[TowerTalk] Bobtail-Curtain

[Don Moman]

> At 09:47 AM 12/11/97 -0800, Carsten, DL6LAU wrote:
> >Hi,
> >
> >I am thinking about building a Bobtail-Curtain antenna for 80m (maybe
> >another for 160m too). Reading in two different sources, one states to
> >try a high L/C ratio for the L/C tuning network, the other source states
> >low L/C ratio... 
> >1. Any advice for good values to start with? (e.g. 80pF for 80m?)
> >2. If I would use a variable air dielectric C, what would be the
> >minimum    plate distance for 1500W (3000W) out ?
> >

Having had two bobtails up for 80m (2 years) and just having put one up
this summer for 160m....  Mine are bottom fed with tapped coil(very
roughly maybe 25-35 turns 2-2.5 inch diameter air wound, tapped maybe 4-8
turns from bottom) and an air variable cap - some surplus 500w rated
commercial tuner modified. The air variables have maybe .25 inch spacing
and all behave well at 1500w. But the bottom of the bobtail where it
enters the tuner needs to be kept quite far from any metal or ground -
just about started a prairie fire with the 80m one the first time I
powered it up!

They are quite sharp tuning - I have motorized the 160m one and plan to do
the rest at a later date. 

I don't have much mileage on the 160m one yet but I have hopes it will
work well. Last weekends ARRL test didn't prove it to work any better than
other high deltas (180') and inverted Vees (145) on the majority of
sgnals, but conditions were not very good from here.

73 Don
VE6JY


 ve6jy@freenet.edmonton.ab.ca 


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