Testing the miniHFPA2 with the Elecraft KX1

I received a query from a reader yesterday regarding tuning up an antenna using the internal ATU in his Elecraft KX2 if it were connected up to the miniHFPA2 amplifier. The reason he wanted to know about this was because he was considering ordering one for use with his Elecraft KX2.

He wanted to know if it is it possible to run an antenna such as a doublet, by tuning the antenna using the KX2’s internal tuner with the amp in bypass mode, then switching the toggle switch on the amp to put it inline. He said that it appeared to him that this procedure would not work because the amp, once in line, would probably change the SWR of the antenna.

I decided to conduct a test to find out if this would in fact be the case. This is what I found:

I carried out the test in two parts:
Firstly, with the KX1 (powered by a 12V supply voltage) connected to a PWR/SWR meter and 50 Ohm dummy load.

On keying down, the PWR/SWR meter read the following: output 3.5W with SWR of 1.0:1

A straight through test with the signal going to the dummy load.Secondly, connected up the miniHFPA2 directly to the KX1, and the Pwr/SWR meter and dummy load.
With the Amp in bypass mode, the reading was 3W output and 1.0:1 SWR.

The only difference now is that the amp has been connected up but left in bypass mode.

With the Amp switched on and placed inline, the reading was 18W output with SWR 1.0:1.

With the amp in action, the SWR remained 1.0:1

Note: the lower than expected power output with the amp inline was due to the fact that the amp is set up for an input of 5W. My KX1 can only supply it with 3W, so the final output of the amp will be lower too. With 5W in, as is the case when connected up to my Yaesu FT-817, it outputs 30W.


First portable operation with the Packer 6m amplifier

I decided to take the bull by the horns and activate a SOTA summit on 6m only, using my newly-built Packer 6m 30W linear amplifier. The summit I chose was Tamborine Mountain, VK4/SE-059.

My rig this time was the Yaesu FT-817 and the antenna was a homebrew 6m dipole, strung up as a sloper.

The rig connected to the amp and the LDG antenna tuner. The battery is a 7a/h gel cell. The power cords are routed through a SotaBeams 4-Way distribution box.

As soon as I put out my first call, the game was on. In the space of a short 30 minutes I had made 15 contacts. Wonderful.

The action came thick and fast and the view was excellent.

One aim of the activation was to test the amp, especially how long the battery would last as it draws around 6A.

At the start of the activation my battery had 12.58V, and at the end, 12.49V. That’s pretty incredible, especially seeing I was operating almost continuously. Input power from the radio was 1W and output 30W.

Another test I carried out (with Peter VK4JD) was to get an idea of the difference the amp made to an actual QSO. On bypass, with 1W, my signal was down some 20dB. So the amp was doing a fine job.

Building a VHF Packer 6m Amp

I was given this kit by Wal, VK4CBW, as he had purchased it some years ago and knew he would not get around to building it.

The kit was produced and sold by http://www.hfprojects.com in America and came well packaged in a series of sealed plastic packets. Everything including the enclosure and heavy duty heat sink were included.

This little amp requires 1W drive for 30W output and features a Mitsubishi RF mosfet module mounted on the heatsink. There is also a filtered Anderson Power Pole DC input that takes 12V at around 6.2A. And measuring only 5.25 x 3 x 3 inches and weighing less than 1 lb, I figured it would be perfect for SOTA or VKFF operations.

I started my working on the well-made PCB.

Populating the PCB

Then I began making the power cable assembly, the RF cable assembly and the switch cable wiring.

The cables were installed inside the top enclosure case.

I had to fabricate a make-shift mounting plate for the Anderson Power Poles as this was missing from the kit. It has been ordered but hasn’t arrived yet. Eager to avoid delays so I could catch the 6m band opening, I made a replacement out of PCB material.

This isn’t perfect but it would do until the genuine item arrives in the post.

After a little fiddling it went in well and did the job.

The mounting plate in place.

Next, the circuit board and amp module were installed and the initial check carried out.

Ready for alignment and the first smoke test.

The bias current had to be set to 0.7A if the amp is to be used for SSB work, or 0.5A for FM. I chose the former.

The bias current set correctly.

I skipped the next step, which was to align the low pass filter as I don’t have the correct instrumentation. But as I had constructed coils L1 and L2 according to the instructions, this wouldn’t be too critical.

The power output test was more important. I connected the amp up to my Yaesu FT-817 (with power wound back to 1W) and attached my homebrew dummy load and an SWP/Power meter. RF output was shown to be a mere 16W. So I flicked the bypass switch and measured the output as 1W with an SWR of 1.0:1. All good there.

Tweaking the coils of L1 and L2 soon produced the required 30W, so it was time to disconnect the dummy load and attach my 6m monoband dipole antenna.

My homebrew 6m dipole strung up and ready for action.

Keying down produced the power output reading I was after.

RF out was now 30W with the SWR indicated as around 1.7:1. Not bad at all.

Next, I attached my LDG auto tuner to the chain and was ready for an on-air test.

All set up and ready for action.

The result was most pleasing. I worked a bunch of VK7 stations (SSB and CW) and well as VK2s and 3s. I am in business and ready to take advantage of the summer openings.

Oh, and all reports received were most favourable. Nice clear signals, good reports and clear audio were what most operators reported back: they were all impressed that I was only using 30W – most stations were in the 200-400W range.

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.


Elecraft KX1 mod

I have now replaced R11 (now 5.6 Ohms) and R30 (now 30.8 Ohms), and squeezed the turns of L2 together more. The result has been most satisfying.

L2 in position before L1 was installed.

L2 in position before L1 was installed.

The power output is now as follows:
9V = 1.87W
12V = 3.14W
13.8V = 3.92W

9V = 1.66W
12V = 3.07W
13.8V = 3.98W

Measuring power levels.

Measuring power levels.

The rig is now performing as it should according to the specifications.

Completing my Elecraft KX1 and first on air QSOs

The final stage of the build process involved final assemble and testing. The last few resistors, a zener diode and a trimmer pot were soldered in. Then it was time to wind and install toroidal inductors. The only tricky one was the transformer, which has two windings.
Next came inserting the metal standoffs onto the PCB.

With the standoffs in place, it is beginning to look like a radio.

With the standoffs in place, it is beginning to look like a radio.

Once that was done, it was time to scrape off the paint on the enclosure so that there is a good earth between it and the standoffs. I did this with a rotary tool.

Having the right tools makes the job easier. Sand paper will also do.

Having the right tools makes the job easier. Sand paper will also do.

I then installed the red filter over the LED display opening, soldered in the final transistor and carried out some voltage checks to see if all was okay. I then attended to the installation and wiring of the internal battery holders. This was a little tricky but didn’t present any problems, except that I applied too much solder to one of the crimp terminals and so ruined it. A quick email to Elecraft resulted in two new ones being mailed out to me that same day. Awesome service.

The PCB in place mounted to the upper part of the enclosure.

The PCB in place mounted to the upper part of the enclosure.

Time now for final alignment and testing.

Testing the transmitter requires taking power readings on both bands with an accurate power meter; one that can read power at QRP levels. I have two; a QRPometer, and a Hendricks dummy load/power meter. I used both.

QRPometer on the left, Hendricks dummy load/power meter on the right.

QRPometer on the left, Hendricks dummy load/power meter on the right.

This is what I read:
20m @ 13.8V: 3.8W
40m @ 13.8V: 2.66W

Hendricks dummy load/power meter
20m @ 13.8V: 3.5145W
40m @ 13.8V: 2.66W

The formula I used to calculate power with the Hendricks meter is as follows:

The instruction manual says that power on both bands should be between 3 and 4 Watts, so clearly my 40m readings are a bit low. I emailed Elecraft and was told the readings look typical, but I want a little more power, especially on 40m as Down Under it was come in handy. I was told to change the values of R11 and R30 to between 4.7 and 5.6 Ohms, and 27 to 33 Ohms respectively. That is the next thing I will attend to, when I can source such low value resistors.

The rig complete and ready for the first on air test.

The rig complete and ready for the first on air test.

Time for the first real test. I plugged in my Touchkeyer P3K and tuned around on 40m on 1 March 2013 and heard ZL1IG Robin calling. I answered and completed my first QSO with this rig. He gave me a 339, which I was pleased about, especially since the distance between us was 1,549 miles. He is in Invercargill and I am in Brisbane.

Two days later, I decided to try 20m and answered FK8CE Dominique, who was calling from New Caledonia, a distance of 891 miles away. He replied and we had a satisfying QSO. He gave me a 599. After that, I tuned around and heard HB9BQR Roland calling from Solothurn in Switzerland. I answered and he gave me a 579. That was fantastic because the distance between us was 10,133 miles. We had a long QSO, so it wasn’t just a case of luck.

The antenna I was using was a simple dipole up at around 15 feet.
Now to wait for the crimp connectors to arrive and then to source some resistors, and the rig will be complete. Perhaps I don’t really need that additional Watt of power!

WSPR at last on my iMAC

Well, it has been a long time coming: I am up and running on WSPR using my iMAC. I have been battling to achieve this for many months now, trying my Linux operating system with limited success, and searching for a decent OS X software package to run it on my iMac.

This evening I hit gold when I stumbled upon George Smart’s web site quite by accident. George had successfully produced a Mac version of the WSPR software and made it available for download. All I needed to do was hit the download button and move the resultant file into my applications folder, and start up WSPR. It couldn’t have been easier.

Here’s the web site: http://www.george-smart.co.uk/wiki/wspr

Anyway, I fired up the program, tuned in my FT-450 (wound down to the min 5W the rig will go to) and waited to see what would happen.

Imagine my delight when I started decoding signals! Imagine my delight, too, when I started being copied by stations as far away as America!

My set up here is the FT-450 connected to my iMac via a SignaLink USB interface. Works like a charm.

The action on my iMac after the initial flurry of contacts. I am impressed.