[Elecraft] Connections to K3 ant 1 & 2

[Don Wilhelm]

Tim,

It all depends on the isolation offered by your particular coax relay as 
well as the power output from your amplifier.
Assuming you have a 2kW amp (I know 1500 is the max, but the math is 
easier with 2k) - then 60 dB of isolation could feed .002 watts into the 
non-selected antenna jack.  That is a +3dBm signal level.

Now consider that the K3 has front end protective circuitry that begins 
at about +3dBm - the receiver preamp is automatically turned off at that 
point, and at +13 dBm, the attenuator is automatically switched in.

So I would conclude that up to a +3dBm signal leaking into the receiver 
is tolerable and would not cause a problem.
If you further consider that this would only happen when the K3 was in 
transmit state, and for the configuration you proposed, the ANT1/ANT2 
internal relay offers additional protection (isolation), 60 dB of coax 
relay isolation should be overkill.  Just how much overkill is cause for 
speculation and additional study.  If the internal relay offers 20dB or 
more isolation, then the required isolation of your coax relay would be 
reduced to 40 dB.  I would guess that rating the internal relay for 20 
dB isolation is conservative, most any relay worth its salt should be at 
least that good.

73,
Don W3FPR

N3XX wrote:
> Hi to all on the list,
>
> I just finished building my K3 kit a few weeks ago (4175).  All went well, 
> and the new xcvr is up & running with no problems.
> The antenna setup at my qth is a single cable from the entrance panel at the 
> house going out to tower #1, through a remote antenna switch to select from 
> antennas on that tower or another connection going to tower #2.  At tower #2 
> is another remote antenna switch to select various antennas on that tower. 
> In the shack I have an amp for 160-10 meters, and an amp for 6 meters.
> I would like to connect my single cable coming in from the entrance panel to 
> a 2 way coax switch,  with one of the ports going to my 160-10 meter amp, 
> and the other going to my 6 meter amp.  Then the 160-10 amp would be 
> connected to the K3 antenna connector 1, and the 6 meter amp would be 
> connected to K3 antenna connector 2.
> Both amps will operate at the legal limit easily, and my concern is that 
> when xmitting through one of the antenna connectors & amp, I will put too 
> much rf back through the coax switch to the unused K3 antenna connector, and 
> possibly damage the K3.
> I have been changing cabling manually but would really like to be able to 
> just operate a switch to make the change.
> So, if anyone on the list doing something similar to what I have in mind, I 
> sure would like to hear about your setup, what kind of switch you are using, 
> how much port to port isolation is necessary to be safe, etc.
>
> Tnx & 73,
> Tim - N3XX 
>
>