[Antennas] Return Loss Bridge Construction

[Mark]

Here's a copy of the Drake VSWR calculator, easy to use if you build one of
these instruments ... 73, Mark  AA6DX
http://home.pacbell.net/aa6dx/drake.html
----- Original Message -----
From: "Ronald KA4INM Youvan" <ka4inm@tampabay.rr.com>
To: "a" <antennas@mailman.qth.net>
Sent: Sunday, May 26, 2002 10:38 PM
Subject: Re: [Antennas] Return Loss Bridge Construction


> >                                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.
>