I am having a strange problem with my K3s/10: the max output power on 20M drops from 11.5W to 7.5W as the freq is moved from 14.0 MHz to 14.35 MHz. All of the other bands stay above 11W across their respective bands. The other interesting characteristic is that if I lower the power to 5W, there is no drop- it stays at 5W across the entire 20M band.
Other relevant data: -All data is taken post Cal -The drop on the 12V line when I key up the transmitter (set for 12W) is the same at both ends of the 20M band: 13.9 to 13.4V as measured by the K3s. -Output power is measured with an LP-100A and is the same as shown on the K3s. -The 20M BPF & LPF are flat to a few tenths of a dB and the SWR<2:1 across the band. -The voltages and waveforms on the drains of the two FETs are identical, and look OK to me. -The bias on both FET gates is ~2.6VDC. -The RF input signal to the KLPA3A (as measured at the XVTR output) is the correct level and remains constant on all bands as the freq is moved across the band. All spurious are down >50 dB. I also verified that the signal level remains constant over the 20M band when the output power is dropping. This suggests that the problem is not with the AGC or with any components ahead of the KLPA3A. Since the problem does not occur at reduced (5W) power, it appears to be due to some non-linearity. The FETs would be a logical candidate if it were not for the fact that the problem only occurs on one band. I checked the temps on all of the 20M LPF toroids and didn't observe any rise. I have no idea where else to look for a band specific non-linearity and have run out of ideas on what else to check. Any suggestions would be greatly appreciated. Bill N0CU -- View this message in context: http://elecraft.365791.n2.nabble.com/Strange-problem-with-K3s-10-could-use-some-suggestions-tp7626121.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
