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My intrests are building test equipment, measurement, qrp, antenna building, Debian GNU Linux.


My selfbuild projects:

HF symetrical 30dB directional coupler 2 - 80 Mhz.

Instead on using tin/tin foil as inner shield i used copper/phosfor bronze foil (in dutch: 'latoenkoper'), which is better suitable because of it's galvanic properties and higher mechanical deformation resistance, giving a little better directivity and less noise. Connect only one lead to the cabinet's earth (see the lead at the right upper connector). Further solder the braid's of the 2 coax lines to the copper foil with as less silver/tin as possible. Don't use lead solder at all. The rest of the build instructions can be found in the ARRL antenna handbook or on many websites.

HF coupler

Graph of the coupler at directed port:

HF coupler directed measurement

M-eight antenne.

For more info to build see the websites of pa0fri or pa9ok. For the tuning capacitor in the midle between the 2 loops, i used a small piece of RG58 instead of a air varco. This works much better if you only want this litle magloop to be used on a fixed frequency. It turned out that for my wanted frequency 145.125 Mhz i need a piece of ~5 cm. It also lowers the Q-factor a bit so i am able to use this cute litle loop between the in's of the repeaters between 145.025 and 145.275. More then enough to get all the intresting repeaters abroad over distances up to 50 - 60 km under normal conditions. Not bad for this small antenna mounted inside of my shack. Needles to say that because of the small 2 sided beams it needs to be pointed exactly at the repeater of your choice.

The biggest advantage of this antenna is not only the gain towards a choosen direction, it performs exceptional well in 'noisy' conditions with a lot of qrm (have tested that under bad conditions with less then 250 mWatt). Don't drive this antenna on lots of RF power. It gets hot easely and will walk away of the resonance frequency very quickly when to much power is aplied. With the rg58 piece as capacitor i can however easely drive it up to 15 watts. More then enough for repeater use. I am curently trying to improve stability further on higher output levels with a tunable golfpipe instead of the rg58 piece. It might as well be that single core coax with a wider diameter is better suitable for this job, however i did choose rg58 for the litle higher pf per meter.

On Januari 12th 2012, i changed the coax-capacitor to a piece of aircell 7 after trying different types of coax, along with a test with twinax cable thin ethernet, turns out that with the later, i can drive the antenna up to 25 watts and with the aircell 7 up to 20 watts.

To be continued.

m-eight antenna


6436450 Last modified: 2015-07-16 00:35:15, 3399 bytes

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