2 x bicone antennas linked together.

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2 x bicone antennas linked together.

Postby Southwales » Sun Feb 11, 2018 6:56 pm

Hi, as you probably know from my recent posts I made 2 bicone antennas, but not got round to using the 2nd as I am fairly pleased with the first, would it work if I was to put the 2nd antenna in the attic about 4 foot apart and wire them both together, so basicly the first antenna will keep the original feed down to my scanner but would then also be linked to the second antenna with a 4 foot piece of coax, good or bad idea? In my mind both antennas pick up the signal and send it down to my scanner but I am sure someone will tell me it will not work like I think it would, would be good if it did though. What I was thinking king was to support the 2nd antenna horizontal To try get the best of both worlds.
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Re: 2 x bicone antennas linked together.

Postby Chris P » Sun Feb 11, 2018 8:02 pm

They would have to be linked by a phased line in order to give you any "gain" and as this would only work for around the designed frequency it would act as an attenuator for any other frequency so linking two antennas would not give you additional signals at the receiver except over a very small range of frequencies .

It is more likely that your received signals will be out of phase at the junction of the two feeders so will detract rather than enhance each other and it is possible that they could even cancel each other completely.

So basically a bad Idea .

In addition the bicone is only omnidirectional in the horizontal plane (ie with the elements vertical) but only bidirectional when the elements are horizontal so the "best of both worlds" theory is also flawed
Regards Chris aka G8FFF nipper or tazmin88
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Re: 2 x bicone antennas linked together.

Postby G4RMT » Mon Feb 12, 2018 8:52 am

3dB gain isn't that useful, and your idea if phased properly will give you a gain in one direction and a null in the other, so if your local airport is in the null, the drop in signal might not be bad news there, as you get some gain somewhere else. Stacking them vertically retains the omni pattern, but lowers the beam angle, reducing the gain at the higher angles. Only you can determine if the advantages/disadvantages work in your favour. Do some research on stacking and baying antenna designs. Gain doesn't create extra signal, it simply controls where the antenna is concentrating it's effectiveness - all around, or just in some directions. Personally, I HATE making phasing harnesses because the measurements and construction need doing very accurately, but for wideband antennas, there is a design problem. To combine signals needs a frequency component to do the maths. This means that one for 230MHz will be ones size, but one for 350MHz would be different - so if you pick somewhere in the middle, it's performance will drop off either side. I don't know if a wideband version can actually work properly with no loss. My thoughts are that a wideband combiner would be lossy - defeating the point of the project.
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Re: 2 x bicone antennas linked together.

Postby m0lsx » Mon Feb 12, 2018 10:05 am

I saw a good example of a lack of thought & phased antennas a few weeks ago. Some muppet had put a CB antenna on either side of his small 4X4 pick up. And at 11 meters these antennas were way too close to each other & unless operating static the phasing would mean that as he drove around, unless it was on a very straight road, his signal strength would be fluctuating wildly & here is Norfolk our country roads are anything but straight.
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Re: 2 x bicone antennas linked together.

Postby Southwales » Tue Feb 13, 2018 5:57 pm

[code][/code]Thank you for the advice, have decided to scrap that idea and not to disturb my original bicone that seems to be working very well at the moment given my location.

I know it is naughty but late at night I heard someone calling out on 446pmr and decided to call back, turns out he was in Newtown, about 20 plus miles be line distance from me, I did not think it would be possible with the bi-cone and about 25ft of pf100 coax with it being 75ohm?, I though I would at least need to be using low loss 50ohm?, I will not do it again just that temptation got the better of me, also would not want to risk damaging my radio if my swr was high, he said he was using a white stick antenna that had snapped in half during recent wind and had taped it back together.
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Re: 2 x bicone antennas linked together.

Postby G4RMT » Tue Feb 13, 2018 7:21 pm

Let's be honest - anybody who uses a Baofeng on 446 is breaking the law the same as you did, and nobody gets dragged off to Guantanamo Bay. I'd also not worry too much about the VSWR - at worst, you get back half your power - which of course is bad, but most hand-helds are designed to work into terrible VSWRs anyway - so are quite tolerant. He heard you, and you heard him - so that's success really.
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