Class E/D of 40 Meters

[K9ACT]

First of all, glad to be back. I finally cracked the code and got a new password.

Since I posted last, I built a 10 Meter Class C transmitter which I am modulating with my QIX sort of PDM modulator and getting the usual great audio reports. I can only run about 30 w carrier but seems to be enough for 10 meters.

Next on my wish list is to get my W1VD Class D rig running of 40 meters.

I have seen tantalizing hints that this is possible but have been unable to find details on the how to or even if.

Is anyone out there doing 40 meters, if so how?

BTW, there are some pics of my Class D and 10 meter rig at the bottom of my radio page.

http://schmidling.com/radio.htm

One more thing, I have moved the Noon Time Forum to 40 meters recently and it has been a smashing success. This is why I am interested in getting one of my solid state rigs there. 7.295 1700Z

Jack K9ACT

[Gilly]

Hi Jack

Doesn't seem that long ago you were on....time goes by quick....

I operate on 40M using a Class E TX / PWM combination....
Has never failed but its low power compared to you guys in the States...
This is a photo during assembly....



Hope the photo comes out showing everything....
I tried to digitally drive but gave up......so I sinewave drive with my only SSB rig Icom IC-735....
Requires appox 12 Watts of power .... and the output is around 110Watts.....
The efficiency is just OK at around 80-85% no more though.....doesn't matter running 100-120Watts really......
The output cores do get hot too after a while....will build another TX maybe in 12 months time as this is OK at the moment...

For your Class D TX I would Sinewave drive first as its easy to do and been all untuned you should not have too many problems....
The Low Pass Filter would have to be different from what you use on 160 / 80M...maybe JAY might give you details if you send him an email.....

Think have answered most of your questions...


Wayne

[K9ACT]

Hi Jack

Doesn't seem that long ago you were on....time goes by quick....

Seems like over a year but I did post on the Chit Chat about my 10 meter project in June and n4lta responded claiming credit for one of the circuits I used. When I tried to get back to him, I was locked out and eventually just gave up until yesterday.

>Hope the photo comes out showing everything....

Very fine but do you have a schematic? I do not understand what you mean by sinwave drive. I was under the impression that it had to be digital. Is this something I could do with my tube driver (6AG7/6146) that I use for my 810 rig.

>The Low Pass Filter would have to be different from what you use on 160 / 80M...maybe JAY might give you details if you send him an email.....

Actually, I emailed Jay a couple of weeks ago but have not heard from him yet.

Thanks for the info,

Jack

[Gilly]

Hi Jack

The design is from Floyd WA2WVL....I have the design somewhere here.....
I think your using 2 FETs while I used 4 FETs so the input transformers need a higher turns ratio say 4-5 : 1.........
They have to be fed out of phase too ... have a look at my photo !......
Yes you can sinewave drive from a Transceiver....something that has a variable output from 1 watt to 100 Watts would be fine....
A voltage input ( drive level ) of 24 Volts PEP is about right......the level can be varied a bit for maximum output efficiency etc:
The output Balun takes a bit of building ..... I used a brass rod as the primary and insulated wire though the brass rod for the secondary. Can send you a better photo if that helps.....
Probably though I would convert from Class D to Class E....the coil is small for 40M and by the looks of things you probably have TX type capacitors in your shack that would be suitable.....

Thats about it...


Wayne

[K9ACT]

Hi Jack

The design is from Floyd WA2WVL....I have the design somewhere here.....

I can't find anything on him or it and I am not smart enough to understand you photo without a schematic.

>I think your using 2 FETs while I used 4 FETs so the input transformers need a higher turns ratio say 4-5 : 1.........
They have to be fed out of phase too ... have a look at my photo !......

I am using 4 11n90's. Is this what you are using? It looks like your photo is chopped off at the right. Is there more to it?

>The output Balun takes a bit of building ..... I used a brass rod as the primary and insulated wire though the brass rod for the secondary. Can send you a better photo if that helps.....

How did you come up with that? Another photo would be great.




Probably though I would convert from Class D to Class E....the coil is small for 40M and by the looks of things you probably have TX type capacitors in your shack that would be suitable.....

What would be the reason to go E?

js

[K9ACT]

I just saved your photo to a file and now can see the whole thing. Still don't understand it but at least it is all there.

js

[Gilly]

Hi Jack

Floyd had a circuit on this forum but I don't think its available any more...
I found the circuit so can email through to you with other photos if you like....
I did change mine though....the output balun someone cannot remember who now gave me the idea....
As for the input transformers most people used FB1020-43 beads.
I found these too large and unless you cable tied them down any movement changed the SWR and drive level making the TX unreliable.....
So I just played around...found some ferrite cores at the local electronic store.....

This worked well...



and eventually settled using cores in the photo on the other posting....

OK too on using 4 FETs ... the turns ratio it that case is 3:1

As for Class E over Class D I just feel you have more control over things so in your case just stick to Class D...
If you need help with the Output Filter just let me know


Wayne

[K9ACT]

I don't know how to relate the two photos. Please send whatever you have especially a schematic. Then we can discuss it more intelligently.

Send to k9act@schmidling.com

If possible, just send two pics with each email or it will boggle my very slow connection.

Thanks,

js

[kf1z]

It isn't any hard task to use an online calculator for the low-pass filter for 40 meter class-D

Plug in the values that are given, and you'll see the constants, then plug in the 40 meter info, and you have it,


really, same as any output filter....

All you need to know is the input and output impedance, the cut-off frequency, the number of elements and you've got it.


Bruce
kf1z

[kf1z]

Jack,

Drive for a Class-E or Class-D transmitter does not have to be digital.

The only requirement is to drive the RF transistor past saturation, out of the linear region.

Sine wave drive works, but more care must be taken to guard against parasitic oscillation.

IXDD414 driver will drive a single FQA11N90 on 40 meters just fine and dandy.

All else is simply scaled to 40 meters from 160 or 75m.
( output filter, Shunt capacitors ( class-E) , and the output transformer "balancing" capacitor in the case of Class-D)

Bruce
kf1z

[kf1z]

Jack,

Drive for a Class-E or Class-D transmitter does not have to be digital.

The only requirement is to drive the RF transistor past saturation, out of the linear region.

Sine wave drive works, but more care must be taken to guard against parasitic oscillation.

IXDD414 driver will drive a single FQA11N90 on 40 meters just fine and dandy.

All else is simply scaled to 40 meters from 160 or 75m.
( output filter, Shunt capacitors ( class-E) , and the output transformer "balancing" capacitor in the case of Class-D)

Bruce
kf1z

[K9ACT]

It isn't any hard task to use an online calculator for the low-pass filter for 40 meter class-D

Hi Bruce,

I never got that far as I was under the delusion that you can't do this on 40 meters.

I tried running my VD Class D on 40 just looking at the output with no filter and got no output and no drain current and the drivers were pulling 5 A so I thought I was confirming my delusion.

Turns out I had mis-wired the drain supply and there was no voltage there.

So this brings me back to getting this working on 40 instead of a new project.

You say one driver will drive one 11N90 but will it drive two as I am doing on 80 meters?

Is it expected that the drivers would pull more than twice the current on 40?

Thanks,

js

[kf1z]

The IXDD414 will ONLY drive one fqa11n90 on 40 meters... not good with 2.


Not sure about twice the driver current on 40, than on 75m, but yes, significantly more.

[K9ACT]

The IXDD414 will ONLY drive one fqa11n90 on 40 meters... not good with 2.

Darn! That would be too easy.

Where I am at now is about 20W out with about 70W in.

I get 40W without the filter so I guess I need some help on that.

For the T filter I came up with L=1.3 uH and C=471 pf but it's not clear what I am supposed to use for the cutoff freq and I presume 50 Ohms is the Z. I juggled things around to make the 80 filter come out close to the one described by W1VD and came up with the above numbers.

I guess the question is, what do I use for cut off freq in this Butterworth calculator. The variables are Cutoff, Zo and number of components (3) in this cased.

js

[Gilly]

Hi Jack and Bruce...

I will post a picture of the waveform of a IXDD414 driving a 11N90 FET at 40M just for the sake of it......
Just have to find my 7Mhz crystal though....
I could be wrong here but I don't think Jay's output filter is a Butterworth design....? its some unusual design of his so if you check his component valves using a butterworth filter calculator they will be different....
But you could still use a butterworth design anyway....and the output fets being pushpull the design would not be all that critical.....I suppose.....


Wayne
VK3ALK