for 5 or 6 hours, with the aerial in the loft, transmitting about 4 or 5w, it was outside of area were you wouldn't get RSL's.
if your not in an area where its considered a problem, you problaly might be left alone, it depends on the power level, how many people could pick it up and the amount of hours its running for. If your not in a area where theres temopory radio stations setting up, as long as your not trying to compeat with commercial stations then thats that. All the times i’ve messed about, i’ve searched not really found anything, most people don’t have interest in this stuff.
it only takes 1 nosey parker going throught the area, specially if its iding itself, even if your relaying a station, they start inquiring, the longer its on the more likely thats going to happen. Just keep a watch over the forums out there if someone starts talking, I would switch off, use a different frequency. Thats the only advice I can offer, I don't know their monitoring capabilities, other than they have monitoring stations in cities and can triangulate signals possibly.

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Re: Shortest FM TX time to not get caught ?

Post by radium98 » Mon May 13, 2019 8:13 pm

this is a BW warehouse amplifier that was having a blf244 as a driver i was having an old design ,and this amplifier use sd1407 from datasheet FT is 30 mhz so i dunno how it work in fm @108 etc.....

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Re: Shortest FM TX time to not get caught ?

Post by Albert H » Tue May 14, 2019 2:08 am

Radium - the amplifier pictured is NOT a genuine BW one - it's a copy with several errors.
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Re: Shortest FM TX time to not get caught ?

Post by radium98 » Tue May 14, 2019 7:58 pm

Transmitter_BW-2.jpg
agree @ Albert H
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Re: Shortest FM TX time to not get caught ?

Post by Albert H » Wed May 15, 2019 1:27 am

That looks like a BW one, but the ones I've seen all had zig-zag output filter coils and enough room (and earth plane) to solder screens between the coils.
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Re: Shortest FM TX time to not get caught ?

Post by radium98 » Wed May 15, 2019 5:41 am

picture?

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Re: Shortest FM TX time to not get caught ?

Post by teckniqs » Wed May 15, 2019 7:51 am

The small ceramic disk capacitor after the final coil into the output coax looks far too small and ready to burn...

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Re: Shortest FM TX time to not get caught ?

Post by Albert H » Thu May 16, 2019 2:07 am

I got some Philips 33pF 1kV ceramic caps (purple tops) and they're surprisingly tiny. I've used them in quick filters for 94MHz rigs as they're close to 50Ω at that frequency. They didn't suffer at all at 120 Watts, despite their small size.
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Re: Shortest FM TX time to not get caught ?

Post by OldskoolPirate » Fri May 17, 2019 10:55 am

This is such a load of shit. You can get away with anything as long as your not interfering or getting complaints. And even then they aren’t gonna turn up at your door within the hour. If the above was the case, there wouldn’t be any 24/7 pirates.

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