[Elecraft] KAT500 Signal Isolation between antenna ports

Jim Brown jim at audiosystemsgroup.com
Sun Jan 19 02:42:25 EST 2014


On 1/18/2014 8:23 AM, Phil & Debbie Salas wrote:
> Take a look at the measured KAT500 isolation numbers in the “Product Reviews” section of my website atwww.ad5x.com.  The isolation varies based on the ports chosen, and the frequency band.  As an example, the isolation on 20 meters has a worst-case value of 36dB between ports 2-3 (when 3 is selected), and a best case value of 65dB between ports 3-1 with port 1 selected.

Yes, BUT -- these are passive networks, and the response of all passive 
networks depends upon the source Z and the load Z at each port. I'll bet 
your measurements were for 50 ohm sources and 50 ohm loads. Real world 
antennas differ widely from 50 ohms even when they are close to 
resonance on the bands of interest, and by a lot more when they are 
resonant on other bands. And if that isn't enough, source and load Z are 
transformed by transmission lines between the antenna, the device (the 
KAT), and the load (the RX). We run into exactly the same issues when 
measuring bandpass filters, a lot of which I published a year or so ago 
in NCJ. Our measurements look great, we do them very carefully, but hook 
real antennas and equipment to these networks and the results can be 
very different.

73, Jim K9YC


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