Re: K2 Power Callibration
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From: "Don Wilhelm" <[hidden email]>
Subject: RE: [Elecraft] K2 Power Calibration To: "Cathy James" <[hidden email]>, <[hidden email]> Message-ID: <[hidden email]> Content-Type: text/plain; charset="iso-8859-1" ""Adding either the KAT2, KPA100 or KAT100 options will include a proper wattmeter in the K2 system and the display will indicate the proper power (if the wattmeter is calibrated properly), but the basic K2 uses only an RF Probe type detector and reports the 'power' based on the assumption that the load is 50 ohms non-reactive. Try a dummy load and if you see a major discrepancy, you can blame the interconnecting coax or the wattmeter - the basic K2 power indication is quite correct when the laod is a 50 ohm proper dummy load. 73, Don W3FPR"" Don, I attribute a fair amount of the convulsions involved in getting my K2 callibrated to an inaccurate wattmeter. It came on the manual tuner I bought. I fed a 50 ohm dummy load through the tuner with it set to "bypass" I got readings on the wattmeter much higher than those that I was actually putting out as we ascertained when we later used a good wattmeter. I think this speaks somewhat to assumptions about what the k2 builder will already have or purchase for the project. I already had a good DMM which agrees in the areas we checked with a really good Fluke - no fluke apparently. The manual for the KPA100 suggest you may have problems if you callibrate with a bad wattmeter. Soooooo, if you can use the rf probe which you build with the k2 kit and a DMM, why not suggest this as an alternative method to anyone who suspects his wattmeter is not good or (gasp) doesn't have one? Or am I all confused. Incidently 5087 works so well, I can't believe the range I get both in and out on ssb 20, 40 & 80- meters with just the 23 foot whip. 73, John KI4NGH _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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John,
One must be careful not to zap the diode in the RF Probe - so measuring directly across the dummy load is good only up to 20 watts or so. A 'scope with a proper probe will handle the full 100 watts of the KPA100 easily. Builders may not have a known good 'scope, and the RF Probe method must be used with some intelligence - many folks do not know the accuracy of their dummy load at the frequency of operation - and both the 'scope and RF Probe methods are highly dependent on knowing the accuracy of the dummy load - it must be entirely resistive for accurate results. Yes, I feel that my 'scope and 1% 50 ohm dummy load (checked for both R and X on several antenna analyzers) will provide better than 5% accuracy for any wattmeter that I calibrate by that method. Of course, I can do a more accurate job at 30 watts or lower because I can read the voltage differences on my 'scope face with greater precision (the 10 volts per division scale) and at higher power, I end up at the 20 or 50 volts per division scale and the interpolation becomes more coarse. 73, Don W3FPR > > I think this speaks somewhat to assumptions about what the k2 builder > will already have or purchase for the project. I already had a good > DMM which agrees in the areas we checked with a really good Fluke - no > fluke apparently. The manual for the KPA100 suggest you may have > problems if you callibrate with a bad wattmeter. Soooooo, if you can > use the rf probe which you build with the k2 kit and a DMM, why not > suggest this as an alternative method to anyone who suspects his > wattmeter is not good or (gasp) doesn't have one? Or am I all confused. > > Incidently 5087 works so well, I can't believe the range I get both in > and out on ssb 20, 40 & 80- meters with just the 23 foot whip. 73, > John KI4NGH > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > 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 > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.375 / Virus Database: 267.15.12/266 - Release Date: 2/21/2006 > > _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Hi
I will throw my two cents worth. I agree with everything Don is saying here however there are several other ways to get a reasonably accurate power out measurement on a K2 or K2/100. The simplest and maybe least expensive is the Elecraft DL1 dummy load kit. This dummy load will handle 20 watts and includes a built in RF probe to measure the power out. You just connect a voltmeter to the probe out test points and use the included graph to convert the DC voltage to watts. Everyone building a K2 should have one of these simple dummy loads/RF indicator kits for calibration and tune up. Another method is to use the new Elecraft CP1 directional coupler/power pick off. With it you can use a QRP watt meter like the OHR WM-2 to measure up to 100 watts. You connect the K2/100 to the CP1 and then out of the CP1 to a dummy load that can handle 100 watts like the Tentec 300 watt load or the OHR 100 watt load. Then the forward pick off from the CP1 goes to the WM-2 set on 1 watt if you built the CP1 for 20 db or the 100 mW range if you built the CP1 for 30 db. The WM-2 will read 0-100 watts. If you don't have a watt meter then you can do the same thing with a scope and a little math by connecting the scope across the forward terminator resistor on the CP1. You should be able to do the same with a RF probe and a DC voltmeter with the 20 db version of the CP1. The 30 DB version may have too low of output for the 30 DB version for use with a RF probe. I also wrote an article several years ago on how to convert the OHR 100 watt dummy load into a 100 watt Pi attenuator with a 20 db down output. This can be used with a scope or QRP watt meter to measure 0-100 watts. I will repost the instructions if anyone is interested. Thanks The other Don Don Brown KD5NDB ----- Original Message ----- From: "Don Wilhelm" <[hidden email]> To: <[hidden email]>; <[hidden email]> Sent: Wednesday, February 22, 2006 6:42 PM Subject: RE: [Elecraft] Re: K2 Power Callibration > John, > > One must be careful not to zap the diode in the RF Probe - so measuring > directly across the dummy load is good only up to 20 watts or so. A > 'scope > with a proper probe will handle the full 100 watts of the KPA100 easily. > Builders may not have a known good 'scope, and the RF Probe method must be > used with some intelligence - many folks do not know the accuracy of their > dummy load at the frequency of operation - and both the 'scope and RF > Probe > methods are highly dependent on knowing the accuracy of the dummy load - > it > must be entirely resistive for accurate results. > > Yes, I feel that my 'scope and 1% 50 ohm dummy load (checked for both R > and > X on several antenna analyzers) will provide better than 5% accuracy for > any > wattmeter that I calibrate by that method. Of course, I can do a more > accurate job at 30 watts or lower because I can read the voltage > differences > on my 'scope face with greater precision (the 10 volts per division scale) > and at higher power, I end up at the 20 or 50 volts per division scale and > the interpolation becomes more coarse. > > 73, > Don W3FPR > > Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] 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 |
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I have to slip a plug in here for my new wattmeter kits... specifically the LP-200 dummy load/wattmeter. You can read about it at www.telepostinc.com. It's like a DL1 on steroids. It includes a 30W dummy load, with a variable speed fan option for 100W continuous rating. It doesn't get nearly as hot as a DL1, even without the fan, but more to the point, it's microprocessor controlled, has digital readout, frequency and temperature compensation, and will accurately display power from 1mW to 120W. It makes a great addition to any bench. I started shipping these about a week ago. I also have a handheld digital wattmeter (LP-300) for field use that will work at QRPp thru 100W that's real slick and will be out in a few weeks, and a high-end digital meter (LP-100) that will go on sale this week, that is based on my cover article in the Jan/Feb QEX. One unique feature of the LP-100 is the ability to display complex impedance, in addition to lots of other professional features. The LP-100 and LP-300 feature a nifty peak responding bargraph display that will follow voice peaks, and display power and SWR simultaneously in both analog and numeric form. The LP-300 can not only be used for antenna tuning, but as a realtime monitor for field operating. It has a battery life of 25-100 hours depending on type of battery and backlight usage. It also has a 12v jack for external power. The LP-100 uses a superfast PLED display, and has lots of unique features. They're all kits, and cover a range of needs. There are links to all three on the above webpage, as well as a link to a comparison matrix of the three. I will be at Dayton with a booth showing these and more. Larry N8LP ww.telepostinc.com Don Brown wrote: >Hi > >I will throw my two cents worth. I agree with everything Don is saying here >however there are several other ways to get a reasonably accurate power out >measurement on a K2 or K2/100. The simplest and maybe least expensive is the >Elecraft DL1 dummy load kit. This dummy load will handle 20 watts and >includes a built in RF probe to measure the power out. You just connect a >voltmeter to the probe out test points and use the included graph to convert >the DC voltage to watts. Everyone building a K2 should have one of these >simple dummy loads/RF indicator kits for calibration and tune up. > >Another method is to use the new Elecraft CP1 directional coupler/power pick >off. With it you can use a QRP watt meter like the OHR WM-2 to measure up to >100 watts. You connect the K2/100 to the CP1 and then out of the CP1 to a >dummy load that can handle 100 watts like the Tentec 300 watt load or the >OHR 100 watt load. Then the forward pick off from the CP1 goes to the WM-2 >set on 1 watt if you built the CP1 for 20 db or the 100 mW range if you >built the CP1 for 30 db. The WM-2 will read 0-100 watts. If you don't have a >watt meter then you can do the same thing with a scope and a little math by >connecting the scope across the forward terminator resistor on the CP1. You >should be able to do the same with a RF probe and a DC voltmeter with the 20 >db version of the CP1. The 30 DB version may have too low of output for the >30 DB version for use with a RF probe. > >I also wrote an article several years ago on how to convert the OHR 100 watt >dummy load into a 100 watt Pi attenuator with a 20 db down output. This can >be used with a scope or QRP watt meter to measure 0-100 watts. I will repost >the instructions if anyone is interested. > >Thanks > >The other Don > >Don Brown >KD5NDB > > > > > > >----- Original Message ----- >From: "Don Wilhelm" <[hidden email]> >To: <[hidden email]>; <[hidden email]> >Sent: Wednesday, February 22, 2006 6:42 PM >Subject: RE: [Elecraft] Re: K2 Power Callibration > > > > >>John, >> >>One must be careful not to zap the diode in the RF Probe - so measuring >>directly across the dummy load is good only up to 20 watts or so. A >>'scope >>with a proper probe will handle the full 100 watts of the KPA100 easily. >>Builders may not have a known good 'scope, and the RF Probe method must be >>used with some intelligence - many folks do not know the accuracy of their >>dummy load at the frequency of operation - and both the 'scope and RF >>Probe >>methods are highly dependent on knowing the accuracy of the dummy load - >>it >>must be entirely resistive for accurate results. >> >>Yes, I feel that my 'scope and 1% 50 ohm dummy load (checked for both R >>and >>X on several antenna analyzers) will provide better than 5% accuracy for >>any >>wattmeter that I calibrate by that method. Of course, I can do a more >>accurate job at 30 watts or lower because I can read the voltage >>differences >>on my 'scope face with greater precision (the 10 volts per division scale) >>and at higher power, I end up at the 20 or 50 volts per division scale and >>the interpolation becomes more coarse. >> >>73, >>Don W3FPR >> >>Elecraft web page: http://www.elecraft.com >> >> >> >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >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 > > > > > Elecraft mailing list Post to: [hidden email] 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 |
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