Softrock RXTX Dividers – Stage 3

The dividers stage takes the local oscillator’s signal and divides it by four, producing two output signals that are said to be ‘in quadrature’. This means they are out of phase with each other by 90 degrees.

The trickiest part of this stage’s construction was soldering in U9, a 74AC74 SOIC-14 SMT that has fourteen small pins (or legs). And even though I took great care soldering them onto their respective pads using flux and a very fine soldering iron, when it came time to test if all was okay, the readings I obtained suggested otherwise. So it was out with my more powerful iron (with a larger tip) and with care, the re-soldering exercise produced near perfect readings on my DMM.

Next on the agenda was something I had been waiting for with anticipation: the frequency output test.

To accomplish this I would need my Hantek 6022BE USB DSO, and both probes.

This is what I observed.


As can be seen, the two signals are 90 degrees out of phase.

Next to do is to build the RX Op Amp.

Softrock RXTX v6.3 – First Smoke test

It’s always a little daunting but it’s also the part I like best – doing the smoke tests. Testing the power supply was really all about ensuring that the SMT caps had been soldered in correctly and that there were no solder bridges.

First I tested current draw with a 1K resister added to the positive probe of my DMM to restrict the current in case of a bridge. I applied 12V power and took readings.

3.0mA so all was in order.

Next I checked the power at the 12V, 5V and 3.3V rails: all fine there.

Now it was time to build the local oscillator.


Once all the components were in place, it was time for the next smoke test.

Once more I needed to check current draw but this time I did this with a 100 Ohm resister instead of a 1K Ohm one. The readings I obtained were excellent. I was now safe to test without the protection of the resister and again got great readings, all of which were under 80mA.

Next up was a frequency test. I set the dip switch on the PCB to 7.046 MHz and applied 12V. I then tuned my FT-817 to 28.184 MHz (four times the local oscillator frequency of 7.046 MHz) and set the rig to CW mode. After attaching a length of coax in the 817’s antenna socket and draped it close to the Softrock, I heard a good, solid tone.

Excellent. Another smoke test passed.


Building a Software Defined Radio

I have decided to melt solder once more and build another QRP radio. This time it’s a Softrock RXTX v 6.3 that Wal, VK4CBW gave me. He said his eyesight doesn’t allow him to tackle such projects anymore.

The kit is fairly complex as one would imagine and although this particular model is now no longer in production, there is still detailed build information on the internet.

The first stage of the build involves constructing the power supply section. This contains many surface mount components, which are tricky to install due to their small size. First to do was to install the board mounting hardware that consisted of nuts, bolts and spacers. Then it was a matter of those pesky little capacitors: eight 0.01 uF caps and eighteen 0.01 uF caps.


The SMT caps all soldered into place.

Next came U5, the tiny 3.3v regulator. At first I couldn’t find this item it was so small. But after about 20 minutes of searching, I noticed it tucked away in a fold of the anti-static bag the ICs came in. Phew.


That’s U5 nestled in among the SMT caps. Notice the liberal amount of flux I used just to help the parts ‘stick’ in place prior to soldering.

I am taking this project nice and slowly so will post regular updates as I go along.

Building an all-band HF Air Choke

Having recently installed an end-fed 10m long wire antenna, the problem I was facing was feedline radiation, or RF into the shack. I knew this was happening because a touch-operated desk lamp would come on and off and I transmitted, which was most annoying.

I needed to build a 1:1 choke balun. So I did a quick search on the internet an arrived at the page of K8DNS (

After collecting the various pieces of gear I would need (thanks Wal VK4CBW for 21 feet of RG58), I proceeded to build this simple choke.

I wound the entire length of coax on a piece of PVC piping I had in my workshop.

I wound the entire length of coax on a piece of PVC piping I had in my workshop.

I held the coils in place with zip ties, then soldered on the PL259 connectors.

All ready for connecting up to my end-fed antenna at the feedpoint.

All ready for connecting up to my end-fed antenna at the feedpoint.

I connected it up to the end fed 80-6m portable HF antenna matchbox system, the UJM-150 that I purchased from Nelson Antennas and put it to the test.

All in place and ready to operate.

All in place and ready to operate.

Initial tests were disappointing: my touch lamp still turned itself on when I transmitted a test signal. Undeterred, I then added two ferrite chokes to the antenna feedline inside the shack and this solved the problem.

One of the ferrite choked taped to the antenna feeder.

One of the ferrite choked taped to the antenna feeder.

The other thing this new setup solved is my ability to tune up on 80m!

SOTA Activation of Mt Mundoonen

Saturday 13 February 2016 dawned hot, with clear skies; a great day to head for the hills and activate another summit.

Tony, VK1VIC , collected me from outside my apartment in Canberra at 9am sharp. It was only a 35 minute drive into New South Wales and up Mt Mundoonen (VK2/ST-053). This time I was going to rely on my Elecraft KX1 at 1W and my Buddistick vertical antenna. Tony would be using his new Elecraft KX3 (the big brother to the KX1) and a trap dipole antenna supported by a squid pole.

Mt Mundoonen (1).JPG

Tony VK1VIC at his operating position

Tony is still getting used to using CW and loved the chance of working some true “gentlemen” who gave him lots of encouragement. He has also recently acquired a Palm Paddle, which is an excellent piece of gear.

Mt Mundoonen (5)

Boy, was it hot up on this summit!

My operating position was far enough away from Tony so as to minimise interference as we would both be operating on the 40m band. The only nice and flat piece of ground I could find happened to be very close to a huge wire dipole that I believe is used for aircraft business.

Mt Mundoonen (4).JPG

I wish I had one like this at my QTH!

All in all, we had a very successful day. I added nine contacts to my log, including two Summit-to-Summit contacts with Andrew, VK1AD, who activated VK2/SW-034 and VK2/SW-027.

SOTA action: three 8-pointers in a day

Saturday 16th January 2016 was always going to be a BIG day for SOTA in VK1; Tony (VK1VIC), Adan (VK1FJAW, Andrew (VK1DA) and I (Grant VK4JAZ) set out bright and early for New South Wales, intent on activating three ‘bad boy’ summits.

First on our agenda was Webbs Ridge (VK2/ST-005), Dingi Dingi (VK2/ST-004) and Baldy Range (VK2/ST-008).

We were well equipped for the expedition. Transport was by four-wheel-drive as this, we knew, was serious four-wheel-drive country.


My set up was all rather standard, and chaotic. Rigs included my FT-817, Hendricks BLT ATU, 7ah battery and 5A solar panel, a CW Touchkeyer and a Boafeng GT-3TP Mk111 hand held. I had decided on using my Elecraft KX1 on Dingi Dingi.


The first summit we activated was Webbs Ridge, which saw all of us working many stations who were keen to add 8 points to their scores. We also worked many Summit-to-Summits.


Tony (left) and Adan in action.

Next up was Dingi Dingi, which was more challenging to get to; we had to make our way through dense bush and thick undergrowth for about 600m.


The going was interesting enough; we came across a few Wombat holes, which could be dangerous if you inadvertently stood in one. They weren’t easy to spot in the dense undergrowth.


The size of these Wombat holes is deceptive. These are large animals.

The trees, too, proved interesting.


We weren’t sure what this was on the trunk of this tree.

By the time we arrived at Baldy Range, it was well into the afternoon and chasers were decidedly more difficult to work. However, we all were able to activate this summit by making the required number of contacts.

All that was left was for us to pack up our gear and head for home.


From left, Tony (VK1VIC), Andrew (VK1DA) and Grant (VK4JAZ)

Mt Majura; another VK1 activation

On Thursday 9 December Andrew (VK1AD) and I set out after work to activate Mt Majura (VK1/AC-034). Being only some 5.9km from my apartment, this summit was a comfortable evening expedition, thanks to daylight saving time.

Don’t be misled by the one point this summit is worth. Although it is only some 890m high, when you climb it is sure feels ten times that.


That’s where we were heading.


It always amazes me what you come across when you get out of the shack and into the great outdoors. Andrew heard this scuffling sound in the grass and spotted a Shingleback Lizard, also know as a Stumpy-tailed Lizard.


When the lizard is threatened, it turns towards the threat, opens its mouth wide and sticks out its blue tongue, which contrasts with the bright pink mouth. 

Once we arrived on the summit, we wasted no time setting up and getting on air. It would only be an hour or so before we needed to head back down as we didn’t want to be on the mountain in the dark.


As always, I erected my Buddistick antenna and connected up my Elecraft KX1 transceiver. Power output was 1W

Andrew was concentrating on the 10m and 6m bands that are part of the SOTA challenge.


Andrew set up his station near the trig beacon

I was more than happy with the ten CW contacts I made on 20m and 40m.

On the way down we came across some of the locals, who seemed interested in what we were doing there.