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How about a good Wattmeter?
Really?
by Bob Hutchinson, N5CNN

The most controversial accessory in Ham radio? Liberal, conservative, accurate, enhanced, embellished, average, peak reading, swinging peak, putt-putt, professional, production standard- what is the real story about SWR/wattmeters?

Hams talk on the air all the time about wattmeters. Old stuff like Heathkit, Nye Viking, Collins, Swan, Drake, etc. New MFJ, Palstar, Vectronics, Autek, Bird, Coaxial Dynamics, Diawa, Kenwood - and on and on. Everybody says theirs is accurate on the frequency that gives the highest reading. What is the real story? I only know about my experiences and conclusions with the inexpensive putt-putt meters and the inexpensive professional meters.

Putt-Putts
I purchased a nice looking Vectronics a while back. It souped up my 1,000 watt amplifier like WOW! I must have previously had some sort of mystery attenuation in the physical length of the coax. Adding the Vectronics to the circuit broke up the mystery attenuation so the amplifier could produce its real power, about 30% more power. No, not really. A call to the Vectronics factory supplied some clarification to the mo-power mystery. They didn't have a lab standard, they use a, as in one, bird wattmeter for calibration of every wattmeter.

I then purchased an MFJ wattmeter. WOW! another mo-power boost of about 25%. I believe this is called inverse attenuation. Hmmmm? Perhaps a few of these products in series could produce the subject for an article about inverse attenuation in an upcoming issue of QST - say April 1 of any year. No, not really.

When I spoke with engineering types about the WOW! mo power, they assured me that one Bird meter was adequate and marketing had nothing to do with how they calibrated  or set the one Bird wattmeter, used as a standard to set other Birds used in production line calibration of putt-putt meters. No error checking for their measuring instrument standard existed.

Well, that's about all there is for a standard when making putt-putt wattmeters. Wattmeters are measuring instruments. Mass producing measuring instruments requires diminishing tolerances down the reproduction line. If a terribly expensive HP instrument up the line is a standard for manufacturing the standards used in production lines to check the Coaxial Dynamics 81000A and Bird model 43 wattmeters and those are used as production line standards to make the putt-putt meters, then, ya-know, all of those accuracy tolerances (in-accuracies) need to be added up.

Accuracy
Yes. If I understand correctly, Coaxial Dynamics and Bird meters in this accuracy classification claim plus or minus 5% of full scale when needle is mid-scale. That's 5% of slug capacity when testing an RF producing device of the proper frequency at half of the slug capacity. For a 2,500 watt slug reading 1,250 watts of RF power the accuracy is plus or minus 125 watts or, one could say, 'accurate within a 250 watt range'. Over the years I have never come across a serious inaccuracy problem with Bird and Coaxial Dynamics meters. In the several years I have used one of each at our bench, in series for average power, they have always read very close.

Review one?
I have used a Palstar active peak reading meter for several months at the test bench. The ARRL tested this WM150 active peak reading meter along with some other brands and published the results in the July QST. Looks good, has 3KW capacity. I ordered ten of these from Palstar for Summer Sweepstakes prizes here.

We received these and I put them out of the way until it was time to ship the first prizes. It is an attractive meter, heavier materials than putt-putt meters I have handled. So, I pulled one to be photographed and reviewed for an article in our review section. At the bench, using the Alpha 87A for power, I could not get a peak reading at any power level. It actually gave a lower reading for peak than for average. Well, trying to find the problem I removed the new meter and hooked up the meter we have been using on the bench in it's place. Worked fine, giving proper peak readings. Tried the new one again. Nope. Back in the box and set aside.

The second meter worked fine, gave proper peak readings at low power. At 1000+ watt power levels it had a high SWR situation that tripped the fault circuit in the 87A repeatedly, indicating a cold solder joint. Set aside.

The third unit demonstrated the same problem as the first. Next morning I tested all three units again. Same result. Three randomly selected units failed to produce satisfactory results. I returned all 10 units to the factory and sent email explaining the situation.

Hmmmmmmmmm, maybe I should call the ARRL and try to get the the one they tested that works and review it. I'm sure it was randomly selected by the factory through the normal ordering process for the ARRL review and test, just like our meters were.

Tough Shitsky
Five days later Paul at Palstar called about the 10 returned meters. He was not exactly pleased-as-punch that we returned his meters. He acknowledged that one had an intermittent RF circuit. A cold solder joint, as we all like to call these mistakes. But, he said the meters did work and would measure RF. He would not say they would measure peak RF, which is the claim of fame for the item.

I told him we like the nice looking product and had hoped to promote it and use 10 in our promotion. Paul said, "As the Russians say, 'tough shitsky'. I don't want to do business with you. You must be incompetent." I said, "Because we couldn't make your meters work?" "Yes."

Please don't jump to any conclusions by his "tough shitsky" or "incompetent" statements as Paul was directing those to me and we, not you, as in you people, right? Well OK then, it's settled, he did not mean you people or we Hams must be incompetent. He only meant you and we, as in me and us, I guess, because I and me and we or us couldn't make the wattmeters order work properly.

Dilemma
Well, the first drawing in our Summer Sweepstakes is looming up in a couple of days and no wattmeters. The Autek Research meter made in Madeira Beach, Fl is used by  lotsa hams that praise it, so I sent email inquiring about buying these for our Sweepstakes. After no response for a few days I re-visited the Autek web and noticed some special conditions under which a customer could attempt to contact them:

2 PM to 5 PM Eastern Time -- Monday, Wednesday and Thursday for technical help.

1 PM to 5 PM Eastern Time -- Tuesday and Friday for technical help
You may also FAX to this same number at these times only.

Call between 1 and 5 PM on Tuesday or Friday, for orders.

Well, I did call in Autek's time slot to inquire about buying 8 or 10 units for our Sweepstakes. The person I spoke with, Bill, displaying his superior human relations and marketing skills said, "I'm not interested "and hung up. Huhhhh? I guess I won't be buying wattmeters from him. How about just buying more Goldline microphones or perhaps a few of the new antique microphones Heil Sound now has available?

Time running out
Manufacturers running out too. Well, instead of giving away 10 putt-putt wattmeters, I'll give away fewer of the "standards". I phoned Coaxial Dynamics in Cleveland, OH to arrange to buy a few of their fine wattmeters, the one with the big white meter face that is so easy to read. Same one we use on the test bench hooked up in series with the Bird model 43. People answered the phone and had good communications skills but didn't say much. They didn't seem to know how to respond to someone that wanted to buy their products. "We'll get back to you on that."

After a few days I re-contacted them. They finally sent an email advising price and availability. Three weeks to ship their Bird 43 equivalent? One more call. I asked about stocking distributors or dealers, "none in the Wireless industry". None? "None."

One last chance
I had bo
ught a couple of Coaxial Dynamics items in the past from Rick at Northern Ohio Amateur Radio Depot - http://www.noard.com, so I called him, he had Coaxial Dynamics wattmeters in stock. Halleluiah! We will have fewer wattmeters for the Sweepstakes but they will be the really good stuff. These measuring instruments are definitely not putt-putt wattmeters. (I decided not to call the factory back and warn them about this Coaxial Dynamics stocking dealer - I don't want Rick to get in any trouble with the factory for having their wattmeters in stock.)

Take a look at the Coaxial Dynamics pictures. It has a graphical big improvement, a big white face taught band meter. We have been using the Coaxial Dynamics in series with a Bird 43 for a couple of years on our test bench. Both are fine meters. Slugs are interchangeable. http://www.coaxial.com/products/81000.htm

Conclusion
If you need a a self esteem boost from the inverse attenuation effect, get one of the inexpensive cross needle, putt-putt SWR/wattmeters. If you want a real power meter for your linear amplifier get a Coaxial Dynamics or Bird. Post an ad or message here at hamradiomarket.com and possibly win a Coaxial Dynamics measuring instrument.

It appears that it is not economically feasible to produce a wattmeter that satisfies all and sell it at the prices demanded by the market today, $80 to $125. Consequently, because it can't really be done, some quality compromises and frustrations occur.

So, how about a good wattmeter? Mo power types are available everywhere. Good, you can get with professional field units from Coaxial Dynamics (best) or Bird (next best). Excellent, high accuracy lab instruments? - Probably not, too expensive.

Bob Hutchinson, N5CNN
President and Founder
Wireless Industry Association
713 467-0077
 

If you would like to publish an article here contact Bob Hutchinson, N5CNN.