[Amps] RE : Bird wattmeter

hermans on4kj at skynet.be
Mon May 7 15:40:14 EDT 2007

Does some one knows the difference between "GOLD" watts and "IRON" watts ?
Hams use cheap "IRON" watts.
One finds expensive "GOLD" Watts only in spacecraft or military gear.....

I dont play piano, so please dont shoot!

Jos on4kj

-----Message d'origine-----
De : amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] De la part de Tom W8JI
Envoyé : lundi 7 mai 2007 18:13
À : Harold Mandel; amps at contesting.com
Objet : Re: [Amps] Bird wattmeter


What is missing from all the "information" given below 
(besides the source) is what the calibration reference 
standard is and what its tolerance of that standard is.
Without that key piece of information we really have no idea 
what to expect.

Also let's be fair. The standard Bird 43 Bird is +- 5% full 
scale accuracy. I'm not sure where 10% below came from. 
Salesmanship?  :-) http://www.bird-electronic.com/products/product.aspx?id=81

and of course you can buy +-1% accuracy meters from Bird: http://www.bird-electronic.com/products/product.aspx?id=548

By the way the model 4381 mentioned below is not a lab grade 
instrument. It's really pretty old. I bought my used 4191A's 
for $200 each. :-)

But this all the point. It certainly sounds like the 
Powermaster is a good meter. So is the Bird. Neither one are 
perfect, neither one are "standards" and they both are only 
as good as the standard they are calibrated against when 

Buy either one and you can measure well within whatever is 
important to a Ham or two-way service, so there is no need 
to unfairly exaggerate one while denigrating the other.

73 Tom


> Tom's reply to the PowerMaster wattmeter drove me to
> inquire
> as to the calibration science behind them, and below is 
> the
> listed response:
> " As shown in Table 2, the PowerMaster
> is quite accurate over a range of frequencies, power
> levels and signal types. The test signals include key down 
> CW, CW at a 50% duty cycle (60 WPM dits) and two tone 
> (PEP). The HP microwattmeters themselves are rated at ±5% 
> accuracy, so any variations are well within measurement 
> tolerances.
> During the PEP testing we discovered that the PowerMaster 
> is more accurate for PEP measurements than the Bird 4381 
> computing wattmeter we normally use for comparison.
> The Bird’s spec is ±8% of full scale for PEP measurements. 
> The Lab used its HP microwattmeter and the 14 MHz 2-tone 
> test fixture that we use to check amplifier IMD to verify 
> the measurements. The PowerMaster was pretty much right on 
> the money.”
> Basically we do calibrate it very well, and we have taken
> the steps to remove the uncertainty in our measurements 
> and or reduce them to the +/- 3% level or better. The one 
> thing that we learned early on using the "slug" type line 
> section meters is they are all really pretty bad.  We even 
> went to one company (name withheld) and purchased a 
> "calibrated meter and slugs".
> We found out it was way off, and not ever reproducible in 
> it readings due to temperature issues.  We ended up 
> finding that the 50 couplers we calibrated it in the 
> morning at 65 degrees, were all different when we retested 
> them in the afternoon when the temperature in the building 
> was a higher 75 degrees.  That is when we got serious and 
> purchased a NIST traceable meter, calibrated attenuator, 
> and "Thermocouple probes".  Then we calibrated out our 
> test cables (loss), and other fixture properties.
> We are for sure much more accurate then a Bird, which is 
> 10% of full scale readings.  That’s 500W on a 5KW slug! 
> And on top of that they don't have a temperature spec 
> which can add another 10% error on top of that.
> Tell your friend to try this, put in a 1KW carrier into
> his favorite slug meter and measure the power, now while 
> watching it turn on a hair dryer on low heat, start 
> heating up the slug and body.  It won't take long, you can 
> literally see the meter move.
> Now try it on a PowerMaster!
> Also I might add that the PowerMaster was not designed to
> just be a peak power meter, it is a station monitor with 
> active alarms.  Used properly it will save some big 
> expensive tubes.
> Please feel free to share this with the good folks on the
> AMPS reflector, and if anyone would like to discuss this 
> we will be happy to do so.
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