I Drew this out from sinus's band 1 tx design probably around 2 years ago now. I built the whole thing but i could never get the dam thing to oscillate. Iv started messing around with electronics again lately and I want to give it another try. Below is the drawing i sent off to the PCB manufactures. I cant for the life of me work out why it does absolutely nothing.

At a glance, C5, C13, C20 and C21 are wrong, they should be connected from end the coils that feeds the transistors to the ground plane and not the supply rail. Show us the circuit diagram to be certain?

Hello XXL

Sorry to hear you have had issues with this design, I have built several of these and they do work! However they do need careful alignment!

From what i can see? Your connections are correct, Except for some 'Symmetry' discrepancies in the oscillator?

I suspect that your design is oscillating? But maybe not at the right frequency?

C5, C13 C20 and C21 as i mentioned are not used, They were originally incorporated to sharpen frequency response @ band 1

C6 is also key in this design! It needs to be adjusted to achieve the relevant frequency range!

Hey Sinus,

What values have you got on RP 1 & RP2?

Thanks. I used a frequency scanner to detect any oscillations. also I don't think it was drawing any power at all. Ill have to build another one as the original one has disappeared. Here is the schematic i re-drew out before remaking the PCB.

@sinus should I put a variable cap on c6 ?

And 10k pots I think I used.

XXL

I built the transmitter on copper clad board late last night and can confirm its oscillating. The only thing is I'm not getting much output power.

Thought I would see 1watt or so but it could be down to L8 but not sure but I was knacked and maybe missed something or forgot to attach a DC link.. Be interesting to see a photo of Sinus version for ideas to see where I went wrong

Tuning range I was able to acheive was 51.6 to 56.7 with the 10k pot you mentioned.

As drawn, it's only going to be good for around 300mW at best. There's not much drive for the 4427, and there's no impedance matching for the 4427 output either.

@gigahertz have you got any pics of your rough build ?

OldskoolPirate wrote: ↑Fri Jan 14, 2022 7:35 pm @gigahertz have you got any pics of your rough build ?

I can do but dont think it would be worth it as its seems It's not 100% wouldnt want to lead someone else up a dead end at the moment.

Albert H wrote: ↑Fri Jan 14, 2022 4:48 pm As drawn, it's only going to be good for around 300mW at best. There's not much drive for the 4427, and there's no impedance matching for the 4427 output either.

Well any advice to matching the 4427 would be helpful

Gigahertz wrote: ↑Fri Jan 14, 2022 4:30 pm XXL

I built the transmitter on copper clad board late last night and can confirm its oscillating. The only thing is I'm not getting much output power.

Thought I would see 1watt or so but it could be down to L8 but not sure but I was knacked and maybe missed something or forgot to attach a DC link.. Be interesting to see a photo of Sinus version for ideas to see where I went wrong

Tuning range I was able to acheive was 51.6 to 56.7 with the 10k pot you mentioned.

Albert H wrote: ↑Fri Jan 14, 2022 4:48 pm As drawn, it's only going to be good for around 300mW at best. There's not much drive for the 4427, and there's no impedance matching for the 4427 output either.

You are both spot on!!

Yes the potentiometers are both 10K panel mount and 50 -56 mhz sound pretty close to what i set mine at!

I doubt you could tune the whole band without adjustment to C6, Also the supply voltage and varicap type will limit the tuning range.

300mW is also the max you will get! The design is very similar to Stephens PLL PRO which is operating in Class A which gives a remarkably flat response across the band! Ideally purposed to drive a small amplifier (Say 5W)
All that aside? It works pretty well alone for short distance transmission.

Here's a better way of using the '4427. It'll give you around 1 Watt, and is pretty flat across the band:
Expand or crush the filter coils as needed to get maximum smoke!

XXL wrote: ↑Fri Jan 14, 2022 2:55 pm Thanks. I used a frequency scanner to detect any oscillations. also I don't think it was drawing any power at all.

@sinus should I put a variable cap on c6 ?

The schematic you done looks pretty accurate to me! Maybe there is a dodgey component somewhere? The whole circuit runs at around 90mA @ 15V so if you aint getting that? There is something wrong

Thinking back, Yes i would have fitted a trimmer cap! it would be so much easier to align!

Albert H wrote: ↑Fri Jan 14, 2022 11:28 pm Here's a better way of using the '4427. It'll give you around 1 Watt, and is pretty flat across the band:

55MHz 1 Watt.png

Expand or crush the filter coils as needed to get maximum smoke!

Excellent Albert!

I may revisit this project, Yet i am planning to design a 'Universal amplifier' which could be utilised alongside this project?

But thats something to ponder on!