Dave Richards AA7EE

January 9, 2012

Living With The K2

Filed under: Amateur Radio,Ham Radio,QRP — AA7EE @ 8:29 pm
Tags: , , , ,

I didn’t know what else to call this post.  Unlike many of the other blogs that I eagerly follow, I usually only blog when I’m building something. I’m a big fan of the blogs that report on day to day operating, with information on upcoming events and contests as well as news on new kits and products , like those by Larry W2LJ and John AE5X. That’s not my modus operandi here though, so you’ll have to excuse me if I go for long periods with no updates.

Living with the K2 is exactly what I’ve been doing for the last month,  and it’s been grand.  It’s not perfect, but it’s pretty close.  Although it’s not the do-it-all-in-one-small-box that my FT-817 was, it does the things I want it to do, which includes a few things the 817 didn’t do.   No need for details here;  the internet is already full of information about both these rigs.

With the help of the K2,  I’ve taken part in the ARRL 10M contest  – 147 QSO’s including the pleasure of working John AE5X and TJ W0EA, as well as various smaller sprints. I came first in the 6 area division in the last NAQCC sprint although to be fair, it only took 5 QSO’s – we really need more participation from California stations. The guys back east have a lot more competition so I’m not exactly sure why there is less participation here. Perhaps we’re all busy BBQ’ing on the beach or something……..(insert your own partial myth about California life here).

I’ve been on the air quite a lot which is a good thing, as building the K2 satiated my desire for building, at least for a little while; I haven’t felt the urge to build anything else since finishing it. However, there will be a few additions to the K2, so in order to help fund them, I placed my Part 15 AM transmitter on eBay.  As of this morning, the bidding is up to $103.50, which will help to fund the growth of the QRP station at AA7EE :-)

After a QSO the other day with Rick AA4W, we had an e-mail exchange in which he asked me what I thought of my K2.  I’ve said much of this here before, but it does sum up what I think of it so far.  Here’s what I told Rick:

“There are only 2 things that are less than perfect in my estimation, and neither of them are anywhere close to being deal-breakers. They are:

1)    Due to the number of bits in the D/A conversion, as you step through the bandwidth settings of the crystal filter when listening to a signal, the sidetone of the received signal varies very slightly. No matter how carefully you adjust the filter settings, you’d have to be very lucky to be able to eliminate this variation completely. With care and luck, my variation seems to be no more than 10-15Hz between settings. It has to do with the way the DC voltage applied to the BFO varactor is generated by the D/A convertor.  Apparently, they could have used more bits, but this would have increased the cost.

2)    On comparing the sound of the receiver to that in my Norcal 2N2, there is not as much of a peak in the center of the audio passband.  I’m assuming this has to do with the fact that the 2N2 is an exclusively CW rig, while the K2 audio stages had to be designed to pass the wider bandwidth of an SSB signal. (EDIT – I have since realized that the relative flatness in the passband of the K2 on CW, compared to the Norcal 2N2, is an advantage. Indeed, I’m even a little embarrassed that I initially thought it wasn’t so!)  From what I’ve read, the KAF2 audio filter, which is a lowpass filter add-on for the K2, is fairly gentle in it’s effect. The DSP option is supposed to work quite well, but nevertheless, there are still some digital artifacts when listening to CW. I am going to try a SCAF – probably the NESCAF, which seems to work well – and has the advantage that it helps a lot in cutting down electrical noise too – and all for just $31.  The only problem is that it is external to the K2, and I really wanted a filter option that was internal.  Incidentally, John K3WWP told me that he loves the DSP in his K2. He said that it is very effective at cutting down the electrical interference that he suffers from at his QTH. (EDIT: I never did try the SCAF. I now have no idea why I would even have thought I needed one – and to this day, 2 years after posting this, I have not felt the need for any additional filtering beyond what the basic K2 offers)

      By the way, if you have the most recent edition of “The Complete DX’er” by W9KNI, he has some very good things to say about his K2.  He likes the relatively unprocessed sound of it, as compared to the more processed sound of the signals as heard on commercial rigs that use multiple conversion in their receivers. You’ll appreciate this too. Someone who comes from a background of only ever having listened on commercially-produced receivers with multiple conversion and much more complex circuitry than the K2 might mistake it’s cleaner sound for lesser performance which of course, it is not.”

The art of delayed self-gratification that I seem to be quite good at has kicked in and I’m waiting a bit longer to see what the first additions to the K2 will be. A KAT2 internal ATU will definitely be one of them.  I would like some audio filtering and I’m trying to decide between an external NEScaf, or the internal KAF2 or KDSP2 modules.

In the meantime, I’m just 4 states away from QRP CW WAS, and quite a lot of countries short of QRP CW DXCC, so there’s plenty to be working on – as long as the A index comes down soon :-)

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