The AM Forum

I am in the process of bringing up a new class E rig that covers 160 and 75 meters.  Well, tonight I cobbled together enough of a tank circuit to actually work on 160 meters.

It's absolutely amazing!  The heat sink is cold, the MOSFETs are cold, the tank coil is cold, the output transformers are - yawn - cold - etc.

The rig is incredibly efficient on 160 - WELL over 90 %.  90% is typical for 75 meter operation.

I did try a couple of CQs, but the band was incredibly static ridden.  Someone tried to answer the CQ, but the static was so heavy I couldn't get a word!  Oh well - at least the rig works  :D

Nothing like a cold rig making the antenna hot!


Extending this concept further, now is the time to build a 500 khz E-rig and break the 100% efficiency barrier. You might be able to sell power back to the aether.    ;)



T

Steve wrote;  "Oh well - at least the rig works"


Are you sure??
After all, the rig was stone cold.
Are you sure it was turned on??
How can you be sure that someone answered your CQ??
After all, you claimed you couldn't hear one word through the static.
Steve, you're beginning to worry me.

Fred

Yeah, the rig was definitely on  :D  The antenna was really up - I was on the grey hair net earlier   8)

I could see the guy calling me - in there on the SDR display, and could hear human sounds which were identifiable, but incomprensible  ;)

I'm suspecting the rig is in the 95% efficiency range on 160 meters.  I have other class E rigs on 160 which behave similarly.  Also, there is much less driver power involved on 160 than is needed on 75, and all of the power used by the driver is converted to heat.  Doesn't affect the efficiency numbers, but does contribute to the heat budget.

It would be nice to have this sort of efficiency (95%) on 75 meters, but we need another generation of MOSFET to do that - MOSFETs with much lower gate capacitance to reduce driver requirements, and even faster turn on times.  We'll be there eventually!!  The first MOSFETs I used almost 20 years ago were much slower and had a MUCH higher gate capacitance for the power (the IRFPG50).  Then came the MTP10N100E, which was discontinued.  Then the IXYS IXFH12N100 (very expensive) and now the FQA11N90.

Guess we'll just have to settle with around 90% on 75 meters for now, which still isn't too bad  ;D ;) :) 8)

FB out here in Central Indiana on 160 this morning.  (7 AM EDST) Glad to have a QSO, Steve.  Things faded away by 7:15, but you were 20/9 initially.  73 Jeff

Steve,
I'm not sure if you heard my message last night but when you were talking I heard a static on your signal that sounded like a loose connection or some sort of break down. You were quite strong and I didn't hear it in anyone else.
I think the 11N90s can run at higher power on 160 above 50 watts carrier per FET.
Heck I run almost 25 watts per FET using IRF840s and they are only 500 volt parts rated at 75 watts. I think I lost 3 FETs since '96. Last time I lost one was keying the rig into a broken antenna and didn't notice the VSWR pegged.

I don't know Steve. Could you REALLY tell if the rig was working...

I mean ... no filament glow, no heat ...  no modulation transformer talking back to ya....

And besides I'd never trust one of those MFJ wattmeters you probably use...

Real radios glow in the dark ... and that's how I know its on! hehe

W2WDX

Eh???  I use a home brew wattmeter.  Real radios put out lots of RF and peg "S" meters  ;D ;)

Sounded real good tonight Steve.

Maybe put some neon bulbs on the antenna to make at least something glow.  So how do you keep the coffee warm??

Sounds like a nice rig.  Still trying to figure out a way to put up a 160 antenna here so I can use the boatanchors there.

Orange LEDs mounted near the MOSFETs? It's not right, that kind of rig is not intended to glow.

Actually, all of my rigs do glow!  Either they have illuminated meters, or there are lots of LEDs scattered around various circuits.  I  use lots of LEDs to show the presence of power, etc.

Was on 160 for about 4 hours this evening with the new rig.  So far, so good !!   8)

Didn't some pricey audiophool gadget come out a few years ago, a mic pre-amp IIRC, that had tubes that only ran the filaments, and all the electronics was actually done with FETs?

Yeah, I've heard of at least one like that.  I think it is a Behringer mic preamp.  It has a tube on display in a little front panel window but it doesn't really do anything.  It may be more than just fil. voltage, there may be some v. on the plate but it is so low (I think what is called "starved plate") that the tube is not really functioning the way a real tube mic. preamp should where the tubes have a few hundred v. on the plates.

rob

Thanks Frank - you should have jumped into the QSO  :)  The rig is coming along for sure!  The modulator is interesting - a 2 phase PWM unit.  So, there are two pulse width modulators operating off the same clock, 180 degrees out of phase.  Each is switching at 120kHz.  The outputs of each of the modulators are connected to their own input inductors as part of the output filter network.  The output sides of each of the input inductors are joined together, and there is a common first capacitor.  The remainder of the filter is a standard single channel Butterworth filter.

With this arrangement, the ripple frequency is doubled to 240kHz, just like a full wave rectifier.  This is much easier to filter.  That's the advantage of a 2 phase pulse width modulator, but it is much more complex than a standard single channel PWM.