Efficiency not what I thought

[k4kyv]

I spent the better part of the day today trying to correct the intermittent arc-over problem in my remote antenna tuner at the base of the tower.  Suspect trash between the plates of one of the air variables.  But I ended up checking the calibration of the DC meters in both homebrew transmitters, checked two rf ammeters against each other, and attempted to get a close estimate of my power output.

I found the old Mirage wattmeter, typical of "ham radio quality" rf output meters, was reading about 33% high on the  high-power scale, compared to the thermocouple rf ammeter working into known accurately calibrated 50-ohm dummy load. Both rf ammeters read the same, so I have a little more confidence that they are accurate, although it is possible that both meters have the same %-age error.  The DC plate voltage meter and plate current meters are right on in the HF-300 rig, as measured with calibrated lab-type reference meters and cross checked with my Fluke DVM, but the plate voltmeter and plate milliammeter in the 8005 rig both read 3-6% low.

I determined that both homebrew rigs, running pushpull triode finals with plug-in coils and swinging link coupling, are  running only 50-60% carrier efficiency, as measured right at the output terminals of the transmitter.  The tube charts give efficiency ratings of about 70% for those tubes.  But then there is the feedline to the tower, and the remote antenna tuner at the base, plus the open wire line up the tower to the antenna.  I'm probably doing well to get 40% efficiency, comparing DC input to the final to the rf input to the radiating antenna.

The Converted Gates BC1-T measured at 70% efficiency, which appears about what it should be, but I haven't yet checked the calibration of the plate voltmeter or plate current meter since I acquired the transmitter, so that efficency reading is suspect.

I'd bet many of us have overly-optimistic estimates of our transmitter power amplifier efficiencies, and our carrier power output, and that's most  likely even more true in the slopbucket community.

Next, to figure out where the rf is going, when comparing the actual rf output to what the tube charts say it is supposed to be.  I had always thought the old swinging link tank circuits were highly efficient, compared to bandswitching tank circuits with all the unused coil turns in the vicinity of the active part of the tank coil.

How many class-E rigs have been measured to actually deliver 90% efficiency to the antenna?

[WA1GFZ]

Don,
Presently my class e 75 meter rig is at 88% and the 160 meter rig is at 90%.
Measure your efficiency at both ends of a band. Better efficiency at the low end means you have too much L in the tank. Better at the high end not enough.

[w3jn]

I built a Class E RF deck (breadboarded and unmudulated) that put out about 700 watts at 93% efficiency, using 100V on the drains.  That was using #8 wire for the output transformer, a hi quality ceramic vacuum variable, and a tank coil made of 1/8 thick by 1/2" copper strapping.  The FETs were mounted on 1/4" copper plates.  Highly impractical but fun to build and play with to see how efficient I could get it.

[KF1Z]

How many class-E rigs have been measured to actually deliver 90% efficiency to the antenna?

My E-rig (QIX design)  runs at 89-90% ... and I have a very messy layout....

However,
Being a class-e amp has no effect on feed-line and antenna losses or efficiencies......


But, it wouldn't be too hard to deliver 90% at the tenna.... I wouldn't think....


Well laid out amplifier at 92% efficiency......
Low-loss feedline at a reasonably short length, and probably NO antenna tuner ......


Let's see....

An amplifier running at 500 watts input, and 460 watts output is 92% efficient....

So, to keep a 90% eff. at the antenna, we could loose no more than 10 watts from transmitter to antenna..

hmmmmmm...........

[K1JJ]

In this day and age of compact class E rigs, I'm waiting for the first extreme efficiency pervert to mount a rig on the top of a tower with the dipole legs coming off the rig's SO-239...

 


T

[Steve - WB3HUZ]

All these so called efficiency numbers measured with a watt meter having a 5-10% error. Yea, right!

[KF1Z]

"In this day and age of compact class E rigs, I'm waiting for the first extreme efficiency pervert to mount a rig on the top of a tower with the dipole legs coming off the rig's SO-239..."

QRP nuts already do that....

Be a fun project ..... wish I had a tower! 

===============================

"All these so called efficiency numbers measured with a watt meter having a 5-10% error. Yea, right!"


Myself, I don't use a wattmeter....yes I have one, but it's really only good for watching needles bounce around.........
Haven't been able to find one worth a darn....(for a price I'm willing to pay...).

I just use the scope...............

[steve_qix]

All these so called efficiency numbers measured with a watt meter having a 5-10% error. Yea, right!

I don't even OWN a wattmeter.  I measure efficiency using a VERIFIED (at a standards lab) dummy load (in other words, I know the EXACT resistance and impedance of the load), and a similarly calibrated oscilloscope.  I measure the RF voltage AT THE DUMMY LOAD with the oscilloscope, and do mathematics to calculate the output power.  There is no other good way to do it because the complex impedance of an antenna (even if very well matched) will cause errors, and of course the accuracy of RF power meters is always in question.  The 'scope into a calibrated load is the only thing I'll really trust.

While we're on the subject, Don, your efficiency MAY be better than you think.  Have you calibrated your current and volt meters?  I have found some to be WAY off (10% off or more), which, when multiplied makes the error even greater.  I always verify (and adjust, if necessary) the calibration of all amp and volt meters using a verified instrument.  Something to check, anyway !!

Regards,

Steve

[Steve - WB3HUZ]

Thanks for proving my point Steve. How many other guys go to such lengths?

[WA1GFZ]

does the term RSS mean anything.
Sorry none of us own real calibrated instruments.
We all own a bunch of old crap that we hope is accurate.
A 10% scope , a 5% load, a 5% ohm meter is what about 12% error. 

[Steve - WB3HUZ]

Which is OK, Frank. After all, who gives a crap if my rig is 90 or 91 percent efficient. It's a matter of a few watts, which make zero difference in the received signal on the other end.

[K1JJ]

Thanks for proving my point Steve. How many other guys go to such lengths?

So admit it...you're saying my Midland SWRS meter is worthless, right?  

So why is it when I thump my mawl down and the mud ducks start quacking, it sez I'm 100% efficient? Caw Mawn.

Flav - Flavor of Love

[WA1GFZ]

yupper, BTW you were putting a nice signal into CT.  on 160 last night.

I just get up tight when I hear wild claims that can't be backed up.
 

[W2VW]

Thanks for proving my point Steve. How many other guys go to such lengths?

So admit it...you're saying my Midland SWRS meter is worthless, right? 

So why is it when I thump my mawl down and the mud ducks start quacking, it sez I'm 100% efficient? Caw Mawn.

Flav - Flavor of Love

Yeah?  Well why R U ducking us in the Super Bowl? Right now your final is 100% efficient and I'm black out.

[WA1GFZ]

Throw away the midland the mud ducks know all and if they are a quacking it means they are a lackin
against the qro.

[W2VW]

Which is OK, Frank. After all, who gives a crap if my rig is 90 or 91 percent efficient. It's a matter of a few watts, which make zero difference in the received signal on the other end.

You'll be sorry when FCC goes back to the old rules.

[Steve - WB3HUZ]

The world is ending tomorrow, so I'm not concerned.

[W2VW]

The world is ending tomorrow, so I'm not concerned.

Have you changed the QST under the birdcage yet? You could be mistaken about tomorrow. The world might not end for another few days.

[Steve - WB3HUZ]

It's already tomorrow in Zulu time. Maybe it's the next day then. No matter what, the ARRL is still evil.

[K1JJ]

Hiram spelled backwards is MARIH.

That's five letters. Hitler had six letters. That's pretty close if ya axe me!

It's scary.

T

[Steve - WB3HUZ]

And if you rearrange the letters in Santa, you get SATAN! 

God Bless Glenn.

[steve_qix]

Thanks for proving my point Steve. How many other guys go to such lengths?

Well, I don't know - probably not many... I got some standard resistances and calibrated meters from the old standards lab at WPI.  With these, I was able to verify [and adjust] the calibration of the measurement instruments I'm using.  I used to work quite a bit with a Professor Howe, who used to run the standards lab.  He showed me how to check and achieve calibration, and it is very interesting, actually.

But, the main reason I did all of this is because as we start approaching and reaching 90 + % efficiency, the errors become a larger and larger part of the equation as the numbers of get closer to 100% (0% loss - which can never happen, of course).

I'm doing experiments using different topologies, circuits, components, etc. and in order for these experiments to be meaningful, there must be a control which can be relied upon.

I suppose if one wanted to be REALLY accurate, you would use the SAME instrument (say, a 'scope) to measure everything - including voltage and current (using a small, precision resistor or a current probe), as well as the RF output into a known load.  I suppose doing things that way would yield the most accurate measure of efficiency, as any errors would appear on both sides of the equation. 
But, I'm not quite *that* anal :-)

Regards,

Steve

[Tom WA3KLR]

Below is a photo of a high efficiency ham shack -  no transmission line losses.

Geez, I hope I don't give Timmy any ideas.  If you feel the urge to step out and take a whiz, that first step is a doozy.

That ain't ladder line, it be 'lec-ric goin' up to the refrigerator and the maul.

[w3jn]

Which is OK, Frank. After all, who gives a crap if my rig is 90 or 91 percent efficient. It's a matter of a few watts, which make zero difference in the received signal on the other end.

Dude, you're killing my bragging rights!  Actually I measured my power with a scope also because my dummy load isn't exactly 50 ohms and it would change resistance as the oil started boiling.  But you're correct, my Fluke 77 has 1.5% accuracy for DC current measurements and the used Tek 2465 has at best 5% accuracy.

Actually I never had the SOB on the air so I could care less about received signal.  It was purely an exercise in futility 

[WA1GFZ]

John,
 You can have the bragging rights of all time best efficiency because all I have is a BS-O-Meter referenced to another BS-O-Meter.