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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?

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    $\begingroup$ could be a capacity hat rather than ground radials - we cannot see what's at the antenna bottom. $\endgroup$
    – glen_geek
    Commented Feb 9, 2023 at 2:11
  • $\begingroup$ I'm thinking it's the same kind of "fan-ish" multiband verts as seen in ham.stackexchange.com/q/18066/8016 $\endgroup$
    – hobbs - KC2G
    Commented Feb 9, 2023 at 18:09
  • $\begingroup$ 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. $\endgroup$
    – Mike Waters
    Commented Feb 9, 2023 at 23:55
  • $\begingroup$ 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. $\endgroup$
    – Mike Waters
    Commented Feb 10, 2023 at 0:12
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    $\begingroup$ @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. $\endgroup$
    – Marcus Müller
    Commented Feb 10, 2023 at 17:54

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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...

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  • $\begingroup$ 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). $\endgroup$
    – Mike Waters
    Commented Feb 13, 2023 at 13:56

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