[Elecraft] K3S relay noise when using Rx ANT IN port

[Bob McGraw K4TAX]

I use a surplus coax relay, one with BNC connectors, and it is triggered 
from the KEY OUT function on the transceiver along with the 12V 
source.   Be sure and use a diode across the relay coil to prevent back 
EMF.   The relay switches the RX ANT port to a 50 load, being a resistor 
mounted in a BNC connector on the N.O contact port.  The common relay 
port goes to the radio  RX ANT IN and the N.C. relay port goes to the 
transceiver RX antenna. It only clicks when the PTT is active and 
released.    As to CW, well that's another issue where the relay needs 
to be held in during transmission or you'll hear it with every CW element.

I personally would be concerned about using solid state switching 
devices in as much as a junction when saturated may be prone to produce 
harmonic related energy.   However, there are circuits which use PIN 
diodes or JFETS, designed correctly, would likely be clean.

73

Bob, K4TAX




On 2/1/2020 4:48 PM, Don Wilhelm wrote:
> Ray,
>
> Your transmit signal is getting into your RX antenna with more energy 
> than is safe for the K3S.  10 meters is not much separation unless the 
> antennas are oriented so one is not in the null pattern of the other.
>
> Using antennas that are of opposite polarization (such as a horizontal 
> dipole and a vertical) may be OK for a 10 meter separation, maybe not.
>
> There are protective devices available that will disconnect the RX 
> antenna when the K3S is transmitting, and use of one of those may be 
> the quickest and easiest solution.
>
> 73,
> Don W3FPR
>
> On 2/1/2020 5:21 PM, raycollins wrote:
>>
>> My K3S is configured to use the RX ANT IN port for a separate Rx 
>> antenna.
>> However, on SSB transmissions I can hear an internal relay operating in
>> synchronism with peaks in transmit power.  I assume this is a relay 
>> in the
>> receiver input protection circuit?
>>
>> Is operation of the relay in this manner normal? Apart from finding the
>> noise rather irritating I am concerned about the reliability of the 
>> relay
>> when it is called upon to operate so many times during a QSO.
>>
>> The Tx and Rx antennas are about 10 metres apart and I am 
>> transmitting 100
>> Watts.
>>
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