Digital Modes

 

Although I'm not in a position to transmit my own digital data at the moment, I have been experimenting with receiving some of these modes, especially FT8 which seems to be very popular at the moment. The mainstay program for doing this seems to be WSJT-X (https://physics.princeton.edu/pulsar/k1jt/wsjtx.html). I do use this software, but I find sometimes that it just doesn't work! One day I turn it on and it jumps straight in and starts to decode. On other days, no matter what I do, it won't decode anything and I can't seem to find a reason or remedy on line for this.

 I have also been using a program called MSHV (http://lz2hv.org/mshv). So far I have found no problems with the decoding, but like I say I am unable to transmit just yet. The FT8 traffic seems to be quite heavy on 24 and 28MHz and it seems to go on all day. I do a lot of my decoding using an old Windows XP machine so I have to be picky which packages will run on it. An older version of WSJX-T will run on XP and so will MSHV.

My SDR of choice is HDSDR, a free program available for download.

My SDR dongle is the Nooelec Smart which can get down to 24MHz and goes up well above 1GHz. I love to decode data streams that are floating about on the airwaves. These include POCSAG pager transmissions, APRS packets from various sources, weather satellite transmissions, plane transponder signals (ADS-B and ACARS) and taxi MDT signals. The software for decoding all of these can be found on line for free. All good fun 😉. 

Vector Network Analyser

Because I'm always tinkering with antennas, a few months ago I saw this and decided to buy one. Probably the best thing I ever bought! The NanoVNA comes in many different flavours. The one I got was the NanoVNA-H. At the time of ordering I thought that the screen would be a bit small, but it is manageable. It measures all kinds of things, half of which I don't really understand. But for measuring impedance, SWR and insertion loss its just great. It can be used for lots more measurements when using the other channel connection like length of cable runs and fault finding etc. but I doubt I will ever use them. Like they say 'Its better to have it and not use it than not have it at all'.

If you are struggling with the screen, there's no need to worry because there is free software, NanoVNA-Saver, that solves that problem. A typical snapshot is shown above. I can now build stuff and test it there and then with this nifty little device. As with all these devices, there are a lot of fakes out there so it pays to read the vendor's feedback. I do recommend that any radio operator should have one in their toolbox.

 

APT Satellites

Another interest of mine is to decode the NOAA satellite APT transmissions. Tune in around 137.1 to 137.9MHz (Wide FM) at specific times of the day to hear these strange signals. Basically, only NOAA15, 18 and 19 are currently operational. Using free software from the internet, you can decode these signals into great pictures. It can also be used to give you a heads-up on the weather coming your way. I personally use WXtoIMG decoding software. You may find your own favourite. Your receiver must be capable of receiving FM at about 40KHz bandwidth to get a proper decode. I find the best way to do this is to use a RTL-SDR dongle and SDR radio program, but it can be done with any FM receiver.

You will also need an antenna that specifically receives APT transmissions. This antenna which I built many years ago is still going strong at the bottom of my garden. It is a QFH (Quadra Filar Helix). It is designed to receive hellically polarised signals like the ones from the satellites. It also doubles as an excellent scanner antenna.

Slim Jim Antenna

(2m/70cm Slim Jim Antenna - Measurements may vary)

 Over the years, I have made lots and lots of my own antennas. I keep coming back to the 'Slim Jim' and 'J-Pole' antennas because in my experience, I don't think there is a better omni-directional choice. They are fairly easy to build and many calculators can be found on line. The measurements in the above diagram were taken from an on-line calculator, but when I built mine I found that I needed a slightly bigger air gap and my connection point was considerably higher up from the bottom. So some experimentation is needed.

Before my licence, and stretching way back to the 1980's when AM was the only choice, I have worked stations all around the world using, in particular, a J-Pole. The problem is at this wavelength (11m), and more so on the lower HF frequencies, the antenna can get quite large. However on 2m/70cm its a completely different story. I try to keep my antennas in the loft now where possible because they can be an eyesore for the neighbours, especially the 11m ones. I am currently running my UV-5R through a loft mounted Slim Jim. I can easily get into the GB3ST repeater in Stoke on Trent which is about 41 miles from my location. The SWR at the moment is 1.3:1 on 2m but about 1.7:1 on 70cm, so its still a work in progress. 
I am currently working on a 3 element Yagi with a simple RC servo rotator. I have only tested this at ground level, whereas the Slim Jim has about a 20 foot advantage, the Yagi is only just comparable with this. Also, the Yagi is directional, so a lot of twiddling to get the best signal with the rotator. It will probably be a different story when I get it in the loft with some height advantage, because as we know on VHF and UHF, height is king. 

UV-5R 2m/70cm Radio

Welcome to my Blog! I intend to document my journey into the mysterious world of amateur radio. I finally got around to sitting the foundation exam. Probably every new licencee's venture into Ham Radio is to buy one of these dinky little 2m/70cm FM radios. Let's face it, its no use lashing out thousands of pounds on an 'all singing all dancing' home base station when you may find yourself limited to what you can do with antennas, or maybe you just discover that the hobby is not for you. However, after the initial joy of tinkering with a few frequencies, I realised that to program this thing manually would be a nightmare. So a little research later, I discovered that I needed to install Chirp. This is where the problems started. I was struggling to get my UV-5R to communicate with the PC. I bought a cheap lead from Amazon thinking this would be OK. Apparently not! After trying countless drivers and set-ups, I finally conceded defeat.

 Then I realised that the radio can communicate using a FTDI UART to Serial USB converter lead. I remembered that I already had a few of these handy CP2102 gadgets lying around because of my microcontroller projects. I immediately chopped the head off the cable I had bought and soldered the wires onto it. When plugged in and connected to Chirp software, it immediatley started to clone the radio. So, to anyone struggling with this, just bear in mind that you will not go wrong with this type of lead. You can knock one up yourself like the diagram above and use 3.5mm and 2.5mm separate jack plugs. Just remember TX radio to RX converter and vice versa. Good luck!