[Elecraft] Rx-In/Out used for exteranl SDR Device

[Michael Tope]

Just a word of caution when doing this. If the SDR input Z is high 
enough, then one needs to be mindful of the length of the cable running 
from the "T" to the SDR antenna input. When the length of that cable 
gets close to 1/4 wavelength (this is 3.2 to 4.4 ft at 50 MHz depending 
on velocity factor of the cable), it will transform the high Z of the 
SDR antenna input into a low Z at the "T" which could load down the K3 
receive path (e.g. 500 ohms -> 5 ohms). If the SDR is close to the K3, 
then it won't be a problem, but if the SDR is placed a significant 
distance from the K3, then it would be better to use two longer cables 
from the two K3 ports to bring the "T" close to the SDR antenna input.

73, Mike W4EF.........

On 12/5/2021 10:35 AM, Bob McGraw wrote:
> I use a pair of BNC to BNC cables, about 4" long, from the RX OUT and 
> RX IN to a "T" connector.  The 3rd port of the "T" goes to the SDR.  I 
> find that the SDR input impedance, is nowhere close to 50 ohms,  is 
> high enough that it doesn't load the signal on the main RX.   Again, 
> no splitter required.   No loss encountered.
>
> Yes, one does have to select RX ANT on the front panel for this to be 
> active.
>
> 73
>
> Bob, K4TAX
>
>
> On 12/5/2021 11:36 AM, elecraft-request at mailman.qth.net wrote:
>> Message: 22
>> Date: Sun, 5 Dec 2021 17:35:46 +0000
>> From: Dave<dave.g4aon at gmail.com>
>> To:elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] Rx-In/Out used for exteranl SDR Device?
>> Message-ID:
>>     <CABiKjG5c=s76xxwaxHJiiQYr+C3RtR_FYRHCb3YsN++=Xnn_=Q at mail.gmail.com>
>> Content-Type: text/plain; charset="UTF-8"
>>
>>> I see about a 3 S-unit drop in signal
>>> level when routing through the splitter
>> Pete (N4ZR), what do you see with a straight cable linking in/out?
>>
>> I have no idea about Minicircuits splitters, but my home made one had a
>> measured 3.1 dB loss at 29.7 MHz.
>>
>> 73 Dave G4AON
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