best first RF project to do

[1608cc]

I know someone who had 20km range with only 20mW

It's possible with highly mounted, high gain antenna. But if you know better... Don't have to believe...

what do you use for the 28v supply.Does it have to be that high?

Why 28V ? I tried 2N3632 and soviet KT's

[Albert H]

Best I've ever achieved was about 18km, fully noise-quietening stereo with 250mW into a 12-element TV Yagi on about 550MHz. That proved to me that UHF links really are the way to go - narrow beam angles from aerials that don't look out of place on any rooftop - and really cheap hardware that can be bought pretty much anywhere - cheap TV tuner-heads and simple transmitter circuits. I used to build a transverter - Band V input, Band II output - directly translated using a PLL oscillator (to avoid buying difficult crystals).

The Dutch 60cm pirates back in the 80s used to get great results at very low power. If you look around the 'net, you can find a lot of circuits and layouts for UHF gear like that.

[Bton-FM]

I was talking about the Varicap supply

[1608cc]

I was talking about the Varicap supply

I used 6.8mH coil and 2n2222 in metal case... But circuit works well on 12V varicap voltage too - only tuning range is narrower and then need to be tuned also by coil

[Culture FM]

I know someone who had 20km range with only 20mW

I think someone needs to lay off what they have been smoking

[1608cc]

Antenna was mounted on Radio broadcast mast, so was very "high"

[Bton-FM]

Antenna was mounted on Radio broadcast mast, so was very "high"

just wondering has anyone smoked wacky tobaccy before climbing a mast?

[Bton-FM]

Am I alright to use reverse bias leds for the varicaps?

[1608cc]

Instead BB105 ok, but to replace BB104 i think it's not good idea. over 30-40pF is needed - just put there a trimm cap

[Bton-FM]

alright i'll grab some from the 'bay

[Albert H]

My little automated, battery-powered 40 Watt weekend devices had a "low power" mode when the programmes were over (or the battery went flat!). The rig would continue to transmit beeps at a few milliwatts into the aerial. This gave the guarantee that it was still there, even if I couldn't hear it from home. When I got close to the site, the "beacon mode" told me that the gear remained where I'd left it. If it had been tampered with in any way, the beacon would change sound or switch off. I'd still return carefully - the RIS mob liked to hide in the bushes to see who came to recover a rig - but I never got caught running my little weekend station.

If you're going to get serious about building gear, you're going to need a good multimeter (NOT a cheap 'n' nasty Chinese one), a dummy load (there are plenty of plans to make your own on the 'net), an SWR bridge (NOT a CB one - they're largely useless at VHF), and a dip meter / absorption wavemeter (the poor man's spectrum analyser). You'll also need a bench power supply - you can get away with a CB one (or a car battery) at first. You'll need a selection of hand tools, and I'd recommend a temperature-controlled soldering iron. You'll also need a drill with a selection of bits and, possibly a small model-maker's drill for drilling PCBs.

I can put some basic circuits up here for you to try. These will give an introduction into what can be achieved using ordinary, cheap components. You might be surprised by some of the parts that can be pushed into RF service. For example: There's the cheap mid-powered "audio" transistor - BFY51 - that can give at least 500mW at VHF and sometimes quite a bit more! Friends of mine in the 'States use IRF540 FETs in their 40 Watt VHF power amplifier design - they buy them for $0.40 each and use a pair in the PA, driven by a single one!

Sometimes, radio pirates have to employ a bit of ingenuity (it was my idea to try the SAA1057 receiver PLL IC for transmitters, for example), and quite a few design innovations have come from clandestine engineering!

[Bton-FM]

@1608cc how critical are the capacitors in the oscillator,will I get away with 15pf?

[1608cc]

They're not critical. Try 10 - 33pF

[Bton-FM]

Ok mate cheers (I’m talking about the 12pf btw)

[Bton-FM]

@albert H have you built your UHF transmitters with only a dip meter?

[Albert H]

Bton

Yes - in the early days! I built a frequency counter that went to 30 MHz, then got an ECL prescaler chip when they became available, and I could then measure frequencies to almost 1 GHz.

[Bton-FM]

If you're going to get serious about building gear, you're going to need a good multimeter (NOT a cheap 'n' nasty Chinese one), a dummy load (there are plenty of plans to make your own on the 'net), an SWR bridge (NOT a CB one - they're largely useless at VHF), and a dip meter / absorption wavemeter (the poor man's spectrum analyser). You'll also need a bench power supply - you can get away with a CB one (or a car battery) at first. You'll need a selection of hand tools, and I'd recommend a temperature-controlled soldering iron. You'll also need a drill with a selection of bits and, possibly a small model-maker's drill for drilling PCBs.

I can put some basic circuits up here for you to try. These will give an introduction into what can be achieved using ordinary, cheap components.

Surely not all of the Chinese multimeters are that bad? What multimeter would you recommend?

Please could you put some of those basic ciruits up here,It would be much appreciated!