[ARC5] Antenna for small yard

[Kenneth G. Gordon]

On 22 Oct 2016 at 17:09, AKLDGUY . wrote:

> It's not a question of how to fit several dozen feet of wire into my yard. Anyone can do that. What 
> I want to know is how do I feed it from the 5-8 ohm, 150pF impedance of the BC-230 and 
> ARC-5?

Yes. We understand that.
 
> I cannot get the rig under the antenna, so there has to be a horizontal feedline, either suspended 
> in air or laid on ground. What impedance feedline do I use?

I cannot see how your feedline under those conditions canNOT be part of your antenna. A 
bare wire will radiate, and laying that on the ground will contribute to substantial losses. 

You can eliminate this issue IFF you do some impedance transformation at the transmitter 
and use coax.

> I'm reluctant to use coax because it means an intermediate conversion from 5 to 50 to 
> ?whatever. It would be better to go from 5 straight to antenna, especially as the aircraft 
> transmitters are designed to work into a very short antenna.

True, but you can easily enough make the TX "see" its proper load. As long as the TX 
"sees" 5 ohms +/- jX-whatever, it will be happy. Your job is to convert that to what your 
choice of antennas must "see" for most efficiently radiating your power.

This is not rocket science.

> Please, no more 50/75 ohm solutions.

Sorry, but at this point, you have only two choices: 1) feed any length of wire you can put up 
as an end-fed almost random length wire, adjusting its length until you see the antenna 
current you wish to see, or 2) put up the 33' low dipole with drooping ends, use an Un-Un 
and use coax.

I cannot see why using an Un-Un and coax would contradict what you need to do there. All 
of that can be hidden. As long as you match impedances, the TX "doesn't care".

Now, I am a very firm believer in the KISS principle, but sometimes we have to bend a little.

I see this as, basically, a two-part problem (only): problem #1 your transmitter must have a 
load of 5 ohms + jX whatever. Problem #2, your best choice of antenna exhibits an 
impedance different from what the transmitter needs. Solution, build a converter: an Un-Un. 
Simple.

Ken W7EKB

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