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

[Bob McGraw]

 From the 3rd port of the T I use a BNC male to BNC male direct to the 
input on the SDR.  Thus my "cable length" on the input of the SDR is 
about 1".

Good point however.

73

Bob, K4TAX

On 12/6/2021 3:01 PM, elecraft-request at mailman.qth.net wrote:
> Message: 8
> Date: Sun, 5 Dec 2021 13:02:36 -0800
> From: Michael Tope<W4EF at ca.rr.com>
> To:elecraft at mailman.qth.net
> Subject: Re: [Elecraft] Rx-In/Out used for exteranl SDR Device
> Message-ID:<60272244-b97c-38dc-f592-97f529abac96 at ca.rr.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> 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