A clipboard for SOTA

One of the challenges I have had to contend with while operating in hostile environments up on a distant summit has been logistical or organisational in nature. You know, trying to deal with various pieces of equipment, pen and notebook, wires, seating arrangements etc, all while trying to decipher morse code, taking notes and ensuring that everything works as intended.

This takes more than one set of hands to do properly.

While sitting on my chair up on The Knobby recently (VK4/SE-097) it occurred to me that the time had come to construct a simple clip board upon which I could mount my Elecraft KX1, my log sheets and anything else I might need. So I headed back down once the activation was completed and rushed straight to my workshop, where I selected some suitable pieces of timber for the job.

This is what I came up with:

sota-clipboard

Better antenna for satellite work

Having worked my fist ‘bird’ with a hand-held, it was time to take the next step and try using a better antenna. The ubiquitous ‘rubber duckie’ has been said by many to be nothing more than an eloborate ground; it’s certainly a compromise antenna designed for simplicity and basic functionality at best.

Wallace, VK4CBW, suggested I try working SO-50 with a gain antenna as it would improve transmission and reception markedly. He offered to lend me his Elk hand-held antenna.

This antenna is a log periodic cut for the 2m/70cm bands and is only two foot long – perfect for satellite work.

I assembled the antenna (it comes with the elements all colour-coded for easy assembly) and put out a call the next time the satellite was within range. Bob, VK3MQ, replied and we had a superb, short, QSO. I was delighted as the distance between us was 1,346 km (836 miles). Not bad for an FM contact on simplex.

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Next I worked Cam, VK4FAAJ, who was using a hand-held coupled to a home-brew yagi he made from a tape measure! Nice copy too, even though he was in my neck of the woods.

 

 

 

Working the satellites

I always wanted to work the satellites as there seems to be something mystical about them. They aren’t called ‘the final frontier’ for nothing.

After talking to Wallace, VK4CBW, it became apparent that this would be quite feasible with a dual-band hand held transceiver and some satellite-tracking software on my computer.

My Boafeng GT-3TP would do fine so I downloaded and installed gpredict into my Surface Pro 4.

I proceeded to monitor my satellite of choice, SO-50, which I chose because it is an FM satellite. Wallace helped program in the receive and send frequencies into my hand-held; receive frequencies starting at 436.805 and progressing down at 5khz intervals to 436.780 would be needed to take the Doppler effect into account. Transmit frequency remains at 145.850.

screenshot-1   As the satellite came within range I headed outside and turned on my hand-held, with the squelch turned right down. Pointing the rubber-duckie antenna towards the ground, I put out a call .. and listened. Turning this way and that, I repeated the call until I heard Wallace reply.

I had made my first contact. The interesting thing about this was that his shack is only some 300m down the road from my shack, but we were communicating via a satellite in space. The pass only lasted around eight minutes or so; brevity is the name of the game here.

My next attempt would be with an Elk antenna, a specially-designed four-element log periodic antenna that Wallace will lend me.

Getting to grips with DMR

I’ve been monitoring developments in the amateur radio world for quite a while now, eager to keep abreast of the latest trends as the world dashes headlong down the slippery road of technological advancement. Most of the action seemed to me to be happening in the digital domain.

Digital voice is where most of the commercial and military world is headed, so I zeroed in on DMR as an emerging amateur radio mode.

D Star has been operating in this space for quite a while now but the proprietary nature of this venture has many sitting on the sidelines. One of the reasons is probably because of the high price of the hardware needed.

Being an open source computer fan for many years now, I became aware of a new mode that is gathering pace world-wide: DMR-MARC.

DMR-MARC is an all-digital group of over 500 DMR-MARC repeaters in 48 countries with 33036 registered users. And both lists are growing all the time. In Australia there are repeaters in NSW, VIC, WA, QLD, with the latest in the ACT currently being commissioned as I write. These repeaters operate on the 70cm band.

My friend Wallace, VK4CBW, also became interested in this fast-growing mode. He decided to take the plunge and imported two DMR hand-held transceivers from a factory in China. The brand is Vitai, which neither of us had heard of before.

When they arrived, we were very pleased with the quality of construction.

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The Chinese make excellent rigs these days.

The first thing we had to do was to register as a DMR user. This we did through the DMR-MARC web site and it wasn’t long before we received our new ID numbers.

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Now it was time to sample the marvels of digital voice communications. We began by working simplex between us; what quality! And our conversations were private too; no other user could listen to our conversations.

It was now time for me to try for some DX. For this, I discovered that most operators monitor a very useful web page, which acts as a control centre for VK operators: it allows us to see who is working on the various channels or talk groups.

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All I had to do now was to select the talk group of interest and hit the PTT button on my hand-held and I would be up and away.

So far I have worked stations in Malta, South Africa and Finland, all with 4 Watts from a hand-held transceiver!

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.