[UK-CONTEST] Antenna for SSB field day

[Chris G3SJJ]

  Not wishing to keep this thread going longer, but reference a (sloping) V Beam you only need one mast, I am sure the Brizzzle guys could give us 
more info!

The Rhombic was just a thought whilst mulling all of this over. Needs modelling but my thinking was that a bi-di rhombic, presumably without the 
termination R would be OK on 20/15/10, but would be high angle on 80/40. The horizontal loop on 80m seems to be popular these days as a a cloud warmer.

Two masts about 100ft apart, feed point on one, termination R (or not) on the other. The other two corners pulled out on poly ropes.

Dunno, but an interesting experiment for plotting on EZNEC and then in a field but we would need some sunspots to see if it actually works on 15/10m!

73 Chris G3SJJ



On 15/08/2010 13:19, Ian White GM3SEK wrote:
> 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?
>
>