Block frequency?

[guddler]

Ok, this is OT but very much technical so I'm going to start off by sticking it in here!

Does anyone know of any circuit I could make up to block certain frequencies from being received?

Let's explain....

Where I live we pick up TV from 2 different transmitters. Our main one is Mendip but we also (sadly) get a poor signal from the Welsh transmitter over the water - Brecon maybe? So the way to deal with that is that when you tune in your telly you unplug the aerial lead until the channel count get's to 50, and then you plug it in. All the channels you want are then found with none of the poor quality guff.

So far so good. Unfortunately, modern tellies have an annoying tendency to nag you when they've found new channels. Mine is particularly annoying as it tends to ignore the fact I've told it not to tell me! All the more annoying is that the programs it picks up are generally of poor quality and welsh!!

SO, since I've got to put a new TV aerial up ASAP (old aerial physically broken and scaffolders have stuck scaffolding right in front of satellite dish!!!), it's made me revisit this. I've found the channel frequencies and discovered that all the channels I'm after lie within the range 700 - 854Mhz.

So I'd like a circuit that will trim out anything below 700Mhz.

Is that possible?

 

[trm]

Sounds like you want a high-pass bandpass filter circuit. I've no idea of the physics you need to consider to filter out sub 700MHz but I do know that analogue circuit design can be a right bitch with problems like the tracks/wiring acting as inductors and sharp track turns generating 'echo' etc, so hopefully there'll be something you can buy instead of design.

Would it be possible to have a highly directional antenna so that you can just pick-up from Mendip?

On the topic of bandpass filtering I found some interesting stuff (but didn't wade through it all) by googling:

http://www.google.co.uk/search?q=improve+tv+reception+bandpass+filter

 

[guddler]

I just found a very good site. It's a bit above my head so I'll get me father round this evening but it explains about my very issue and I think what we need is a variable attenuator. The princely sum of £6

 

[trm]

Nice one That sounds right as you can attenuate anything below 700 meg to whatever level the TV tuner considers a ghost or sideband to get rid of the crap.

 

[guddler]

There's actually an even simpler option!

Most sites seem to tout wideband high gain aerials. These aerials do the whole frequency range. Often poorly. Since I now know that the transmitter I want to pick up from it in group C/D I can buy a non wideband aerial that is specifically for groups C/D (the upper third of the spectrum). That way it shouldn't be able to get any of the unwanted signal.

That's my understanding anyway.

£26 job done.guddler2011-07-21 17:02:26