Rigs

My first attempts at QRP was with a homebuilt one-transistor transmitter “many years, many, many years ago”. I didn’t measure its output power, but it can’t have been many tenths of a watt. That was not a success – due to the circuit or me I don’t know… So when I say QRP I mean output powers above about one watt but definately less than the, more or less agreed, definition of five watts.

The Heathkit HW-8

For some time I used a Heathkit HW-8 transciever. This is a fairly simple design but was quite revolutionary for its time. Its output power is a couple of watts, 2-3 depending on frequency and it covers the 80, 40, 20 and 15 meter ham bands. I got it as a Christmas gift from my parents when in my late teens and remember building it in record time. It took me two days – and most of the nights as well:) With just a simple makeshift antenna consisting of a random length wire laid out on the floor in my room I made contacts with countries as far away as Spain.

hw8

My HW-8 QRP rig.

I still have it but don’t use it much anymore, mainly due to its size. Modern components can make wonders and the rigs get smaller and smaller.

Recent addition: I have in fact started using the HW-8 again. I always found the receiver very noisy but have now fitted a modern NE5534 Low-Noise Op-Amp to it. The result is fantastic. It really is a whole new receiver. What I did was 1) tap the signal before the active audio filters 2) insert a very simple low pass filter out of a LC-net (240 uH and 0.1 uF) just before this signal tap and 3) replace the third opamp audio stage with half of a NE5534. The noise disappeared almost completely. This radio has less noise than my TS930-S now. It is really fun listening on it nowadays. I find myself sneaking into the shack just to convince me over and over again that it sounds so good!

hw8-audiofilter

I was really looking into adding a diplexer before the gain stages but my junk box wouldn’t allow me:) This is what it became. Still a good improvement. On the other side of the PCB is the NE5534 Low-Noise Op-amp soldered directly onto the IC-socket. It doesn’t show in the picture but some legs of the IC are not inserted anylonger.

Another fun thing to do is to install a double-sideband modulator into it. My HW-8 now also send DSB with acceptable quality. I found a description on how to do it on pages at KL7R’s website (local file: hw8mod). The only things I did differently were 1) I used shottky diodes in the mixer (BAT46) 2) used a 10 mH choke instead of the 40 turn toroid and 3) powered the opamp from the VFO-offset voltage. This way I can use a simple 2-way SPDT switch to change between DSB or CW. I don’t need a separate “offset-off” switch. I also did not care to include a PTT-switch, I hold my morse key down instead. If you want more details on this then mail me!

hw8-dsb

The DSB mod is very easy to make and install. I can se no reason why not to have it. It took me about two hours to build and install. (Though assessing what had to be done and getting components etc took longer.)

SmallWonderLabs SWL+

After being off the ham arena for many years I wanted to find out what today’s QRP-rigs looked like. Searching the web for “QRP” (there are lots and lots of enjoyment out there!) I stumbled on SmallWonderLabs website. The rig that cought my eye was the small single board SWL+. It was available for the 30 meter band, which I had never used as I didn’t exist in my early ham years.

The 30 meter band covering 10.1 to 10.15 MHz proved to be a nice acquaintace. It is an odd creature both when it comes to propagation, regulations and activities. The maximum power allowed is 150 watts, as opposed to kilowatts on the other bands. It was likely to be fairly free from nearby strong stations and as such exemplary for QRP. The propagation is a mix between 40 and 20 meters which basically means that one can expect good medium range coverage until late at night generally, and perhaps even all through the night in the summer. Being a so called WARC-band there is no contesting on it. Which means that the band at the weekends isn’t full of competing kilowatt stations giving lots of QRM. 30 meters is otherwise a rather relaxed band with a particularily friendly athmosphere. All in all a perfect band for a QRP rig!

OLYMPUS DIGITAL CAMERA

My SWL30+ with one of the two acc-paks, key and earphones. The leftmost knob controls the audio level and the other the frequency.

The rig comes in kit form and is quite easily assembled in a night or two. I must recommend anyone building the kit – or anything else for that matter – to use a current limited power supply! Of course I knew that, but the only power I more had easily at hand was two NiMH accumulators… As they happily give 50 amps, given half a chance, I blew the final transistor and surrounding components in a jiffy:( A local electronics dealer had replacement parts so I was quite soon on the road again.

Its output power is about 2 watts and it really is a fun radio. When assembling it I chose a tuning range of 10.102 to 10.132 MHz and that is plenty on this 50 kHz wide band. Most activity appears around 10.105-10.120 MHz. Of course it is a CW-only (morse code) radio, but as CW has a 13 dB advantage over SSB (that equals twenty times more power!), establishing contacts all over Europe is no problem.

I put the circuit board inside a metallic box with a nice blueish finish. To complete the station I have to add external batteries, earphones, aerial and of course a morse key. I use two 1500 mAh NimH accumulators connected in series. These accumulators also double as the power switch, when they’re connected the rig is “ON”. The most sturdy morse key I have is an old swedish military key ripped from a 10 W transceeiver from 1939. It has a pleasant feel and is also pretty small compared to other keys. Ideal for portable operations.

Enter… The KX1

I have had much fun with the SWL+ rig but the many necessary accessories can be too many at times, specially when backpacking, where low weight and small size is paramount. After a weeks trekking that extra weight really starts to be noticeable. And a weight of 26 kilos is enough anyway. So I am always on the lookout for smaller rigs.

In the autumn of 2003 I heard of a new kit from Elecraft called KX1. It looked to be the smallest shortwave rig I had ever seen. And it was packed with features too. Fully equipped it covered three ham bands, 40, 20 and the 30 meters I have come to like so much. (In 2006 Elecraft released a 80 m mod as well.)

OLYMPUS DIGITAL CAMERA

The KX1 with attached paddle and earphones but sans aerial. 6 AA-cells are inside and are enough for many days of fun! I made a white cap of styrofoam to cover the controls during transport. With its rubberband fastening it weighs practically nothing and does its job well. Not high tech but it works. The key, earphones, BNC-to-SO-239 converter and a piece of wire (for emergency aerial) is kept in a small 5×7 cm (2″x2.7″) pouch. A truly portable rig!

There was an add-on, or rather add-inside, aerial tuner meaning I should be able to connect any old wire and still get the signal out. The VFO is a rock stable DDS (Direct Digital Synthesis) chip from Analog Devices. That chip is controlled via a serial channel administered from a microprocessor (PIC 16F876). Bringing a microprocessor on board is piece of true genius. By clever design the processor is made to interact with many other parts of the transciever giving us total control of it in many aspects.

First of all there is an accurate frequency readout, displayed on three seven-segment-LCDs. But the microprocessor also makes possible three revolution rates for the VFO: 0.1, 0.01 and 1 kHz (well, four actually if you are in USB or LSB readout mode, where the step can be 5 kHz) and a RIT (Receiver Incremental Tuning) too.

Then there is a built in keyer for use with a tiny mini-paddle. Then there are settings for sidetone level and pitch. Transmit/Receive delay in milliseconds, up to 255 ms. There are three frequency memories, two transmit memories, settable morse rate from 8 to 40+ WPM, iambic mode A or B and settable battery level warning. I probably have forgotten some features too. Did I mention that the batteries are inside the cabinet? Hmm, I’m rather sounding like a sales brochure by now… on the negative side then… it is more noisy than the modified HW-8 above and there are some internal overtones that one can hear sometimes.

The best of it all is that the power consumption is practically nothing, meaning that it actually can last for weeks on the 6 AA-size cells inside. A mere 30 milliamps receive and some 700 milliamps on transmit. You can plug in anything between 7 and 14 volts in the receptacle. Reverse polarity protection is also catered for. With the built in batteries its output is about 1.5 watts and with 14 volts it turns into a 4 watt powerhouse:)

OLYMPUS DIGITAL CAMERA

The inner workings of the KX1. The ATU, Automatic Antenna Tuner, is the small PCB-strip above the main board. Space is precious and there are not many millimeters left between the two halves when put together.

For a presentation at the local club I made the map below indicating what distances are reasonable to expect with this rig and a simple aerial. In fact, the aerial was 10 meter length of AWG24 hanging between a window and an apple tree in the garden. A better aerial would giver better results, of course. The entire presentation is in swedish and is available, converted from Apples Keynote format to  pdf (10 Megs)

kx1map

Sample QSO:s during the first few evenings of the KX1 with an end-fed 10 metre long antenna.


Ideas and feedback are most welcome. Mail to sm5jab


Advertisements
Gallery | This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s