groundplane aerial

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mix fm
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groundplane aerial

Post by mix fm » Mon Dec 31, 2018 9:36 am

ive noticed a couple of stations in birmingham using groundplane aerials lately, they dont stick out as much as the dreaded diploe... more money thou... aint sure about the gain on these,
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Steve Marshall
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Re: groundplane aerial

Post by Steve Marshall » Tue Jan 01, 2019 4:18 pm

A 1/4 wave ground plane has no gain over a standard half wave dipole.

Again a half wave end fed vertical also has no gain in real terms, but a 5/8 wave ground plane vertical is said to give 3dB of gain compared to a dipole. A 3dB gain is the equivalent of doubling your power (EPR - Effective Radiated Power).

How does it magically do this?

All that actually happens is the radiation pattern of the aerial is changed, so a 5/8 wave vertical will give you some good distance, as the radiation pattern is lower and more horizontal (more towards the horizon) and less of the radiated power is going upwards towards the sky.

A lot of things can effect what aerial is best to use at a certain site, but for example locally you might well find that a 1/4 wave ground plane gives better performance than a 5/8 ground plane does, because locally more of the radiated power is angled downwards so to speak, so for an FM pirate, local coverage will seem better, and as these aerials will cost less than a 5/8 wave version, it is a no brainer really. Cost will also be a factor as a 5/8 wave aerial requires a loading coil at its base for matching (SWR), where as a 1/4 wave does not.

I know Exile from Eve Hill flat in Dudley had some great success with a 5/8 collinear and 100 watts or so, and from the top of Dudley back then they had some excellent coverage. I think Dimension also used a vertical too from the top of The Wrekin when they were on as well, and again as both of these sites are very good to start off with, they both had very good results.
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Re: groundplane aerial

Post by Dave » Sat Jan 19, 2019 4:39 pm

Speaking for Dimension:

106.4 from the Wrekin was an end fed.
92.2 was a dipole.

The end fed for us out further, and improved the signal in Birmingham and on the Wirral. The problem was the signal wasn't great in Telford - it was going straight over the listeners heads.

Simple dipole produced a better local signal. As the advertisers were in Telford and Shrewsbury, that's what we went with.

Lesser consideration - dipoles were cheaper and easier to obtain, which when you're losing a TX site every fucking weekend....

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Re: groundplane aerial

Post by Steve Marshall » Sat Jan 19, 2019 5:19 pm

Agreed about the local signal Dave, others have had better local coverage with a 1/4 wave ground plane or dipole
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Re: groundplane aerial

Post by rowl3y » Sun Feb 24, 2019 8:59 pm

We used one for Mix .. ofcom took it ..

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