[Elecraft] Adjustment for more output power for K2

[Larry Phipps]

Measuring power is not as easy as one might think. The lab where I had 
my HP-436A calibrated told me they thought it would be safe to advertise 
an LP-100 calibrated against it at 0.1 dB accuracy. That works out to 
~2.3%. If I recall correctly, their reference had a certificate that 
said something between 0.01 and 0.02 dB compared to an NIST primary 
reference. They have their equipment re-certified once a year, but at 
those levels, even temperature and humidity can make a difference.

I don't feel comfortable claiming a 2% accuracy and so rate the LP-100 
at 5%, but several owners with access to NIST traceable lab 
instrumentation have verified a 2-3% accuracy.

One thing to remember about the LP-100 is that I calibrate the meter at 
the center of each band to within 0.1% of my HP-436A, and of course the 
correction values for each band are saved and recalled based on the 
reading of the internal frequency counter in the meter. Because of this, 
the relative band-to-band error of the LP-100 should be very close to 
that of the HP-436A.

73,
Larry N8LP



Siu Johnny wrote:
> Hi Don,
>
> Thanks a million.  You have just hit the nail on its head.  Yes, 
> correct, the difference in power output readings between K2 and LP100 
> is within 10%. It is wonderful to have you in this reflector. Bearing 
> in mind, I am not a radio man by profession and can easily head to the 
> wrong direction.
>
> Could please advise how I can use antenna analyser to achieve better 
> power output with the LPF?  Do you mean feeding the output of the 
> antenna analyser to the antenna jack with W1 terminated with 50 ohm load?
>
> Thanks a lot indeed. Playing with K2 is really another kind of fun 
> which cannot be obtained from factory made transceivers.  Regrettably, 
> there are not many hams in Hong Kong exploring this area.
>
> TNX & 73,
>
> Johnny Siu VR2XMC
>
>
>
> From: "Don Wilhelm" <w3fpr at earthlink.net>
> Reply-To: <w3fpr at arrl.net>
> To: "Siu Johnny" <jcpsiu at hotmail.com>,<elecraft at mailman.qth.net>
> Subject: RE: [Elecraft] KAT2 power calibration
> Date: Tue, 7 Nov 2006 00:09:59 -0500
>
> Johnny,
>
> Things are not always perfect, so you can expect some variation.
> The 1N5711s in the KAT2 are not entirely frequency independent,  and the
> detector in the LP100 is similarly frequency dependent. The exact results
> will vary with the particular 1N5711 diode that is in your KAT2 and the
> particular diode detector in your LP100.
>
> OTOH, you have to believe something.  Take into consideration the 
> potential
> errors of everything in the calibration chain:
> My previous emails with Larry have revealed that he uses an HP836A for 
> his
> reference - consider that the HP836A is good to 2% (that is optimistic) -
> then, your LP100 may be good to 5% of the actual reading, and the KAT2 
> may
> also be good to 5% of the actual reading, the total window for error is
> 12% - you said only that the KAT2 reading is higher than that of the 
> LP100,
> but you failed to say by how much.  I would expect that it should be well
> within my optimistic error of 12% (1.2 watts at a 10 watt level).
>
> This is a lesson in calibration practices - every potential error in the
> calibration system must be accounted for.  If you want to obtain 
> labratory
> standard practice, the standard should be 10 times more accurate than the
> device being calibrated.  I doubt you will find that level acceptable 
> in any
> wattmeters available today.  You may just have to be satisfied with some
> reasonable discrepancy.  Alas, it is not a perfect world, especially 
> not in
> the wattmeter arena.
>
> All in all, I have found that the KAT2 agrees with my 100 MHz 'scope (and
> 150 MHz probes) and and along woth my precision dummy loads I can 
> achieve a
> KAT2 calibration within 5% across all bands.  I believe the LP100 is 
> rated
> at 5% too.  So if you are no more than 10% different between the two, you
> are doing pretty good.  That is a whole lot better than the 'run of mill'
> amateur grade wattmeter which is speced at 20% of full scale.
>
> Your output power 'tweaking' is not related to the power output 
> reported by
> the KAT2, but I am glad that you achieved good results by using Gary's
> advice.  If you have an antenna analyzer, you can 'tweak' the LPF for the
> best SWR across the bands and obtain even better results than those 
> obtained
> by 'tweaking' for maximun power output.  If you attempt that, be certain
> that you terminate the LPF in 50 ohms - which means removing the W1 
> jumper
> and inserting a 50 ohm load (this can be done easily at the K160RX 
> header if
> you have that option installed).
>
> 73,
> Don W3FPR
>
> _________________________________________________________________
> ÓëÁª»úµÄÅóÓѽøÐн»Á÷£¬ÇëʹÓà Live Messenger; 
> http://get.live.com/messenger/overview
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>
>