A quick introduction: by day, I'm a DevOps Engineer at Red Gate, a software company in Cambridge, UK. Outside of work, I enjoy both amateur radio (hence the callsign, M0VFC) and community broadcast radio at Cambridge 105. This blog aims to span all those interests - so feel free to ignore the posts that aren't relevant!
Feel free to get in touch on Twitter (@rmc47).
73 / Best wishes,
Rob
When out contesting with G3PYE/P, we often use Gavin, M1BXF's Icom IC-910 transceiver. A fine rig to be sure, but it doesn't have an internal voice keyer (or digital voice recorder) - a feature still lacking in the brand new IC-9100, for reasons best known to Icom.
Instead, we use SM3WMV's PC-based Voice Keyer software. This plays a pre-recorded sound file when you press one of the function keys, and puts the radio into transmit using the RTS line of a serial port.
So far, we've used this and a home-brew data interface to feed the audio into the data port of the rig, but there's a problem - this doesn't go through the rig's compressor, so average transmit power out is rather lower than using the mic.
To improve on this, we decided to build a small interface which accepts two audio sources (PC and microphone), two PTT lines, and routes the appropriate source to the radio when its PTT is activated. This avoids the mic being live when the voice keyer is transmitting, and prevents PC sounds being transmitted when using the microphone and foot switch.
The circuit is simple - a relay for audio switching, and a few transistors to drive the relay and pull the output PTT line low when the PC PTT is activated. A potentiometer on the front allows control of the PC audio level.
Here's the breadboard for an initial test:
And mounted in its box:
Under test with an IC-7000:
And the finished project!
This tuesday is the 23cm UK Activity Contest, where it will get its first on-air test. I hope to work some of you then!
Finally - another item off my TODO list!
My 12v bench power supply is a Watson W-30AM. It's a decent enough PSU, and competitively priced. However, they appear to have a design fault - the fan speed controllers fail... in the "fan off" state.
Mine did so a couple of years ago at a special event station operation, and consequently got rather warm, rather quickly. We performed some quick field surgery and hard wired the fan to +V, which took care of the problem, albeit rather noisily.
This evening I finally made the repair: the LM358 op-amp on the speed control board had let its magic blue smoke out (quite obviously). A quick replacement, along with the rather scorched looking 390 ohm resistor adjacent to it, and it's behaving as it should again. Total cost about £0.50.
I mentioned earlier that I thought it was a design fault: of the four people I'm aware of who have these supplies, three have independently failed in exactly this way...
(As an aside, I'd never buy another linear power supply. They weigh far too much, and leave nice dents in my car's metalwork when you drop them. Decent switch-mode power supplies are smaller, lighter, more efficient, and work every bit as well.)
Although the majority of my radio operation is out portable, I occasionally play a bit from home as well - both on HF and VHF. Living in a semi-detached house in a residential area, with a back garden just over 40' long brings inevitable compromises for HF antennas...
Initially, I ran a 1/4wave vertical for 40m using a fibreglass pole planted in the flower bed, and a good number of radials dug into the lawn at regular intervals. Nice and simple, but very noisy on receive, and not terribly good on transmit either - most of the radiation went straight into the surrounding houses. Including a neighbour's hi-fi system - not good.
The next attempt was an off-centre-fed dipole for 40m, fed about 1/3 of the way along its length. The feedpoint was supported from the alloy pole that holds my VHF colinear, on the side wall of the house. This fitted very neatly: the short end hooked over the gutter at the front of the house, and the long end dropped to the rear fence. The OCFD gave me greater flexibility in terms of bands (with an ATU) - effectively all of 40-6m were somewhat usable. Since putting it up, the neighbour also reported no further issues with his hi-fi. However, the noise was unceasing (S9), and transmit performance remained poor. Time for something better...
On a whim, I tried making a balanced, horizontal version of the 7.6m "Rybakov" vertical - 7.6m either side and fed with a 4:1 balun. The ATU matched it (but then, the LDG Z-11 will match pretty much anything), but TX performance was well down - probably 20dB. Modelling in EZNEC showed a feedpoint impedance that suggested almost all of the 100w was likely being dissipated either in the tuner or the balun!
Suffice to say, that didn't stay in the air for very long, and was quickly replaced by a hastily constructed half-size G5RV. The G5RV is something of a politcally charged antenna - there are those who swear by them, and those who claim they're little better than a leaky dummy load. My view is roughly as follows:
Given these, I'd done a reasonable job - the ladder line was pulled away from the metal pole, and there was only a couple of feet of coax before it hit the ATU. Performance was pretty good - the noise now at S5, and at least some of the RF leaving the radio seemed to be making it into the ionosphere.
However, the ladder line as it was looked messy from the road, and any good solution I could think of for fixing it more permanently would involve either lots of visual clutter, or introduce significant effort to any maintenance of the antenna. The ATU also seemed a little unhappy on some bands (particularly 30m), and there were some effects I can't explain.
So today, that's come down after only a couple of weeks in the air, and has been replaced by a pair of nested dipoles for 40 and 20m with a common feeder, the former also doing a reasonable job on 15m. The 40m dipole runs between the back fence and a convenient post at the front of the drive, and the 20m is tied off to the gutter at the front and back of the house.
After a previous bad experience with a 10m and 20m pair of dipoles where there was significant interaction between the two when trimming them, this installation was much easier, and they present a good match on both bands.
Noise seems reasonable (S5 or thereabouts); I've not yet tried firing it up on transmit. No doubt in a week or two's time, something else will be up there instead!