Class E/D of 40 Meters

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Re: Class E/D of 40 Meters

Postby kf1z » Tue Apr 17, 2012 7:40 am

I just built a 40 meter version of his "100 watt" rig.

All I have to do to go from 75m to 40m is change the low-pass filter.

Works fine, at 75 watts carrier,
The efficiency dropped by about 3-5 % to about 87% on 40m.

Now, this is 2 mosfets and 2 drivers total.
May be that the higher power designs doesn't play as well on 40m.

But this little one is working better than I expected.
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Re: Class E/D of 40 Meters

Postby K9ACT » Tue Apr 17, 2012 9:02 am

kf1z wrote:Now, this is 2 mosfets and 2 drivers total.
May be that the higher power designs doesn't play as well on 40m.


That's interesting. The higher power also implies more than one fet per driver which apparently is a serious problem. This seems to be why I can only get 100W out of the 200W version even with the Class E output.

On the other hand, I also built a 100W version as an exciter for my pair of 8000's rig and was not able to get the results you are getting with it. However, I am able to get about 30W running the whole deck on a single 12V supply which is really nice as an exciter. This also only works with the tuned output.

js
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Re: Class E/D of 40 Meters

Postby kf1z » Tue Apr 17, 2012 8:47 pm

Yes,
Two mosfets ( at least the FQA11N90) on one driver at 40 meters will give trouble.
(as shown by the scope pictures earlier)
for 160m and 75m , one driver per pair of fets is dandy.

But we know that already. It has been said quite often that one driver ( IXDD414) for each FQA11N90 is needed for 40m.

I was actually supprised at how well this one played by simply changing the low-pass filter from a 5mhz cut-off to a 9mhz cut-off.

'Digital' drive, from a square-wave source ( an Si570 based vfo )


Funny though, at 12volts, I am only able to get about 18-20 watts output and about 75+ watts with 24 volts.

This week sometime I plan on converting this rig to 4 mosfets/4 drivers.
Then see how it plays. I expect that the results will be different. :-)

First though, I may use up some type 61 ferrite, and see how things go on 75 and 40m with those cores.. and THEN make the step to 4 devices.
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