Antenna Matching Question

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Polecat
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Antenna Matching Question

Post by Polecat » Mon Feb 10, 2020 9:42 am

A friend of mine runs FM broadcasts for festivals using a Jaybeam folded dipole.

His rig feeds directly into the antenna which surprised me as I understood a folded dipole to be 300ohm.

He wasn't much help with my questions. Seems an engineer sorted out the setup some time ago and all he does is hook it all up at each event.

I'd like to understand whether he's running a mis-matched setup or I'm just not getting it.

Any thoughts?
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Ignite
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Re: Antenna Matching Question

Post by Ignite » Mon Feb 10, 2020 9:52 am

They are 50ohms. Here is the link for the antenna specs https://amphenolprocom.com/products/bas ... 82-7050088
This seems to be a standard off the shelf antenna that I've seen used for RSL, community and lower powered commercial stations in the UK.

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teckniqs
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Re: Antenna Matching Question

Post by teckniqs » Mon Feb 10, 2020 10:24 am

Yes from what I understand the actual folded aerial element part itself it indeed 300 ohms but there is a matching transformer before it inside the 'centre-cap' to convert it to 50 ohms.

...I experimented with a couple of these about 20 years ago, one of them had the usual rounded off elements but the other one had flat metal pieces bolted to the end of each two elements (like in a rectangle) ....

Big dirty heavy things they were and although giving me a great SWR on all the different freqz I tried them on, it was nowhere near as good as when I compared them to a properly cut resonant dipole.

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Re: Antenna Matching Question

Post by Polecat » Mon Feb 10, 2020 10:50 am

Informative responses. Thanks both!
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Albert H
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Re: Antenna Matching Question

Post by Albert H » Tue Feb 11, 2020 1:33 am

They're very broadband, but very lossy. However, they can be stacked - the bandwidth reduces, but a good match can be achieved by varying the spacing between the elements. I've used these stacked where we've needed a bit of frequency agility with the minimum of adjustment.
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Re: Antenna Matching Question

Post by Polecat » Tue Feb 11, 2020 7:14 am

Thanks Albert. Probably ideal for the festival thing given that distance isn't a big issue and frequency may change each time. Learning as I go along.
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