By Sean Gilbert, UK
| I've been playing about on 6m (50 MHz) lately and have noticed a rather strange phenomena with regard to my somewhat limited antennas. For 6 (and Band I TV) I use a simple home made aluminium dipole, made from an old scrap antenna. this exhibits a nice low SWR at resonance and is fed with 50 ohm coax.
This dipole is mounted as high as I can get it in my attic and has allowed me to work 60 countries on 6m, but a couple of weeks ago I pressed the wrong button and found myself using my 18/24 MHz inverted vee dipole (also in the attic, about the same height and same orientation as the standard half wave dipole for 50 MHz) for receive.
I noticed that signals seemed to be rather strong on this antenna, and in fact were considerably stronger than on the 'proper' dipole.
This seemed rather strange given that it is not exactly resonant on 50 MHz. However, further investigation showed that the increase in signals was only apparent when the signal was coming from the North or South (the signals I had listened to were from Spain), which is 'off the end' of the 50 MHz dipole and hence is the lowest signal pickup point for that antenna.
|Now as I said, the inverted Vee is pointing in the same direction but gives a very noticeable increase in N/S signals, whilst being weaker than the half wave in all other directions. I can only put this down to the fact that the inverted vee is acting like a 3/2 wavelength dipole at 50 MHz. thus giving it some gain and altering it's radiation pattern, and also being an inverted vee there are probably some vertically polarized signals getting through. I notice a similar difference on the HF bands when switching between the vertical and the indoor wires. One will be better than the other for a particular signal. but it is always worth trying the other antenna as on a number of occasions I have been surprised by which antenna is yielding the most readable signals.
The moral of this long winded story? Try to ensure you always have at least 2 antennas to choose from, it may make the difference between hearing a new one and just listening to static (as I found out a couple of years ago when I heard ABC on 120m when I was disconnecting the antenna! Plugged in I couldn't hear it, but just using the centre conductor of the feeder as a random wire allowed it to become audible. Ever since then I have had at least 2 different sorts of antenna connected and it has paid off on numerous occasions!
Sean D. Gilbert, United Kingdom, September 2003