Dave Richards AA7EE

December 3, 2011

The 3rd and Final Stage Of K2 Assembly

The K2 has been finished for about 3 weeks and it’s time I made the post concerning the final stage of assembly. After completing the second stage and gaining a working receiver on 40M, the majority of the work was done. At this point it felt as if I was about 3/4 of the way through, and I think I probably was. The final basic  K2 consists of 3 boards – the front panel board which you can’t see in this photo, as it’s obscured by the control board which sits behind it, and the RF board. All boards are now fully populated with the exception of the occasional jumper or connector here and there which are reserved for extra options. The on-board frequency counter is shown plugged into the test point that reads the BFO frequency – useful in regular operation if you want to adjust the filter settings:

Although I know my own toroids don’t look as pretty as the pre-wound ones from Mychael AA3WF would have,  I’m getting better at winding them, and they don’t look too bad at all.  There are many examples of attention to detail  in this kit. One of them is that when you pull the toroid leads tight and then solder them, the toroids are actually straight on the board. Often in kits, the holes for toroid leads are placed such that when you pull the leads through and solder them, they are skewed just a little. It’s a small point, but it makes boards look a bit messy. Hats off to Elecraft for helping to line my toroids up in nice neat rows:

A view from above:

Here’s the view from underneath. Note the nuts securing the 2 PA transistors to the case:

The 2 chassis pieces that I received for the back of the transceiver had already had the green masking tape removed. That was a little disappointing, as I wanted to leave the tape in place over the holes that are currently unused.  I’m sure Elecraft would have replaced them for me but it didn’t seem worth contacting them about. I’ll use some regular masking tape:

What a beaut!  -

Everything about the K2 seems to be working the way it should. Sensitivity and handling of strong signals seem fine.  I plan to measure the minimum discernible signal at some point when I get a calibrated signal source. There are only 2 things that are not quite as perfect as I’d like them (though neither are deal-breakers):

Firstly, due to the way that the transceiver handles the D-A conversion, when stepping through the filters, the BFO is not on precisely the same frequency for each setting of the filter.  My filter settings are (nominally) 1.5K, 1K, 700Hz and 350Hz (though I understand the real bandwidths are narrower in practice). When receiving a signal and stepping through the bandwidths, the signal is at the same pitch except when the 350Hz filter is selected, when it lowers in pitch about 15 – 20 Hz. It’s not a lot, but to someone like me who is sensitive to pitch, it’s a bit annoying.  No matter how hard I try to adjust the BFO frequency, I cannot get it any closer. I understand this is due to the number of bits in the D-A convertor and was one of those compromise decisions that often have to be made during product development.

The other thing is not really an issue. It’s more of an indicator of how used I get to certain receivers and how I often am very picky about how I want my radios to operate. I suspect I’m not the only operator who wants his rig to operate exactly the way he wants it to so that it “fits like a glove”.  On comparing the K2 receiver to the Norcal 2N2 receiver, I notice 2 things. Firstly, the rushing background band noise seems to be pushed to a lower level in the background by the 2N2′s filtering.  It’s difficult to make a direct comparison though, as I don’t know the exact bandwidth of the crystal filters in the 2N2 and the K2  – this would be something worth measuring.  The K2 has more audio output power, so part of it may also be that I simply have the AF gain turned higher on the K2, creating the illusion of more rushing background noise.  On some very weak signals, I find that the 2N2 has a very slight edge.  I don’t think this is a sensitivity issue; I think it has more to do with the audio filtering – the audio on the 2N2 seems to peak more sharply at a fairly specific frequency (I set up all my rigs for a 500Hz sidetone), while the K2 doesn’t have this extra peak. My guess is that the audio circuitry on the 2N2 is tailored more specifically to CW, as it is a CW-only rig. The K2′s audio chain needs to accommodate wider SSB signals so needs to be fairly flat with a passband of a few KHz.  So I think the next step is to figure out some kind of extra audio filtering for the K2 – perhaps a KAF2 or the DSP option?

These 2 small points aside,  I’m happy with my K2 so far. Sure, it’s fun to compare figures and performance characteristics, but there is another very important factor that determines how useful a transceiver will be to the operator, and that is the feature-set and how easily accessible those functions are. No complaints in that regard yet.  Considering the relatively small size of the front panel and the fact that each button controls 2 different functions, Elecraft have made the most often-needed functions the easiest to access. I found it straightforward figuring out how to record and playback the keyer memories, as well as using the Fast-Play function, by which you can playback certain keyer memories with a single button push (great for contest operating).  Use of the dual VFO’s and operating split was intuitive – even for this guy who is fairly new to the world of operating split-frequency on HF.

In the few weeks since having it, I’ve worked T2T, YN7SU, HA3UU, JE4JPQ, JF1RWZ, PA0LEG, CO8WZ, 7N1PRD, BD4FM, CA2LQA, HL2DC, JE2UFF, DK1AX, CO6RD, PV8ADI, ZP6CW, ZP9MCE, GW4EVL, PJ2/W8WTS, C6ATA, JF1SQC, JR3NZ, JA6WFM, ZM1A, UA0ZAM, JF1NSD, JA7FTR, XE1CT, XE2B, JA5FDJ, PW7T, ZS4TX, PV0F, LS1D, C5A, HK1N, LW5EE, XE2AI, HK1R, JR1MQT, LU8YE, LT1F, VK4KW, JA1KGW and PY3ED. Oh – and a bunch of Stateside stations too :-)

I think this rig is a keeper.  I’m already contemplating either the audio filter or DSP filter, the QRP internal tuner, the 160M option and (shock horror) perhaps also the SSB option :-)

EXTRA NOTE:  It is now the end of July 2012 and I’ve owned this K2 for 8 months.  I’d like to add to the comments I made above about my comparison of the K2 audio response to that of the Norcal 2N2, which had been the main rig I was using for CW before. I had been used to the more peaked audio response of the 2N2 but after a few months with the K2, realized that the K2′s flatter response within it’s passband was preferable. I can now work a CW station slightly off-frequency without having to engage RIT.  With the 2N2, if I was working a particularly weak signal, adjusting the RIT was sometimes a necessity to maximize copyability of the signal.  My preference for a peaked response was based merely on what I was used to.

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8 Comments »

  1. Congrats on wrapping up the construction Dave. I built my K2 in 1999 – it’s SN #524 and remains the only piece of radio gear I wouldn’t sell or trade. I have all the options (except 100W) and though I didn’t get the SSB option until just a few years ago, I use for the digital modes and wish now I had gotten it sooner.

    Have fun, stay young, pound brass!

    73 de Jeff, KE9V

    Comment by Jeff Davis — December 3, 2011 @ 2:04 pm | Reply

    • 524 – you were a fairly early adopter! The fact that you still have your K2 speaks volumes Jeff. Even though the K2 is now something like 12 years old, I think I’m going to be keeping mine for quite a long time too, and adding a few options as I go along.

      Comment by AA7EE — December 3, 2011 @ 5:10 pm | Reply

  2. FB Dave – sounds like you’re having fun – and thanks for providing the vicarious build for the rest of us! I’m curious as to how you’ll use the K2 once the dust settles…rag-chewing, DXing, tinkering with add-ons, etc. You seem to have a great start in the DX category.

    Comment by John AE5X — December 3, 2011 @ 2:07 pm | Reply

    • Since I haven’t worked a great deal of DX in the past, almost every one I work now is a new one so for the time being, I’m definitely going to be working some DX John. Rag-chewing’s not really my thing, though that could change one day I suppose. There is definitely some option-tinkering in my future :-)

      Comment by AA7EE — December 3, 2011 @ 5:16 pm | Reply

  3. Dave… the toroids look great.

    Comment by Bill N5AB — December 4, 2011 @ 10:47 pm | Reply

    • Thank you Bill.

      Comment by AA7EE — December 4, 2011 @ 11:04 pm | Reply

  4. Hello Dave…It was a pleasure to work you this morning on 15 meters. We didn’t hear each other very well, but I caught the call and knew it was you immediately. I think you did the same with my call here. The band was changing and I got bits and pieces of everything. Sorry propagation wasn’t good but still a good coast to coast QRP contact. I’m always happy with those!

    I had a dipole stretched between the bedroom window and the bathroom. (indoors). This morning I worked one in New Mexico, and another in Washington state. I actually reduced power to 1 watt while working him.

    72′s and Happy Holidays,

    John N8ZYA

    Comment by John N8ZYA — December 24, 2011 @ 6:55 pm | Reply

    • Yes, the moment I heard your call, I knew it was you John. Great to work you for the first time, and I hope we get to do it again under better conditions. Considering your indoor antenna, I think we did very well. If only I could get a beam up at this end…..!

      Comment by AA7EE — December 24, 2011 @ 7:07 pm | Reply


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