Topband: Recycled ferrites for 160m

[Jim Brown]

On Wed, 21 Jan 2009 11:49:27 -0800, Michael Tope wrote:

>I would also use a relatively 
>low impedance for the shunt element in the voltage divider. This will 
>reduce errors caused by probe and stray fixture shunt capacitance at 
>higher frequencies (and also the phase angle error if the DUT is 
>reactive and not resistive). 

EXACTLY! There's nothing "magic" about 50 ohms -- it's simply a value that 
we often get for free built into our spectrum analyzer voltmeter. We could 
improve accuracy at lower values of unknown Z by using lower values of load 
Z. Something as simple as adding a second 50 ohm load across the voltmeter 
input yields a 2:1 improvement. One reason 50 ohms is convenient is that 
there it's easier to find 50 ohm loads that are likely to be good to a 
fairly high frequency. The tricky part is connecting them in parallel 
without adding capacitance. :) 

73,

Jim K9YC