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160, 80 and 40 meter class D exciter




 
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Author Topic: 160, 80 and 40 meter class D exciter  (Read 2956 times)
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W9BHI
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« on: December 10, 2019, 05:36:56 PM »

Hello all,
I am looking for someone that could help me design a class D exciter that could produce around 25 watts of unmodulated carrier to drive a pair of 4-400a's.
There would be no need for an audio modulator.
I would like to make it band switched for 160, 80 and 40 meters.
I would be using a DDS vfo with a square wave output.
Any takers?
Thanks,
Don W9BHI
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N4LTA
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« Reply #1 on: December 12, 2019, 01:25:08 PM »

I think there are a few people here who can give you some guidance, but designing would require testing a prototype and some experimenting.

If I was going to do it myself, I would use a couple of GaN Mosfets in a  configuration like Nigel uses with a modern low side driver ICs. You could also use a half bridge with transformer gate drive.

At 100 watts  - you could use relays to switch in the required output filters for each band.

I am in the middle of testing this type of class D circuit now. I have not completed my project yet.

Pat Bunn

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W9BHI
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« Reply #2 on: December 14, 2019, 10:36:40 AM »

Pat,
Thanks for the reply.
I would be interested in the results of your project when you get it done.
Don W9BHI
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w9jsw
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« Reply #3 on: November 22, 2021, 07:19:22 AM »

Did anything result from this query?
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W9BHI
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« Reply #4 on: November 22, 2021, 01:47:58 PM »

Not really, Pat had the fire and I know he had bigger fish to fry than class D projects.
I would like to see if someone is interested in designing (building) 500 watt carrier class D RF decks for 40, 80 and 160 meters.
I would be happy to fund the design and for having some blank circuit boards made.
Thanks,
Don W9BHI
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M0VRF
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« Reply #5 on: November 22, 2021, 03:47:06 PM »

I've got single band class E 20W designs for each band and can't see any design covering all 3 bands with a single Tx? Surely the only way to do that is to use the old way and use a linear?

Re the 500W version, this is something I'm working on but wont be giving any boards away only built and tested units at some cost. Not sure what you're expecting to pay but I offered some KW PWM modulators on here a while ago and got offers of $30 including postage so not sure what to expect??? They'll be SMT which most folk on here don't seem to like but has been the norm for 30+ years!

8 x C3M CREE SiC FETs and either the W1VD type or something akin to Steve's original design. Got PCBs for both on order, so some experimenting to do!

I've got a 4 FET 100W design I've been selling for years and have lots of PCBs for those which I would be happy to sell at a 'reasonable' price, again they're SMT but can build up.

Not a fan of VFOs so the 100W has 64 (or 16/32) channels , the 20W I mentioned earlier are either single channel with a pre programmed Cardinal CPP oscillator or uses a programmable AD9833 DDS via a USB adapter to any in band frequency.

Products are aimed at broadcasting rather than Ham use and used as backup TXs by AM stations + a few in AUS on 5MHz.

You could however bypass my Freq gen and just drive from your vfo? The 20W versions would be ideal as I modulate them to 100W+ pep so if you just want 25W drivers just use 3 separate TXs.

Just PM if you want any circuit details/pics etc..

That's it...
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vk3alk
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« Reply #6 on: November 24, 2021, 04:33:39 PM »

Hi Don..

To make a 3 bander is quite simple and easy to do but you just have to know a few things…..
To keep it short for reliability and simplicity the best TX modules to use are H Bridge design….
On 160M and 80M its very easy to make a dual bander as at those frequencies these modules act as switch only and resonances are a long way away…..
40M is a little more difficult due to the lack of squarewaves....
To overcome this you use the gate capacitance of the FETs and add a bit of inductance to assist the driver in developing enough voltage swing...
On my posting of a 40M transmitter you can see things although now the output transformer is different….…
This TX works on 160M 80M and 40M without any extra components added during band switching ….
Have tested the transmitter on all bands to 300 watts only which is the limit of my bench test power supply …… efficiencies are well into the 90% region….
Of cause the choice of FET is critical to all this ....  since this semiconductor business has happened they are not being manufactured for another 18 months…..

Wayne
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