KAT500 Signal Isolation between antenna ports

[jh3sif]

I am experiencing poor signal isolation between antenna ports of KAT500.

ANT1: Open
ANT2: Open
ANT3: Antenna connected

On selecting ANT1 or ANT2, I hear signal from ANT3 although signal level is lower than ANT3.

ANT1: Antenna connected
ANT2: Open
ANT3: Open

On selecting ANT2 or ANT3, I hear signal from ANT3 although signal level is lower than ANT1.

ANT1: Antenna connected
ANT2: Open
ANT3: Antenna connected

On selecting ANT3, I still hear signal from ANT1 (increased noise level from ANT1).

I have not experienced such poor inter-port isolation with my ICOM TRX with 4 antenna ports.

Any idea for improving inter-port isolation?

73 de JH3SIF, Keith




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[Phil Salas]

Hi Keith – Take a look at the measured KAT500 isolation numbers in the “Product Reviews” section of my website at www.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.  You might want to select the antennas and ports to maximize isolation.  As an example, port 1-2 isolation is much worse than port 1-3 isolation.  So I put my 6-meter beam on port 2, and my two HF antennas on ports 1 and 3.

You can easily hear signals that are very far down from a desired signal.  Measurements made in my old telecom days indicated that you can usually hear tones as low as 90dB down!  And, of course, if the signal on the unselected antenna is hotter than on the selected antenna, things can sound worse.

Phil – AD5X

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[jh3sif]

Hi Phil,

Thanks for the info. I read the product review.
I will try to find better combination of antenna connection to the ANT1/2/3 ports.
Local noise is very strong in my location, sometimes S7 to S9 in worst case. So bigger antenna picks up more noise. When my 14MHz quad is connected to ANT1, the noise from the 14MHz quad goes to TRX on selecting ANT2 or ANT3.
If the unselected ports went to ground level, we would have better isolation.

73 de JH3SIF, Keith


On 2014/01/19, at 1:23, Phil & Debbie Salas <[hidden email]> wrote:

> Hi Keith – Take a look at the measured KAT500 isolation numbers in the “Product Reviews” section of my website at www.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.  You might want to select the antennas and ports to maximize isolation.  As an example, port 1-2 isolation is much worse than port 1-3 isolation.  So I put my 6-meter beam on port 2, and my two HF antennas on ports 1 and 3.
>
> You can easily hear signals that are very far down from a desired signal.  Measurements made in my old telecom days indicated that you can usually hear tones as low as 90dB down!  And, of course, if the signal on the unselected antenna is hotter than on the selected antenna, things can sound worse.
>
> Phil – AD5X
>
> ______________________________________________________________
> Elecraft mailing list
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>
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[Jim Brown-10]

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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[Phil Salas]

“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”

Jim - You are absolutely correct.  Antennas resonant on different bands should improve things.  My measurements were made in a 50 ohm system.  However, without knowing what the other antennas are, a 50 ohm system measurement at least gives a feel for the isolation.  In my case, I have two different antennas resonant on some of the same bands (vertical and dipole), and a 6-meter beam.  So the 50 ohm measurement makes sense for the same-band antennas.  Putting these two antenna on Ports 1 & 3 improves isolation quite a bit (over Ports 1/2 or 2/3).  And the 6-meter beam on Port 2 will have more isolation between the antenna on Ports 1 and 3 since it is not resonant on the HF bands.

Phil – AD5X
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