best first RF project to do

Bton-FM · Post by **Bton-FM** » Thu Feb 27, 2020 8:29 pm

What would you lot say the best first RF project is assuming you already have basic electronics knowledge?

1608cc · Post by **1608cc** » Thu Feb 27, 2020 8:38 pm

Better sound quality and more stable than one transistor bugs. Very hard to make it not working... It was my first serious RF project

Bton-FM · Post by **Bton-FM** » Thu Feb 27, 2020 8:46 pm

What transistors did you use, I have BF199's here do you reckon they will work?

1608cc · Post by **1608cc** » Thu Feb 27, 2020 8:56 pm

I used BF199 (BF240, BF494 will suit too). It works with many low power RF transistors. There's some modifications thats makes this circuit working better. This is Seiler oscillator. It's very universal - you can widely experiment with components values. Coil is 5 turns on 5mm dia.

XXL · Post by **XXL** » Thu Feb 27, 2020 9:00 pm

Probably just make an oscillator on a selected frequency would be a good start. That’s what I did.

Bton-FM · Post by **Bton-FM** » Thu Feb 27, 2020 9:01 pm

Did you build this on copper clad with islands?

1608cc · Post by **1608cc** » Thu Feb 27, 2020 9:03 pm

Bton-FM wrote: ↑Thu Feb 27, 2020 9:01 pm Did you build this on copper clad with islands?

exactly

XXL wrote: ↑Thu Feb 27, 2020 9:00 pm Probably just make an oscillator on a selected frequency would be a good start. That’s what I did.

On my schematic there's just a simple oscillator

. Only two things more : modulation circuit on BB105 varicap - to allow frequency changes by audio signal, and buffer to improve frequency stability - antenna connection don't change the freq.

Bton-FM · Post by **Bton-FM** » Thu Feb 27, 2020 9:08 pm

also have you added a pll to this before?

1608cc · Post by **1608cc** » Thu Feb 27, 2020 9:12 pm

Yes - based on SAA1057. You must throw out 100k trimm and connect there PLL voltage output. The reference signal You can take form emitter of first transistor.

Bton-FM · Post by **Bton-FM** » Thu Feb 27, 2020 9:14 pm

did you use the pira one?

1608cc · Post by **1608cc** » Thu Feb 27, 2020 9:21 pm

Not completely - Hardware is from pira (with small changes), and soft (with some changes too) form : http://www.easy-soft.net.pl/artykuly/ba ... ci-saa1057

Software is your choice - it easy to write it yourself using basic or c.

Bton-FM · Post by **Bton-FM** » Thu Feb 27, 2020 9:24 pm

I know Fcuk all about coding haha

1608cc · Post by **1608cc** » Thu Feb 27, 2020 9:30 pm

well, there are some old programs that allow to control SAA1057 and TSA5511 from PC. But if I remember they operate on archaic LPT port

Bton-FM · Post by **Bton-FM** » Thu Feb 27, 2020 9:32 pm

would you say this could be worked into something fit for broadcast or not?

1608cc · Post by **1608cc** » Thu Feb 27, 2020 9:38 pm

This little two stages circuit ? I think it has too low power

But if you marry it with PLL and amplifier stage - of course

But, even with small power with high mounted antenna there's possible to cover big area - I know someone who had 20km range with only 20mW

Bton-FM · Post by **Bton-FM** » Fri Feb 28, 2020 7:35 am

Yeah I meant with an amplifier

Bton-FM · Post by **Bton-FM** » Fri Feb 28, 2020 4:04 pm

how much power does this output?

1608cc · Post by **1608cc** » Fri Feb 28, 2020 4:54 pm

A few mW (i guess <10mW) - output power can be adjusted by change of oscillator emitter resistor. If You want to add next stages, better idea is get rid off the buffer stage and put there high gain amplifier on dual gate mosfet or BFR91/96.

Bton-FM · Post by **Bton-FM** » Sun Mar 01, 2020 9:35 pm

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

teckniqs · Post by **teckniqs** » Sun Mar 01, 2020 9:38 pm

1608cc wrote: ↑Thu Feb 27, 2020 9:38 pm I know someone who had 20km range with only 20mW

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