Updating my portable station with a KX3

After receiving quite a good annual bonus, I looked at my wish list and decided to buy a new portable HF radio. Based on my massive satisfaction with the Elecraft K2, the decision was quite easy really. Yes, I’ve joined the KX3 brigade.


I ordered it in kit form from Waters & Stanton on Good Friday and it appeared at my front door the following Tuesday. I reckon it took about 3 and a half hours to assemble. Why would anybody buy it assembled?

Included in the purchase were the KXFL3 roofing filter, KXAT3 internal ATU and KXBC3 battery charger. I also bought the MH3 microphone.

I debated about the ATU and charger as I will mostly be using this portable. I nearly always use tuned antennas when portable and I will be using a LiFePo4 battery pack for external power. That said, there are bound to be occasions when I would like to tune up a piece of string; and I’m nervous about taking the (homemade) LiFePo4 4S1P pack through airport security. So, I may end up using some Panasonic Eneloop Pro 2450 mAh NIMH batteries for overseas activations.

First impressions are excellent. The receiver sensitivity is superb: even better than the K2, which is pretty good.

KSB2 problem found, and solved

I finally solved the problem with my KSB2 board. It turned out to be a poorly soldered joint on one of the transformers that terminate the filter. I found it by writing down everything I knew about the problem and using that to systematically exclude different elements in the system.

The final clue was that receive audio was poorer through the KSB2 filter than through the variable filter on the RF board. Poorer, but not absent. That pointed me back to the filter.

I was ready to rip the filter out and rebuild it from scratch, but decided to have one more look at all the joints using an X3 magnifier. I could just see that one of the leads from T1 primary had an annulus of solder and that I could see the copper end of the wire. Sussed: I obviously hadn’t fully stripped the insulation when I made the transformer. A continuity tester confirmed the problem: high, but not infinite, resistance.

It was a 5 second job to re-solder the joint: leaving the iron on long enough for the remaining insulation to bubble off. Just for completeness, I re-did all the other solder joints as well.

The result is that the board now works fine. I’m not completely happy with the performance, or of the filter alignment, but that’s for the next post.

More modules built


After a break, I’ve been back building more K2 modules. I’ve built the KIO2, KNB2, KDSP2 and KAT2 modules over Christmas. That’s the lot.

All but the KATU module worked straight away, but I’ve got a problem with the latter. I’ve still got to resolve the lack of Mic gain on SSB and absence of RF in 20m before I try and debug the ATU.

The picture shows the KDSP2, KNB2 and KAT2 modules. The KIO2 is already attached to the top cover of the radio.

It’s done, the K2 is complete

At least as far as the basic unit anyway.


After getting over the VCO problem, I’ve been able to make steady, if slow, progress towards completion. The filters are only roughly peaked because I don’t have an RF signal generator. I will rectify that later as my next project is to build an RF signal generator controlled by an Arduino.

I still have a number of option modules to build and install: KSB2, KAT, KNB2, KIO2, KBT2 and KDSP2. None are too difficult and I can pick those off at my leisure.


Making progress again

OK, we got past the problem with the VCO.

After tracing through the signals, I checked the levels on DIN and CLK against the indicative levels in the manual. They were the wrong way up!

At this point I got on to the Elecraft mailing list and started asking questions. Luckily, Don Wilhelm W3FPR was on hand to offer some advice. Essentially, the main reason for the VCO not locking was likely to be the values of L3 and T5 being such that the voltage swing on the PLL couldn’t get the VCO to change frequency enough to lock. The advice was to either adjust L3 or change the turns on T5.

I didn’t want to disturb T5 unless it was really necessary, so I did a bit of thinking. The PLL is calibrated when the K2 is switched on for the first time. The MCU swings the VCXO through its full range and measures the relationship between PLL data and VCO frequency. It uses the results to program the EEPROM U3. What if, I reasoned, if the EEPROM calibration had not completed properly? I decided to give the rig a full reset (hold keys 4-5-6 in when switching on).

Bingo! Immediately, the VCO locked on.

Next step was to adjust L3 to set the voltage range so that the VCO works on all bands.

More problems – my fault this time

I had to tweak T5 a bit, but I got the VCO to lock OK on some bands, but not on others.

Turned out that I had put a 47nF capacitor in C74 instead of 47pF. Not much difference!

Anyway, I changed it and all bands work OK.

Lastly, for this evening anyway, I got as far as checking the BFO frequencies.

Ahhh, we have a problem

Testing the K2

  • Resistance checks
    • Pass
  • Assemble the Case and plug in the Front Panel and Control Board.
    • It’s starting to look like a radio now. Isn’t it small!
  • 4MHz Reference Oscillator Calibration Check
    • The target is 12090 kHz +/- 30 kHz. Mine is running at 12099.45. Pass.
  • PLL Reference Oscillator Range Test.
    • Target range is between 9.5 and 15kHz. Mine is 13.38kHz. Pass.
  • VCO test
    • Target is to be stable in the range 8 to 10MHz. Mine is 12.099.45 MHz. Fail 🙁
  • Time to get digging.

Finally building my Elecraft K2

Picture of an Elecraft K2

Back in 2003, yes 2003, I splashed out and bought an Elecraft K2. To my mind at the time, it was the best radio there was at a price point I was prepared to pay. (Note: Even now, it’s still right up there with the best). Also, it came as a kit; which attracted me. I did a lot of circuit construction in my early days as an engineer and l have kept my eye in over the years.

I started to build it, and got as far as completing the front panel and control boards. Then life intervened (big time!) and the K2 ended up in a box awaiting further work.

Well the time has finally arrived to make progress again. It’s only been 11 years after all!

The kit is on the bench and I’ve started to build the RF board. I try and spend an hour a day on it. I usually work from home, so I get to spend the hour between stopping work at six and supper time at seven to do some construction. It’s better than spending it stuck in a traffic jam. If I’m lucky, I get another hour in after supper.

I started in the middle of May and progress is good. I have cheated a bit, and bought pre-wound toroids from The Toroid Guy. It’s not the winding, it’s just the time.

The best investment has undoubtedly been the Panavise 333 circuit board holder. It was expensive, but definitely worth it.