Home-Brew

my K2 Transciever
my K1 transciever

Kit Building & Homebrewing

One of my favorite passtimes is building things, and ham radio has lots of opportunities for building stuff. From true homebrewing, i.e. designing and building gear from scratch, to buying and assembling kits, from ‘accessories’ like antenna tuners and SWR bridges, to complete transcievers, to computer interfaces, there are lots of ways for hams to ‘roll their own’ gear.

Kits are a great way to get started in homebrewing. Kit building can be very educational, and give a lot of satisfaction when complete, while being relatively ‘safe’ in the sense that the design is (typically) already tested and proven. Lots of great companies sell kits. One of my favorites is Elecraft, based in California. I’ve built three of their transceivers, the K1 and the K2 and the KX1.

Although kits are a good way to get started, not all kits are created equally. The best one use proper printed circuit boards, and include everything needed to bring the project to completion, including a proper enclosure. Some include just a circuit board and parts, and some include just the circuit board and schematics.

One of the best things about kit-building or homebrewing, is that if something should go wrong with the gear later, you’re usually able to handle the repair yourself — after all you built it! Plus, if you want to make changes, or you want to modify it or adapt it in some way, you already know all the inner workings, making it much simpler to get in there and tinker.

Another great way to get started in homebrewing, is through your local radio club. The Peel Amateur Radio Club for example, has regular Project or Homebrew Days.


The K1 Transceiver
K1 in use

This is my Elecraft K1 Transciever. I’ve done quite a few modifications to it, and have upgraded it with many of the available add-ons.

The modules / modifications I have for it are: 4-band filter board configured for 80M-40M-20M-15M, 2-band filter board configured for 10M and (empty), backlit display, K6XX CW tuning indicator, noise blanker, internal Antenna Tuner, and a digital interface.

Some notable changes to the face of the unit include a different, aluminum knob set, and (only visible during transmit) a red ‘on air’ LED. The K6XX indicator is a blue LED that glows through the RIT/XIT LED.

K1 RF Board

The K1 is a great ‘little cousin’ to the K2. The K1 is CW-only (it does receive LSB but the filter bandwidth is only 850 Hz at most). It is a very small, very easy-to-build radio, with an amazing receiver and great-sounding CW. It’s a very fun kit to build, and a very easy radio to understand and work with. It’s also quite suitable to modify in various ways.

K1 top

Inside the radio, everything but the speaker plugs directly with sockets and headers, so there are no wires. Some of the modifications I’ve done have (unfortunately) added wires to the rig, but I’ve done my best to keep the wires to a minimum.

K1 interface

I’ve added a 6-pin mini-DIN port to my K1 which allows for computer digital interface. It uses a pinout almost identical to the TNC port on many Yaesu mobile radios. There is audio-out, Key (ptt), ground, plus a +6v out pin. Of course, there is no audio-in line in this case since the K1 can’t send modulated audio. The audio-out and key in lines are enough though to allow a computer to do your CW for you.

I’ve also added a small switch to turn the backlight on and off. With the backlight off, my K1 only draws about 60 mA on receive. The backlight only adds about 15 mA but still, if running on batteries, every little bit counts.

digital interface wiring

The internal wiring for the Digital Interface, connects to +6volts, ground, the audio out (line level), and the DOT and DASH lines.

This image, and all subsequent images, can be enlarged by clicking them.

The K1 noise blanker helps eliminate pulse-type noise such as from power lines and automobile ignitions. I don’t have any of that around here at the moment so I can’t test the noise blanker, but it was a simple little module to add, and it’s nice to have it just in case.

Noise Blanker

Below is my four-band filter board. I’ve configured it for 80 meters, 40 meters, 20 meters and 15 meters. The 20/15 meter half works just as Elecraft designed. The 80/40 meter half has undergone substantial tinkering. The bandwidth is about 150 kHz, and I get a full 5 watts out on 80 meters throughout that bandwidth.

The only problem is the low-pass filter. It’s good on 40 meters, which means 80 meters has no low-pass filter (or rather, it is possible for harmonics to be emitted on 80 meters). So, when transmitting on 80, an external low-pass filter is required. As-is though, 80 meters works great on receive.

four-band filter board

The components I modified on the KFL1-4 board to change Band-1 to 80 meters and Band-2 to 40 meters are as follows:

Premix Band-Pass Area:
X4 = 11.5 MHz; X3 = 15.0 MHz
C5a & C6a added in parallel to the variable caps, both are 68pf.
C11 & C12 were changed to 120pf each.
C10 is 10pf.
RF Band-Pass Area:
CL is changed to 680pf, CM is changed to 710pf (680 + 33)
CEa & CFa were added in parallel to the variable caps, both are 150pf.
CK is 10pf.
No changes were made to the Low-Pass area.

Below is my two-band filter board. It’s configured right now just for 10-meter operation. It also has most of the parts populated for 80 meters, but no 80-meter crystal is installed. So for now it’s a one-band board.

I get between 3.5 watts and 4 watts out on 10-meters, and the bandwidth is over 200 kHz. By the way, all the work and experimenting to get 10-meters to work on the K1 proved somewhat academic, as I can’t use the band anyhow – I run a 10-meter beacon here from home.

The component values I used for 10-meter operation are as follows. Please note that the part numbers given all assume that 10-meters is to be Band-2 of the 2 band board.

C6, C10: 82pf
C7, C9: 47pf
C8: 1pf
C16, C20: 220pf
C17, C19: 33pf
C18: 2pf
C24, C26: 68pf
C25: 150pf
L9, L10: 8 turns #26 wire
X2: 36.0 MHz (fundamental)

The following changes were made to the RF board: T3’s windings were squeezed as tight as possible; R11 was changed to 33-ohms; R31 and R32 were removed.

two-band filter board

k1 antenna tuner

This is the K1 internal antenna tuner. It does a fine job on every band I’ve tried, 80 through 10 meters, and can tune my 90-foot random-wire to 1.5:1 or better.

One of the features I think is really slick about this ATU is that it plugs directly onto the filter board, so there are no dangling wires whatsoever. It’s an ingenious design. I can only guess that this is one of the improvements that evolved into the K1, after Elecraft first made the K2.

This image shows where I have installed the K6XX visual CW tuning indicator. I had to make some slight modifications to the board, but it’s hot-glued directly to the back of the K1 front panel board. The ground plane is also directly connected in a couple places with soldered wire jumpers.

I used fine enamel wire (aka magnet wire) to make the rest of the connections. A very bright blue LED is on the face of the front panel board, and shines into the side of the RIT/XIT indicator.

I do have a pretty good ear for music, but when it comes to CW, I have a hard time judging the tone of received signals, so I do appreciate the visual indication. I’ll be adding one of these to my K2 as well. The only thing it needs is an ‘Off’ switch; I find the flickering light can be distracting sometimes.

k6xx installed


The Elecraft K2 Transciever

K2 Front View

This is my Elecraft K2 Transciever. I haven’t done too many modifications to it yet, although it has been upgraded with many of the available expansions and add-ons.

The extra modules currently installed are: 160-meter module, SSB module, VCO shield, Noise Blanker, internal Antenna Tuner, Audio Filter, 60-meter / Transverter module, and computer IO module.

There have been a few minor modifications I have made to it here and there. On the face of the unit, the only notable modification is to change the LED bar graph from the stock green to a brighter red. Why? Just to be different. Honestly. Oh and I changed the Band + and Band – buttons to black instead of grey. I think it looks better, personally. I’ve also changed the pan-head ‘chassis screws’ on the top and sides to the counter-sunk flat-head screws used on the K1. I just have to change the speaker screws and it will be all smooth and neat.

I think it’s a great radio, and was a really fun kit to build. It took me four days to build the basic unit, and a couple more to build all the extra modules.
For now, the only other modifications I plan are a USB interface to replace the RS232 on the IO board, and perhaps a K6XX visual CW tuning indicator.

K2 Rear View

Here’s the rear-view of my K2. The enclosure comes with all the holes pre-drilled and labeled, to accomodate all of the options and extras.

In a couple cases I have made modifications to the modules, to suit me better. Most noticable from this view are changes to the 160-meter module and the automatic Antenna Tuner module.

For the 160-meter module, it normally also includes a receive-antenna jack. I wanted 160-meters but did not want or need a separate receive antenna. So I didn’t bother to install the BNC jack, and I didn’t install the associated relay either. I just left a wire jumper to keep the RF path intact.

The internal Antenna Tuner has two antenna options. Again, I just have the one antenna so didn’t need two choices. Initially I was going to just leave out the jack and relay and use a wire jumper. Then I changed my mind and put in the relay, but instead of a second BNC plug, I added a built-in dummy load. So if I select ‘Antenna 2′ I get a 2-watt, 50-ohm dummy load.

Of course, with both the Receive antenna and the Antenna-2, I can always install the other components later on if my requirements change.

The unused holes in the back of the rig are covered from the inside with black electrical tape, or the factory grey masking tape that hasn’t been removed yet. This is to help keep dust out, as well as improve the look, in my opinion.

K2 Left Side

This view shows the insides of the K2, with the left side panel removed. This gives a pretty good view of the way the radio is organized, with most of the optional boards mounting directly with plugs and sockets. Only a couple of the optional boards require stringing wires (ATU and IO boards, mainly.)

It’s funny what you don’t notice, till you put it on a web page. You can see towards the middle of the RF board, that C75 (a blue NP0 capacitor) wasn’t properly seated. After seeing that while editing this web page, I’ve gone and fixed it in the radio. While I was at it, I made a small modification of the value of C71…

When the K60XV option is installed, C71 is 120pf and is used for setting the VCO voltage for both 40M and 60M. My tests showed that after installing the option, 40M continued to work well, but my VCO voltage on 60M was way too low (less than 1 volt at 5300 kHz). Normally the solution is to adjust L30 but I didn’t have an L30, having the magnetically shielded T5. I had T5 all perfect for ever other band, and didn’t want to start messing with it just because of 60M (which for me is receive only anyways). So instead, I played with the value of C71. I found that adding another 10pf got me almost perfectly within specs on 60M, while still staying well within parameters on 40M. Another 3 or 4 pf would probably have been perfect, but again, I can’t transmit on 60M and it’s within parameters, so I’m happy.

K2 Right Side

This view of the K2 is from the right side panel. This also illustrates a design change I made to the layout. I didn’t like the way that the ATU and IO boards plugged into the K2’s control board, so I changed things a bit, to use a single ribbon cable to clean things up a little. It makes it neater as far as removing and replacing the lid and so far everything still seems to function ok.

For the following images, you can click on the small image for a larger view.

K2 VCO Shield

An inexpensive option for the K2 is magnetic shielding for the VCO toroidal transformer.

I wasn’t sure if I needed it or not, but it sounded like a good thing to have so I went ahead and ordered it. With it, the slug-tuned inductor L30 is removed (or in my case, never installed), and the VCO transformer T5 is wound onto a smaller core. The core is then encased in a shielded cylinder which helps keep the VCO stable in the presence of strong magnetic fields.

The 60-meter band is a new ham band, only available to the hams in certain countries. To my knowledge, Canada is not one of them. However, Elecraft has bundled the low-level transverter module with 60-meter capability. I am thinking of building the 6-meter transverter so I went ahead and built the 60m/Transverter module. It’s a very simple module to build — no toroids! Most of the parts are on the bottom of the board, making it pretty boring to look at when installed. You can see an image of it installed by clicking here.

With the 60-meter / Transverter module and the I/O module, the K2 is able to directly communicate with any of the Transverters that Elecraft make, as well as a large number of other Transverters available.

The 60 M / Transverter is installed over the 40-meter band-pass filter area.

K2 60M / Transverter Module

K2 160M Module

The 160-meter / receive antenna module is another very simple small module. It allows the K2 to operate on 160-meters, and adds the option of having a separate receive antenna that works on any band.

As noted above, I didn’t bother with the receive antenna option, but the 160-meter option works great.

The 160-meter / receive antenna module is installed over the 80-meter low-pass filter and antenna jack.

The K2 has two audio filter options: an analog audio filter, and a DSP filter. Both options install onto the Control Board, and both include a real-time clock function.

I opted for the analog audio filter for two reasons: I can understand how it works; and it was less expensive. It has a low-pass filter function that is always-on, to remove some of the hiss and atmospheric noise, and it has a two-stage active bandpass filter for CW or data signals.

The clock function is displayed on the normal LCD screen in 24-hour time. I keep mine set to UTC.

K2 Audio Filter

K2 Noiseblanker and Sideband Modules

The standard ‘stock’ K2 can receive USB and LSB but only transmits in CW. The SSB module allows the K2 to transmit in USB/LSB, as well as digital modes, in addition to the standard CW. It also includes a special fixed-bandwidth crystal filter for both receive and transmit. The filter bandwidth is normally 2.2 kHz; using the mod info posted on the Elecraft website, I assembled my SSB module for a 2.6 kHz filter. So far, I use both CW and SSB about the same amount. It’s nice to have but the K2 is a great radio either way.

The noise blanker module for the K2 is designed to filter out pulse type noise, such as from power lines or vehicle ignition systems. I can’t say how well it works as I haven’t needed it yet. But it was a fun little add-on so I’ve got it in there just-in-case.

The noise blanker and SSB boards both plug directly onto the main RF board. The noise blanker is in the foreground in the image and the SSB board behind it.

My ATU was built to Elecraft’s design, with the one exception noted. Instead of the 2nd antenna jack, I added an internal dummy-load. It is made by using two 100-ohm 1-watt resistors in parallel, right on the ATU control board in the 2nd BNC connector’s position. When I get some small 3-watt or 5-watt resistors that fit, I’ll upgrade the internal dummy load accordingly.

K2 ATU

K2 IO board

For the I/O board, I don’t really need an RS232 signal. What I want is USB. My computers are all Macintosh and I don’t want to have to carry an extra dongle around. So when I assembled my I/O board, I omitted rather a lot of components. D2, D3, D4, X1, C9, C10, C14, L5, and Q1 were all left out. I added a socket for U1 so I could play with it but remove it easily. It does work just fine, without all those parts. D1 and C8 are all it needs to draw its negative voltage supply from the computer rather than generate it internally.

When I build my USB adaptor, it will probably go directly above the I/O board and use the internal battery switch for a hole through which the USB cable can be inserted. I only need the /K2-TX and /K2-RX signals, and Ground, to drive a USB chip. The chip I have in mind works at TTL level, so the level-converter is not needed.

This is a better view of what was partially visible under the right-hand panel. Here you can see both the IO board and the ATU are plugged into the “Aux2″ board, which is hot-glued to the lid. A single ribbon-cable then goes from the “Aux2″ board, to the Control board.

The ribbon-cable and connector are much easier to manipulate than the two heavier cables that were originally supplied, and it allows me to remove either the IO or ATU independently if I wish, as neither are soldered in place.

I’d have used a ribbon-cable for the ATU’s control wires but the hole spacing at the ATU is not .1″ so my headers wouldn’t fit.

inside of lid

A few toroids

Toroids! Almost all the Elecraft kits require the winding of toroids. The ten you see in this picture are from only two optional modules – the ATU and the noise blanker. I don’t even know how many toroids are in my K2 altogether.

Personally, I don’t mind the winding at all, although I find the stripping and tinning to be a bit tedious. Heat-stripping them with a hot soldering iron seems to be the best method.

Happily, I can boast that I have yet to have a toroid fail due to poorly tinned leads. (Touch wood!) I tend to wind them in batches like you see here, taped to some cardboard so they are identified. Then I strip and tin the leads while they’re still on the cardboard. Finally, I install them onto the circuit board as directed by the instructions, just pulling them from my cardboard as I go.

I’ve been interested in trying out some of the digital modes, like PSK-31, so I wanted to put an interface port on my K2 that would allow me to plug it directly into an interface unit, or even a TNC or whatever else I might want to use. I already have some equipment and cables around the shack here, and I’m all set up using 6-pin mini-din connectors. These are the kind of connector used by Yaesu on some of their radios.

What I’ve done is used a 16-conductor ribbon cable, mounted to the Mic configuration header on the back of the Front Panel board. This ribbon cable goes around the Control board and up to a small circuit board that I’ve attached to the left side of the radio near the top. I also made one change to the Front Panel board – formerly, pins 7 and 8 of the Mic configuration header were both Ground. I’ve changed pin 8 so that it now carries fixed-level received audio (taken from the top of the AF Gain pot).

The new small circuit board gives me access to all the Mic lines, including my audio out modification. This allows me to have my mini-din interface connector, and also moves the Mic configuration header out into this area rather than sandwiched between the Front Panel and Control boards.

The 6-pin mini-din connector carries the following signals: Data (Mic) In, Data (Audio) Out, /PTT-DIT, Ground, and +5VDC. Click here to see the digital connector pinout.

Digital Interface Port

Digital Interface hookup