[UK-CONTEST] Antenna for SSB field day

[David G3YYD]

  To make a 40m dipole have a low SWR on 15m you add about 20cm of wire 
a 15m quarter wave from the centre of the 40m dipole. Of course do this 
on both sides of the dipole! This will have virtually no impact on 40m 
as it is still a high current point on 40m but on 15m it will be a 
voltage point and will capacitively load the dipole to bring it  down in 
frequency. Trim the extensions to centre lowest SWR  to centre of 15m.

The ends of the wire will be a high voltage point on 15m therefore 
ensure it does not get too close to any other wire. I use mono-filament 
fishing line - light in weight, strong and a good insulator.

David G3YYD

On 13/08/2010 16:34, Callum MØMCX wrote:
> Yes. The 40m legs are resonant on 7 mhz and 22 mhz however the K3
> tuner handled the slight mismatch on 15m.
>
> I designed it for rapid deployment using caribinas and paracord at
> around 10m to feedpoint. Terry was very happy with it and had it up in
> a few minutes at 5B4. Coax was 7mm Aircell, very light but similar
> characteristics to 213.
>
> It was a fun project and took a weekend to iron out all the bugs. 80m
> was not factored in but additional legs could easily be manufactured.
> It rolls up to the size of a toilet roll.
>
> Callum McCormick
> 07976 631881
>
>
> On 13 Aug 2010, at 15:52, "Andy Swiffin"<a.l.swiffin at dundee.ac.uk>
> wrote:
>
>>>>> On 13/08/2010 at 01:01, in message
>> <BLU0-SMTP65CE1C78DE7A40C15CB2B0C6980 at phx.gbl>, Callum
>> MØMCX<callum at mccormick.uk.com>  wrote:
>>> Rob, you are right. Terry (G4MKP) and I knocked up a very
>> professional
>>> fan dipole for 40, 20, 15 and 10 for his 5B4 holiday.
>> wouldn't the 40m dipole and the 15m dipole fight?   A 40m dipole is
>> itself resonant on 15  as a 3/2 wave dipole.  Or are you meaning you
>> actually only had 3 dipoles (40, 20 and 10) for the four bands?
>>
>> Andy
>> gm8oeg
>>
>>
>>
>> ************************************************************
>> Please consider the environment.  Do you really need to print this
>> email?
>>
>>
>>
>> The University of Dundee is a registered Scottish charity, No:
>> SC015096
>> _______________________________________________
>> UK-Contest mailing list
>> UK-Contest at contesting.com
>> http://lists.contesting.com/mailman/listinfo/uk-contest
> _______________________________________________
> UK-Contest mailing list
> UK-Contest at contesting.com
> http://lists.contesting.com/mailman/listinfo/uk-contest