Re: NEC-LIST: Wheeler cap Q

In a message dated 5/31/00 9:31:03 PM Eastern Daylight Time,
lbt007_at_yahoo.com writes:

<< Hi.
 
     Can somebody summarize the technique of using a technique called
 'Wheeler Cap' method to estimate radiation efficiency? I have pieces
 of it, and I would like to double check that I have it right.
 
 Thanks.
>>

1) build a 'cap' of 1/4 wave radius;
2) stick your BALANCED antenna inside the cap;
3) measure the return loss at resonance;
4) remove the cap (free space or low reflection environment);
5) measure the return loss at this resonance;
6) determine the differential return loss;
7) translate that into ohms;
8) take the return loss of 5) and translate into ohms;
9) divide 7) by 8) and multiply by 100 for efficiency.

NOTE: S11 return loss is always ambiguous on the equivalent ohmic
value so you need to need to be careful as to which side of 50 ohms
you're on:-) Also, if your cap isn't a 1/4 wave it won't work as an
efficiency measurement. Finally, this is not a good method for
non-electrically small antennas as the antenna itself approaches the
cap diameter in size.

73
Chip N1IR
Received on Mon Jun 05 2000 - 18:13:39 EDT