K2 Base Low Power output on High Bands
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After a several month hiatus from radio, have discovered my K2/100 (S/N 3010)
has some issues with transmit power on some bands and a receive issue on 10m and 12m. I am the builder of this K2. In Feb. of this year, I wrote the reflector looking for help with “K2 base low xmit power on all bands @ > 10 watts”. Don Wilhelm suggested “Since you current draw at settings above 5 watts is excessive, I would first suspect that T4 may have been wound for "better efficiency at 5 watts" - which should not be used in a K2 that will be operated at greater than 5 watts because it becomes more inefficient as the power is increased above 5 watts. Check T4 to see how many white turns are on T4 - it should be 3 turns, but if you find only 2 turns, rewind T4”. I checked the windings on T4 and Don was spot on. The 3-4 winding (white wire) only had two passes thru the bino. I removed it and re-wound both green and white wires. I went thru transmitter adjustments again on pages 72 and 74. Now reading the output power using my same setup gives the following results with power set to 10 watts, and read on the LP-100 watt meter: 10m = 7.70w @ 3.30A 12m = 7.10w @ 2.66A 15m = 9.70w @ 2.22A 17m = 10.10w @ 2.32A 20m = 10.50w @ 2.40A 30m = 10.00w @ 2.26A 40m = 10.70w @ 2.24A 80m = 11.20w @ 2.42A 160m = 10.80 @ 2.38A I also replaced the PA transistors at that time, but did not replace Q11 and Q13 The above were the readings after rewinding T4 and replacing the PA transistors in Feb. 2019. Fast-forward to today. To perform the following tests, I have removed the KPA100, removed the KSB2 (installed jumpers between pins 1-3 of J9 and J10, C167 installed between pins 7-12 of J11), KNB2 removed (installed jumper between pins 1-6 of J12), K160RX removed (installed jumper between pins 1-7 of J14). With power set to 10 watts, an Elecraft DL1 Dummy load connected to load side of LP100 watt meter and the K2 BNC antenna port connected to LP100 watt meter, power supply connected to K2 DC barrel connector J3 (supplying 13.3 VDC), key-down using paddles connected to J1, reading current with K2 internal meter: 10m = 1.02 w @ 1.38 amps 12m = 1.81 w @ 1.46 amps 15m = 3.90 w @ 1.52 amps 17m = 3.70 w @ 1.52 amps 20m = 6.40 w @ 1.84 amps 30m = 8.30 w @ 2.26 amps 40m = 10.90 w @ 2.10 amps 80m = 7.10 w @ 2.42 amps Then proceeded to Page 10 of K2 Appendix E and performed receiver signal tracing in attempt to find receive issue on 10m and 12m. Here are the readings using RF probe and external signal generator, comparing 30m and 12m: PLL section Page 10, # 2 30m = .765 12m = .721 Page 10, # 3 30m = .310 12m = .341 Page 10, # 4 30m = .642 12m = .632 BFO section Page 11, # 1 30m = .448 12m = .445 Page 11, # 3 30m = .032 12m = .035 LPF section Page 11, # 9 30m = .132 12m = .054 >>>>>>> low Page 11, # 10 30m = .126 12m = .036 >>>>>>> low Page 11, # 11 30m = .042 12m = .021 >>>>>>> low Page 11, # 12 30m = .039 12m = .020 >>>>>>> low So, I am seeking assistance on correcting the low power output on the high bands and the receive issue on 10m and 12m. Thanks for your assistance Mike Harang K5MMH -- Sent from: http://elecraft.365791.n2.nabble.com/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
Re: K2 Base Low Power output on High Bands
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Mike,
The current draw now looks to be in line with the power output, but your output drops off with increasing frequency. First measure the voltage at the base of Q7 and Q8 during transmit. If it is not in the range of 0.60 to 0.64 volts, replace Q11 and Q13. Since you are measuring the receive signal path, and have verified that the internal K2 signals are OK, you apparently have a problem in the T/R switch or the Low Pass Filter. I suspect the T/R switch first. Make certain all the RFCs in the T/R switch are not open - including the RFC3 toroid, and check the orientation of diodes D1 through D5. In receive, do you have 8 volts at the anode of D4? The cathodes of D3 and D4 should be at least 0.4 volts (preferably 0.6 volts lower than the anodes. Is RFC3 wound on a gray ferrite core? If wound on a black core, that is your problem. Once you do those checks, skip to the Transmit Mixer, Buffer, Bandpass Filter, T/R Switch tests during transmit (or TUNE) on page 14 of the manual Appendix E. At which point in the sequence does the RF voltage drop significantly lower than the Expected value - ignore any RF voltages which are higher than the Expected value (except for the T-R Switch #1 which should be lower than Expected). 73, Don W3FPR On 10/3/2019 8:45 PM, K5MMH wrote: > After a several month hiatus from radio, have discovered my K2/100 (S/N 3010) > has some issues with transmit power on some bands and a receive issue on 10m > and 12m. I am the builder of this K2. > 10m = 1.02 w @ 1.38 amps > 12m = 1.81 w @ 1.46 amps > 15m = 3.90 w @ 1.52 amps > 17m = 3.70 w @ 1.52 amps > 20m = 6.40 w @ 1.84 amps > 30m = 8.30 w @ 2.26 amps > 40m = 10.90 w @ 2.10 amps > 80m = 7.10 w @ 2.42 amps > > Then proceeded to Page 10 of K2 Appendix E and performed receiver signal > tracing in attempt to find receive issue on 10m and 12m. Here are the > readings using RF probe and external signal generator, comparing 30m and > 12m: > PLL section Page 10, # 2 30m = .765 12m = .721 > Page 10, # 3 30m = .310 12m = .341 > Page 10, # 4 30m = .642 12m = .632 > BFO section Page 11, # 1 30m = .448 12m = .445 > Page 11, # 3 30m = .032 12m = .035 > LPF section Page 11, # 9 30m = .132 12m = .054 >>>>>>> low > Page 11, # 10 30m = .126 12m = .036 >>>>>>> low > Page 11, # 11 30m = .042 12m = .021 >>>>>>> low > Page 11, # 12 30m = .039 12m = .020 >>>>>>> low > > > So, I am seeking assistance on correcting the low power output on the high > bands and the receive issue on 10m and 12m. > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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