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ubergeek85
07-09-2009, 06:27 PM
Hi all.

I'm looking to either buy or (preferably) make a (not so) small UHF amp, but google isn't bringing up much. It's for a small... project. It'll be operating somewhere between 470 and 700Mhz (maybe higher).

Google isn't bringing up much other than small (1w) projects. I'm hoping to hit at least 50w, if not more.

By the way, I have an old 600w car amp that has some power MOSFETs I might be able to use if need be.

Can anyone recomend either a readymade amp or a good project one? Thanks.

Erayd
07-09-2009, 06:30 PM
I assume you have a licence? You can't run unlicenced on the UHF bands at that kind of power.

ubergeek85
07-09-2009, 06:32 PM
Um... let's say yes?

Erayd
07-09-2009, 06:36 PM
Heh, well reading between the lines I'd say you're in for a pretty hefty fine and possible confiscation of your equipment. With that much power, you'll be stepping on other people's toes very quickly, and those kinds of squashed digits attract official attention.

ubergeek85
07-09-2009, 06:37 PM
Yeah, it was a bit of a long shot...

I was planning on something like this (http://www.instructables.com/id/How-To-Save-Analog-TV/)

Erayd
07-09-2009, 06:46 PM
Yeah that isn't such a smart idea here - unlike the US, our analogue channels are still live. Even in the US, it's not smart - you'd still get some pretty bad consequences.

ubergeek85
07-09-2009, 06:48 PM
It seems you have some experience with this...

Erayd
07-09-2009, 06:49 PM
Not personally - I just have commonsense and some relevant knowledge.

ubergeek85
07-09-2009, 06:51 PM
I guess I'm in the same boat - just without the common sense...

R2x1
07-09-2009, 06:51 PM
Plus there are a few subtle differences between a "car amp"and a UHF amp.

Start with a clean slate - Use valves, then when you make a mistake, the coroner can make wise statements on why you shouldn't have done that.

ubergeek85
07-09-2009, 06:54 PM
Thus, why I wanted to use MOSFETs...

Surely the only (main) difference between a car audio amp and an RF amp is the freq it is designed for?

somebody
07-09-2009, 06:56 PM
Talk to BillyT and/or GrahamL - they're probably the most knowledgeable about this sort of stuff here.

R2x1
07-09-2009, 07:04 PM
Thus, why I wanted to use MOSFETs...

Surely the only (main) difference between a car audio amp and an RF amp is the freq it is designed for?
There is a wee bit of a difference between 12,000 Hz. and 700,000,000 Hz. (There is a bit less difference between a torch battery and a 230 volt supply.)
A volcano and a firework differ mainly in scale, but the side effects go a little deeper ;)
UHF is "Interesting" when you can use short lengths of wire as insulators. This causes unusual effects when you have what appears to be short leads on capacitors that stop them having the capacity to do what you wish. It can lead to some interesting study, but it is not quite such a trivial exercise as it appears at first glance. Good fun though.

ubergeek85
07-09-2009, 07:07 PM
I see...

tweak'e
07-09-2009, 08:09 PM
Yeah, it was a bit of a long shot...

I was planning on something like this (http://www.instructables.com/id/How-To-Save-Analog-TV/)


Yeah that isn't such a smart idea here - unlike the US, our analogue channels are still live. Even in the US, it's not smart - you'd still get some pretty bad consequences.


It seems you have some experience with this...


Not personally - I just have commonsense and some relevant knowledge.

to add, i've known a few illegal ones that where running for years, but also know of ones that got found out and had all the gear confiscated.
they where also a lot lower powered than what your thinking of doing.
by memory they lost all the amps, solar panels, batteries etc. we are talking fairly substantial $$$ worth. no one was prosecuted simply because no one owned up to owning the gear.

i was involved many years ago in building one (legally) and had a certain level of power to keep under, transmission range etc. it also had a yearly fee for the license.

high powered ones tend to cause interference for a very long range which is how they get found out.
i've even had video extenders which i've picked up and tracked back from over 2km away.