When I was at school I once thought I'd like to be an engineer, now I live with one and feel I had a lucky escape. While I think about clouds and ocean waves, he thinks about 1/4 wave lengths, the impedance of free space, the coefficient of friction of in a vacuum and other such important considerations in day to day life !
However, this weekend I too have had to think about 1/4 wavelengths, the speed of light, impedance of free space, radiation efficiencies and voltage standing wave ratio (VSWR for those in the know). Why you might ask? Well one of my tasks is to make an emergency HF/SSB antenna for Coppelia, if disaster strikes, we need our radio to talk to people!
On Coppelia we have a very smart ICOM antenna tuner, which manages (using inductors and capacitors) the difference between ideal antenna length for a given frequency and the length antenna we have. This is an excellent device, as the ideal antenna length for the one of the emergency frequency is 32.687m - and Rob's budget does not extend to a mast that tall. However, if in the case of a less than ideal day, one that might involve damage to the usual antenna, there is a strong chance we may also sustain damage to our tuner. So my job this weekend has been to work out the length of antennas required to make emergency transmissions with the greatest chance of success without the tuner.
The ENGINEER has been of great use in this area, with his encyclopedia of equations, all mentally stored in "things I did at university", has enabled me to develop to table below. Note this is the ideal antenna length and does not include cabling to the radio itself, which will consist of shielded cable
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