Dave Richards AA7EE

November 2, 2016

An Improved Knob for the K2 – plus the KAF2 and KNB2 Options

Lately, I’ve been thinking more and more about how the K2 is not going to be available for ever. As a literal statement, it is obviously true. I suppose it would be more accurate to say that with the way that a few of the original leaded components in both the K2 and some of the options, have been replaced by their SMT counterparts, and the fact that the audio DSP option, the KDSP2, has already been discontinued due to unavailability of one of the main parts, I wonder how long it will be before this happens with the K2 itself. Who knows? It could be imminent, or it could still be some years off. I am so attached to my K2 that I would be dismayed if any of the options I wanted were to become unavailable before I had a chance to assemble and install them, so I have been working towards acquiring all the options I might possibly need, which is basically everything except the KPA100 100W PA and KAT100 ATU, and the KDSP2 (already discontinued). I decided that I cannot justify the extra cost of adding the 100W option, especially as having 100W is just not that important to me. As far as the KDSP2 goes, although I was initially a little miffed when it was discontinued, I later realized that I am not so keen on the audio artifacts that this type of audio DSP produces, and that the KAF2 was most likely a better option for me. I purchased the KAF2, KNB2, and the KBT2-X options a couple of months ago and, uncharacteristically for me, let them sit for a while – after a thorough inventory to ensure all parts were present. At the time, I was scratch-building an SST for 20M, and modding a WBR for 30M. With those 2 projects behind me, I began work on 2 of these options.

First though, a quick word about knobs – or to be more precise, the main tuning knob on the K2. Many find the stock tuning knob to be perfectly serviceable the way it is but others (myself included) find it just a little less than ideal. Compared to tuning knobs on most commercial rigs, the one on the K2 has a rather sharp edge, the effects of which can become obvious if you tune a lot by resting one finger against it. Unless your knob has the (now unavailable) finger dimple, this is probably the way you tune.

Reading the Elecraft reflector archives on Nabble, I found a rather useful tip that, at least partially, solves this problem at no cost. A recommendation was to use one of those small, thick rubber bands that are used in the produce section of the market to hold bunches of broccoli together. I found a yellow one at my local Whole Foods that looked rather nifty on the K2. It could have been a slghtly tighter fit on the knob, but it worked, and it did improve the ease and comfort of tuning. Considering that it cost nothing (the gentleman in produce said I could have it), it was well worth trying –


Another solution I’ve been thinking of was purchasing one of the heavy weighted knobs manufactured by Fred N8BX’s company, 73CNC.com. From the various reports, and the video on the product page, it looks as if it provides a very smooth and silky feel to the tuning. I was sorely tempted. The only possible downside I could find to this heavy knob was a comment from Don W3FPR, on the Elecraft reflector archives. He was wondering if the extra weight would put more stress on the encoder shaft, leading to early failure. At the time, there were no reports, and no data, so it was purely speculation. The knob appears to be very well balanced. It is extra weight on the shaft though. In the meantime, another solution presented itself, in the form of more posts in the aforementioned archives, about the suitability of the FT100 knob, which some have used in place of the stock K2 knob. Someone commented that the rubber ring that fits around the FT100 knob also fits around the K2 stock knob and makes the act of tuning much more comfortable.

The FT100 knob and rubber ring are not available from Yaesu parts any more, but I did find an eBay seller in Taiwan who still has some for sale. It’s a bit more money than it was when Yaesu still supplied it but at $20 inc shipping, I thought it was worth a shot. As of this writing, the seller still has some. This rubber ring is Yaesu part # RA0068200. It is a tight fit over the K2 knob and at first, I didn’t think it was going to fit. It does require some stretching, but once you’ve got the ring stretched over the edge of the knob, it’s a fairly simple matter to push and snug it all the way down. Perhaps the color isn’t quite as eye catching as the yellow brocolli band, but it provides a superior tuning experience –

After a week or so of using this rubber ring, I think it’s going to be my long term solution.

Now onto the assembly and installation of the KAF2 audio filter and KNB2 noise blanker options. Here’s the obligatory photo of the packets as received from Elecraft –

The KAF2 audio filter has 3 elements to it – a clock (as in, one that tells the time, and displays it on command on the main display), a low-pass filter for greatly attenuating everything above 3KHz, such as hiss, and the high-frequency components of splatter, and a bandpass filter consisting of 2 cascaded sections that, on it’s narrowest setting, has a -3dB bandwidth of about 80Hz. If you operate exclusively phone, the KAF2 doesn’t have a lot to offer but for CW ops, it looks like it could be very useful. Thank you Erica, for packing the parts into the bag –

I don’t have much to say about the process of assembly. If you’re reasonably experienced at soldering and following instructions, putting these kinds of things  together is a snap. Here’s the finished board –

This is the underside of the board. At the far right-hand side, you can see the 33pF NPO capacitor which forms part of the frequency determining circuit for the clock, with the 32.768KHz crystal. The manual gives guidelines for adjusting the value of that capacitor if the clock gains or loses too much. Mine is only losing about 0.5 seconds/day, so I got lucky the first time –

Another view of that 33pF capacitor –

The CR2032 3V lithium battery will be inserted in the holder on the right edge of the board, so that the clock keeps time when the K2 is switched off –

At the lower left of the board in the next shot, you can see the switch S1, which can be used to switch the KAF2 in or out of circuit once installed. The two blue trimpots just to the left of the battery holder adjust the center frequency of the two cascaded bandpass filter stages –

Installation is fairly straightforward. There are a few components that have to be removed from the main K2 board as part of this process, as with installation of the KNB2. For removal of components, I recommend the use of quality solder braid, for which I use the Soder-Wick brand. Their size #2 seems to works best for most things. Radio Shack solder-braid doesn’t wick solder up very well unless you brush some liquid flux on it before use. The danger with that though, is that you can easily apply too much flux, and end up making your board look a bit messy. Later on in this post, you’ll see where the KAF2 installs in the K2, as well as a video of it in operation but first, let’s assemble the KNB2 noise blanker option. Elecraft employee Dylan did the honors with the packing of my KNB2 –

As with the KAF2, assembly is straightforward with the help of the detailed manual, so I won’t say much about it, other than to show you the completed board –



Here’s the inside of the K2, showing the KAF2 installed on the control board, behind the front panel. You can see the KAF2 board by looking for the microcontroller chip with the white “KAF2” label on it –

– and here’s another view of the inside of the K2, with the KNB2 noise blanker board installed right next to the KSB2 SSB option board. In this next shot, the KNB2 is at center left –

A wider shot of the internals of my K2, showing it’s current state. You can see the boards for the following options beginning at the bottom right, and progressing in a clockwise fashion – K60XV 60M option, K160RX 160M, and separate RX antenna option (with the blue toroids), KNB2 noise blanker option, KSB2 SSB option, and KAF2 audio filter option. To the left of the shot on the inside of the top cover, you can see the underside of the board for the KAT2 internal 20W ATU –

The big question is how well these options work. Here are two videos to show you. First is the video for the KAF2 option –

– and here’s the KNB2 noise blanker in action. Note that I made this video before the KAF2 video, when the yellow rubber band was still on the main tuning knob –

I still have the internal battery option to install but have not yet decided whether to go ahead with it, as I rarely operate portable. I purchased it in order to make sure that I have it, in case I ever change my mind. After using both the KAF2 and KNB2 options a little, I’m satisfied that they were worth the cost, time, and effort to install. The only option that I don’t have which I am still undecided as to whether I want, is the KIO2 serial interface. It’s tempting to order it, just in case, though I have never connected a rig to a computer, or felt the need to. If I did a lot of contest work, it would be useful.

PS – there was a KAF2 video which Jingles the blind cat crashed (again) but, sadly, it didn’t make the cut!






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 🙂

September 30, 2012

Building and Installing The Internal ATU, SSB Adapter and 160M Receive Options For the K2

F5VJD’s DSB80 is not completely finished.  I need to get rid of the chirp, and the first step will be to clear up some of my shaky grounding practices. I’d also like to build a sidetone oscillator. However, I spent a lot of time and put quite a bit of work into getting it into the case and wiring it up, and I really needed to take a breather before continuing with it.

In the meantime, Eric WA6HH posted a heads-up to the Elecraft reflector that there would be a slight price increase on several of their products in mid-September.  No more information than that was provided.  I knew that at some point I wanted to assemble several options for my K2 and, not knowing whether the options I wanted would be affected by the price increases, decided to go ahead and order them. As it turns out, mid-September came and went, and the options I ordered are still the same price but that’s OK – I wanted them anyway.

After working on the DSB80, assembling a few Elecraft K2 options would be a nice bit of relaxation. All I had to do was follow the instructions and everything would work – kind of like knitting a sweater according to a pattern. You do what they say and as long as you execute well, it works out perfectly.  That has been my experience with Elecraft so far, and these options were no exception.

The options I ordered were the K160RX 160M receive option, the KAT2 20W internal ATU, and the KSB2 SSB adapter. The 160M receive option was a bit of a no-brainer at just $40. I don’t do that well on 80 with my current antenna, so the chances of me doing OK on 160M are pretty slim, but one day I’ll be in the position to put up an antenna for 160M and on top of that, I was keen to see how far beyond the band edges I’d be able to receive – it was a way to increase the general coverage capabilities of the K2 just a little. Plus, the ability to have a different antenna for receive could be useful. The internal ATU would make operation simpler.  I’d been using an MFJ manual tuner, and wanted to be able to hop bands and frequencies more quickly (yes, lazy I know).

The SSB option wasn’t in my head when I first built the K2. I was so into CW, and loved the simplicity of a high-performance rig assembled solely with CW in mind.  However, very occasionally, I have heard stations on SSB that I wanted to contact. One station in particular was in the Philippines who was calling CQ with no-one coming back to him.  I don’t remember the band, but he was so loud that I knew he’d be able to hear even a QRP signal from me. It was one of those moments where I thought it’d be neat to speak into the mic and make an instant, easy contact with a DX station. Plus, even though I don’t use digital modes much at all, it would allow me to use WSPR occasionally if I so desired. I was also harboring a fantasy that I might want to start rag-chewing on phone one day but in retrospect, that was probably an unrealistic hope 🙂 As it turned out, the novelty of having SSB was starting to wear off after 2 QSO’s, and was mostly gone after the 3rd.  It’s still a good extra capability to have though, and I do like going through the process of assembling, installing and aligning circuits.

The K160RX 160M receive option is  a simple little board that doesn’t take long to put together, so I decided to have a go at it first. The board is upside-down in the first shot.  Sorry about that. Hmmm – looks like a couple of my foster cat’s hairs made their way onto the relay on the right-hand side. Those long-haired cats leave their marks everywhere…….. 🙂   (Scroll to the end of this post to see where those hairs came from.)

Installation of this option is straightforward. On receive it tunes down to about 1600KHz, though with reduced sensitivity.  I’m not yet sure what the upper limit is. The board adds a 160M lowpass filter for the separate RX antenna, and switches in extra capacitance in the bandpass filter on the main RF board for 160M.  I’ve only heard one station on Top Band so far, though I’m sure the next Stew Perry contest will change that. Here’s what it looks like installed in the K2:

Looking from the rear (the plastic “boot” over the antenna connector is to remind the user not to use that BNC when the internal ATU is installed – it is supplied with the internal ATU kit –

Next up was the KAT2 Internal 20W ATU. This next picture of  the top-side of the partially completed LC board (the ATU is comprised of 2 boards) is posted here to illustrate a point.  I had a Twitter conversation recently with a ham who wants to build the K2, yet has a problem with his soldering generating a large amount of residual flux.  He couldn’t figure out why after soldering, his boards have so much flux on them.  I referred him to the Elecraft soldering guide and after reading it, he concluded that he was putting too much solder on his joints. This reminded me of Don W3FPR, who repairs and aligns a lot of K2’s, saying on the Elecraft reflector that he sees a lot of K2’s with way too much solder on them.  If you use a thin and mildly active solder along with a small tip on your soldering iron, you can easily regulate how much solder flows onto the joint, and ensure that you use the right amount and no more.  I use Kester RMA 285 in .02″ diameter (the RMA stands for “Rosin Mildly Active”.)  My tips are 1/32″ and 1/16″ diameter chisel tips – that’s 0.8mm and 1.6mm.   With boards that have plated-through holes, thin solder and a small tip will allow you to apply enough solder to fill up the hole and just a little more. From what I’ve read, ideally, you want to avoid a concave shape of solder in the hole – you should have a very small fillet of solder leading up to the lead, with the operative phrase being “very small”. I veer towards making the joint almost flat with the board – though flush cutters won’t allow me to make the joint totally flat. If you are applying the minimum amount of solder needed to make the joint, you wont have problems with solder bridging adjacent pads and causing unwanted shorts. You also won’t need to clean the flux off with a flux cleaner, because there won’t be much, and mildly active rosin isn’t corrosive enough to cause a problem if left on the board.  I think I did end up applying a little flux cleaner to this board eventually, but this picture was taken before applying it. What little flux there is, is honey-colored and hard to see in this picture, but I hope it illustrates the fact that unless you’re very particular about appearance, you don’t need to use flux cleaner if you’re using the right kind and amount of solder:

Another view of the top-side of the partially completed LC board:

Incidentally, if the board you’re soldering on doesn’t have plated-through holes, you will need to apply more on top of the joint in order to make a reliable connection. The capacitors on the above board are bent over per the instructions in order to achieve the necessary clearance. The underside of the LC board contains all the relays. If you look closely, you’ll see that relay K13 is not quite parallel with the other relays. These kinds of oversights on my part drive me potty but are of no consequence to the performance of the circuit:

I don’t have a picture of the whole of the top-side of the completed control board, but here’s a view from the side. It’s not a very good photo technically either but it’s all I have. Sorry about that. Note that the NPO cap behind the toroidal transformer is not the stock part (in case you were wondering why yours looks different.)  The stock part is a monolithic cap. I thought that I might have damaged mine (long story) so replaced it with this part. As it turned out, the stock part was fine, but as this NPO cap does a perfectly good job in it’s place, I left it in –

The finished KAT2 Internal 20W ATU:

At the bottom is the control board, and on top, the LC board, containing all the capacitors, inductors, and the relays that switch them all in and out of circuit when finding a match. The pink piece of foam underneath was simply to raise the ATU to the right angle to get a good shot.  I have become a bit lackadaisical recently, as I really should have looked for a way to support the board that wouldn’t be visible to the camera. I’m slipping.  Sometimes I just want to take the pictures and get to the next part of the project:

The completed unit showing the underside of the control board, with the 2 trim-pots that set the readings for forward and reflected power:

The KAT2 20W Internal ATU installed in the top cover of the K2. I’ve placed black electrical tape over the unused holes to prevent dust from getting into the K2.  My top cover was supposed to have been supplied with green tape over these holes, but it had already been removed when I received it.  Not a biggie:

Phew – only one more option to go – the KSB2 SSB adapter. I loved assembling the KSB2 board, as it is a little more densely packed than the K2 or any of the other options I had built so far. It’s fun building small things. Here’s the top of the completed board, showing all those lovely crystals (it’s a 7-pole crystal filter) –

The manual says to install the crystals flush with, and tight against the board.  I usually try to build my circuits so they will be as reliable as possible and although there was an insulating solder mask on the top of the traces that connect to the crystal terminals, there was, in my estimation, the slightest chance that if the integrity of that solder mask were to be breached, there was a possibility of the pads being shorted out by the metal underside of the crystal casing.  It’s a long shot but why risk it if you can avoid it? I spoke with Richard at Elecraft who confirmed to me that if I were to space the crystals above the board by the thickness of a piece of paper, it wouldn’t adversely affect the performance of the filter. That was all I needed to hear, so that is what I did.

Although I have definite OCD tendencies, I do keep them in check on a regular basis.  Functionality is an important factor and although it’s nice to have all my toroids looking neat, I recognize that there is no difference in functionality between a toroid with perfectly spaced turns and the ones that look like mine in the picture below. Some of my toroids turn out looking really nice and some of them look just OK, but they all work just fine 🙂  –

The underside of the SSB adapter board. RFC1 and RFC2, though marked on the underside of the board, are actually installed on the top-side. They are wound on very small FT23-43 cores and the only reticence I had about top-mounting them was that it was hard to avoid the windings coming very close to the metal cases of the adjacent crystals. I know the windings are covered in insulation, but I’m not overly keen on it. Unavoidable though. You can see how close the mini toroidal chokes are to the metal crystal cases in the direct overhead shot of the board, 2 pictures above. Here’s one of the underside of the board –

There are several reasons I post many pictures of my projects. I know there are times when I’m assembling something and I want to know how other people do it.  Occasionally, if an instruction in a manual is unclear to me, or can be interpreted in different ways, I’ll go foraging through the internet to see what other people who built the same thing ended up with. Perhaps I can help a few people by offering up my pictures. Also, it’s fun taking pictures!

Before adjusting the carrier balance, the instructions in the manual say to place the wiper of the carrier balance trim-pot at approximately mid-travel. I did this and found that very little further adjustment was necessary to null out the carrier. I have only performed a rough adjustment using the S-meter of the K2 so far, but I’m pretty close.

All these options required a small number of modifications to the main RF board on the K2. Some builders who are reticent about desoldering components from their beloved K2’s have opted to use the Rework Eliminators.  I did think about it but decided against using them for 2 main reasons. Firstly, I’m cheap frugal and was already stretching my finances a bit even by buying just the basic K2. Secondly, I’m quite good at soldering and desoldering and don’t find it a nuisance at all to have to partially disassemble a rig and desolder a few components in order to fit a new option.  I have actually enjoyed the partial disassembly of the K2, as I got a chance to renew my acquaintance with it’s innards. The K2 PCB’s are high quality boards. You’d have to apply an awful lot of heat for a long time in order to damage them.  I did turn the flux darker in color in one or two places, but a quick application of flux remover with a plumbers flux brush took care of that.  The places on the K2 board where I have removed jumpers and desoldered components still look really good.

As a continuation of the last topic,  I hope you’ll allow me to air a few more opinions about soldering and the K2.  I do understand how someone who hasn’t built a K2 before would want to protect their investment. The Rework Eliminators are very appealing in this regard. In my opinion, they could be useful if you are going to be changing options a lot. Even a good board in the hands of an experienced tech will start to look shabby if soldered and desoldered enough times. Now that I have installed the 160M receive, internal ATU and SSB options, I doubt very much that I will need to remove them. If you’re experienced at soldering, the lack of Rework Eliminators  in my opinion is not a problem. If you’re not experienced at soldering, in my opinion also, you shouldn’t be building a K2.

Please don’t interpret the last sentence as a discouragement from building one of these absolutely brilliant rigs. If you have any inkling to build a K2 – please do.  It might be the last chance you’ll get to build this kind of a kit at the component level.  It’s certainly a classic of our times.  If you’ve ever thought that you’d like to build a K2 – definitely do it, but make sure that you can solder well before you start.  $740 plus tax + shipping (at time of writing) is a lot of money to spend on something if you’re just going to drown it in solder.

If your response to this is is something along the lines of “But my soldering isn’t very good and it’s always been that way” then I challenge you to improve it. It can be done.

As part of installing the SSB option, some extra components have to be installed on the control board – some capacitors, a couple of transistors, and a set of header pins for configuring the mic wiring for whatever mic you will use. For configurations that require adjacent header pins to be connected together, you can use jumper blocks.  The mic I decided to use was an old Heil Traveler headset.  I didn’t like the bulk of the thicker wire and adapter cord (that in my case was configured for an FT-817) and the small plastic box that contained a PTT button and freq up/down buttons, so I chopped it all off and got to decide how I was going to wire it to the 8-pin mic plug.  I decided to go with the straightforward configuration that the Elecraft MH2 mic uses i.e. adjacent pins connected to each other.  If I decide in the future to use any different type of mic, I’ll probably use a home-made adapter cable so that I don’t have to go into the K2 and re-configure for each different mic –

Here’s the KSB2 SSB Adapter installed on the K2 main RF board.  There is a hole in the SSB adapter board that allows the frequency counter probe to be attached to TP2, but I’m a little concerned that although it can also still make electrical contact with TP1, if I want to seat it fully into TP1, it looks like I’m going to have to file some of the edge off the KSB2 board –

Those blank holes on the back of the K2 are starting to fill up.  The blank holes are supposed to be covered with green masking tape as supplied, but that tape had already been removed on the covers supplied to me, so I have covered the few remaining holes with black electrical tape. Looks OK and keeps the dust out –

I’ve had a few SSB QSO’s with the K2 so far and out of 5 QSO’s, 4 of the stations gave me unsolicited reports of excellent sounding audio. One station said that perhaps I could use a few more highs and a little less on the low end, but that I should be careful about messing with the audio too much as it already sounded very good.  I may adjust the carrier placement in the filter pass-band just a little to accentuate the highs, but I think I’m pretty close.

Assembling and installing these options has been an enjoyable exercise.  It has given me the opportunity to re-familiarize myself with the insides of the K2 and has only solidified my liking for this rig, as well as my respect for Elecraft. The ham community is very lucky to have this company making these great products for us.   My budget has taken a bit of a beating this month, but I’m hoping to be able to get the K60XV 60M option pretty soon 🙂

Oh – and those hairs on the relay in the very first picture in this post? They came from Chala – a 10 year-old kitty who I’m fostering right now. There is a group that goes out every night and feeds the feral population here in Oakland. Chala was amongst those cats, but one of the volunteers brought her into the shelter because she was not doing at all well on the streets. She’s a shy kitty with a very sweet nature, and was unable to defend herself from the other cats. She was in really bad shape when first brought into the shelter, but is slowly starting to settle down and get comfortable here. She’s a sweetheart and as you saw from the photo of the K160RX option (if you were looking carefully), is already starting to leave her mark on my construction projects 🙂

Chala is pondering how the K2 will perform on 60M when I build the K60XV option.

August 9, 2012

Adjusting The Crystal Filter Settings On The K2 And Achieving Maximum Intelligibility with Narrowband SSB

Filed under: Amateur Radio,Ham Radio,QRP — AA7EE @ 9:48 pm
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When I first built my K2 about 8 months ago in November and December of last year, I initially set up the variable bandwidth crystal filter as per the suggesting settings in the K2 manual.  Shortly afterwards, I downloaded Spectrogram v5.17 and followed the filter set-up procedure described by N0SS on this page.  Incidentally, as of the time this post is being written, the page that is linked to for downloading Spectrogram no longer has the download. Version 5.17, the last free fully free version, is more than adequate for setting up the K2 filters and it’s still available if you look around the internet a bit.

I did reasonably well aligning most of the filters but noticed while on the narrowest CW setting – 200Hz, that it attenuated the signal quite a bit. On looking at the response curve in Spectrogram the other day, it became obvious why. Tuning the receiver so that it received a tone of 500Hz (my selected frequency offset) placed the signal halfway down the lower skirt of the pass-band of the filter. Heaven knows that I was thinking. With every other bandwidth I had set up, the filter pass-band was centered nicely on the 500Hz mark, but the 200Hz filter pass-band was way off.

This incorrect filter setting had arisen as a result of  a misunderstanding of the way that the K2 filter adjustment process works. I don”t understand exactly what is happening inside the K2 during this but the best way I can currently describe it is as follows: When adjusting the BFO frequency for a particular filter setting in order to move the passband, the CW note (or pitch of the SSB signal) also changes. When you move to the next filter setting, or hit the menu button to finalize that particular setting, the BFO frequency is re-calculated, and you will hear the signal at the correct pitch again. Call me slow, but I wasn’t noticing that recalculation step. As a result, I was reticent to move the filter pass-band very far during adjustment of the settings for fear that once they were finalized, as I stepped through the different filter settings, the CW note (or SSB signal pitch) would change significantly. What a handicap my misunderstanding presented!

The other difference in the way I was adjusting the filter settings this time around was that instead of using band noise, I decided to build a simple wideband noise generator. The circuit is described by N0SS on this same page on the Elecraft site.

Boy, I like simple circuits. The ubuiquitous Altoids tin was the way to go for this one. I could have built it ugly-style, but the MeSQUARES are so easy to use.  No need for a circuit board – I just glued the MePADS directly to the tin and used the tin as the ground plane:

Here are the Spectrogram plots for the 4 CW filter settings I chose.  For the widest one, 1000Hz, I didn’t center the filter pass-band on the 500Hz mark, as that would have placed part of the filter response curve on the other side of the BFO signal,  meaning that the receiver would no longer be a single-signal receiver. For this bandwidth, I placed the 500Hz mark (indicated by the vertical red line) a little to the left of the center of the pass-band. Although the nominal bandwidth of this setting as reported by the K2 was 1000Hz, I estimated the 3dB b/w as about 500Hz and the -6dB b/w about 690Hz:

The nominal 700Hz b/w was closer to 335Hz at the -3dB points and 440Hz at the -6dB points:

The nominal 500Hz bandwidth looked to be about 250Hz at the -3dB points and 380 at the -6dB marks:

While the 200Hz nominal bandwidth checked in at the only slightly lower figure of 240Hz at the -3dB points and 340Hz at the -db points, it sounded a lot narrower than the 500Hz nominal setting. This was only an estimate.  The shape of the curve in Spectrogram is not static – it does move around a little,  so there is room for variation in the measurements:

I’m really happy with the way the 200Hz setting sounds. It’s a shame that it was incorrectly adjusted for so long.  I had read that the signal is attenuated if you wind the filter down to 100Hz, so I assumed that the attenuation I was experiencing was normal. Turns out it was normal – for a filter in which the signal is centered halfway down one of the skirts! This got me thinking about the small number of complaints I’ve read from K2 owners who say that their K2 sounds terrible, and can’t help wondering if they have not yet learned how to set up their filters properly.

Which brings me to the next part – adjusting the filters for SSB. I never used to think of anything other than bandwidth when thinking about filters. For some reason (and this is evidence of my particularly inflexible way of thinking) all I thought about was the width of the filter. “How narrow is it?” was my only question.  I never gave much thought to the importance of exactly where in the pass-band the BFO is placed. Once again, I don’t know why. I seem to never pay attention to things until I’ve been beaten over the head with them many, many times.

Things aren’t so critical if your SSB filter is 2.5KHz or wider, but as you dial the pass-band of your SSB filter down it can get pretty hard to retain good intelligibility.  I Googled the general subject and found this really interesting article by G8JNJ titled “Improving the Intelligibility of SSB Transmissions”.  Originally published in Radcom in Feb 2009, it gives some good tips for achieving the maximum clarity of SSB transmission and reception in the limited bandwidths we amateurs use.  To simplify, the article says that the range  up to 8KHz is all that is needed for intelligible speech.  Trouble is, we amateurs use bandwidths of much less than that.  In western languages, most of the energy in the vowels takes place under 500Hz. The vowels are what help another person determine that it is you who is speaking – they do a lot to give your voice it’s unique identity that makes it sound like your voice.

That’s all very nice (and it is) but the vowels don’t contribute anywhere near as much to intelligibility as the consonants do. Consonants occur at higher frequencies than the vowels, and the range 800 – 5000 Hz is particularly important. That still represents a bandwidth of 4200Hz though.  Going further, Martin says that the area around 1600-2000 contributes the most in terms of consonants.

Now we’re getting somewhere.  So the range from 800 – 2000 Hz is particularly critical. That’s a bandwidth of just 1600Hz!

I didn’t follow these figures faithfully when adjusting my settings for the SSB filters in the K2, but I did follow some general rules based on what I had just learned. Incidentally, I don’t yet have the KSB2 SSB option for the K2, so am using the CW filter to receive SSB:

The wider bandwidths were easier to adjust. I set them to allow more bottom end and as a result, they are more pleasant to listen to. By the time I got down to the 1600Hz (nominal) setting, I had to set the lower cut-off at about 800Hz to achieve maximum intelligibility.  Without having first read the Radcom article by G8JNJ, it wouldn’t have occurred to me to set the lower cut-off so high, but I was surprised at how clear the audio is at that setting, even if it’s not really that pleasing to listen to.

In the following screen captures, the markers are set at 300Hz and 2500Hz. That doesn’t mean anything – they’re just markers to show you where the 300Hz and 2500Hz points are, in case that helps you to interpret the filter response curves. The 2490Hz (nominal) setting was easy. The -3dB point at the lower end looks to be around 300-400Hz. It sounds fine:

As we go down in b/w to the (nominal) 2200Hz setting, the lower -3dB cut-off looks like it’s around 450-500Hz (my rough estimate only). It definitely sounds more restricted at the lower end but still has plenty of clarity:

The 2100Hz response curve looks very similar. I’m not sure why I picked 2 bandwidth settings that are so close to each other. I may well change this:

Look at the 1600Hz (nominal) setting. I’ve set the lower -3dB cut-off point to what looks like around 800-1000Hz.  There’s a lot less fidelity than the wider filter settings, but not much less in the way of intelligibility:

I’m pretty sure that at some point in the next few months, I’ll be building the KSB2 SSB option; not so much because I want to become active on phone, but more because I’m interested to see how the filter compares to the CW filter in the basic K2. The CW filter does have quite a bit of ripple in it at the wider settings, and it’ll be good to have an SSB filter with a flatter top to the response. I’m also keen to spend a little time setting up the transmit audio to see how it sounds. It wouldn’t hurt to have the SSB option fitted.

January 9, 2012

Living With The K2

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