[TowerTalk] Matching a Delta Loop

[TexasRF at aol.com]

If you have some 75 ohm coax available you can build up a series matching  
section:
153 degrees 50 ohm coax connected to the feedpoint followed by 146.5  degrees 
of 75 ohm coax.
 
You can also make a stub match from all 50 ohm coax:
A length of 88 degrees connected to the antenna and a stub of 71 degrees in  
parallel at the end makes 50 +j0
 
Or:
a length of 50 ohms 130 degrees long shunted by a 106 pF capacitor on the  
end also makes 50+j0.
 
I like the series match because it just replaces feedline that you have to  
use anyway to get into the shack. No special Tee connectors are needed, just  
normal PL259 and double female connectors to hook everything up.
 
The above lengths are based on an assumption the feed impedance is 79+j0.  If 
it is different and you can quantify R+j the series section can be "tweaked"  
to compensate and still reach a good match.
 
There are other solutions as well but some of them will require changing  the 
size of the loop and who wants to do that?
 
73/K5GW
 
 
In a message dated 10/18/2006 3:03:26 P.M. Central Daylight Time,  
philc at texascellnet.com writes:

I  hastily threw together a 30 meter Delta Loop this summer in order to  get
KH8SI in the log for a new one on CW. Using the formula, the resonant  point
came out 10.105 mhz (great, first try!) but the feed-point impedance  is 79
ohms. 

What is a good method of matching this antenna to 50  ohm coax? I don't want
to use ferrites. I'm using a line-flattener in the  shack now, but I robbed
it from another project, and I need to return  it.

This antenna is a real "keeper;" I was able to bust the pile-up on  2nd call.
The apex is a 50 feet on an 80 foot Rohn 25 tower.

Thanks  in advance for any suggestions.

(((73)))
Phil Clements,  K5PC




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