Trends in Amateur Radio

It’s always been accepted that one of the attractions of amateur radio was that it involved the building of kits; if you needed (or wanted) a better or more specific transmitter, receiver or transceiver but couldn’t afford to purchase one from your local retailer, you bought one in kit form and built it yourself.
Kits were ordered over the phone and posted to you. Some were better than others but all had potential risks involved, such as the odd missing component.

The Elecraft KX1 kit came professionally packed with a great instruction manual.

This kit from Virgil Stamps at http://www.hfprojects.com is a good example of a well-produced kit that involves soldering all the components into place in the PCB.

And it wasn’t only on the electronics front that you could heat up your soldering iron and get busy; making a suitable antenna was also a huge part of the hobby.

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

Baluns are also popular construction projects with homebrewers.

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

Of course, you didn’t have to stick with kits if you needed to construct a radio; you could always build one from scratch with components you happened to have in your proverbial junk box.

I built this regenerative receiver using what I happened to have on hand at the time.

Test equipment is also easy to build from kits.

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

I have noticed a trend beginning to appear in the world of amateur radio, and that’s a swing away from ‘melting solder’. I first noticed this with the advent of the Elecraft KX3 a few years ago. For the first time this world leader in kit production began marketing a rig that only required mechanical construction; all the electronics came pre-manufactured and only needed slotting into place in the enclosure, which needed first to be put together by the ham. This was due to the high number of surface mount components present.

And now Virgil Stamps, proprietor of the beautifully designed and manufactured HF linear amplifier that is aimed at the SOTA and WWFF fraternity (http://hfprojects.com/) has gone this route with the launching of his latest offering, the HFPacker Amp MiniHFPA2. By all accounts it looks like this new trend in amateur radio is here to stay, but as long as it helps get more people on air, that’s sure to be a good thing.

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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 v 6.3: RX Switching and RX Muting

This stage handles the muting of the RX section when I PTT goes high. After soldering in all the component, the testing went according to plan, until taking resistance readings of the power rail.

The initial current readings were as expected, but when I switched the DMM over to read resistance levels, nothing registered. I was expecting to see around 7 Meg ohms at the 12V test point, 950 Ohms at the 5V test point and 10 K Ohms at the 3.3V test point. Resistance readings of the band pass filter’s secondary windings were fine.

That’s where I left things for the night. My philosophy is to sleep on it when things get tough.

It was at around 4am the next morning that I woke suddenly with the answer as to why the resistance readings for the power rail were non-existent: I was taking the readings with the power to the PCB turned on! So I took readings again, this time with the board dead and all was just as it should be.

Still flushed with success, I decided to push on and continue with the rest of the testing. All readings on my DMM were as they should be, so it was time for the best part, to solder in a temporary antenna, connect up a lead to the input of the computer’s sound card, start up the software (Rocky in my case) and see if the rig could detect a test signal on 7.046 MHz (the centre frequency of the 40m band that the rig is tuned to).

This is the spectrum before sending a test signal from my FT-817.

This is the spectrum before sending a test signal from my FT-817.

Now came the moment of truth.

The test signal is clearly visible now. The spike at 7046.7 is the signal. It has a mirror image at roughly the same distance to the left of the centre frequency. This is due to ground loops on the PCB.

The test signal is clearly visible now. The spike at 7046.7 is the signal. It has a mirror image at roughly the same distance to the left of the centre frequency. This is due to ground loops on the PCB.

Once the rig has been completed and installed into an enclosure I will try to filter out any signal images that mayexist.

This completes the build of the main board. Next is the difficult part: the PA filters.

 

 

Softrock RXTX v6.3: PTT circuitry

The PTT circuit is all about connecting the PTT and Keyer inputs up to the SDR software via a serial interface. However, the DB9 connector will be installed in a later part of the build. I will be using instead, a USB I2C interface as both my Surface Pro 4 and my Compaq laptop, which runs Arch Linux, don’t have serial ports.

This stage involved installing four caps, 12 resisters, a diode, an RF choke and four transistors.

All appeared to go well until it was time to carry out some tests. Current tests proved spot on, and so did the initial voltage tests. Until it came time to prove that the transistors were turning on when voltage was applied to the PTT_IN connection.

What is supposed to happen is this: when 12V is supplied to PTT_IN, Q1 turns on, pulling R21 and PTT_IN to a low level. Q2 then turns on and I should be able to measure about 12V at S12V. This means the rig is transmitting.

I did not see this on my DMM. My reading was of the order of 0.02V.

So it was out with the schematic once more (I had become quite familiar with this piece of paper). I started by tracing the power supply to the transistors to see what was wrong and why Q2 wasn’t turning on. After much thought, I noticed that two vital resisters were missing on my PCB.

These resisters were missing on my PCB

These resisters were missing on my PCB

It was then that I decided to check if any other components were also missing. What I discovered was that I had omitted to solder in all the capacitors and all the resisters for this stage! No wonder Q2 wasn’t turning on.

Once this slight oversight had been corrected I ran through the test once more, with perfect results.

Next will be the RX Switching stage.

 

Softrock RXTX v6.3: TX Mixer

The next stage in the project was to construct the TX Mixer stage. The job of this stage is to provide the modulation of the Dividers’ output signals by the four I and Q signals from the Op Amps. The result is a double sideband RF waveform that will be coupled into the PA stage.

This stage centres around U3: FST3253 which is a SOIC-16 Dual 4:1 Mux/Demux Bus Switch. There were also four resisters, a capacitor and two connector sockets that completed the build.

When that was done it was time to test if all was as it should be.

This was when I hit a snag.

First, I had to jumper the hairpin bend of R26 (which hadn’t yet been installed) to ground and then jumper pins two, three and four of socket J1.

R26 needed to be jumpered to ground.

R26 needed to be jumpered to ground.

Current readings were fine, and so were the initial voltage readings. But when it came to measuring the voltage on pins 7 and 9 of U3, instead of getting around 2v I was reading 0.01v.

I tried again but this time noticed that when I turned on my power supply (12V DC) the current surged to around 2A before settling down to more normal levels. I cut the power and began scratching my head.

All the solder joints looked fine as did the components, which were all in the right places. That’s when I decided to take a break and sleep on it.

After the dust had settled, I decided to consult the schematic. I started by tracing the 5V power route, through U4 and into U3. I could see its path to ground was through pins 1 and 15, then on to the as yet uninstalled R26 to ground via C43. So that’s why I needed to insert a jumper.

I then connected up my DMM and swung the switch to the continuity setting. Probing the jumper connection I had inserted into R26 produced nothing. So I probed R26’s other hole and bingo. I had jumpered the wrong whole!

My mistake was immediately apparent.

I had presumed the jumper needed to be in the whole marked with a white circle around it (to indicate that’s where the body of the resister fits). The instructions called for jumpering the hairpin of R26, which I suddenly realised was not the hole indicated by the circle, but the other one.

Resoldering the jumper took only a few seconds, but the satisfaction I received from a full set of good readings lasted quite a lot longer.

This little exercise highlighted to me the importance of being able to read a schematic diagram.

 

Softrock RXTX v6.3: Building the TX Op Amps

This stage has a fairly high component count, so patience was the order of the day. I decided to take it nice and slowly so as to enjoy the process. It would also make sure I didn’t make any mistakes.

The stage consists of four unitary gain op-amps, arranged in pairs. The left channel’s input resolves to two signals: 0° and 180°. The right channel’s input resolves to two signals: 90° and 270°.

Each of the 14 resisters was checked with my DMM to ensure I had the correct ones for insertion into the PCB; it’s easy to mistake brown for red in the colour coding on the tiny resisters.

The Op Amps themselves (IC SOIC-8 dual Op-Amps) were also tiny beasts each with eight pins that required careful soldering so as to ensure no solder bridges or spashover on any of the adjacent empty holes. For this task I used a very handy suction tool that Wallace, VK4CBW, gave me some time ago.

OLYMPUS DIGITAL CAMERA

Positioning U1 on the underside of the board with the suction tool.

Once all the components had been soldered into place and I was certain there were no cold solder joints or solder bridges, it was time to conduct the usual current and voltage tests according to the instructions.

Thankfully my patience paid off with all reading being as expected.

Next is to tackle the TX mixer.

Softrock V6.3 build: The RX Mixer Stage

The mixer stage acts like two traditional direct conversion mixers operating in tandem. It centres around U10, a SOIC-16 Dual 4:1 Mux/Demux Bus Switch. A 2-pin and 3-pin socket also needed to be installed along with three resisters. And for testing the stage, an 80/40m Band Pass Filter board also needed to be built.

Care had to be taken once more when soldering the tiny pins of U10 into position.

OLYMPUS DIGITAL CAMERA

This is the underside of the PCB with U10 top middle.

Building the BPF was relatively simple, with the exception of winding the two coils; these take time and care but aren’t particularly difficult to do.

OLYMPUS DIGITAL CAMERA

The 80/40m BPF board in place.

Testing went well. Current and voltage readings were as expected. The only test I was unable to carry out at this stage was to test it with Rocky, a SDR software package that shows a chunk of spectrum. This was due to my Linux laptop’s sound card not showing up in Rocky.

Next will be to build the TX Op Amps.