Blocking freeview

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Phoenix
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Blocking freeview

Post by Phoenix » Thu Oct 11, 2018 11:11 pm

Is there any kit available to block out freeview reception
Just very local like a noise generator

SD-E1102
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Re: Blocking freeview

Post by SD-E1102 » Fri Oct 12, 2018 9:05 am

A powerful PMR 446 radio may do it if it's near the aerial as it used to do to my tv when you got it near.
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Albert H
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Re: Blocking freeview

Post by Albert H » Fri Oct 12, 2018 12:21 pm

Phoenix - why would you want to do that? It's going to attract unwanted attention. An easy way is to put a pin in the aerial coax!
"Why is my rig humming?"
"Because it doesn't know the words!"
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Re: Blocking freeview

Post by Phoenix » Fri Oct 12, 2018 12:39 pm

Nah
I need to make a point to some people
About 100 yards should do it
Something left in a hedge with a battery

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Re: Blocking freeview

Post by 3metrejim » Fri Oct 12, 2018 1:30 pm

You could do a lot better than trying to interfere with the signal, which for 100 yards distance, might be upsetting more than just your 'target'.

Get a high powered infrared LED and interface it to a 'TV-B-Gone' gadget, then point it, through a lens, towards the window on your 'target' where the TV is. Not sure of the effectiveness while curtains are closed, but it should work, and turn off other remote control devices and not just TV's - should be quite some fun. I've been able to see a visible version at a distance of around 100m reflecting from a matt surface so it's likely an infrared version should get just as far.

well, what do you know - it's already been done...


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Re: Blocking freeview

Post by McDonalds » Fri Oct 12, 2018 4:36 pm

soon as I turn on 30 watt transmitter I could make it block freeview very easy but chose a dial that blocks the least which I find is near 87.6.

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Re: Blocking freeview

Post by yellowbeard » Fri Oct 12, 2018 4:47 pm

A hunnerd yards? You are not going to do that with something cheap and broadband chucked in a hedge. You are trying to overcome a high power transmitter on the best broadcast site in the area, with a mixed polarity signal and digital error correction. You would need to be on the multiplex frequency without drifting off when chucked in the hedge, and have a decent bit of battery sapping power going on. You'd be better off setting fire to a brown paper bag of dog shit on their doorstep, ringing the doorbell and legging it. :whistle

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Re: Blocking freeview

Post by radium98 » Fri Oct 12, 2018 5:11 pm

JAMMER search ..

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Re: Blocking freeview

Post by Albert H » Sat Oct 13, 2018 1:03 am

A pin in their aerial down lead will screw their reception completely! As Yellowbeard points out, you're not going to do this with a simple piece of battery-powered transmitting gear!

Just for an example (on a rather different scale, but the principle applies....).

Back in the 1970s and 80s, BBC World Service, Voice of America, and Deutsche Welle were deliberately jammed in the Soviet Union. The western powers assembled the most powerful transmitters ever built and connected them to huge directional arrays so that the power pointed at the Soviets was gigantic. The Russkies tried (mostly unsuccessfully) to jam the western signals, and at one time they were expending almost 60% of their entire power generation just to run their unsuccessful jammers!

This was Economic Warfare of the most effective kind - the Soviets were building nuclear and hydro-electric power stations just to supply power to jamming transmitters! The BBC, VOA and DW used to vary their transmission frequencies by 10 kHz to dodge the jamming, since it would take the Russians days to realise and change the jammer frequency!, and most Russians who wanted to hear these "foreign" stations were smart enough to construct and use a directional loop aerial, which could be used to null out the jammers!

Jamming is generally ineffective!
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"Because it doesn't know the words!"
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Re: Blocking freeview

Post by nrgkits.nz » Sat Oct 13, 2018 11:43 am

Get a universal remote control and point it in their window.

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Re: Blocking freeview

Post by 3metrejim » Sat Oct 13, 2018 12:41 pm

Albert, the best 'jammer' for digital OFDM transmissions is a high powered pulse, repeated quickly enough (but at a random time interval) to corrupt multiple random symbols and overload the error detection and correction. If you tried to generate a signal with ordinary methods you may find it complicated, and needing high power - but there is a much easier way. All you need to do is charge a piece of low impedance co-ax cable (or use multiple identical length pieces in parallel) up to near their breakdown voltage (a simple camera flash unit feeding into a diode multiplier is good), and then have a small spark gap near the charging end. The co-ax cable length is calculated to be a 1/4 wave at the centre frequency. An antenna with an impedance significantly higher than the cable(s) is attached to the far end of the cable(s). It's just a UHF version of the 'spark-gap' transmitter (the very first radio transmitters - before valve and transistors).

If you work it out, you get a very high peak power (it's way higher than you'd expect) for a few uS, and due to the nature of the spark gap, the repetition time is random. On an analogue tv this results in multiple dancing dot's all over the screen (unwatchable). With digital, so many errors are introduced that the signal is undecodable. Also there is a delay in re-acquiring the signal, so the 'jammer' could be pulsed for power savings. Power requirement is probably less than 2 watts continuous, but I never measured it (ran from 3v - two 1.5 volt AA batteries). The downside is that it is audiably noisy (small spark) and it can damage, or disrupt, nearby electronic devices due to the high peak power. These type of devices have been researched by the military in the past - for directly disrupting electronic devices, although disrupting technology has now moved on.

These devices create a great deal of interference, and I definitely DO NOT recommend anyone to build one (I have missed out an important component and what it's purpose is), this forum is meant to be about keeping signals _clean_. Also, I think the penalties, in the UK anyway, for deliberately jamming a signal are almost the same as for recklessly endangering life by arson (lit bag of dog poop on the step), if you get caught...

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Re: Blocking freeview

Post by Albert H » Sat Oct 13, 2018 10:42 pm

I still think that a pin in the coax is the way to go!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: Blocking freeview

Post by radium98 » Sun Oct 14, 2018 7:51 am

i built a little jammer of 1w for fm band from a french magazine i dont remember it is name but i did not use it it just built for fun and it use 2n 3866 / mrf 237 it was just to oscillator as i remmber .Albert will do the explain :)

http://www.raptorzone.co.za/fm_jammer.html

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Re: Blocking freeview

Post by Albert H » Sun Oct 14, 2018 5:01 pm

Radium - the circuit shown in that link will be useless as a jammer - the noise generator and sawtooth sweep circuits may work, but the transmitter design is a joke. It's a very old-fashioned circuit, "designed" to be peaked at ONE operating frequency. There are too many points of adjustment - the "designer" didn't know how to calculate the values required, and admits in the text that it was "trial and error".
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: Blocking freeview

Post by sinus trouble » Sun Oct 14, 2018 9:20 pm

Use a microwave magnetron!! Destroy every electrical device in the area! :lol: :lol:
I am as stupid as I look! :|

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Re: Blocking freeview

Post by nrgkits.nz » Mon Oct 15, 2018 2:55 am

Why go to so much trouble, all you need is a pin in the coax like Albert said, you could even inject your own signal if it's analogue and play p0rn on their screen.

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Re: Blocking freeview

Post by McDonalds » Mon Oct 15, 2018 5:09 pm

You could have this connected to an amp but need to know what channel they are on you could bloack it with your own. ?
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