[Skimmertalk] SDR antenna near main TX antennas

[Bob Wilson, N6TV]

On Sun, Sep 17, 2017 at 7:03 PM, Jorge Diez - CX6VM <cx6vm.jorge at gmail.com>
wrote:

> how can you measure if the main antennas of a station (for example yagi
> monobanders, 4SQ for low bands) will affect the SDR´s antenna when
> transmitting at full power (1.5 kw)?
>
> There´s 3 towers with main and SDR antenna, distance between towers is
> 30-50 meters
>

What is the distance between the closest transmit antenna and the SDR?
What is the Rx Antenna?  What is the Tx Antenna?


> A Receiver Guard <https://www.dxengineering.com/parts/dxe-rg-5000> will
> protect SDR but will be enough?
>

Yes, with reasonable separation (30 meters?).


> Only way to know is trying and wait to see what happens with the SDR? :-)
>

Yes.  But you will find that it is usually NOT practical to run an SDR for
skimming with a separate antenna at the same QTH where you are contesting,
especially if you are constantly CQing.  With a receiver guard, you will
not "blow up" the SDR, but all the signals that leak through can generate a
huge number of temporary "decoders", overloading the PC's CPU, and you may
end up self-spotting (even spotting yourself as a busted call can get you
disqualified).

My recommendation is to turn off the SDR and skimmer if you are CW
contesting from the same QTH, or better yet, move the skimmer SDR to a
separate QTH.

Another option is to use transmit bandpass filters and the RX ANT OUT jack
of your transceiver to feed the skimmer SDR, but skim only one band at a
time.  That way the bandpass filters keep RF from other bands out, and the
T/R relay of the transceiver makes it impossible for RF to enter the SDR
when you're transmitting.

73,
Bob, N6TV