Re: K3 ANT 1-2 isolation

Posted by Guy, K2AV on Apr 29, 2012; 8:06pm
URL: http://elecraft.85.s1.nabble.com/K3-ANT-1-2-isolation-tp7500652p7511706.html

You are getting some really worse numbers than I did.

You may have ant2 only terminated on one end of its cable connections,
which would be really worse on 6 meters than 160.  There is one of those
bitty jacks that needs a cable attached to it and then terminated.  It's
the "other" antenna connection that allows you to listen on whichever of
ANT1/2 the TX is NOT using.

Out on Core Banks, NC, we were using doublets at right angles on the same
pole to ANT1 and ANT2, receiving with diversity.  There was 30 dB
separation with the two antennas hanging on the same pole.  How much better
does it have to be inside the K3?

You need to terminate the internal K3 connection of ANT2 when you make the
measurement.  Also the shields of both cable connections at both ends need
to be grounded as well as terminated.

73, Guy.

On Sun, Apr 29, 2012 at 9:28 AM, Mike Harris <[hidden email]> wrote:

> Interesting.  I looked at it from the other direction.  With the K3 ANT1
> connected to a dummy load and ANT2 connected also to a dummy load via my
> WM-2 QRP wattmeter.
>
> With 100W out at ANT1, out of ANT2 I measured 30mW at 50MHz down to 1mW
> at 7.1MHz.  A range of -30dB to -50dB.  50MHz is not in the WM-2 spec,
> however, 25mW was measured at 28.2MHz which gives -36dB.
>
> There are obviously potential measurement errors there so no one needs
> to take it as absolute. Perhaps someone with access to precision
> equipment could also do the test.
>
> Regards,
>
> Mike VP8NO
>
>
>
> On 28/04/2012 12:27, Mark - G4AXX wrote:
> > The isolation between ANT 1 and ANT 2 varies from -76dB at 1.8MHz to
> -46dB at
> > 50MHz.
> > This is measured with a signal generator, using the K3 S-meter, with ANT
> 2,
> > AUX RF and RX ANT IN terminated in 50 Ohms.
> >
> > http://elecraft.365791.n2.nabble.com/file/n7509068/ANT1-2_leakage.jpg
> >
> > The isolation between AUX RF and ANT 1/2 is>95dB (1-30MHz), rising to
> -70dB
> > (52MHz).
> > This was measured with an N2PK VNA.
> >
> > I have tried to dress the unscreened wires from ANT 1&  2 to the ATU in a
> > way to minimise coupling, but the coupling is dominated by the
> capacitance
> > of relays K18&  K19.
> >
> > Using ANT1/2 for Diversity reception means the receivers are never truly
> > independent. There is likely to be more coupling inside the K3 than can
> > usually be achieved by physical separation of the antennas.
> >
> > Operating Diversity reception with the SUB RX fed from the AUX RF BNC
> input
> > is the way to go.
> >
> > 73 Mark G4AXX
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