The AM Forum

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

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

N4LTA

Pat,
Thanks for the reply.
I would be interested in the results of your project when you get it done.
Don W9BHI

Did anything result from this query?

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

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...

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

You could probably use a single IXDD614 driver IC looking into  the primary of a transformer.  They work very well at 16VDC, and 16V at 3 amps is 48 watts input.  Even if the driver is 50% efficient (which it is not - it's better than that on 40 meters) it would probably do the job just fine.

Easy enough to try it out.... and simpler than designing and building (and debugging) a discrete component driver.

Just a thought.........

Steve

Actually resonating the input enables the IXDD to loath along...
On 40M in single band mode you only need appox 9 volts on the IXDD at 450mA ....
You just have to be mindful about the resonant point...
Its a low Q circuit and even with a Q of 5 ( not sure what it is really ) with 10 volt applied to the IXDD that would give 50 volts on the Gates of the FETs blowing them up....
You have to use maths to work it out and go from there....
In reality you will never find resonance you just have to get close to it indicated by rising gate voltage....

Wayne

   
возбудитель класса D 160 метров max9700

модулятор tpa3122

TPA3116D2 far better and $6 from CH on a PCB.

TPA3122

Bit of a random post?

Not sure why you'd quote an inferior part?

It's only 15W whilst the TPA3116D2 is 50W.

J.

Just curious..if you are using a 4-400 why worry about driver efficiency?

Efficiency?

Not sure what you're saying as both parts are class D and 90% efficient.

Post is however somewhat random with 1/2 a schematic.

Btw I do sell 15W a m. transmitters that can be used to drive a valve linear. They have a programmable dds and use the tpa3116d2 as a pwm modulator for a single ended class e stage.

The initial request was from 2019, about 4 years ago. I know for a fact that Don has a motherboard with 3 of JBs little single band transmitters mounted that is being used to drive his 4-400 rig.

Let's put this thread to bed...

John