This is an ongoing project. Updates will be posted as new information becomes available.
Last Friday, I activated a couple Parks on the Air sites with a friend using his Yaesu FT-857. After parting ways for the day, I intended to activate a few more parks with my Elecraft KX2. I was surprised when my KX2 would not tune the EFHW I brought with me. The best it could do was 25.4:1 SWR on the 20m band. Normally this tuner can handle anything and I was feeding it a resonant antenna, minimal tuning required. I tried swapping feedlines on the EFHW, no luck. I tried disabling the tuner, reenabling the tuner, no luck. I tried swapping feedline, again no luck. I tried pulling the EFHW out of the tree and putting up a linked dipole, still no luck. Unfortunately I didn’t have a backup radio and was running short on time and decided to pack it in.
A weekend later, I have the luxury of time and air conditioning to sort this out. I connected the KX2 behind my MFJ-986 tuner which is connected to a ladderline-fed doublet. I connected the radio to a power supply providing 13.5V on receive and 12.9V on transmit, per the KX2 display.
I disabled the internal antenna tuner, set the mode to LSB to let in the most noise, tuned to an empty part of the band, and found that I can adjust capacitance and inductance on the MFJ-986 and hear a resulting change in band noise volume on 80m, 60m, 40m, 17m, 15m, . The same process does not produce a change in band noise volume on 30m, 20m. I tuned for 20m and 30m on my FTX10 to ensure inductance and capacitance were set correctly. Additionally, on the 20m & 30m bands, an SWR reading is not available.
I followed this up with some transmission testing. Here are my notes:
- On 30m, I get an SWR reading! Manipulating the tuner produces expected swings in SWR reading. Stuck relay?
| Band | Tuner | Tuner Induct. Setting | Tuner Cap. Setting | Power Setting (KX2) | Power (KX2) | Power (MFJ) | SWR (KX2) |
|---|---|---|---|---|---|---|---|
| 80m | BYP | 50 | 6.5 | 10W | 10W | 16W | 1.0 |
| 40m | BYP | 21 | 7.5 | 10W | 9W | 14W | 1.0 |
| 30m | BYP | 14 | 7.9 | 10W | 1W | 1W | 1.0 |
| 20m | BYP | 10 | 2.9 | 10W | 1W | 1W | missing |
| 17m | BYP | 6 | 7.3 | 10W | 10W | 14W | 1.0 |
| 15m | BYP | 4 | 6.8 | 10W | 10W | 15W | 1.0 |
| 12m | BYP | 2 | 3.2 | 10W | 10W | 13W | 1.0 |
| 10m | BYP | 1 | 2 | 10W | 10W | 14W | 1.0 |
Potential Causes
In the KX2 schematics, 20m and 30m-specific circuitry appears on:
KX2 RF Board - LPF, T/R(page 14)KX2 BPF Board(page 15)
Speculating on cause:
- Bad relay?
- Open component?
Next Steps
- Try resetting the software (recommendation from W8WZ).
- Open up the case, look for signs of mechanical or electrical compromise around the 20/30m circuitry.
- Send it to Elecraft :(