Your 2020 builds!

[Bton-FM]

Here's what I've been working on this recently :

1wattboard.jpg

Probably nothing you haven't seen before apart from the Microcontroller, which like a few most of the RF transistors is mounted underneath the board. It's an 8 Pin SMT chip with my own firmware I wrote for it to control the TSA5511. I could make add buttons to tune up and down the band (I've written another code to do that) but I'd rather not give thieves the opportunity to retune my kit!

The oscillator and driver stage is similar to a design Albert posted on here a while ago but I've used more modern transistors that are cheaper. The aim of this was to make a board that is as cheap as possible, so its not a big deal when it inevitably gets taken. So far it's doing a watt near the top of the band at 13.8V supply, perfect for driving an MRF101.

I'm going to do a second revision of this as there's a few things I need to add, like a different varicap for modulation, OLPD, and a 33V tuning supply so that it can tune right the way across the band without stretching the coil.

[sinus trouble]

Excellent work Rev and Bton!

Its great to see ideas and designs from others!

[Bton-FM]

Hi Albert,

That isn't the circuit I've actually used, just an example (from the interweb) of the push-pull arrangement. I used a centre tapped toroid-wound inductor for the oscillator with a secondary winding to feed the synthesiser. The 2f is taken off from the emitters which are joined together and then go through an inductor to ground. And I use PNP transistors in the oscillator so the coil is at ground rather than at +VCC. 2SA1206 are nice devices for that.

Yes, you have to use 3 x 74HC4020 - one to divide the reference crystal down, one as a 'prescaler' and one as the divide-by-N, the only nice thing is that they're all the same chip, though on my Band-I RX I've managed to get away with just two as the PLL reference frequency doesn't need to be so low. I've got a second synth in development which is on-frequency rather than f/2 using MB501 pre-scalers and the old workhorse MC145151, which together should get to at least 600 MHz. Will be interesting to see how that prototype fairs and how many resistors I've missed off that design...

I'm using traditional BB809 varicaps for a decent frequency range on the VCO and modulation is applied directly to them.

Rev

Are you using the usual CA3089 IF strip for you Band I receiver ?

[Gigahertz]

Nice work Rev and Bton-FM!

Anyone working on anything?

Decided to sent the Corsair into "Pimp my rig" and they done a nice custom job

New face and heatsink with a small fan.......

[reverend]

Are you using the usual CA3089 IF strip for you Band I receiver ?

I am, yes. Looked at some other options but as I have a cupboard full of old CA3089 chips, it seemed silly to buy something new.

Rev

[Bton-FM]

Are you using the usual CA3089 IF strip for you Band I receiver ?

I am, yes. Looked at some other options but as I have a cupboard full of old CA3089 chips, it seemed silly to buy something new.

Rev

It seems like the way to go even after all these years.

The only other affordable options I found were made by a company called ‘New Japan Radio’.The lead time on them was about 5 months!

[reverend]

I think you're referring to the NJW2311 which is a nice chip but as you say, difficult to get hold of. There's the NE/SA 605 which you can easily get for about a quid each. Once my supply of CA3089's is exhausted I might start looking around for something new.

Rev

[Bton-FM]

I was referring to the NJM14570 which can be had for about 40 pence. I might look into them when I can no longer find microwave tuners.

[reverend]

And here is the updated version. Runs nice and cool at around 600mW with a 13V supply (though I think there's more to be squeezed out of it somehow - probably the matching after the 2N4427). Thinking of offering some kits of this, probably on eBay.

Rev

[Albert H]

I recognise that synthesiser!

[sinus trouble]

Nice work Mr Reverend!

VERY Neat SMD soldering too!

Whats the population of components on the underside?

[reverend]

Hi Sinus,

There are no components on the underside - everything's on top! The SMD's are pre-mounted (JLCPCB) which reduces some of the laboriousness of the soldering. Took me about an hour to assemble and worked first time on switch-on!

Rev

[sinus trouble]

Hi Sinus,

There are no components on the underside - everything's on top! The SMD's are pre-mounted (JLCPCB) which reduces some of the laboriousness of the soldering. Took me about an hour to assemble and worked first time on switch-on!

Rev

Sounds good! Especially if you are looking to sell on Peebay! I once sold a few items on there and generally encountered problems with users, I guess i just had a bad experience? Anyways i think they will sell quite well!

I like your oscillator configuration despite the bad reputation of previous designs as power oscillators.
As a small signal source? It has great potential!

The logic side is also Nice N Neat!

[reverend]

Thanks for the nice comments Sinus.

Yes, I guess the problem with Fleabay is that you don't know what kind of wally might buy it and how bad their construction techniques might be. Don't want to spend hours troubleshooting other people's awful soldering. You would hope that anyone buying a kit like that would have some knowledge but then again, maybe not. Might offer just a couple to start with and see how it goes. Alternatively, now I have the design right, I could update the board with loads more SMD and build them myself and offer them as completed units. Might be safer?

Rev

[LeeCavanagh]

I could update the board with loads more SMD and build them myself and offer them as completed units. Might be safer?
Rev

You could do both, there will be those people who cant be bother to build, even if capable, and those who cant build, and those who want to save a few pennies by buying the kit form, i guess it comes down to how much you value the time it takes to make them, and how much that will add to the overall price, I’m sure you will find the sweet spot without breaking the bank... good luck, looks a good layout, how does it look on a scope when completed? Is it low spurious?

[reverend]

Thanks for the ideas Lee, appreciate that there may be those who enjoy the building part of a kit (and know what they're doing). I'll probably do both then... Kits coming soon.

As for the output, everything's at least 60 dB below the carrier worst case. Still looking to see if I can get the f/2 down even lower, but put through any kind of power amp (which typically post a loss rather than a gain around 50 MHz), it's far down in the noise. When connected to a (resonant) antenna it's gone.

Rev

[Premier-Carousel]

You could do what both Heathkit, Maplin, and even SSTRAN used to do. Accept non working kits for diagnosis and remedial, charging an hourly rate.....

[Albert H]

Stephen used to do that at NRG. It was usually best just to supply a new, completed board, and put the one that was returned into the junk pile. You wouldn't believe the state of some of the boards - randomly fitted ICs, often the wrong way 'round. Components with legs broken off. The occasional board that had bee powered directly off the mains.....

We used to have competitions to see who could find the junk pile board with the most errors!

[Premier-Carousel]

Ah yes, I was a frequent visitor to Moss Towers, and saw many such creations. Normally while filling my face with one of Christine's rather splendid curries.....

[reverend]

Have put a few kits on Fleabay if anyone is interested... https://www.ebay.co.uk/itm/224360099323

Rev