Sunday, 12 September 2010

New Beacon Antenna

Being close to Bletchley Park last week also placed me close to Moonraker's shop - I couldn't resist popping in for a poke about.

Despite warnings to the contrary, I was tempted to buy a couple of monoband whips and a centre piece to make up a (very) short "dipole". I had already been persuaded of the usefulness of short base-loaded whips in using my Walkabout antenna and so - given that they aren't exactly expensive - I got a brace of 30m antennas.

I've been wanting a permanent antenna solution for the multi-mode 30m beacon (being frustrated by giving over the station g5rv to beacon duties). Although I haven't yet finished my experiments with loops, I decided to give the whips a try...

I used to have a 2m colinear mounted on the end of my garage, but I wasn't getting much value out of it (I only occasionally fire out an APRS signal on VHF and I can't match the erudition of those using the CB proxy which 2m NBFM seems to amount to). So - I pulled down the colinear and put up my new "runt" dipole in its place.

I left the beacon running overnight with the usual 50mW output and here's the performance, plotted as spot count in each contiguous 10-minute interval, (shown in red) against the "average" performance experienced over recent weeks (in blue)...

Bottom line is - whatever the shortcomings of the new antenna and its radiating environment (low down, close to my garage and extension roofs), the performance isn't really significantly short of the average achieved with the g5rv! I did miss my occasional overnight dx - but this first night's data isn't exactly statistically significant.

The g5rv runs pretty much N-S, whereas the new "runt" dipole runs NW-SE. This seems to have given me slightly better projection into Scandinavia than I was achieving with the g5rv (actually, I was getting signals up into arctic Norway when the g5rv's centre connections were faulty - obviously this was result of the inevitable disruption to the radiation pattern, accompanying the observed disruption to the load presented to the transmitter)...

Clearly, I need to collect more data before jumping to any conclusions but - for now at least - I am enjoying the luxury of a dedicated 30m antenna for the beacon, leaving my main antenna free for whatever else takes my fancy !

...-.- de m0xpd


  1. That's impressive by any standards. I wonder how it would fare as a dedicated antenna for 30m APRS?

  2. Interesting and useful information that you have provided here on your post.Thanks.

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