Many thanks to Karl (K5KHK) for sharing this guest post, which originally appeared on his blog, Karl Heinz Kremer’s Ramblings:
A Digital Station in Your Pocket
by Karl Heinz (K5KHK)
How small can a complete station to work FT4/8 be? With the QRP-Labs QMX, we have a transceiver that certainly fits the bill for a small station. By itself it can only be used for CW, to use the digital modes, one has to combine it with a computer. Even the smallest laptop is too big the fit into the pockets of my cargo pants – we are trying a pocket sized station after all 😉
In this article, I will describe how to use a QMX transceiver and an iPhone to activate a POTA park with FT8.
The Components
My QMX is the original that was released at FDIM 2023, so it covers 80m to 20m. Mine is serial number #20.
My iPhone is small enough, but unlike Android based phones, the QMX cannot be connected directly to the phone. Apple sells a “camera adapter”, which plugs into the phones Lightning port on one side and provides a USB connection on the other end. $29 for the original Apple part was a bit hard to swallow, so I opted for something cheaper straight from China’s “we clone everything” factories: https://amzn.to/3WDSfUc
[Please note: All Amazon links are affiliate that support QRPer.com.]
The picture shows both a USB and a lightning port on the adapter. This should allow the phone to be powered/charged while the adapter is being used – more about that later.
Another limitation is the antenna: The QMX does not have a built-in antenna tuner, and even my QRP sized ZM-2 would have to live in a different pocket 🙂 My plan is to use a resonant antenna so that I would not need a tuner.
The easiest antenna with a good match is a dipole, but that is a bit more challenging to deploy in the field, so I opted for an end-fed halfway (or EFHW) antenna with a 49:1 transformer. I 3D printed a winder that allowed a BNC connector and the transformer to be mounted on the wire winder:
The design came from Thingiverse: https://www.thingiverse.com/thing:2871679
Because I am using a different toroid for the transformer, I had to remove the “bump” that is holding the toroid in place. Going forward, I may change the design a bit more to have so that I can fit more wire on the winder.
For those familiar with the transformers usually used for EFHW antennas, the picture shows two things that are different: As I’ve already mentioned, I am using a different toroid (the Fair-Rite 2661102002 core, which is a type 61), and a different winding pattern. More about that in a future post.
To power my station, I am using a TalentCell rechargeable 12V power bank: https://amzn.to/3snTyr8
First Test
With everything in place, I tried to make a quick FT8 contact from home with this setup, but with my “big” EFHW antenna in my backyard. Because it was just a quick test, I did not even bother to hook up the charging cable for my phone (more on that later).
The software I am using is iFTx, which supports both FT4 and FT8.
I connected the phone to the adapter from above, connected the adapter via a USB cable to the QMX, and connected the QMX to a 12V power supply (unlike anywhere else in ham radio, 12V here means 12.0V and not the usual 13.8V), and hooked up the antenna to an antenna tuner and then to the EFHW in my back yard.
I answered an FT8 CQ call and successfully completed the FT8 exchange. The software does the automatic sequencing of the different messages, so it is very straight forward to use. With this first contact, I verified that the iPhone/adapter/QMX setup does work.
The Real Test
The next attempt was while camping at Hamlin Beach State Park (US-2068). I set up everything just like at home, but because I was planning on being on the air for a while. I also hooked up the cable to charge my phone while I was operating.
I was able to receive stations, but could not transmit. What made the troubleshooting more complex is that during setup, I created some sparks (that is why I do not like the barrel connector for power). I was pretty sure that the QMX was not involved, but not being able to transmit kind of suggested that I killed the finals. So I put everything away and used my KX2 instead.
Back home, I did some troubleshooting and hooked up a straight key to the QMX and it worked: I was able to finish a few CW QSOS without a problem, so the finals were definitely OK. I then set up the system again for FT8, and sure enough, I was able to make a contact. Because it was a quick test, I did not bother to use the power cable for the phone. By now, most of you probably know what the culprit was, but because I did not spell things out like this, I was still in the dark.
Success At Last
Fast forward a few more days… We went back to Hamlin Beach State Park – but this time to the picnic area – and I set up my station again. And sure enough, once everything was set up, the QMX did not transmit. This is when I took a step back and reviewed everything I had done so far, and slowly I came to the realization that when I provide power through the adapter to the phone, the QMX would not transmit.
I was able to finish my FT8 activation with my pocket sized digital station. I did run into one problem however: iFTx allows to automatically determine one’s grid square – which of course is important for FT8. When I enabled that, it correctly put me into FT13 at first, but a few QSOs later it switched me to JJ00aa – I reported this as a bug to the developer.
Using iFTx with the iPhone
The connection from the phone to the QMX is audio only. iOS does not allow an application to open a serial port connection (unlike Android). This means that the QMX will not receive any frequency information from the phone, and also no PTT signal. For this setup to work, the operator has to make sure that the QMX is tuned to the correct frequency that the correct band is selected in iFTx, and that the QMX is set to VOX mode (this is in the Digi Interface menu).
When configuring iFTx, it is possible to select a “Special Interest Activity” like POTA. This is then added to the CQ call as in “CQ POTA K5KHK FN13”.
As I’ve mentioned before, the application will automatically sequence the correct messages when a station answers the call.
Once the QSO is completed, it will be logged to the iFTx internal log, which can be exported via the usual “send to” methods available in iOS (e.g. email the log, save as a file, …).
When exporting the log, there is a choice of exporting everything, or only the new QSOs since the last export. This will create an ADIF file, which can be submitted to the POTA program, or imported into any other logging program.
At the end, I was successful in building a “pocket sized” digital station based on the QMX, I just need a fully charged phone and cannot depend on charging it while operating.
Click here to check out more articles from Karl on his blog!