[Amps] Bird wattmeter

[sccook1 at cox.net]

My watt meter is a dead nutts on the dial.

I talks into the mike-re-phone and puts the fire to the wire.

If ya knows how to tune 'em right -- a par of 500 zulus will flat boogie -- guts, feathers 'n all.

That's old cowboy for: "I like my pretty watt meter."

-S

---- Harold Mandel <hmandel at barantelecom.com> wrote: 
> Dear Tom,
> 
> As my first posting in the above topic mentioned, the
> Bird wattmeter is good for observing trends.
> 
> Tune it up, watch for the most smoke, be happy.
> 
> There ain't any precision, Tom. The average Joe's
> watching to see his amp make 500 or a thousand watts
> when he screams into the mike or holds the key down
> while twiddling the knobs and he could care less
> that the meter's off by 5, 10 or even 20 percent.
> 
> Lookit: Joe has to spend four thousand bucks for
> a Hewlett-Packard or whatever, and even those are
> sloppy. 
> 
> It's a question about the application. I'm happy with
> a Coaxial Dynamics analog using Bird slugs for the
> ham station. It's just toys, and whatever I end up with I end up
> with.
> 
> However, for the salt mine, we gotta use a calorimeter and go through
> all the math to get a Proof-of-Performance report, but that's
> a 250 pound machine that dims the lights when the pump starts.
> 
> Hal 
> 
> -----Original Message-----
> From: Tom W8JI [mailto:w8ji at w8ji.com] 
> Sent: Monday, May 07, 2007 1:13 PM
> To: Harold Mandel; amps at contesting.com
> Subject: Re: [Amps] Bird wattmeter
> 
> Harold,
> 
> 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 calibrated.
> 
> 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.
> > _______________________________________________
> > Amps mailing list
> > Amps at contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> > 
> 
> 
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