CW Key Shaping

Written on 11 November 2019

I’ve replaced the 40m Class E PA in my QRP transceiver with a class D amp so that it will work on more than one band (with suitable LPF of course). I had my first two ever 60m CQ QSOs with it at the weekend. I have a key shaping circuit using the same values as in the class E amp but the key up and down transitions were too fast so I changed the component values to increase the delay. I was surprised by the resulting waveform for key down:

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Rotary Encoder

Written on 30 September 2019

My 40m homebrew transceiver is controlled by an Arduino Nano clone. The tuning knob is a rotary encoder which has three pins - ground, A and B. A and B are connected to digital inputs with an internal pull-up resistor, so when the pin goes active a logical zero is read. Rotating the control produces two square waves in quadrature. For example, a series of counter-clockwise clicks produces the following:

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Audio Switch

Written on 4 September 2019

This is the audio switch I am using to mute the receiver when transmitting. When switching to transmit we need to mute the receiver quickly but we want the switch back to receive to be slower. This is to avoid clicks and thumps.

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SOTA 20m Dipole vs EFHW

Written on 31 August 2019

I’ve now tried the 20m dipole on a couple of SOTA activations. So how does it compare to the EFHW? It works, but I felt it didn’t offer any benefit over the EFHW. Of course, this is not a fair comparison. I didn’t use the antennas side-by-side so location and propagation would have had a huge influence on my observations. I just didn’t feel like I was getting as many QSOs as I do with the EFHW. There are also some practical advantages in favour of the EFHW. I should also point out that, since the EFHW works on 40m, it is twice as long as the dipole.

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ABV Calculator

Written on 10 July 2019

I have written ABVCalc which is a little Android program to calculate the ABV (Alcohol by Volume) of beer from the original and final gravities. You can enter gravities as, for example, 1044, 1.044 or 44. It also calculates the apparent attenuation.

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SOTA 20m Dipole

Written on 2 July 2019

I have had a lot of success with my EFHW antennas for SOTA activations but discussion on the RSGB Technical Forum made me wonder if the matching transformer was too lossy. If it is open- or short-circuited you would hope for an infinite SWR, although in practice 10:1 would be good. I was getting around 2.5:1 when open and 6 or more when shorted. So it appears to be lossy, although it clearly works and is easy to deploy. It is inherently multiband too (a half-wave for 40m is a full-wave for 20m, for example).

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Portable EFHW Antenna

Written on 23 June 2019

This is based on an article published in Sprat 177 (Winter 2018/19). There is also an update at the end.

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Crimping coax connectors

Written on 20 June 2019

I used to really hate wiring up coax connectors. I’d decide I needed to wire up a lead for some purpose and order the plugs. They’d arrive and then get put in a box somewhere never to see any cable. Soldering PL259 UHF plugs never seems to work. Although the centre pin is easy to solder, if you don’t file it down it then sticks in the socket and forcing it apart breaks something. Then trying to solder the braid seems impossible. If you manage to apply enough heat to the plug’s body to get a decent joint, it melts the dielectric and you get a short between inner and braid.

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Where to buy stuff

Written on 19 June 2019

Unfortunately there isn’t a single place to get all the tools and components you will need for home construction. These are the sites I have used and recommend:

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