[Antennas] Return Loss Bridge Construction

[Charles Greene]

At 01:38 AM 5/27/2002 -0400, Ronald KA4INM Youvan wrote:
>>                                However, it is a precision instrument, is 
>> expensive because of the precise isolation requirements between the 
>> ports, and it requires a couple of expensive pieces of test equipment to 
>> use with it, namely a spectrum analyzer and tracking  signal generator.
>
>   However, a return loss bridge can be built inexpensively if done with
>some care and used with an RF sweep generator, a diode detector, and
>a simple oscilloscope, the only caveat is:    If the sweep generator
>doesn't put out around +20 dBm and you don't use a hot carrier diode
>detector, the trace will be too small to be useable. (I suppose you
>could follow a lower powered generator with a MMIC amplifier or two.)
>
>   When you put an antenna on the DUT port (positioned in the free)
>the frequencies where energy is lost TO RADIATION are what show on the scope.
>(as a negative bell curve) Great for measuring the bandwidth!
>The transmission line in use (match or length) changes this very little
>(only as an antenna tuner would) although the match can be measured.
>   You can use a good directional coupler to observe the same things.
>   It is the ideal device for antenna tuning and development on a budget.

Ron,

The return loss bridge referenced by Dennis in his original message;
http://www.qsl.net/n9zia/wireless/appendixF.html
may be able to do this.  I would think the layout would be important to 
retain isolation between the ports.  Unfortunately, the site does not have 
pictures of the layout, that I can find.




73, Chas, W1CG