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Sunday, 26 February 2017

Magnetic loop antennas–a follow up

As I have mentioned previously I have a desire to build a magnetic loop antenna for HF use, primarily with my CRT SS9900 on 10 metres, though something that could cover 12 through to 10 metres meaning will work on CB as well as I still have a keen interest in that side of things despite holding an amateur radio foundation licence and hoping to go for my intermediate exam very soon, as alluded to in my last post.

My antenna situation as you know is very poor right now, made worse due to the fact I live in a first-floor flat, though I have a CB antenna in the attic it functions very poorly with high SWR readings and the need of a tuner to prevent damage to rigs connected to it, though this antenna works on 10-meters as well the tuner does not and to get the SWR to safe levels requires it be tuned with both sides turned all the way up to 10 (the unit is a Euro-CB EM-110 and is really suited to 11 metres rather than 10 metres), 2 metres is currently done with an antenna on a biscuit tin, also poor but it does work.

This is where the magnetic loop comes in, and I saw a YouTube video showing a design made out of copper tubing, with a power meter on the larger loop itself, a variant of this design was also on YouTube by an English member of Charlie Tango (of which I am a member with the callsign 26CT730) for CB use, with the right capacitor and correct dimensions I should be able to build a loop to this design (without a power meter fitted to the loop itself as I intend to fit the loop with a remote tuning system utilising a stepper motor and gearbox) and be able to start using 10 metres, despite the poor conditions at this time on that band I am eager to give it a go, also as I have not played with 11 meters since I scrapped my old car this would be a good opportunity as I understand CB is alive and well and there are regular nets held now, even on the midblock using AM and SSB since those modes became available to UK CB operators in 2014, but naturally I am keen to give 10 metres a go, whether I get a working magloop before or after I get my intermediate remains to be seen however I intend to make sure I get on 10 metres regardless, I have invested in equipment for that band I may as well use it.

I know I can get copper and plastic tube locally but for a suitable tuning capacitor I may have to look to rallies to do so, the requirements are that the tuning capacitor will work happily up to 4kV (though I suspect 50 watts is far below this but I like the idea of a safety margin).

The antenna will be connected with a suitable SWR meter in line almost permanently, my Zetagi Mod. 203W is perfect for this as it covers a frequency range of 26-30MHz for TX power measurement and 3-200MHz for SWR measurement.

I will post more on this subject as it progresses

 

73 de M6RSQ

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