Tranklid but Immobile HENTENA on 50MHz (1: Design)

I’ve been a mobile ham for quite a long time, and when I first moved to an apartment building, I “almost always operate ham radio from my car.”  Recently, on the weekends, if I feel like it, I’ll drive to a nearby area with a good view with my mobile whip antenna.

By the way, most “mobile antennas” are vertical antennas that are earthed to the car body; in fact, as far as I know, all commercially available mobile antennas are vertical antennas such as whips.

Why aren’t there any horizontal antennas?  Has anyone wondered this?

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I have never used a radio while driving.  The only way to communicate while driving maybe  “using a phone” and “not changing the frequency” and “using FM mode with a good S/N ratio”. 
The only people who meet all of these criteria are probably VU truck drivers.  They don’t even tell their callsign, and I don’t even know if they have ham license or not…… I don’t care, but please don’t use the satellite bands!   Oops, I’ve gone off topic….I’ll back to the point.


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The first reason why mobile antennas only have vertical systems is that, if the antenna is horizontally polarized, it will have a directivity of at least a figure of eight, which is obviously not suitable for communication while driving and changing direction.

The second reason is the regulations.  According to ”Road Transport Vehicle Safety Standards (of Japan)”, “bumper bases” cannot be used because they protrude from the outermost edge of the horizontal projection of the body (I’ve certainly not seen them recently), “trunk lid bases” can only protrude up to 70 mm from the body surface, and “any part of an antenna less than 2 m above ground level must not have a sharper part than 2.5 mmR”, and so on.

Oh, is that so?!

All the mobile amateurs should take a look at this.  In particular, the regulation of R<2.5mm seems to be from the viewpoint of preventing injury, so I think it applies even if the antenna is only used when the vehicle is stopped.  We have to be so careful.

However, the “Road Transport Vehicle Safety Standards” do not regulate the strength of the antenna itself. (Hmm… Is that okay?)

Well, with the above in mind, this time I will design and manufacture a vehicle-mounted version of the “50MHz Hentena”, the first antenna I made before my amateur radio debut half a century ago.
Design concept:
(1) The antenna height will be full size, half the wavelength of 50MHz = 3m.   At this point, the height will exceed the regulation (H<3.8m) , so it cannot be used while driving.
(2) The antenna width will be 30cm. There is no deep meaning to it, but I will make it about the same as the protruding width when the door mirror is not folded.
(3) Since it is an ungrounded antenna, it will simply be fixed to the mobile trunk lid base using an M-P connector.  it has no effect electrically.
(4) If the element sways too much in the wind, the SWR may become unstable, and because we want to improve the reproducibility when installing, we will avoid using copper wire this time and make it out of aluminum pipe.

(5) To avoid causing inconvenience to those around when installing and taking down, we will use a structure that allows it to be assembled while extending it upwards.


→50MHz Tranklid but Immobile Hentena Part-2 (Manufacturing)

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