Wednesday 20 August 2014

HF and Medium Wave 65-ft Inverted L

The SRC X65 with its original box, now long gone.
I've been using a 65ft inverted L with a 9:1 unun for some time. It was originally made by the Snowdonia Radio Company (SRC), but I have had to rebox it as the unun box cracked and filled with water.

With a new box and stainless steel bolts and fittings, the antenna works well from 20m – 10m, with coverage of 40m and 80m as well, although performance isn't fantastic on these lower bands.

The antenna is a vertical for the first 8m, supported on a fibreglass fishing pole. It then goes off at quite an acute angle down to the garden fence. The pole is held against a tree trunk with a couple of bungee cords and has a single earth stake. It is fed with RG213 coax with a 10-turn choke at the feedpoint.

What I did notice was that the antenna didn't work very well on medium wave, long wave or with LF aeronautical NDBs, so I thought about trying something.

The unun box now has a DPDT switch attached that switches out the unun and feeds the antenna directly. This has made a big difference to medium wave with signals romping in. The switch is waterproofed so all I have to do is go outside, flick it if I want to use the antenna on medium or long wave, and flick it back to engage the unun, which gives a better match on the upper HF amateur bands.

Without the unun I also get a better match on 80m, which is a bonus. Simon and SRC are no longer trading unfortunately, but you can build your own 9:1 unun quite easily.

While it is no Flag, Kaz or Wellbrook Loop, it does make a simple omnidirectional antenna for SWLs and hams.

No comments:

Post a Comment