50MHz Mobile whip antenna
(Budget 1,800 yen US$18)

1. Pre-face

Those who has started their ham radio with 144MHz or 430MHz think a 1.5m of 0.25 wavelength of 50MHz a slight longer, but the band has unique characteristics so we have much fun on the band.

Recently we can get grass fiber fishing rod in DIY shops around 1,500 yen.

Considering attaching antenna connector on its base, we can utilize 1.2 m of the rod. So it is suitable to make whip antenna for 50MHz band.

2. Principle

This antenna works as 0.25 wave length antenna.
Cut rod is just 1.2m, it is a little bit short than 0.25 wave length.
So we use a loading coil. Too big loading coil sacrifices on antenna efficiency.

There are three type of loading antenna in its position.

A. Top loading: Loading coil is placed on the top of antenna. Used in MW broadcast antenna technique.

B. Center loading: Loading coil is set in the middle of antenna. Radio amateur always use this type.

C. Base loading: Loading coil set at the bottom on antenna.

This time I use B. center loading technique.

3. Parts and build antenna.

Refer to the figure. Material is grass fiber fishing rod. If the rod is thick enough use MP5 connector the you can get 1.2 me antenna.

If you have thin rod, MP3 connector is appropriate, then you need to cut the rod about 1m.
Loading coil is made by 0.8mm enamel coated copper(PEW) or poly urethane coated copper wire(UEW).

First cut the rod in appropriate point where you can attach a connector, whether MP5 or MP3, with it.

File the cut end and painting till you can see surfaces of grassfiber. Attach the connector with epoxy glue.
Do not forget put the wire in the rod.

At the middle of the rod wind wire 18 turns with narrow space (loading coil), then wind wire to the rod with wider space. Solder at the both end the loading coil and at the connector.

4. Adjustment

Find the resonant frequency first using SWR meter between 50MHz and 54MHz. When the frequency of the bottom of SWR is lower than 50.0MHz then re-wind wires or visa versa.

after rough adjustment, make the frequency of the bottom of SWR 50.7MHz varying wire spaces.

Apply epoxy glue at the coil and other points. Then you may see the resonant frequency become lower side. After glue dried, check SWR again to see it stays on 50.5MHz or adjust the wire at the top of the rod.
In my case though the bottom of SWR is [1.2],it is OK practically.

5. Impression.

The length of the antenna is 1.2m, a bit longer relatively as 50MHz use, so SWR characteristics is "broad" then it can cover all frequency for SSB,FM use.
Also it is just 52g weight including the connector due to its grassfiber material.

On the air I could get JA8 stations(500Km) with help of sporadic E and 2.5WSSB at New Year QSO party of '94.
Since then still this antenna is active even in '99.Simplicity is a key to long-lived.

7. Supplement.

The adapters in the picture make you on the air at 21MHz.
Translator 7K4BFU ex. JA8FND

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