Aerials - VHF


1. J or Slim Jim for 144MHz

The following aerial was built by Victor G1PKS:

The prototype aerial was cut exactly to size using 16swg enamelled copper wire on a one inch (25mm) square wooden support, no tuning adjustments were necessary to obtain less than 10% reflected power and the results on the club net were extremely good. A final version was made in 6mm copper pipe and mounted inside a capped plastic waste pipe to protect it from the weather.

The plastic tube does not appear to have any significant effect at RF and a piece remained cold after a session in the microwave oven. However, it did crack and break cleanly around the point of contact with the metal mast clamp after some 8-9 years of operation and it is suggested that efforts be made to avoid sharp or short points of contact with other inflexible items. Maximise the radius of curvature by the use of a flexible material between the plastic and the clamp.

2. Repairs to J-Beam 18 element 70cms Yagi

This aerial is 30+ years old and although wearing fairly well the rear two elements had begun to weaken and the plastic cable housing eventually ceased to be waterproof - see below.

I rebuilt the rear two elements from 8mm microbore fittings and purchased a waterproof plastic box and waterproof cable gland from a local electrical supplier to replace the original plastic housing. The rebuilt assembly was fairly easy to install in the new box and attach back on to the aerial. See below:

The waterproof box was sufficiently large to accommodate the coaxial balun inside. The new elements were degreased, given one coat of cold curing acid etch primer followed by three coats of paint and the aerial reinstalled on the rotateable mast.

3. 144MHz Aerial: A similar renovation process was applied to my 8 element J-Beam 2m yagi with the same type of waterproof box but the coaxial balun was mounted externally with two waterproof cable glands. It was not necessary to replace the driven element.