First Class CW Operators' Club




Jim Henderson KF7E (FOC 1726) lives in Arizona, USA and is one of our resident experts on propagation.

Here he explains some of the more scientific aspects which affect the way the sun affects our hobby. Remember the sun is a huge radiator of both electromagnetic energy throughout the spectrum, as well as particles. The spectral energy is not uniformly distributed, and different types of solar events produce radiation that can be 'weighted' with more energy in some spectra than others.

Here is a spectral content graphic for 8 Feb of 2002:

With the sun as quiescent as it is, flux near the theoretical minimum limit of a quiet sun, the amount of UV is a small percentage of the total spectral radiation. It may be the most efficient part of the spectrum to create the kind of ionization in the F layers that we all enjoy, but it's contribution is overshadowed by both the particles in the solar winds as well as the dynamic polarization of the interplanetary magnetic field.

Even at the very peak of a 'good' cycle, the amount of % increase in this very efficient UV radiation is on the order of just several percent. Small changes do good things.

But during certain solar events characterized by big energy releases (M and X Class flares for example) there is often a useful short term increase in the UV. Of course the X-rays also released, being of shorter wavelength and higher energy, often counter the enhancement from the UV and cause the Big Bad Blackouts...

While it is obvious that we are suffering from a dearth of ionizing solar radiation these days, it is also rather nice not to have to suffer the effects of several days of greatly increased absorption due to one of those X-ray flares and coincident SIDS.

'It is an ill solar wind that blows no good'...

Or maybe: "DX IS, but weaker now."


A Low Cost Antenna Test by Chris G4BUE/N4CJ

A Novel Approach to Antenna Selection by Dennis F5VHY


Something getting too hot? This little project started as a simple way to quieten down an MFJ-4525MV power supply, controlling the rear fan so that it came on only when needed. As a plus, it can also save quite a bit of unnecessary power usage.  Since then, I have also used it to control a couple of other fans (one cooling my webcam) and, with a relay instead of the fan load, it could be used to do various other heavier (AC) tasks, if needed.

It is all very noncritical and the parts came from my junk box. I simply adjust the pot so that the fan is off at room temperature and check that, when I grab the thermistor between my fingers, the fan turns on. With such a small parts count, it can be made very tiny and fit almost anywhere. With the decoupling shown it also performs well, even next to very high RF fields (like inside a PA).

From my favourite supplier, BGMicro, the parts cost is minimal:

Thermistor: 50k RES1400, $0.33; FET IRF521 $0.49; Pot: 50k RES1422 $0.15.

See, the parts really are non-critical! A tiny square of vector board (or vero board) is all that is needed to make a handy little circuit. If your fan needs to idle all the time, but needs a boost, then dropping a suitable resistor across the FET drain-source would work. The IRF521 can be used to switch 8A of load.

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