[BC] Antenna matching tuners: if from scratch

[RichardBJohnson at comcast.net]

Yes! If you have a true triple-stub tuner, in principle you can match anything to anything, but only within a narrow frequency range! When I worked for RCA service, we used a sweep generator, a large roll of coax for a delay line, and a diode detector connected to a low-frequency scope for antenna measurements. This works because, since the frequency is being swept, it will have changed by the time a reflected signal, that traveled the delay-line both ways, mixes in the diode. This produces a low-frequency "tone" that can be observed on an ordinary scope. RCA used 'cookies' within a transmission line section for matching their antennas, both FM and TV. These were ceramic discs of a high dielectric constant. If you had two discs, 1/8 wave apart, whatever mess one did to the Z would be undone by the other. This allows the reactance to be changed. Three discs allow the resistance and the reactance to be changed, just like a triple-stub tuner. There were some combinations of cookies that provided a good match, but horrible bandwidth, while there were others that provided the same match but with a better bandwidth.

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: "Thomas G. Osenkowsky" <tosenkowsky at prodigy.net>

The correct way is to use a network analyzer to
examine the bandpass. There may be several
combinations that produce a 1:1 VSWR at
carrier, but the bandwidth and performance
under icing conditions may be unacceptable.

Tom Osenkowsky, CPBE