Feature Articles
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- Written by: Maintenance Guy
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After satisfying myself with regard to the operational integrity of my new 15m monoband EFHW on the Lunchtime Net last week, I thought it time to add some complexity into the mix and see if everything continued to hold together like it generally does at my home QTH.
As you can probably see from the photograph below, having taken the A272 east to the northern boundary of Chailey Memorial Common, the dog was pretty exhausted. The good news was that the mag-mount had kept the 10m whip in place on the roof magnificently.
Once there, I dispatched the wife around the common with said dog, while I set up the radio gear. Other than the End-Fed antenna (being sensible for a moment, it's a self-constructed plywood drive-on mount with Barenco tilt-base, custom 1m alloy support pole, 10m DX Commander Classic and a home-constructed 49:1 QRO impedance transformer) I'd chucked just about everything else I could think of in the boot with which to test its capabilities.
I started with my NanoVNA to check the antenna resonance in the field as opposed to on my driveway, and surprisingly it was quite different. Sadly the radiating element was too short, but not by that much. The analyser displayed a superb-looking dip at around 21.8MHz, and with reasonable bandwidth. Click the image below to enlarge.
I'll address this length anomaly later, but I'll be cutting an element for each band, so I'll just reuse this one for 12m.
Next up was my LDG IT100 Autotuner connected to the trusty Icom IC-706 MKIIG. I've only rarely used this tuner, as I have my preferred MFJ-949E manual tuner back in the shack. It's a great bit of kit though, and it's going to be given a good workout this summer whilst I'm out and about. It happily tuned my End-Fed on 17m and 20m, but I left it at that for today. Too much other stuff to get through, and I just wanted to make sure it still worked and was happy on the (spare) car battery.
Last week, I invested in a Huawei Category 4 LTE USB dongle so that I can have decent internet access in the field. I don't have a mobile phone for reasons I won't bore you with, so this was the best solution for me. Having pre-configured it at home, it worked perfectly in Chailey which was surprising seeing that Chailey has only recently been connected to mains electricity and sewerage.
An old Dell laptop was pressed back into service running Windows 7 with the usual WSJT-X suite as well as some other bits and bobs. With CAT control hardware & external sound card connected, I had to do the usual dance of the Windows USB-COM fairies and then make the requisite changes in WSJT-X before letting Dimension 4 re-synchronise my clock via the 4G dongle. I was then looking at a screenful of FT8. Way more FT8 signals than I usually see on 15m, so something was working.
A very low noise floor in the car-park helped to offset the cacophony of shoutyness from the irritating contesters on the band. A few 100W full duty cycle transmissions later and a handful of QSO's in the mental logbook (no, I don't keep a proper log either - have I no shame?) as well as an impressive number and distribution pattern of signal reports registered on PSKreporter, I moved on to my final test of the afternoon.
The Icom packed safely away, I connected and fired up my fantastic SDRPlay RSPdx SDR receiver. With SDRUno running on the laptop, the full beauty of a slice of spectrum crammed with every type of amateur transmission was displayed. I simply love this software, and chuckle to myself every time I use it knowing that it looks a million dollars and costs as much as good manners. Click to enlarge. Do I have to keep saying that?
To be honest, I'll exploit any opportunity to post a screenshot of this software. Here, it's dealing with signals on the 40m band and beyond, albeit using my single 15m (6.7m physical) element.
Anyhow, the objective of checking and testing interoperability of all the various tech I'd gathered together for the day (which shall forevermore be known as /p0 day) was complete, and it was time to head home for tea.
More tales from the trails soon. How will a 20m element work? Will I have to employ a little foldback/linear loading? Will a small loading coil bring the 10m resonance point down, like it does on a 40m EFHW setup? Is anybody reading this nonsense anyway?
Stay tuned.
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- Written by: Alex M0TOT
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Here is another project of mine.
Maybe someone will find a use for this small piece of kit.
There are a few spare PCBs available, and I can provide a schematic to go with it if required.
Regards,
Alex
M0TOT
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Should anyone wonder why non-radio articles appear regularly in our 'Feature Articles' section, let me refer you to the MSARS constitution:
The aims of the Society shall be to further the interests of its members in all aspects of Amateur Radio and Electronics.
and Alex is one of the most prolific contributors of articles on electronics projects.
Here is yet another of his creations. This time he has shared a very useful looking generic stepper motor and driver circuit, for which I can immediately think of a number of real-world uses.
A note on unipolar and bipolar stepper motors
Unipolar and bipolar motors each have their own pros and cons, and the choice of one over the other is dependent on the application it will be used for.
Bipolar stepper motors use a single, large coil per winding, which creates more powerful magnetic fields than unipolar alternatives. This in turn results in higher torque figures achieved at the motor output shaft. Because the coils of a bipolar stepper motor can change polarity, this also means that all phases can be put to work at once, further increasing potential torque output. The main disadvantage of a bipolar stepper motor is the requirement for H-bridge circuits to reverse the polarity of the circuit.
Unipolar stepper motors use tapped coils, of which each side can be independently magnetized. Because the current running through each coil will be running in a different direction dependent on which side of the coil is magnetised, the polarity of each phase can be reversed without reversing the current of the entire circuit. However, because only half of each coil is magnetised, unipolar stepper motors suffer from reduced magnetic force, and thus reduced torque. Unipolar motors are simpler to install and operate than bipolar stepper motors, because their circuitry does not require the use of H-bridges.
You can see the motor circuit in operation by clicking the image below. The video file is around 13MB in size.
Berni M0XYF
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Sometimes you come to realise that the simplest, original discoveries just stand the test of time, and there's little point looking for an 'upgrade'. That's why I've held on to my first wife for so long, despite the deteriorating audio output.
The same is not typically true of digital technology, as we're forever telling Russell.
However, going back to first principles is usually a great place to start when you're tackling something new or refreshing long neglected skillsets.
My personal journey and this particular technology have never crossed paths and that's a shame, but it feels a bit like an old friend all the same. I'm talking about RTTY, or Radio Teletype.
Radio Teletype was 'invented' in 1922 by the US Navy, and it was way ahead of its time. It's quite amazing that it's still around today albeit in a slightly different format. This is a terrific endorsement of its simplistic and therefore fundamentally robust architecture, and is a refreshing alternative to some of the proprietary tosh being touted around the world of digital radio today.
Of course, some of you will be spitting at the screen and muttering something about CW, and I'm certainly not trying to decry the incomparable digital daddy, but RTTY was one of the very first recognisable M2M computer protocols.
This is not meant to be a history lesson, but rather an attempt to contextualise my preoccupation with re-visiting RTTY without prejudice.
Why would I even want to do this? I guess the stock answer would be 'well, why not?', but in my case there is a compelling requirement at the heart of my ongoing research and development project to transpose a simplistic messaging system onto a modern, robust and secure radio communications protocol. More of that another time maybe, but here we are unapologetically blowing the cobwebs off of two bits of software called flrig and fldigi.
So having covered my ignorance of all things RTTY upfront, here is just a snapshot of where I got to over the past weekend. There was actually plenty of RTTY action on 40m, and (thankfully) it didn't even seem to be because of a contest. A great opportunity then to try some decoding.
After the not insignificant task of configuring the software to work with my radio, I was very happy to snatch my first strings of intelligible data out of the air, quickly followed by the sending of some of my own. That was a bit daunting, I can tell you, and I did elicit a couple of 'THIS FREQUENCY IS IN USE!" responses whilst trying to navigate the very congested RTTY spectrum. Ho hum. That's what happens when you try out a new mode on a new radio and with several bits of 'new' software I guess, but how else are you going to figure all this stuff out?
Well, for good measure, I also found out that RTTY CQ calls are spotted on the Reverse Beacon Network, so another new experience for me.
I'm having so much fun right now. There is way too much cool stuff to learn in this hobby, and I'm furiously trying to soak it all up like Spongebob Squarepants on steroids.
Whatever you're doing in radio these days, I hope you're enjoying it half as much as I am. If you're not, then try something different! Learning a new skill is remarkably rewarding.
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- Written by: Alex M0TOT
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Alex Henderson M0TOT has kindly forwarded details of a Morse Code practice project he has recently constructed using a pencil sketch of an LF Oscillator design given to him by Merv M0WVE.
Alex then took the next logical step of squirting the audio output from his build into the line-in socket of his PC soundcard and then mapping this to the input of the excellent free Audacity AV software to display the resulting waveform and allow tuning and optimisation of both the signal and operator technique, which is the whole point after all.
Alex reports reasonable results, and says that it's better than listening to Morse recordings on 78 RPM vinyl. I have no idea what that is. No idea.
Apparently, the circuit diagram is based around a 'T' notch filter, which is like a low-pass filter back to back with a high-pass filter leaving a sharp narrow notch pass band in between to clean up the tone.
I was signposted to Alexander Lang's well-written blog for a reference article on T Notch filters if you're interested in further reading: https://langster1980.blogspot.com/2017/02/how-to-make-twin-t-notch-filter.html
Connecting LF Oscillator to PC and Using ‘Audacity’ Audio-Visual Software
PC Settings (Windows 10 OS)
Settings > System > Sound > Input Devices > Linein (Realtek (R) Audio) > ‘Device Properties’ > ‘Enable’
Setting-up ‘Audacity’
Audio Host = MME
Playback Device = Speakers: (Realtek (R) Audio)
Recording Channels = Mono
Recording Device = Linein: (Realtek (R) Audio)
LF Oscillator (50 to 1200 Hz)
1. Fit 3.5 mm stereo socket as an output (to PC) and use stereo patch lead or 4-way stereo lead.
2. The stereo jack socket, from the LF Oscillator, should be wired as a ‘mono’ connection. The ‘Ground’ is soldered to the sleeve and the ‘Mic’ is soldered to the tag and tip.
3. The stereo patch lead is connected with one end to the LF Oscillator and the other end to the PC audio input.
4. The Morse Key uses a 6.35 mm mono jack plug.
5. For the music ‘buffs’: 50 Hz = Note ‘G’ to ‘G#/Ab’ and Octave ‘1’ and 1200 Hz= Note ‘D to D#/Eb’ and Octave ‘6’.
Alex has once again offered to produce a few PCBs if anyone is interested in having a go themselves. These are around £30 on fleabay, so save yourself some money.
