K2- Is the Power display really representative of PEP?
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K2- Is the Power display really representative of PEP?
 
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Hi,
I've probabaly seen this discussed before, but can't remember ... I have noticed that the power output on my K2 differs from measures PEP going to the antenna. Mostly it displays between 14.8and 15.2. However, when measuring with a wattmeter and dummy load I notice that on 18m I get 18W PEP, and on 15m down to 12W. On 10m it's at 8W. So my question is, is the power level that you seen on the display really just a scale for adjusting power, or is it at true reading. I'm starting to wonder if my Watt meter is inaccurate (a Yaesu 60 model) ? 73 Robin _______________________________________________ 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 |
Re: K2- Is the Power display really representative of PEP?
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Robin,
The base K2 power display is a simple diode detector (an RF probe is similar), and it will be reasonably accurate if and only if the load inpedance is 50 ohms resistive. Your antenna may be something quite different. You might say that the base K2 power output indication shows the power that would be present if the antenna load were actually 50 ohms resistive. If you have the KAT2 or KAT100 or KPA100 installed, they contain a true wattmeter, but these must be properly calibrated to provide a good reading. In general, wattmeters can be trusted to only 10 to 20% of their full scale reading - so if you are reading on a 100 watt scale, the actual power may be off by as much as 10 to 20 watts!!! Use the lowest scale that will handle the power being measured. Actually some are better than that, but should not be trusted until they are properly calibrated. I calibrate (or verify) wattmeters by connecting a 50 ohm dummy load and measuring the RF voltage across that load with my 'scope (an RF Probe could also be used) - then do the math to determine the power. When using the 'scope, the formula I use is Vp-p ^2/400 and for an RF Probe that reads RMS voltage the formula would be V^2/50 (these formulas are only for a 50 ohm load). Check the dummy load beforehand with an antenna analyzer to be certain it is a good 50 ohm resistor at the frequency you are using for the calibration. In other words, trust nothing for accuracy until it is verified. 73, Don W3FPR ----- Original Message ----- I've probabaly seen this discussed before, but can't remember ... I have noticed that the power output on my K2 differs from measures PEP going to the antenna. Mostly it displays between 14.8and 15.2. However, when measuring with a wattmeter and dummy load I notice that on 18m I get 18W PEP, and on 15m down to 12W. On 10m it's at 8W. So my question is, is the power level that you seen on the display really just a scale for adjusting power, or is it at true reading. I'm starting to wonder if my Watt meter is inaccurate (a Yaesu 60 model) ? _______________________________________________ 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 |
Re: K2- Is the Power display really representative of PEP?
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Hi and thanks for the answers so far,
To give a bit more detail... I'm not using any antenna tuner in my K2, it's the basic K2 with SSB module and battery pack, but for the power out measurements I'm using a DC PSU. I've set the K2 to CW and keyed the microphone, with the Power turned full clockwise... The output reading is on the YS-60 is using the 20 watt scale. The dummy load is true 50 Ohms, and this is what I get... Band Mhz K2 LCD YS-60 80m 3.500 15.2 18 40m 7.050 14.8 16.5 20m 14.200 14.8 14.5 17m 18.150 14.8 14.5 15m 21.200 14.8 12 10m 28.500 14.8 8 It seems like a lot of disparity on 10m, but I would have thought that even if the winding on the 10m toroid were not perfectly spaced, it shoudn't be that far off? 73 Robin _______________________________________________ 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 |
RE: K2- Is the Power display really representative of PEP?
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Robin, you're measuring REQUESTED power, not the actual power. The actual
power is shown on the bargraph. The actual power appears on the LCD display ONLY in TUNE mode, not when you key the mic. Check the ALC action on 10 meters. (Press and hold the RF/ALC button so the screen says ALC briefly). Now key the mic and talk. At least one bar on the bargraph - the bar on the extreme RIGHT end - should flicker when you talk on 10 meters. The bargraph reads backwards when showing ALC so you won't forget which meter mode you're in. The flickering bar says that he K2 is making all the RF you are REQUESTING (by setting the POWER knob) and is beginning to back down the audio gain automatically. (Within the limits of the circuits, the more audio, the more RF output). You may see several bars flicker on 40 meters. The RF stages in the K2 have more gain on the lower frequencies. Ten meters tends to be the band where the output is lowest. Still, you should see ONE bar flicker when the POWER control is set for 10 watts. If you aren't seeing one bar flicker in ALC mode, then the K2 isn't making the full 10 watts on ten meters. You can verify that by pressing RF/ALC again to go back to "rf" monitoring and talking into your mic. You probably won't see all the bars light up, indicating 10 watts on peak. Keep in mind that the RF output is "peak" reading, but the peaks may be very brief. Normally you will see the last bar on the right flicker only slightly at a full 10 watts. Ron AC7AC -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Robin Kiszka-Kanowitz Sent: Sunday, November 07, 2004 9:09 AM To: W3FPR - Don Wilhelm; [hidden email] Subject: Re: [Elecraft] K2- Is the Power display really representative of PEP? Hi and thanks for the answers so far, To give a bit more detail... I'm not using any antenna tuner in my K2, it's the basic K2 with SSB module and battery pack, but for the power out measurements I'm using a DC PSU. I've set the K2 to CW and keyed the microphone, with the Power turned full clockwise... The output reading is on the YS-60 is using the 20 watt scale. The dummy load is true 50 Ohms, and this is what I get... Band Mhz K2 LCD YS-60 80m 3.500 15.2 18 40m 7.050 14.8 16.5 20m 14.200 14.8 14.5 17m 18.150 14.8 14.5 15m 21.200 14.8 12 10m 28.500 14.8 8 It seems like a lot of disparity on 10m, but I would have thought that even if the winding on the 10m toroid were not perfectly spaced, it shoudn't be that far off? 73 Robin _______________________________________________ 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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