I am having an anomaly with the TX Mon power measurements on my P3s. The power varies significantly depending upon where I put the TX sensor in the RF chain (K3 -> BPF -> Alpha 87A -> Coax Stubs -> Tuner -> Antenna Coax.) I have a 3" coax jumper on the appropriate end of the P3's TX sensor. I get similar results on both of my radios connecting the TX sensor in the same place in the RF chain. For instance, on 20 meters, with the K3 set to full power and the Alpha 87A in standby, the P3TX Mon displayed power is as follows:
TX Mon Location Watts @K3 RF Out 106 -> 6' coax -> @ BPF Input 101 That is a 5 watt measured decrease in a 6' piece of RG-213. @BPF Output 92 That is a 9 watt measured decrease through an Array Solutions W3NQN design BPF. -> 6' coax -> @Alpha 87A RF Out 86 That is a 6 watt measured decrease in a 6' piece of RG-213 and through an Alpha 87A in standby. The Alpha 87A RF Output LEDs show just over 100 watts (the 4th LED flickers.) That indicates to me the TX Mon power displayed is incorrect. When the Alpha 87A shows full output (all green LEDs lit) the TX Mon reads 1329 watts. That is a 13+% difference. I don't have any other power meter as a reference. I have measured both coax jumpers and the BPF individually using an AIM 4170 and a 50 ohm load. The SWR is flat at virtually 1:1 for each. The SWR displayed on the P3 is almost the same when measured at the K3 (1.53:1) and on the AIM 4170 at the end of the coax to the antenna (1.48:1.) Does anyone have a good explanation for this? I know there is a calibration method for the TX Mon, but I that doesn't explain the measured power drop in the RF chain with the amp in standby. 73, Ken, K6LA / VY2TT ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
