Hello,
I consider trying a so called flower pot antenna (without flowers or pot).
Till now I could not find info about the optimum height above a flat ground to the lower end, where the common mode choke is. My first guess is 4m agl and 5m of cable from the ht to the choke. The objective is a low takeoff angle.
Does anybody have calculations, simulations or even experimental results to this? TU in advance.
73, Johannes
Hi Johannes,
I have a slim Jim which is similar. From experience about 4m or higher gets best results.
I don’t notice much difference between 4 and 6m. Below 4 and I can notice that the performance to hear distant stations can become compromised.
There are times that my mast falls over some of the way and I don’t notice 
Tim
Hello Johannes, the originator of the Flowerpot antenna was vk2zoi (sk). Here is a link to his website -
https://vk2zoi.com/flower-pots/
It details everything about it and how it got its name and detail on how to build it.
Geoff vk3sq
Hi Johannes,
For a while I was using a 3m pole, which means the choke was just over 2m from the ground. I’m not saying it’s optimal, but it worked and I have managed a S2S of roughly 120 miles with it.
I’ve since got myself a 5m pole (still a compromise between size/weight and height), though I’ve not tried it in anger. On a few of my activations, I feel that the extra 2m of height would have helped but I’ve never done a side to side comparison.
I’m a big fan of the 2m flowerpot. Very happy with mine.
Hi,
Very happy with the flowerpot, I normally use it with the trekking pole (it’s made of carbon).
I haven’t tested it more than 1 meter away.
73 José
Hi Johannes
A flower pot is just a vertical dipole without the complication of a feedline at its centre. I modelled the antenna for 145.5 MHz at various heights
| choke height m | gain dBi | peak radiation angle |
|---|---|---|
| 1 | 2.07 | 11 |
| 2 | 3.5 | 8.5 |
| 3 | 4.5 | 7 |
| 4 | 5.1 | 6 |
| 5 | 5.6 | 5 |
| 6 | 5.9 | 4 |
This simulation assumes flat ground !
My model has 1m height in the antenna design, so the chart is the 6M case (5m added)
We want low-angle radiation with VHF from hilltops to reach the chasers, so the rule is - the higher the better. Choose your height according to the size of pole you wish to carry !
By the way I find that a carbon-fibre pole does significantly affect the SWR, but I can’t really gauge the effect on the radiation efficiency.
Cheers
Rick
You can hang the vertical antenna for 2m (e.g. Flowerpot) on the top of the mast and operate it together with a horizontal antenna (e.g. Endfed).
To attach the mast, I simply bent a shrink tube.
73 Armin
Hey, thank you all
for the comprehensive information, for the numerous field reports and especially to rick for the simulation results.
My first asumptions are confirmed and I can go on. I will report.
btw to Armin: I will not attach the antenna to the mast. I run a nylon string to the top and down again. So I can change height easily and I can exchange the antenna for another one without bringing the mast down.
btw to rick: I distrust the carbon material too. It is possible to compensate the detuning influence, but we can not compensate the resistive losses it causes.
Thank you all again, 73, Johannes
Hi Johannes
Also don’t forget to use a low-loss coax, as you will need maybe 7-8 meters for the feed line at the highest. My actual flowerpot is made from RG-174 to keep it small and lightweight but I feed it with M&P Hyperflex 5 which is ideal.
Rick
Hi Johannes,
I raised a similar discussion a few years ago. My conclusion was that for a vertical antenna on 2m FM the higher that you can get it, the better. The true height above RF ground is unknown on a real summit. The tilting effect of gradients are sharp edges are difficult to model. The higher that you go the more lobes are created and if you are unlucky you may end up with a deep null on your preferred signal path. But overall, the higher the better is my takeaway .
I wouldn’t worry about the science too much. Height and ground type can vary from summit to summit. A pointed summit v a rounded one v a plateau will yield different results. I find that the chasers operating conditions make more of a difference than my own.
I certainly noticed holding it vertical helps in marginal conditions.
Thank you for the additional hints. I will take them into account.
Its clear, that the antenna characteristic is not exactly predictable. Lobes and notches will vary with the geometry of the summit and the properties of the ground. By varying the antenna height when listening to a weak signal it could be possible with some luck to readjust the angle of a lobe with good gain.
Johannes
