[KAT500]schematic

[ab2tc]

Hi all,

Will a schematic be forthcoming soon for the KAT500? I have noticed that the port to port isolation between the 3 antenna ports is rather poor, even worse than the RX/MAIN antenna isolation on the K3 which has received plenty of complaints in the past. I am guessing that unused antenna ports are not grounded on the KAT500. Had they been, isolation should have been much better. I am surprised that Elecraft pays so little attention to these things. If the antenna relays are of the changeover kind and have been oriented "correctly" adding a ground shunt should be easy. But we need schematics.

Anyway, it's still a great product. Happy new year!

AB2TC - Knut

[Phil Salas]

“...I have noticed that the port-to-port isolation between the 3 antenna ports is rather poor...”

I measured about 42dB isolation on 6M from port 1-2.  And this stays pretty constant down to 15M and then gets better fast.
I measured about 61dB isolation on 6M from port 1-3.  This gets better very fast, going to 75dB on 10M.

I use ports 1 and 3 for my two HF antennas (43ft vertical and 20/15/10M rotatable dipole), and put my 6M beam on port 2.

Phil – AD5X
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[ab2tc]

Hi,

How did you measure that? They are very different from my measurements. Here is what I did:

Put radio TX in Test mode to protect the XG3.
Connect XG3 to antenna 1 at -74dBm on 10m.

Measure:
port 1: -76dBm
port 2: -107dBm (port connected to another antenna switch which presents a short circuit).
port 3: -110dBm (port connected to dummy load from Ridge Electronics).

The measurements are taken with LP-Pan/NaP3. That's a mere 34dB in the best case. BTW the numbers confirm what I can easily observe during normal operation. What are other people seeing?

AB2TC - Knut

Phil & Debbie Salas wrote

“...I have noticed that the port-to-port isolation between the 3 antenna ports is rather poor...”

I measured about 42dB isolation on 6M from port 1-2.  And this stays pretty constant down to 15M and then gets better fast.
I measured about 61dB isolation on 6M from port 1-3.  This gets better very fast, going to 75dB on 10M.

I use ports 1 and 3 for my two HF antennas (43ft vertical and 20/15/10M rotatable dipole), and put my 6M beam on port 2.

Phil – AD5X
<snip>

[Geoffrey Mackenzie-Kennedy-3]

Knut,

FWIW I found that the isolation between the ANT 1 and 2 ports of my KAT100
on 15m was only approx 40db.  To increase the isolation between ports, not
only did I have to add a relay to ground the port not in use, but I also had
to replace the relay-to-port unshielded wiring with coax.

Sounds as though you could have a similar problem with the KAT500.

73,
Geoff
LX2AO


On January 01, 2013 at 6:53 PM, Knut AB2TC wrote:

> Hi,
>
> How did you measure that? They are very different from my measurements.
> Here
> is what I did:
>
> Put radio TX in Test mode to protect the XG3.
> Connect XG3 to antenna 1 at -74dBm on 10m.
>
> Measure:
> port 1: -76dBm
> port 2: -107dBm (port connected to another antenna switch which presents a
> short circuit).
> port 3: -110dBm (port connected to dummy load from Ridge Electronics).
>
> The measurements are taken with LP-Pan/NaP3. That's a mere 34dB in the
> best
> case. BTW the numbers confirm what I can easily observe during normal
> operation. What are other people seeing?
>
> AB2TC - Knut

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[Phil Salas]

“...How did you measure that? They are very different from my measurements. ..”

I measured the isolation with my Array Solutions VNA2180.
Phil – AD5X
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[ab2tc]

Hi,

Ah, so you measured loss directly from, say, port 1 to port 2 with a VNA (vector network analyzer). Those will be different numbers and not what I had in mind. What I am interested in is how much an unwanted signal on one antenna port is attenuated when another antenna port is selected. Or vice versa, when transmitting, how much power goes out the two ports not selected. This loss could be improved significantly if the unselected ports could be grounded, which is why I am interested in a schematic.

AB2TC - Knut

PS. We now have about 19F and my remote KAT500 is showing no signs of distress.

Phil & Debbie Salas wrote

“...How did you measure that? They are very different from my measurements. ..”

I measured the isolation with my Array Solutions VNA2180.
Phil – AD5X
<snip>

[Phil Salas]

"..Ah, so you measured loss directly from, say, port 1 to port 2 with a VNA
(vector network analyzer)...."

I should have been clearer.  I connected the VNA output to Port2, the VNA input to the radio port, and I selected Port 1.  So isolation measured was Port2 to common when Port1 was selected.  Then I did the same measurment, but connected the VNA output to Port3, and the VNA input to the common with Port1 selected so I could see isolationf from Port3 to common with Port1 selected.  Email me and I can provide those scans if you'd like.

Phil - AD5X
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[ab2tc]

Hello again,

Hmm, that should produce similar results to mine. One possibly important difference is that the VNA ports are perfectly matched 50ohm ports, but that shouldn't make that much of a difference. Have you ever tried to connect a dummy load to one of the ports (leaving the KAT500 in the normal shack wiring otherwise), select it and see how much stuff leaks through from the other two ports? I will send you an E-mail so you get my E-mail address. But I don't doubt your interpretation of the scans.

AB2TC - Knut

Phil & Debbie Salas wrote

"..Ah, so you measured loss directly from, say, port 1 to port 2 with a VNA
(vector network analyzer)...."

I should have been clearer.  I connected the VNA output to Port2, the VNA input to the radio port, and I selected Port 1.  So isolation measured was Port2 to common when Port1 was selected.  Then I did the same measurment, but connected the VNA output to Port3, and the VNA input to the common with Port1 selected so I could see isolationf from Port3 to common with Port1 selected.  Email me and I can provide those scans if you'd like.

Phil - AD5X
<snip>