Flowerpot antenna

Maximus · Post by **Maximus** » Sat Feb 20, 2016 2:10 pm

Hi Necks.
I've been googling different aerial designs to replace the 1/2 wave NRG that I managed to melt/destroy.

Stumbled across the flowerpot and was wondering if anyone had tried one of these yet, scaled down to 3m band. If so, did it work alright in comparison to the normal dipoles that everyone seems to use?

Link:
http://www.barc.asn.au/resources/Antenn ... l_Band.pdf

Double stack:
http://vk2zoi.com/articles/dual-band-hi ... lower-pot/

Link:
http://www.mds975.co.uk/Content/amateur ... as_05.html

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sharky · Post by **sharky** » Sun Feb 21, 2016 8:38 pm

I really like the look of this, It resembles the coax vertical dipole; but has a choke at the end of it.
I don't see any reason why it wouldn't work, expect the same gain ( maybe slightly just more ) than a dipole but you can clamp it right at the top of your mast..
Have a browse of this : viewtopic.php?f=11&t=288
You could always try the 5/8 one

Maximus · Post by **Maximus** » Sun Feb 21, 2016 10:39 pm

Nice one Sharky. Looks easy enough to build. Will have to remember to paint the 5/8 black to blend in lol

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Albert H · Post by **Albert H** » Sat Apr 30, 2016 2:31 pm

After the questions about a "discreet" (that's the correct spelling in this context) vertical, I found some 50mm white PVC pipe in my cellar. I scaled for 88MHz and tried three slightly different designs:
The first one was the 1/2-wave. After some messing about, I got it to match, and a quick field strength test on 88MHz with a Watt going in, I found that it was about the same as a Pawsey-stub fed dipole (my reference).
The second one was a 5/8-wave. This was slightly easier to match, and the field strength was about 2dB better than the reference dipole. The bandwidth was slightly wider than the first version, but the VSWR shot up either side of resonance - you're not going to build this for 93MHz and use it on 94MHz!
The last version was a 7/8-wave. This needed a matching balun and was fiddly to get right, but when properly resonant, it was 3dB better than the dipole.
I built these last weekend, and had all three on poles on my flat roof. We had some high winds during the week, and they rattled so much that I had to take them down!
This morning, I examined the 7/8 version, and used a few drops of hot-melt glue inside the aerial to stop it rattling. I also fitted a 32mm diameter plastic pipe up the tube to make it more rigid.
It's pretty windy right now, but I can't hear it rattling!
The match is very close to 1:1 and the radiation angle seems sensible. I've painted it with acrylic silver-grey and it's difficult to see from the ground against a cloudy sky!
This - and its double-stacked brother could be great aerials for our use! Cheap and quite easy to make - though an antenna analyser is almost essential for tweaking. I expect (not) to see these in use soon!

Maximus · Post by **Maximus** » Sat Apr 30, 2016 6:21 pm

Nice real world experience there. I remember having a play with a fiberglass vertical years ago.
The 5w transmitter and aerial chucked out over 5 miles. I was really impressed.

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Maximus · Post by **Maximus** » Sat Apr 30, 2016 6:22 pm

The aerial was only 8ft above the ground, but was heard for miles

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Albert H · Post by **Albert H** » Sat Apr 30, 2016 10:39 pm

The Band II dingbats around London don't seem to have much clue when it comes to aerials. They just bung up a dipole or a twin dipole, with no attention paid to matching correctly. They seem to think that the aerial is the least important part of the setup. In fact, I can get superior coverage out of 50 Watts into a correctly designed and aligned aerial than these idiots get with their 300 and even 500 Watts.
A proper aerial can double the radiated power - and put it in the right directions - for much less money than a bigger rig! Stephen Moss used to build that 1/2-wave aerial. It gave a doughnut shaped radiation pattern, with little energy wasted upwards or downwards. This is one of the most effective aerials for its size. I used to make a 5/8-wave job with groundplanes. This gave a similar radiation pattern to Stephen's aerial, but put much less energy downwards - it was really weak at the bottom of the block!
I used to make an end-fed colinear as well. This was properly omni-directional and had lots of useful gain. From the ground, it would look like a CB aerial, and this confused the DTI guys for quite a while!
Another aerial that I used a lot was the "improvised j-pole". This was just a 1/4-wave stub with a couple of jubilee clips attached to the end of the coax. We used it on railings, TV aerial masts, scaffolding and any other bit of elevated vertical metal at least 3/4-wavelength long. I bit of wire-wool to clean up the metal, and a couple of minutes to clamp and match it, and you were away. I had a small, battery-powered rig with an SWR bridge built-in that I'd use up the block to set up the aerial before I'd connect the main rig!

shuffy · Post by **shuffy** » Sun May 01, 2016 12:45 am

Albert H wrote:the "improvised j-pole". This was just a 1/4-wave stub with a couple of jubilee clips attached to the end of the coax.

Presumably the "hot" side of the stub had some sort of clamp on it and you slide the feed point up and down the stub until it matches? I imagine you had to get lucky with whatever you found as a radiator?

Maximus · Post by **Maximus** » Sun May 01, 2016 7:12 am

I have one of the 50w NRG verticals. The signal was phenomenal until I stuffed too much power into it and melted the thing.
It's sat around somewhere waiting to be repaired.

Albert's 5/8 reminds me of the big analogue television transmitters before the DSO. If you lived within a couple of miles of the 1MW monsters, the signal would be terrible.
It would either fly over the top of you or swamp the tuner with loads of reflected signals and ghosting.

I've seen 25bd mast head amps fitted to the aerials within a stones throw from the tx site lol

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Albert H · Post by **Albert H** » Sun May 01, 2016 10:40 pm

shuffy wrote:
Albert H wrote:the "improvised j-pole". This was just a 1/4-wave stub with a couple of jubilee clips attached to the end of the coax.
Presumably the "hot" side of the stub had some sort of clamp on it and you slide the feed point up and down the stub until it matches? I imagine you had to get lucky with whatever you found as a radiator?

That's pretty much it! About 20 years ago, when the old VHF 405-line TV was switched off, there was a great supply of link aerials up blocks! There were also some fairly tall poles that the Band I and III aerials had been fitted to - these were excellent for the "improvised j-pole"!

EFIALTISFM · Post by **EFIALTISFM** » Sat Jan 15, 2022 6:25 pm

Here is a quick 1/2 Wave Flower Pot Antenna, built in under 1 hr, specs for 98Mhz, RG58 on 32mm conduit, ran with 4Watt board, meter showed a tad under 4W, SWR 1.2:1. Couple days ago ran on 106 and worked like a charm.

related info @ "the BAZOOKA Antenna topic" viewtopic.php?f=11&t=2803&start=40#p35439

Here is a quick snapshot on rooftop. Windy day...