Topband: inverted L antenna match system

[Charles Moizeau]

More radials will reduce losses.  Crudely put, they will reduce dc losses at the base and they will also reduce rf losses by capturing some of the rf that is radiated by the antenna but splashes off the ground instead of zinging away into space, and then recycling that rf at the base feedpoint. 

It is my belief that if the point of maximum radiation is made to occur higher on the vertical section of the antenna, then the rf will splash further away from the base, and this suggests the need for longer radials to gather in the errant rf.

Will more radials change the feedpoint impedance?  Yes.

Will more radials change the SWR? Ceteris paribus, Yes.

Will the SWR go up or down? It can go either way, but I didn't care, for I was able to twiddle the matching device,  a series variable capacitor hooked between the hot side of the feedline and the vertical radiator, and achieve a progressively lower SWR after increasing the number of radials. 

Will the bandwidth be reduced with more radials?  Yes, after the system is tuned for minimal SWR?

Is reduced bandwidth a problem?  Not for this QRPer who hangs out close to 1.810 mHz.  And if I want to go way higher in the band, I insert a high power antenna tuner located in the shack into the works and make the necessary adjustments to reduce the SWR.

What about coils?  Why bother introducing their certain losses if you can do a design that avoids them?

72,

Charles, W2SH

  

> Date: Mon, 31 May 2010 05:00:32 -0700
> From: tzitzikas_ee at yahoo.com
> To: topband at contesting.com; w2sh at msn.com
> Subject: Re: Topband: inverted L antenna match system
> 
> thank you all of you for your answers. 
> 
> So more radials, means lower swr?
> 
> Do you think that the variable capacitor is all i need for low swr? If
> i will not achieve swr<1.5 what do you think about to try to use a
> variable coil, which will be connected between the common point (of
> capacitor and 50ohm coax from transmitter) and ground. It will help to
> achieve low swr?
> 
> How many uH must be this coil?
> 
> i mean something like this http://tzitzikas.webs.com/COUPLER.JPG
> 
> (without optional turns which are in series with capacitor). 
> 
>