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I work next to "Koninklijk Marine Kadettenkorps Afdeling Oostende" (Royal Marine Cadet Corps Ostend). They have an antenna that I've been wondering about for years now:

enter image description here

It is a vertical antenna, likely HF bands with four radials angled about 45 degrees from the vertical. So far, completely normal.

However, the verticals are pointing up. I've never seen this kind of antenna. For I long time I thought maybe someone just made a mistake while putting it together, but I can't honestly believe no one would have fixed it over time.

I am not proficient in any NEC program to simulate it myself. What is this kind of antenna used for?

Dieter Vansteenwegen ON4DD
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    could be a capacity hat rather than ground radials - we cannot see what's at the antenna bottom. – glen_geek Feb 09 '23 at 02:11
  • I'm thinking it's the same kind of "fan-ish" multiband verts as seen in https://ham.stackexchange.com/q/18066/8016 – hobbs - KC2G Feb 09 '23 at 18:09
  • This is very interesting! However, I don't think that anyone could model this antenna, because of at least 2 unknowns: 1. what is inside the black areas in the lower (larger diameter) and 2. upper (smaller diameter) vertical sections? One can only guess. For all we know, the black area in the upper section is a feedpoint. – Mike Waters Feb 09 '23 at 23:55
  • Changing the angle of radials on a ground plane changes its feedpoint impedance. Might the elevated radials (which seem to be connected) serve to increase it? Just a thought. – Mike Waters Feb 10 '23 at 00:12
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    @MikeWaters I agree with that this is sadly all guesswork, unless someone happens to recognize their antenna model in the photo (which might reasonably happen!); my bit of speculation: this electrically "widens" the upper half of the antenna, and assuming actual (dirt) ground is used as (zero-potential) ground plane, that would make the antenna more wideband; somewhere between a monopole and a discone. – Marcus Müller Feb 10 '23 at 17:54
  • I'll go and have a look if there is a position from which I can see the bottom of the antenna, but I don't think so. Just realized I know someone who works at radio comms for defence, he might know either the antenna or someone with more info. I'll ask. – Dieter Vansteenwegen ON4DD Feb 11 '23 at 14:46

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Found it through help from a friend.

It is a differential correction (dGPS) transmitter for Ostend on 312kHz.

A seemingly similar antenna (for same frequency band) can be found for example on the Banten website., with the datasheet here: Datasheet.

In case the datasheet ever gets lost (dead link), the most important things to note are:

  • Frequency: 200-1800kHz
  • Max power: 250W
  • Capacitance: 130pF (@300kHz)
  • Vertical polarisation

The radials would be to increase bandwith.

Still looking around to find more on the antenna design though...

Dieter Vansteenwegen ON4DD
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  • Very good! If no one else posts a better answer soon then you should mark this as accepted. This keeps the bot from automatically pushing it to the top (because no answer is accepted). – Mike Waters Feb 13 '23 at 13:56