6dB COLINEAR VHF ANTENNA

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Re: 6dB COLINEAR VHF ANTENNA

Post by Ivan on Thu Oct 19, 2017 7:21 am

Hi AlexM,
Harry wrote "The stub is folded to form two parallel bars, 5cm apart joined together at one end." Yes, it can be bent from one piece of conductor. But if you make ALL the antenna from one piece, you will not be able to tweak its VSWR.

BR from Ivan

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Re: 6dB COLINEAR VHF ANTENNA

Post by alexm on Thu Oct 19, 2017 7:08 am

Looking at the pictures it is difficult to see the end of the stub as the coax covers it, is it joined such that the entire antenna is a single conductor? If so, then using a thin bore copper tube, would it possible to simply bend the entire antenna out of a single length. If I did build this, I might have to find an alternative to liberating a chopping board from the kitchen though Smile

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Re: 6dB COLINEAR VHF ANTENNA

Post by alexm on Thu Oct 19, 2017 6:29 am

Thanks for the response, how easy is it to bend the aluminium rod, I always thought it was quite a brittle metal and therefore not something for home working (I don't have a workshop), certainly my experience of aluminium has been that it breaks when bending. 15mm copper pipe for household plumbing is relatively cheap from a local builder's merchant, certainly cheaper here than a solid aluminium or copper rod. Certainly food for thought as I work out what to do for an antenna.

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Re: 6dB COLINEAR VHF ANTENNA

Post by Admin on Wed Oct 18, 2017 9:56 pm

Hi Alex,
I chose aluminium because of the price, weight and availability.
Copper would be great, and a tube with higher diameter would also increase the bandwidth.

The only thing I have against copper is tarnishing. Aluminium oxide is a good conductor, but copper is not. But at 144 Mhz the "skin effect" should be deep enough to realise the lower resitance of copper, and even allow you to silver-plate it (silver oxide is a good conductor).

If you do use copper then I would suggest that you varnish it or spray is with some form of laquer, or waterproof paint. Antennas last years if treated to a nice coat of insulation against the elements. Aluminium near chimneys also siffers heavily if not treated to an isolating coat of paint.

Very best regards from Harry and thanks for the tip, really good idea.
BR Harry - SM0VPO

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6dB COLINEAR VHF ANTENNA

Post by alexm on Wed Oct 18, 2017 9:42 pm

I'm new to this and just in the process of organising my initial exam having only previously used commercial radio equipment in the past...

I've been looking at your 6dB COLINEAR VHF ANTENNA page and you use aluminium rod, is there any reason not to use copper rods?

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