KF1Z 's new 75 meter class-E

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Postby frank carcia » Mon Jun 18, 2007 7:35 am

Caps should be in parallel with orange drops that are designed for RF. Disc ceramics or MLCC ceramic caps. Silver mica or mica RF caps.
Wound foil caps have a high ESL. fc
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Postby kf1z » Mon Jun 18, 2007 8:29 am

Alrighty then.....

So, just to clarify......

Are you saying there should be an orange drop along with the others?

Or is it best just to use the ceramics etc... by themselves?


And yet another dumb question.... are the silver micas the 'old buzzardly' flat, brown square caps with 'dot' color codes? I've got a pile of those.


thanks Frank.....
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Postby frank carcia » Mon Jun 18, 2007 11:59 am

You want a broadband DC bypass so use both. The old postage stamps will work if the voltage rating it high enough but you really want to use some ceramics like .001 to .01. I had a jar of .005s so used those.
RF will be on the power leads if you don't do the right low Z bypass.
I had a total of about 2uf which will make up part of the pdm filter output value. You want all your RF to appear across the transformer primary not shared with the dc lead.
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varying the drive duty cycle

Postby kf1z » Wed Jun 20, 2007 1:55 pm

Well, been playing with varying the drive duty cycle today....

Wow, interesting!

First off, it looks like with the vfo/driver scheme I was using, (vfo, flip-flop, ixdd414 drivers).....
That there is some overlap in the square wave between modules....
I'm guessing because of rise and fall times of the drivers/flip-flop combo...??

I'll do more testing and report back......

But, with my new window comparator circuit (thanks Frank) I set the square wave duty cycle to 50%,,,
The way I did that was to set the time one module's drivers are 'on' (meaning the time they JUST start to leave 0 volts.) the other module's drivers are 'off' (just getting TO 0 volts)

My immediate results were that with the old sheme.... my efficiency was about 88% ( 282 watts rf out for 320 w dc in)

And then switch to the 'new' scheme, and got a NICE class-e waveform, and about 93 (+) % eff... (300 watts rf out for the same 320 watts dc in....)


So it appears that the overlap in the old driver set-up may have been causing some problems...
Though I haven't measured very close yet, to determine where the 'turn-on' voltage of the drivers are or anything like that yet......


More testing later!
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Postby frank carcia » Wed Jun 20, 2007 2:39 pm

Cool,
Maybe Steve might be interested in a run of pc boards using the circuit
as part of his kits. The surface mounted parts work well over a solid ground plane. Also chip parts make the leads nice and short.

I'll listen for you on 75 tonight but can't get on. Hopefully my HPSDR breadboard will come to life after 4 late nights of building the breadboard up on a plate, setting up a network, downloading and configurating software and adding an interface board to the computer......and also making room on the bench.
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Postby frank carcia » Thu Jun 21, 2007 9:54 am

BTW I think you should use a cap on the input of the comparator circuit to isolate it from DC offsets on the input.
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Postby kf1z » Thu Jun 28, 2007 6:18 pm

So good so far........

The rig has been ok fine for the past week or so... no problems...

Well, one problem....

Something in the amplifier is acting an awfull lot like a tweeter....

Not sure yet what it is, but the high frequencies of modulation are mechanically vibrating something in there to the point of feeding back through the microphone....

It either the shunt caps, the output transformer or the series inductor....

I think.........

Sounds like it's right on the heatsink... but hard to get my head in there by the coil to find out!!!!

I'll use Steve's suggestion, and use a paper towel tube or something to get in there and see if I ccan poin-point it.
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Postby frank carcia » Sun Jul 01, 2007 7:35 pm

get some plastic tubing so you can probe around 1/4 inch fits in your ear.
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Postby kf1z » Wed Oct 03, 2007 9:49 pm

Just an update, since it's been a while...

Never did figure out for sure what was making the mechanical feedback,
But did find out that if I use a dynamic microphone, OR cut out all high frequencies with an EQ, the noise is not present.....
So, all I've done is cut back on my high end a bit, and will determine the actual culprit some other time....

The rig has been working great....
And I have been on the air with it on a semi-regular basis...

operates nicely from 3700-3945khz....
Seems to retain it's efficiency/output power across that spread.
(with the obvious re-tuning)


Unfortunately though, I still haven't finished the packaging of the amplifier OR the modulator....
But, winter is coming..... maybe, just maybe it'll git done by spring!
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Re: KF1Z 's new 75 meter class-E

Postby KM5TZ » Thu Jan 17, 2008 9:04 pm

Hi Bruce,

I followed this thread... lot of good info.

Please share the values you ended up with in your 2 x 6 rig?

output transformer turns ratio? 1:1 or 1:2?
shunt cap?
tune, load and inductor tank values?

You indicated at one point that you had an overlap problem in the IXD drive signals. Did you have to adjust the duty cycle of the drive to the IXD drivers and if so what worked best?

Efficiency?

Thanks!
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Re: KF1Z 's new 75 meter class-E

Postby kf1z » Thu Jan 17, 2008 11:45 pm

Ok....

Well, Most of that is in these 5 pages "somewhere"... :-)

But, The out-put transformer is 1:1, with each being made up of 6 SB-1024 ferrites. (2 transformers).

Each shunt cap (x2) made up of the copper heatspreaders with kapton insulation/dialectric ) ended up around 1700pf.

The Tuning cap is a 500pf vaccum variable , and the loading cap is a 4x465pf air variable, padded with 2 x 470pf MC micas.

The inductor is approx 5.7uH .

-----

Any time you use a 50% duty cycle ( same time off, as on ) there is overlap on the Mosfets, due to rise and fall time delays.
This can chew into efficiency...

I found that on my 75 meter transmitter that lowering the duty cycle to around 43 to 46 % "on time" , the efficiency went up by a few points....

Right now, I do not have that circuit in the transmitter, but I am in the process of rebuilding the modulator , and the VFO/driver section is next , and this WILL be built in!


With the normal 50% duty cycle though, my transmitter has been running around 89 to 92% efficient ( keep in mind my test equipment is NOT "lab standards"... Just using analog panel meters for voltage/current, and the scope+dummy load for power out.
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Re: KF1Z 's new 75 meter class-E

Postby frank carcia » Fri Jan 18, 2008 11:24 pm

I was looking at the bolt pattern of the spreader and I think any heat may lift the ends. Try this. Measure the shunt C with the heat sink at room temp. Then heat it up and see if it changes. 1:2 transformer will raise your output Z allowing lower cap values. My spreader in the 75 meter rig is smaller and has 11 bolts through it. You only have 4 in the middle. If it isn't stable the value will change with heat.
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Re: KF1Z 's new 75 meter class-E

Postby kf1z » Sat Jan 19, 2008 9:46 am

frank carcia wrote:I was looking at the bolt pattern of the spreader and I think any heat may lift the ends. Try this. Measure the shunt C with the heat sink at room temp. Then heat it up and see if it changes. 1:2 transformer will raise your output Z allowing lower cap values. My spreader in the 75 meter rig is smaller and has 11 bolts through it. You only have 4 in the middle. If it isn't stable the value will change with heat.



I actually tried that Frank when I first built it..... I did a lot of testing...

I was worried bout the caps changing values, but saw "none"...

They don't get warm enough to change much ... usually just warm to the touch...


I tried 1:2 transformer a while ago.... killed my efficiency...
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Re: KF1Z 's new 75 meter class-E

Postby frank carcia » Mon Apr 14, 2008 7:27 am

That loading cap looks like it needs a lower Z connection to ground. Looks like the coax is the only ground termination. I don't see why you mounted in plastic blocks. The frame should have a low Z to ground.
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Re: KF1Z 's new 75 meter class-E

Postby kf1z » Mon Apr 14, 2008 10:16 am

The plastic blocks were part of the cap.....

I wanted to raise the cap up, just so the knob wouldn't be at the bottom of the face.

There's a 2" wide brass strap at the back, bolted to the case.
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