[UK-CONTEST] 80m Low Dipole

[Steve Knowles]

Hi Jim,

As small antennas go I would expect your inverted-L to be good for really 
close locals and fairly good to EU (I use a variation myself) but not too 
bright for anything in between.

The dipole and inverted-V will probably perform about the same at this low 
height - largely omnidirectional and high angle - but the inverted-V will 
have a lower impedance.  You might like to consider using a folded dipole 
element to get the radiation resistance up to a more sensible level where 
ATU and antenna losses will be less.  A reflector on the ground can do no 
harm, though the amount of good it will do depends upon the earth 
characteristics.

What may be stuffing you is the "dead zone" - the gap between where your 
ground-wave peters out and the nearest point at which your skywave is 
returned to earth.  That's dependant upon the Critical Frequency, and 
there's not a lot you can do to influence that.  It's a common problem on 80 
& 160, particularly in winter, (the [really] old RSGB propagation 
predictions always used to warn against it) and can lead to a complete 
absence of signals from around 10 miles out (depending on your antenna) to 
several hundred miles out.

With summer conditions I think you just have to rely on frequent band 
changes and picking up a few contacts at a time.  If you can arrange both a 
horizontal and vertical antenna it's clearly an advantage.

73

Steve


----- Original Message ----- 
From: "mm0bqi" <mm0bqi at blueyonder.co.uk>
To: <uk-contest at contesting.com>
Sent: Wednesday, July 11, 2012 1:43 PM
Subject: [UK-CONTEST] 80m Low Dipole


With IOTA almost upon us it is time for the 'BQI annual antenna question,
this year it is on 80m options.
Last year's question was on HF vertical dipoles.  Real world conclusion
from the contest was that they worked okay but did not set the heather on
fire.  I am in the process of constructing the baluns described by GM3SEK
just in case I go down a similar route this year. (These must be one of the
best bang for buck items as the ferrites are only £3 each.
Complete WORKING balun for less than £12 can't be bad!)
>From the Summer Isles I find it very difficult to work the six or so island
groups that are within a couple of hundred miles.
I also find a distinct lack of nice 15 point G stations in the log.
This year I will use the same inverted L as last year, 12m vertical section
on a fishing pole and then 8m sloping down at a shallow angle with 4
elevated radials.  Seems to work okay into EU.
Is there anything to be gained by one of these two options?
1.  Straight dipole, ends at 10m.
2.  Inverted V with apex at 10m.
I suspect because of the low heights both would perform in a similar
manner.  Would putting another dipole on the ground/few feet off as a
reflector make any difference?  Now that the antenna rules have changed I
could try this.
My previous experiments with low dipoles have on the whole produced no
advantage in filling in this blank hole.  Maybe I just need to watch my
time for moving to 80m to ensure I catch as many Gs as possible!  Time on
the island will be short so very little time to experiment but I would like
to try something new.
Anyway all thoughts on the antenna situation would be appreciated.
73
Jim, MM0BQI
GM1J from EU092, Summer Isles. (Is this the first 2012 IOTA plug on the
reflector?)
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