Vertical Antenna ?

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Vertical Antenna ?

Postby 742-xx » Sun Jun 04, 2017 4:57 am

After quite a while playing with end-fed random wire antennas I'm looking at something a little more 'permanent'.
Up to now I've been using two 30 feet fibreglass poles and about 90 feet of wire, which I put up when Iwant to use the radio and put away when I'm finished.

I've been looking at the SIGMA Ham Radio Antenna SE-HF-X80 VERTICAL RADIAL. This retails at about £85. However, one review suggested it's nothing more than a CB antenna which has been renamed and had its price trebled !
I think this is the CB antenna they're referring to - Sigma Venom 1/2 Wave. This retails at £24.

So, finally to the question ! I only want to recieve - I have no interest in transmitting. Would the CB antenna be any use for HF?
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Re: Vertical Antenna ?

Postby m0lsx » Sun Jun 04, 2017 10:19 am

Hi...Those short end fed antennas are a big compromise. I have a homemade wire variation of the Sigma.
The original & best commercial versions of these antennas were made by Snowdonia & at much better prices that Sigma are selling them for.
My variation of this antenna is a short wire that is designed to be taped to the side of a fiberglass roach pole for portable operation & it has a connection point at the balun for counterpoises.
These vertical multi band antennas like the Sigma are normally cheap half or 5/8th wave CB antenna minus the loading coil. So they are not good at 10 meters as they have lost the required loading coil & get electrically shorter & shorter on every other HF band. IF you load these antennas at the base with a remote tuner they become half reasonable due to the lack of coax loss & IFyou add plenty of counterpoises they become a good compromise.
Nigel, M0CVO use to do, (& may still do) a Balun with two SO-239's to fit to the bottom of your own CB antenna if you want to use your own CB antenna. And these are often available for free via sites like Freegle/ Freecycle upon request.
But compared to something like a ZS6BKW it is a very poor antenna.
A ZS6BKW is similar to a G5RV. But unlike the G5RV it is resonant on several different bands & a good RX antenna. The G5RV is a 20 meter antenna that is a compromise antenna else where & which is renown for being deaf.
If you have limited space or if you want a fold up portable vertical for occasional use then a CB multi band antenna can be a good choice. My wire version for example can be more easily hidden in a tree, or taped to guttering or laid on a roof. But without some counterpoises, do not expect it to work very well & what ever you do put plenty of ferrites on your coax or add a 1:1 balun as the Coax will give you all sorts of issues in the shack other wise.
I know some of the ex CB brigade use ugly baluns. But on a multi band antenna these are not ideal as each band has it's own requirements & it also draws extra attention to your antenna by neighbours & it adds a lot of extra weight to your solder joint at the PL-259, especially on windy days & unlike a 1:1 you cannot tape it to your mast. As that will alter it's resistance value.
A 10 to 30 MHz air wound (Ugly) choke takes around 17 feet of Coax on a 4 inch former. Imagine that swinging around in the wind. On the other hand a small waterproof box with 5 feet of coax wound around a ferrite core achieves the same results & is far better results multi band..
Take a look at..
http://www.karinya.net/g3txq/chokes/

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Re: Vertical Antenna ?

Postby 742-xx » Sun Jun 04, 2017 1:56 pm

Thank you for your, as always, very full answer.
When I finished work this morning I did get 20 feet of speaker wire (the same length as the CB antenna) and fastened it to a fibreglass pole that I use, I also used a balun I have from another wire antenna I have. I put this half way down the garden and I'm not sure if I was just lucky with the conditions but I got some strong contacts on 7mhz.
So as always it's a case of experimenting with what actually works where I am.
Thanks again.
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