Saturday, 5 July 2014

Notes from the Shack, July 2014

Under the Whip

Pardon the title! A while back I discovered that my 30 year old mobile mag mount, made by Larsen, only matched on 2 metres. On 450 it was more than 4:1 VSWR across the entire band. On close inspection it should not have been a surprise as the housing for the coil that separates the upper and lower halves of the antenna had broken open exposing the interior which had become a congealed mass of rusty metal. It was a wonder it matched OK on 2 metres.

More recently, the club acquired a couple more mag mount dual band antennas from a local donor, and I decided to test them as well. Initially I did this using a filing cabinet as a ground plane but when neither worked on either band I tried them on top of my Toyota to see if they'd fare any better. They didn't.

Eventually I found that one of the donated antennas worked fine matching less than 1.5:1 across both bands if I mounted it on my Larsen base. It works well even on the shack filing cabinet.

What have I learned? To trust but verify. Seemingly good antennas can go bad and need to be watched.


I'm now the happy owner of a vehicle with a permanent antenna mount on the roof. I expect that most of the time it will sport a 1/4 wave whip about 19" long because that's all the clearance I have into the garage. Long trips may give me the chance to run with something a little larger. I'm happy to have a rig in the car again!

I wrote this back in March but neglected to publish it. Better late than never.

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