[NLRS] ANDREWS HELIAX QUESTIONS

[Dr. Gerald N. Johnson]

On Fri, 2006-05-12 at 08:57 -0400, w0zq at aol.com wrote:
> 
> Hi Kris.   Can't help you directly, but here is one idea.   Do you have a 50 ohm dummy load and a SWR meter ?   You can make a "cheap" dummy load with a PL259 connector and a 1 watt 51 ohm carbon or metal film resistor or two 100 ohms in parallel, etc.   Don't use wire wound resistors.    Simply connect your dummy load on one end and your SWR meter on the other end and pump in a few watts of RF.   If the SWR is very close to 1:1, you have 50 ohm.   If its closer to 1.5 to 1, you have 75 ohm.  
>  
> 73, Jon
> W0ZQ 

But Jon, the SWR seen by the meter if the line is any multiple of a half
wave long will be 1:1 (half wave repeats) and if the line is an odd
multiple of a quarter wave long the input of a 75 ohm line with a 50 ohm
load will be 100 ohms for a 2:1 SWR. The input Z will be something in
between 50 and 100 ohms at other frequencies.

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer