Topband: T antenna Resonance Dimensions and Z

[Herb Schoenbohm]

Dave Sharred wrote:
> I have some vacuum variables that I may take over; should we need to match them a little. A makeshift coil should not be such a problem. WE may need to raise that feed impedance a little; if they come out at 20 Ohms; may be higher depending on ground resistance.
>
>   
> Dave
> To avoid the need for housing, coils and caps at the feed point if you 
> feed is not reactive is to simply change the impedance.  If you don't 
> want to wind a ferrite device to do this why not consider running two 
> paralell runs (this would make 25 ohm coax) of RG-8 that are 1/2 wave 
> of electrical length (free space minus the VF amount which is arround 
> 66% with solid core coax.)  This will repeated the feed point 
> impedance at the shack and your  tuner...most rigs have them 
> today...or the output network of your amp should handle this with a 
> loss would between none and nothing.

I still think, however, making the top a bit longer and thus slightly 
inductive and using just a fixed series cap you have a simpler solution 
with a feed point value closer to 50 ohms and the ability to fine tune 
at the point of interest on the band with a large current mica that may 
not require a housing but only a plastic cover.

Herb, KV4FZ