[Elecraft] K3: Using a K3 to route antenna signals to external devices...

[Joe Subich, W4TV]

On 2019-04-08 4:31 PM, Bob McGraw K4TAX wrote:

 > I don't find the input impedance of the SDR Play/RSP1 to be
 > anywhere near 50 ohms.   In fact it is much higher.    Thus the result
 > of using a simple BNC "T" does not load the signal of the main
 > receiver.

However, since the K3 receiver is relatively close to 50 Ohms, it
*WILL* load the input of SDRs with high input impedance - to the
extent that the SDR *can* lose 10 dB or more of sensitivity.  The
splitter works to protect the sensitivity of *BOTH* receivers -
if that were not the case why do you think Wayne bothered to include
a splitter in the design for the KRX3!

73,

    ... Joe, W4TV


On 2019-04-08 4:31 PM, Bob McGraw K4TAX wrote:
> I agree with Joe in the procedure.   As to using or the need for a 
> "splitter", I don't find the input impedance of the SDR Play/RSP1 to be 
> anywhere near 50 ohms.   In fact it is much higher.    Thus the result 
> of using a simple BNC "T" does not load the signal of the main 
> receiver.  If your SDR receiver does present a 50 ohm input, then you 
> can expect to loose about 3 dB of received signal.
> 
> And correct, the SDR will be protected when one is transmitting.
> 
> 73
> 
> Bob, K4TAX
> 
> 
> On 4/8/2019 3:22 PM, Joe Subich, W4TV wrote:
>>
>>
>>> The answer indicated connecting the SDR antenna to some connector in
>>> the rear of the radio, and pressing some number of front panel keys
>>> to route the signals from the antenna to the SDR...
>> Connect a splitter, input to the RX Ant Out jack, one output to the
>> RX ANT IN jack and the other output to the Antenna input of your SDR.
>>
>> Press the RX ANT button to activate the RX ANTENNA Out/RX ANT IN path.
>>
>> > Also, is the output from the K3 at zero or close to zero when
>> > transmitting? i.e. is it safe for the SDR?
>>
>> Yes, the RX ANT Out/IN path is on the receive side of the T/R switch.
>> There is no RF (or only leakage) present in transmit.
>>
>> 73,
>>
>>    ... Joe, W4TV
>>
> 
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