Topband: Beverage impedance change in cold WX solved

[Mike Waters]

This is interesting, Steve. A couple of questions:

1. Just to be clear, Was this a two- or a single-wire Beverage? In my tests
here, changing the termination resistance (at the shack end) on my two-wire
Beverages had an almost zero effect on the pattern or F/B ratio. That
seemed to be true even if I did not use a termination resistor. Others have
reported similar results.
  Of course, that is not the case with a single-wire Beverage terminated at
the far end. I assume that yours was.

2. Was your resistor an Ohmite type OX or OY? That's what I and many other
folks use.

3. What effect does this have on the F/B ratio? That would be easy to
determine during the daytime using AM broadcast stations.
There also ought to be an easy way to model how this 10% change (!) in
termination R affects the F/B ratio. It *would* affect the return loss.

On Tue, Jan 21, 2020, 6:08 PM VE6WZ_Steve <ve6wz at shaw.ca> wrote:

> A few days ago I posted a video explaining some experiments I did adding
> short radials to my feed and termination grounds on the Beverage.
> During that week temperatures went as low as -41 C at the station.
>
> The mystery has been solved.
>
> ... I also show that the ceramic termination resistor I use has a very
> high negative temperature coefficient (-1300 C). This results in an
> INCREASE of  30 to 40 ohms in my 470 Ohm termination resistor.  Therefore,
> the termination could be 40 to 60 Ohms too low!!  I show in the video that
> the resistor does indeed increase by 40 Ohms when I chucked it out my back
> door at -30C for an hour. ...  This seems to indicate that the main cause
> of the Beverage miss match is the temperature coefficient of the wire and
> the termination resistor. ...
>