[UK-CONTEST] 80m Low Dipole

[Darren G0TSM]

Here I'm currently playing with a 40/80 inverted V fed at 40ft/12M. I 
use one feeder but the dipoles are arranged in a sort of 'squashed X'. 
Just tuning around 40M in the daytime G*s can be anything up to 6-8 S 
units better on the dipole compared against a vert with elevated 
radials. I haven't really tried 80M yet but results are promising around 
Eu. The reason for the squashed X config is that this arrangement 
basically guys a 12M spiderpole, without needing any more nylon rope.

73 Darren G0TSM


On 11/07/2012 23:31, Steve Knowles wrote:
> 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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