Guest Ketchup Posted December 27, 2014 Share Posted December 27, 2014 Hi, I am trying to understand the wiring of the broken VHF antenna I have. The coax cable basically has 2 wires. So I presume one is for transmit and one receives... or have I got that wrong. If right? Is the antenna itself containing 2 seperate wires within the fibreglass whip? Cheers and merry christmas Link to post Share on other sites
Island Time 1,235 Posted December 27, 2014 Share Posted December 27, 2014 2 Wires would be unusual. Normally there is a co-ax with a core, and a braid over it. The core carries the signals, the braid is a shield. If the antenna itself is broken, and you can see two wires, then sometimes there are windings to increase the length of the antenna. Pic of the problem?? Link to post Share on other sites
Guest Ketchup Posted December 28, 2014 Share Posted December 28, 2014 Thanks for the reply. Sorry my mistake. I put my glasses on and there is only one centre wire. So the outer braid has no function other than as a shield? How come it has contact with the outer case of the male plug? The reason I ask is - when I connect the centre wire I receive but cannot transmit until the shield braid is connected/makes contact with the plugs outer case. Link to post Share on other sites
erice 732 Posted December 28, 2014 Share Posted December 28, 2014 radio wave transmission, and antennas, can be mysterious things you want the shielding braid to connect with the plug body so that can pass the connection on to the antenna base where it may use the ground plane to act as a reflector in this way your '1/4 wave marconi' antenna acts more like a more efficient 1/2 wave antenna Link to post Share on other sites
Island Time 1,235 Posted December 28, 2014 Share Posted December 28, 2014 Well said Erice, absolutely correct. And explained better than I would have! VHF sets use the co-ax side as a ground plane for transmission. Just as an aside, SSB sets do not, and require a ground plane connection, so don't think they are the same! Link to post Share on other sites
Guest Ketchup Posted December 29, 2014 Share Posted December 29, 2014 Thanks Erice. That's what I thought might be happening. After all why else would the braided cable be attached to the outer caseing of the plug. Thanks all. Link to post Share on other sites
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