KAT2 further Questions
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Thanks Don for the reply. I have since found that I had installed R6 before
I was suppose to so those voltages I quoted were "loaded down" not isolated. This might further explain why I do not have a left over resistor and the voltages being slightly low. Next issue I realize that the instructions state that the SWR into 50 ohm 1:1 and slightly off on higher bands. Mine shows a 1:1 until 20 meters 1.3:1 it continues to get worse until 10 meters is 2.3:1. I have also noticed that power control is not right. With a wattmeter inline with the 50 ohm load, power requested and indicated on the K2 and power read on the output don't agree and get worse as frequency increases. In most cases the power output is less than requested and indicated on the K2. I attempted to tune a "20 meter" dipole strung around the basement. I found the 160 and 17 meters did not tune. 15 meters tuned > 3:1. The rest tuned < 2:1. Some bands (lower primarily) the power is reduced to 2 watts and tuned up. Other bands it looks like it is tuning up at full power. I had to wind T1 twice during the build and I am still not sure I wound it properly. Any more thoughts and ideas?? Richard Kent K2 5296 _______________________________________________ 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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Richard,
If your power output indication varies with frequency, then it could be that the KAT2 wattmeter diodes are frequency sensitive. BUT, I must ask - how do you know your dummy load is not frequency sensitive as well, and what is the accuracy of your external wattmeter? Many wattmeters available to amateurs are frequency dependent and the accuracy is no better than 10% of FULL SCALE - so if your wattmeter is on a 100 watt scale it could be incorrect by as much as 10 watts - at any power level!! If you have an antenna analyzer, you can check the impedance of your dummy load on all bands - and if you have the external wattmeter and the dummy load connected at the same time, that is another potential source for error. You can do better calibration with a known dummy load and an RF Probe than you can with most wattmeters - just use ohms law to determine the power, but then if you don't have an accurately known dummy load impedance, your results will be off. Do not depend on the ads of the dummy load manufacturer unless it is a commercial grade dummy load. Some amateur grade dummy loads are only good enough to provide an acceptable load for the transmitter. We really need to know your setup details before we can comment intelligently. I do not trust any measuring device (particularly dummy loads and wattmeters) any further than its parameters have been verified. Check out your measurement equipment first before attempting to fix a non-problem. I would not expect the KAT2 to successfully tune a 20 meter dipole to 160 meters, there is just not enough inductance and capacitance available. As for 17 meters, it will likely depend on the feedline and its length - there may be a very high impedance at the feedpoint and the the L networks used by the Elecraft tuners do not do well into very high impedances. 73, Don W3FPR > -----Original Message----- > > Thanks Don for the reply. I have since found that I had installed > R6 before > I was suppose to so those voltages I quoted were "loaded down" > not isolated. > This might further explain why I do not have a left over resistor and the > voltages being slightly low. Next issue I realize that the instructions > state that the SWR into 50 ohm 1:1 and slightly off on higher bands. Mine > shows a 1:1 until 20 meters 1.3:1 it continues to get worse until > 10 meters > is 2.3:1. I have also noticed that power control is not right. With a > wattmeter inline with the 50 ohm load, power requested and > indicated on the > K2 and power read on the output don't agree and get worse as frequency > increases. In most cases the power output is less than requested and > indicated on the K2. I attempted to tune a "20 meter" dipole strung around > the basement. I found the 160 and 17 meters did not tune. 15 > meters tuned > > 3:1. The rest tuned < 2:1. Some bands (lower primarily) the power > is reduced > to 2 watts and tuned up. Other bands it looks like it is tuning up at full > power. I had to wind T1 twice during the build and I am still not sure I > wound it properly. Any more thoughts and ideas?? > > > > Richard Kent K2 5296 > > _______________________________________________ > 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: 7.5.432 / Virus Database: 268.15.9/571 - Release Date: > 12/5/2006 11:50 AM > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.15.9/571 - Release Date: 12/5/2006 11:50 AM _______________________________________________ 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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-----Original Message-----
From: Don Wilhelm *snip* You can do better calibration with a known dummy load and an RF Probe than you can with most wattmeters - ---------------------------------- Here I need to confess my ignorance. I used the RF probe that came with the K2 to measure K2 output into a dummy load. I got odd results. The voltage would continually increase. It would start out at say 13 VDC. I'd measure for 20 or 30 seconds and it's count up to maybe 16 VDC. I'd back off and then put the probe back on the test point and it would start at maybe 15.5 VDC and count up, going past 16 and continuing. I figured it might go through some rise time as the cap is charging but I never saw it settle out at a value. What's up with that? My dummy load is a TenTec. It's basically a big 50 ohm resistor. I've measured it with the MFJ analyzer and it is flat SWR (50 + 0j ohms) to 60 MHz or so. I've NOT measured it after it heats up though and probably should. Does an RF probe measure RMS, peak, or peak to peak? So confusing ... :-) - Keith N1AS - - K2 5411.ssb.100 - _______________________________________________ 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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Kieth,
The RF Probe that comes with the K2 will read the RMS value of the RF voltage. The RF detector in the DL1 will indicate the zero to peak RF voltage and the display on an oscilliscope will be the peak to peak voltage. It is normal for the power to increase a bit over time due to heating of the transistor junction. During a TUNE operation, the power control action is reduced - think about it, if you are using a manual tuner with the K2 and the K2 corrected for power fluxuations quickly, it would be difficult to find a match on the manual tuner. During keying and normal operation the K2 power control circuits operate in a tighter loop and should control the actual power output more quickly. So - those 'creeping' RF voltages MAY be an indicator of what is really happening. The capacitor should charge up in a single cycle of the RF Voltage, and that is only microseconds - a buildup of charge over a few seconds would only occur if you used a very large capacitor (several uF) instead of the .001 uF capacitor. If your dummy load increases value with heat, that would explain a drift, but 15 volts RMS into a 50 ohm load is only 4.5 watts, and if your dummy load is large, the heating should be minimal - you did not indicate the power rating of the dummy load. Consider too that your DMM may not indicate the correct value initially - it depends on how fast it responds DMMs measure in fixed cycles of time, so if you apply the voltage in the middle of one of these periods, the first indication will be low and you have to wait for the second period before the reading is correct. But if you have a bare K2 (no KAT2, KPA100 or KAT100), the power output indicated on the K2 display should follow what you are reading on the RF Probe - if it does not, one of them is incorrect, and it is difficult to say which one without more information. All I can say in that regard is that I have found the 1N5711 diodes (used in the K2 for RF voltage sensing) are quite consistent. > -----Original Message----- > Here I need to confess my ignorance. I used the RF probe that came with > the K2 to measure K2 output into a dummy load. I got odd results. > > The voltage would continually increase. It would start out at say 13 > VDC. I'd measure for 20 or 30 seconds and it's count up to maybe 16 > VDC. I'd back off and then put the probe back on the test point and it > would start at maybe 15.5 VDC and count up, going past 16 and > continuing. > > I figured it might go through some rise time as the cap is charging but > I never saw it settle out at a value. What's up with that? > > My dummy load is a TenTec. It's basically a big 50 ohm resistor. I've > measured it with the MFJ analyzer and it is flat SWR (50 + 0j ohms) to > 60 MHz or so. I've NOT measured it after it heats up though and > probably should. > > Does an RF probe measure RMS, peak, or peak to peak? So confusing ... > :-) > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.15.11/575 - Release Date: 12/6/2006 12:22 PM _______________________________________________ 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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