[UK-CONTEST] Antenna for SSB field day

[Ian White GM3SEK]

Chris G3SJJ wrote:
> Ian, maybe very originally doublets figured strongly. One of the 
>trophies for Low Power Contest has an old style Bell tent and two masts 
>with a doublet stretched across, with sagging open wire feeder!
>

Yes, I've seen that one - it is a work of art, but hardly a model of 
good antenna engineering!


>I think there is a greater awareness now of propagation spread, as you 
>say, but I am not sure the basic rules need tinkering with to 
>accommodate that. GM3POI won NFD Restricted section many times with 
>well researched vertical system.
>
Having done NFD with the Orkney team for the past two years, it was 
Clive's exploits with Dennis F5BVY that set me off on this trail. Our 
club here at home has a need for a multiband vertical, and it would 
definitely be a bonus if it could be used for NFDs in the Restricted 
sections as well. But as soon as I started sketching out some 
preliminary designs, I came up against these strange quirks in the 
rules.

Without giving away too many technical details, a vertical antenna would 
obviously have to use the full allowable height, to maximise the 
radiation resistance and feedpoint efficiency on the lower bands.

But the current RSGB NFD rules require two *different* maximum heights 
in the Restricted sections. For SSB NFD it's 15m, but why is it only 11m 
for CW NFD - with Top Band to cover as well? That extra 4m makes a 
notable difference for both horizontal and vertical antennas.

Anyone who is using a doublet or similar can easily change the height 
between 11m and 15m; but for vertical users this is a show-stopper. 
Making full use of the maximum available height for each contest would 
require a complete redesign, and the construction of two totally 
different antennas.

That discrepancy between the two RSGB NFDs needs to be looked at 
urgently. (Hint: the height limit for the Eu/DARC CW NFD is 15m...)


Then we come to the rule about "two supports". Anyone who has chosen a 
vertical, or even an inverted-V, is now limited to only *one* additional 
support of any height whatsoever.  In many cases, by far the best 
technical option would be to use the available mast sections to make two 
shorter poles - but no, that is not allowed.

I am not saying that anyone intended the rules to end up this way. What 
we're seeing are the unintended consequences of a rule-making process 
that said: "We know what the best antenna is for everybody - the doublet 
- now what should the rules be?"

Those rules have permitted some kinds of innovation [1] but other good 
options have been closed off without even noticing they exist.


>It seems to me the concept of one single element antenna is established 
>and a good leveller

"Established" doesn't automatically make it the best kind of leveller, 
or mean it cannot be improved. We have already seen how easily the 
"established" rules can fall victim to the Law of Unintended 
Consequences.

A far better way to limit the overall scale and resources of a 
Restricted antenna - but this time, without limiting the technology - 
would be to specify "one active element per band", a maximum overall 
height (which should surely be 15m for both NFDs) and a new rule to 
limit the total *length* of above-ground supports (specifically *not* 
the total number).




[1] Surely the V-beam and the Rhombic weren't in the Restricted section?


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek