[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
More information about the Elecraft
mailing list