Straight end fed antenna required

[Elopid]

Hi all,

I need a discrete fibreglass type aerial for FM broadcast band. I was told that Sandpiper Antennas can build me one but we phoned them and they no longer built custom antennas.
I have no time to build one does anyone know a good place to get one from? It must just be one single straight pole without any radials or ground planes.

Cheers all, eLo

[Spokes]

I don't know where your based mate but chances are you will have to wait for shipping, in which case if you have the knowledge it would probably be quicker to put one together yourself! I remember Walters & Stanton had some straight antennas for FM but I think they could hold 200w might be worth a look if it helps you out

[Elopid]

Hi there Spokes,

Preferably I'd rather something which can handle in excess of 300w but I'll certainly take a look, many thanks EloPiD.

[Albert H]

A "straight, end-fed" antenna isn't going to be much use, unless it's a very big (8") diameter fibreglass tube with stacked folded dipoles inside it! Jaybeam used to make a "taxi" aerial like that for the bottom of the band (88MHz), but they stopped making those in the early 80s.

If you're concerned about your aerial being seen, paint it! We always used to use acrylic paint - usually grey or pale blue - to paint aerials and their masts. With a sensible choice of non-shiny colour, your antenna won't be visible even quite close to it!

[SoundFm]

Albert you're right. Jaybem do a colinier but it's only rated at 200w. It's for Band 2 but only from 99.5 MHZ so no use if you're using the bottom end of the band.
See link here ----> http://www.amphenol-antennas.com/getatt ... 73xxx.aspx

[Maximus]

Albert you're right. Jaybem do a colinier but it's only rated at 200w. It's for Band 2 but only from 99.5 MHZ so no use if you're using the bottom end of the band.
See link here ----> http://www.amphenol-antennas&#4 ... x.aspx

It does say other frequencies available upon request.
So they might be able to make you one lower down the band.

[Albert H]

You should be able to see the problem - it's 6m long and only 3dBd gain - that's only 3 dB better than a single (properly matched) dipole.

If you allow phasing stubs, you can get 6dBd out of a 3.1m aerial! Add ground planes and you can alter the radiation pattern to minimise the signal radiating into the building supporting the aerial!

[NOYB]

No gain, but this antenna is discrete, good quality and does upto 250w:

http://www.amphenol-antennas.com/getatt ... 34xxx.aspx

Or if money is a problem, make your own - effectively it's a conventional dipole, but the feeder is going up the inside of the lower element. There are various ways to construct one physically and then shroud it in rigid plastic/ fibre glass tube.

Or if gain is essential, a shrouded "Slim-Jim" antenna - possibly made from copper microbore pipe to stay thin, or normal rigid 15mm pipe (but latter will end up needing drainpipe probably)?

[Maximus]

Was going to mention the 6m length as well lol

I've seen community stations use the 3m 0db version and that looked pretty big strapped to the side of a building.

Why not try building a colinear 'flowerpot antenna' that I posted on here a couple of months ago. It also has a matching section at the bottom, plus it's relatively cheap and easy to build.

Pjeva has also built something similar using heliax rather than rg58.


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[Maximus]

A friend was putting 1K into a a quad bay folded dipole array. He wasn't satisfied with regards to penetration through high rise buildings/sky scrapers.
We ended up lopping a (very high, overlooking the sea) quad spear-head array to combat the high rise buildings.
The signal is still shit!
Literally several K!


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[Albert H]

In New York they found that vertical polarisation didn't work well amidst the high-rises. They all now use circular polarisation and complain about the multipath distortion!

[Maximus]

Interesting, didn't realise vertical was bad around high buildings.

Never even experienced multipath until I visited Grantham in Lincolnshire. The town is at the bottom of a bowl and they use 50w repeaters. Whilst walking though town, the strength is strong but the multipath makes the stations almost unlistenable whilst walking around with a Walkman.


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[Elopid]

Hi all,

Wow thank you for so many replies, I tried a similar posting a few months ago and didn't get a lot of response.
Yes something like the straight Jaybeam antenna is what I require, I don't want to pay stupid money for one though as I understand those antennas (being for the commerical market) go for silly money.
I've kind of hit a wall with this at the moment, I don't want to pay more than £100 for the aerial or it just makes things start getting too costly. At this rate I'm tempted to just spend a day building my own end fed dipole simply out of 2 elements, coax and a fibreglass tube.

Cheers all, eLo

[Albert H]

Hi all, At this rate I'm tempted to just spend a day building my own end fed dipole simply out of 2 elements, coax and a fibreglass tube.

That's pretty much what you're going to have to do. Look at the "flowerpot" antenna (don't let the silly name put you off), and also consider the plastic-pipe "Slim Jim". To test your plastic pipe, you MUST do the microwave oven test - if you get plastic piping that gets hot, it's not going to work too well.
http://radio.xtreamlab.net/omni-aerial.html shows you how to make a cheap and effective vertical without groundplanes.

[Elopid]

Thank you everyone for your help, I'm still a bit stuck with this one. If I can find anything like that Jaybeam straight antenna reasonably priced up to a maximum of £100 then I'd like to go for something like that, otherwise I think I'll have to get building one which can take a lot of time!

Cheers all, ELo

[Analyser]

Quite expensive, but how about this...

http://www.ebay.co.uk/itm/FM-BROADCAST- ... cpRrxQckvg

[Albert H]

Really - get some coax, plastic pipe, end caps, glue and a pole to support the antenna with brackets or clamps as necessary. Build the "Flowerpot" antenna. Build the version with some gain. Assuming that you can solder a plug on to a piece of coax and can follow some simple instructions, this is your best bet. You'll be able to make them for £15 - £20 each. You will need an SWR bridge, and it's a good idea to have a 1 Watt board on your frequency for alignment purposes. You're certainly not going to be able to just buy what you want at the price you can afford.

[Santiago]

Any diagrams for this flowerpot antenna Albert?


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[Albert H]

http://vk2zoi.com/articles/half-wave-flower-pot/

The article gives the way to build them for 2m amateur band. They're easily scaled for 3m broadcast band!

[Santiago]

Thanks


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