VCO transmitter design ?

[SOUNDTX]

Hi fellow necks,

As it's coming up to winter I'm after a project to do in the evenings has anyone got a decent VCO design I could try won't be used into a antenna just want to start with something like the old London band 1 link but for band 2

[Albert H]

Do you mean a VFO-based circuit?

The problem these days is that most receivers use a PLL, and if you're slightly off-frequency, it'll sound horrible. Also, if you don't have the experience and the right components (and a really good frequency counter and lots of patience), you're going to find it difficult to make a frequency-stable oscillator that can handle varying temperatures.

I used to build VFO rigs way back in the 70s, (when receivers were analogue-tuned and had AFC). With lots of effort and component selection, I could get a quarter-frequency oscillator based rig stable to within 20kHz at best.

A PLL is just two cheap chips these days - there's no reason not to use one! If you want to get really minimalist (and don't mind multiplier stages) you can make a PLL with just a PIC on its own!

[yellowbeard]

I get the impression you only want to have a play about, so here is a couple of thing to try:
There is a couple of swanky VCO's here - I am going to have a play myself with the nicom one the next time I am making PCB's:

http://mkmbroadcasting.blogspot.com/search/label/vco

There is a simpler but still decent design here (You have to click the "Transmitters" link in the sidebar):

http://home.deds.nl/~radio102/freddos/default.htm

That one has a simpler PCB, and probably would be easier to make by scoring the design onto a blank piece of copper clad, heating up the areas you want to remove with a soldering iron and peeling them out with a pliers. You could also hack the copper out with a dremel.

[rigmo]

What you think for this old old idea...

[SOUNDTX]

Albert I just want to learn with something dont care if its starts on 87.5 and a quick blow on it and shoots half way up the band. It's not going to be used on air I have the basic tools, frez counter etc. I tried a few designs on electronic DIY and wasn't have much luck just want a design that people can confirm works and parts are fairly easy to get hold of

I used to build VFO rigs way back in the 70s, (when receivers were analogue-tuned and had AFC). With lots of effort and component selection, I could get a quarter-frequency oscillator based rig stable to within 20kHz at best.

Why not share some sketch of designs then ??

[SOUNDTX]

I get the impression you only want to have a play about, so here is a couple of thing to try:
There is a couple of swanky VCO's here - I am going to have a play myself with the nicom one the next time I am making PCB's:

http://mkmbroadcasting.blogspot.com/search/label/vco

There is a simpler but still decent design here (You have to click the "Transmitters" link in the sidebar):

http://home.deds.nl/~radio102/freddos/default.htm

That one has a simpler PCB, and probably would be easier to make by scoring the design onto a blank piece of copper clad, heating up the areas you want to remove with a soldering iron and peeling them out with a pliers. You could also hack the copper out with a dremel.

Thanks YB Ill go check them out

[SOUNDTX]

rigmo is this pll can i just take everything out from orange box ie chip from circuit will it still work cant cleary see transistors are can you confirm them as I search online if i can get em

[SOUNDTX]

went for pira easyFM VCO in the end just trying to find a source of Q2/Q3

[Albert H]

You probably won't find the BFR96 easily in small quantities. You can get a reasonable result by using BF199s for all three transistors. You won't get as much as 400mW (probably 150mW), but it will be enough to go 'round your house and garden!

[Shedbuilt]

For what you’re trying to achieve, I agree on Albert’s approach, but if you wanted something nearer to the BFR96, I think the BFR106 is probably pretty close, and Mouser have those with MOQ 1.

[Albert H]

Try this:

OldVFORig.png

If you use NPO capacitors in the oscillator, and screen the oscillator, you'll find it's reasonably stable! Peaked up, it'll give you a couple of Watts. The oscillator runs at half the output frequency.

[MiXiN]

The old 5W Stentor is pretty good.

I still have it here somewhere, and taking into consideration it's a VCO design, the drift was minimal when it had warmed up.

[SOUNDTX]

You probably won't find the BFR96 easily in small quantities. You can get a reasonable result by using BF199s for all three transistors. You won't get as much as 400mW (probably 150mW), but it will be enough to go 'round your house and garden!

Tried BF199 and made it unstable I did checked pin outs on the 199's and also no output

[SOUNDTX]

The old 5W Stentor is pretty good.

I still have it here somewhere, and taking into consideration it's a VCO design, the drift was minimal when it had warmed up.

Nice one MiXin some bits turned up today made everything upto the BF245 and works fine so far and sounds pretty good the only thing with this design is the MRF237 are well expensive but not after anything with high output anyway.

Can hear it around the house also in the garden.

[MiXiN]

The old 5W Stentor is pretty good.

I still have it here somewhere, and taking into consideration it's a VCO design, the drift was minimal when it had warmed up.

Nice one MiXin some bits turned up today made everything upto the BF245 and works fine so far and sounds pretty good the only thing with this design is the MRF237 are well expensive but not after anything with high output anyway.

Can hear it around the house also in the garden.

A good alternative to the MRF237 is the Mitsubishi 2SC1947, but they're also pretty expensive.

The 2SC1947 and MRF237 sometimes pop up on eBay; I think I picked up around 20 MRF237 from the USA ages ago for around £1.50 a piece.