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@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@w8ji.com]
> Sent: Monday, May 07, 2007 1:13 PM
> To: Harold Mandel; amps@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 Â5% 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 Birdâs spec is Â8% of full scale for PEP measurements.
> > The Lab used its HP microwattmeter and the 14 MHz 2-tone test ïxture
> > that we use to check ampliïer IMD to verify the measurements. The
> > PowerMaster was pretty much right on the money.â
> >
> > 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. Thatâs 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@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
>
>
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