Dave Richards AA7EE

September 22, 2013

Building and Installing the K60XV 60M Adapter and Transverter Interface Option For The K2

When I first built the CW-only 10W basic K2 about 2 years ago, I was fairly certain that the basic version was all I would need.  Indeed, at the time, it was. I had made a commitment to operate QRP CW exclusively and was having no trouble sticking to that. So although the basic K2 was a fairly good chunk of change, I was able to justify it. Thing is, that it just begs to be added to. There was plenty of empty space left in the case and although some options, such as the 100W internal PA, promised to relieve me of a good portion of my ham radio budget, there were others that required a lot less (oooh – 160M receive and a separately-switched receive antenna for $40, ooh – SSB for $130, ooh – a nice AF filter for $90, ooh – well, you get the idea.)  So it was that in short order, I ended up with the K160RX option, the 20W internal ATU, and the KSB2 option.  In that post, I did mention that the K60XV 60M adapter and transverter interface option would most likely be the next to be added, and that is how it panned out a few days ago.

Living just 50 miles away from Elecraft is great. I called and spoke with Madeleine in the morning, and the next day this arrived via US Priority Mail (First Class Mail would have cost just 2 bucks and very possibly would have gotten it here in a day also, or 2 days max). The small envelope to the right was an extra headphone jack (just in case.)  Whenever I order from Elecraft, I include a few of the more commonly needed extra parts. Heavily used headphone jacks on the K2 tend to wear out over time – especially if physical stress is placed on them, such as that from a bulky adapter. This probably won’t happen to mine but it will be good to have if, some years down the road, I need a new jack and the current part is no longer available –

Jingles, a new addition to the family (who is blind, but you’d never know it) was trying to ascertain what a K60XV is and what it means for her –

She then figured it out and cast her vote –

There aren’t many parts, and the board doesn’t take long to assemble.  Modification of the main RF board inside the K2 in readiness for the installation probably takes as long, but I’ll get to that a bit later. Here’s the K60XV board after assembly –

I suppose it’s hard to imagine how I can make such a meal out of a fairly simple project by taking so many pictures, but I sure do like taking pictures –

There were a small number of inconsistencies and points I felt could have been made a bit clearer in the assembly manual. I’m going to send Elecraft an e-mail with my suggestions for corrections in the next few days. I won’t detail them here, as it may well confuse if they have been corrected by the time you read this. I will mention the more salient ones in the text of this post though.

There was a diagram showing which side of the board the multi-pin connectors P1 and P2 should be soldered. I found the diagram a bit confusing, so figured it out by looking at the board and the space it was going to fit into in the K2. This photo should help though. look at how wonderfully thick that high-quality board is – and just get a gander at those large plated-through holes. Beautiful!

After finishing the board, the main RF board of the K2 has to be modified to accept the new option.  A jumper has to be removed, and a small number of parts have to be removed and new parts substituted – the exact details of which depend on which revision of the main board you have. Good quality solder-wick is a boon here, and helps to suck up all the solder from those plated-through holes. These boards are well-made, so will not be damaged, provided you have a good iron, good solder-wick, and don’t completely fry the thing 🙂  The other main modification is the addition of a length of RG-174 coax to the main board as shown here –

The assembly manual recommends putting a short length of heat-shrink tubing over one end of the co-ax as follows (to prevent the braid from inadvertently making contact with the board). The screws that secure the PA transistors to the heatsink are prevented from falling out with small strips of electrical tape applied to the top side of the board. One of them is visible here –

I thought that it would be a good idea to use heat-shrink tubing on the other end of the cable too, so I did just that.  I had some tubing that was a little narrower in diameter than that supplied with the kit, yet it still fitted over the co-ax, so I used that instead –

A view from the top.  There are 2 sets of holes for the transverter input/output sockets. The user can either install BNC’s in the top cover, or RCA phono sockets in the lower heatsink plate. I decided to go with the latter, and you can just see the 2 phono sockets poking out of the back in this shot. The K60XV board is at the back of the K2, to the left of the K160RX board. The large plated-through holes are so you can still easily adjust the 40/60M, 80M and 30M bandpass filters without having to remove the K60XV board –

One more shot, showing the 3 options I now have installed in the main case (20W internal ATU in the top cover, but that is not visible here, of course) –

On finishing the installation, and switching the rig on, 60M was coming through just fine.  Readjustment of the VCO inductor, L30, was required to keep the VCO voltage within an acceptable range for all bands. This is fully covered in the K60XV and K2 manuals.  I completed the alignment process and was soon hearing much band noise on the 60M amateur band (no activity heard until the next evening) and plenty of AM broadcast stations on both the 60M and 49m broadcast bands.  Funnily enough, the first signal I heard was Radio Havana, Cuba, promoting a film screening that was happening just a few miles away in San Francisco!  I have since heard a few ragchew QSO’s on 60M USB as well as W5GHZ calling CQ on CW, though he didn’t hear me calling him. There was one slight problem with the testing process of the transverter interface part of the option. When in transvert mode, the K2 can develop a low-level signal (1mW or below) to send to the transverter. Firstly, I noticed that when set to an output power of 1mW (at the transverter output phono jack), the K2 was only generating 0.2mW. A few Google searches revealed something that was also in the assembly manual, had I taken the time to read it thoroughly. When using the internal 20W ATU, it has to be taken out of auto mode in order to develop the full 1mW. You can do that either from the menu, or directly from the front panel by pushing the “Display” and “Ant 1/2” buttons simultaneously. Problem solved? Not quite, as the K2 was now putting out about 50mW – more, but still not enough.

At this point, it was 2:30 am and time for bed. I went to sleep, and woke up the next morning concerned that I had made some kind of boo-boo with the board assembly and/or installation. However, another Google search revealed yet another solution that, had I not been so dog-tired the night before, I would have seen in the assembly manual.  For anyone with a K2 that has the internal 20W ATU, there is a 47 ohm resistor at the input of the op-amp on the ATU control board that can load down the transvert interface to the point where it won’t develop the full 1mW output power. The recommendation is to swap that 47 ohm resistor for a 470 ohm (supplied with the K60XV kit). I did so and – bingo! – the K2 was now putting out 1mW into the transverter output when in transvert mode. I love it when things work 🙂

This would be a good time to talk just a little about using the K2 to receive out of the ham bands. Being optimized for the ham bands, with bandpass filters centered on those portions of the spectrum, sensitivity does fall off as you tune away from them. Then as you continue tuning, at some point, the VCO loses lock and you can’t tune any further. However, within these limitations, you can cover most of the SWBC bands with the K2, albeit at reduced sensitivity for some. If you’re a casual SWL only, the reduced sensitivity isn’t as important an issue at it might seem. Each K2 will vary in terms of it’s out of band coverage and sensitivity outside the bands for which it was designed, but this report from Neil WA7SSA will give you an idea of what you can expect.

“But the K2 isn’t set up for AM”, I hear a few people say, “it only receives CW and SSB.”  I have actually seen this argument made in a few online forums and of course, the K2 receives AM quite well, as long you take care to accurately zero beat the carrier. Doing this is easy. Let’s say yours is set up for a CW offset of 500Hz. You select either LSB or USB. I’ll use LSB for this example. Tune away from the carrier until you reach zero-beat with the spotting tone. Let’s say that zero beat occurs at 9580.52KHz.  Subtract 500Hz form this figure and that is where you need to tune the receiver. In this example, you would retune to 9580.02KHz.  Easy! If you were using USB, you’d add 500Hz. Use whichever sideband provides nicer sounding audio. Of course, the width of the crystal filters limits how good an AM broadcast station can sound on the K2, but you get used to the slightly restricted audio. Sensitivity on the 49M BC band is a little low but you can still listen to the stronger regulars on that band (Arnie Coro fans take note!)

Here is a short clip of Radio Habana, Cuba on 6000KHz in the 49M band recorded from the headphone socket of my K2 using the 7-pole crystal filter in the KSB2 option. This filter has a -3dB b/w of about 2.3KHz – less than is ideal for AM SW broadcast reception. This should give you an idea of what to expect when listening to SWBC stations on the K2 –

Funny how that back panel continues to fill up with connectors…….

And if it’s not too much of an imposition, please allow me just one picture of the new addition to the family. This is Jingles. She is 7 years old, blind, and completely adorable. Unfortunately, just like my other 2, she has shown no interest so far in learning the code but she has valiantly (and successfully) taken on the task of leaving little tell-tale pieces of fur on my various homebrew projects as a reminder of her presence 🙂

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