[Elecraft] K3 Watt-meter question!

Fri May 29 14:08:34 EDT 2009

The Bird 43 watt meter is one of the few genuine antiques that are still available for use by amateur radio operators.  I am not sure but I would not be surprised if the 43 comes from being designed in 1943.  I know they are advertised in my 1964 ARRL Handbook and have not changed in appearance since.  They are still advertised to be +/- 5% of full scale accurate, the same as the $100 Daiwa.  For our purposes, such as not violating the 5 watt limit for QRP I would venture that the K2 or K3 wattmeter is plenty accurate enough for nearly all our purposes.

Other watt meters such as the Elecraft are probably more accurate and less expensive.  And that is assuming that you buy a factory new Bird 43 rather than one off the Buyer Beware table at a ham fest.

Willis 'Cookie' Cooke 
K5EWJ

--- On Fri, 5/29/09, David Yarnes <w7aqk at cox.net> wrote:

> From: David Yarnes <w7aqk at cox.net>
> Subject: Re: [Elecraft] K3 Watt-meter question!
> To: "Ron D'Eau Claire" <ron at cobi.biz>, elecraft at mailman.qth.net
> Date: Friday, May 29, 2009, 10:01 AM
> Hi All,
> 
> Over the years I've seen Bird Wattmeters for sale at dozens
> 
> of hamfests, as well as over the internet.  Typically
> these 
> are very "pricey", and require all sorts of
> accessories.  I 
> have no doubt that this is, more or less, "the standard" 
> when it comes to wattmeters.  However, my question is
> (and I 
> ask this seriously), just how often am I apt to really need
> 
> something that is so precise?  I have an Elecraft W1,
> and 
> several other wattmeters around the shack, including an OHR
> 
> W-1.  I think the two I specifically mention are
> relatively 
> accurate, although perhaps not quite up to "Bird"
> standards. 
> All wattmeters need to be calibrated, and need to be 
> re-calibrated if you change ranges significantly.  To
> be 
> honest with you, the only time I have any real concern
> about 
> being 99.9% accurate is if I'm crowding the 5 watt limit in
> 
> a contest.  My solution is to just set it for 4.5
> watts, and 
> my conscience is clear!  Otherwise, whether it's 5
> watts vs. 
> 5.2 watts, or 100 watts vs. 101 watts, doesn't seem to make
> 
> much difference.  Should I care????
> 
> Dave W7AQK
> 
> 
> ----- Original Message ----- 
> From: "Ron D'Eau Claire" <ron at cobi.biz>
> To: <elecraft at mailman.qth.net>
> Sent: Friday, May 29, 2009 9:10 AM
> Subject: Re: [Elecraft] K3 Watt-meter question!
> 
> 
> > Jim, you said "supposedly accurate". A Bird wattmeter
> is 
> > accurate only if
> > it's been properly calibrated and handled carefully -
> 
> > especially the
> > "slugs". Bumps and bangs can easily ruin the
> calibration 
> > (That's why all
> > Birds used in critical applications carry calibration
> 
> > stickers showing when
> > it was last checked - normally no less often than 
> > annually - and is
> > carefully handled and stored in approved containers).
> >
> > Let's assume the Bird is recently calibrated and
> treated 
> > kindly:
> >
> > 1) Its calibration is then dependent upon using the
> right 
> > slug. You probably
> > know better, but a surprising number of Bird owners
> think 
> > the frequency
> > range on the slug isn't very important. I believe the
> 
> > proper Bird 43 element
> > for 6 meters is the type A slug spec'd for 25-60 MHz.
> >
> > 2) Are you allowing for the normal error in even a 
> > perfectly-calibrated
> > Bird? That's +/- 5% of *full scale*. IIRC the Bird 6
> meter 
> > slugs have full
> > scale ranges of 25 or 250 watts. If you're measuring
> 100 
> > watts with the 250
> > watt slug, the possible error in a properly-calibrated
> 
> > Bird is +/- 5% of 250
> > watts *anywhere* in the scale. So at 100 watts
> indicated, 
> > the actual power
> > may be anywhere between 87 and 112 watts.
> >
> > That's plenty good enough accuracy for nearly all
> field 
> > use, including for
> > showing that transmitter power levels comply with FCC
> regs 
> > (although when I
> > demonstrate a marine transmitter to FCC engineers,
> it's 
> > *their* Bird that is
> > the final word ;-)
> >
> > Now, the K3 has simply another wattmeter built in, so
> it's 
> > normal for the
> > two wattmeters to disagree by the sum of their
> possible 
> > errors.
> >
> > You asked, "Which one is more accurate?" One of the 
> > Elecraft engineers would
> > have to answer that, but let's assume the K3's built
> in 
> > wattmeter is as good
> > as the Bird. In that case a perfectly calibrated Bird
> on a 
> > perfectly
> > calibrated K3 may disagree by as much as 15 watts at
> 100 
> > watts giving you an
> > indication of anywhere between 85 and 115 watts on the
> 
> > Bird when the K3
> > meter says 100 watts.
> >
> > And don't forget that assumes everything is in perfect
> 
> > calibration. In the
> > real world, it's not unusual to see a greater error.
> >
> > That's why it's not normally considered important for
> 
> > owners to worry about
> > the K3's power calibration. Unless you have some 
> > laboratory standards to
> > compare to each other and to the K3, it's almost 
> > impossible to improve on
> > the default factory settings.
> >
> > Ron AC7AC
> >
> >
> >
> > -----Original Message-----
> >
> > Gentlemen,
> >
> > How accurate is the built-in watt meter indicator in
> the 
> > K3???
> >
> > I'm asking because when I've used a supposed;y
> accurate 
> > "Bird 43" while
> > measuring the K3's various
> > outputs on the various HF bands there seems to be a
> slight 
> > discrepitancy
> > between what the K3 is
> > showing and what's actually there according to the 
> > "BIRD!!!"  I'm
> > particularly interested in the
> > output readings as concerns "6 metres!" Which is MORE
> 
> > ACCURATE???
> >
> > Regards,
> >
> > Jim/nn6ee
> > S/N 2406
> >
> >
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