Topband: T antenna Resonance Dimensions and Z

[Dave Sharred]

-----Original Message-----
From: Herb Schoenbohm [mailto:herbs at vitelcom.net]
Sent: 19 January 2010 20:45
To: Dave Sharred
Cc: John G3PQA; Martin Platt; TopBand List
Subject: Re: T antenna Resonance Dimensions and Z




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



Thanks for those extra tips Herb; we will have to consider these options
too.
Any additional comments on sources for Large current mica caps (on line
catalog ranges) would also be appreciated.


73

Dave
G3NKC