[Elecraft] Diversity receive and isolating antennas

[Jim Brown]

On Thu, 24 Jun 2010 10:04:28 -0700, George A. Thornton wrote:

>Anyone familiar with this situation able to give me some guidance?

In addition to the the good comments you've received about isolation 
based on antenna orientation and location, consider using a simple 
passive attenutator on the RX antenna input if you hear the COR 
clicking. Especially on the lower HF bands, noise received on the 
antenna is much greater than noise internal to the K3, so you can 
often use 10-20dB of attenuation without degrading signal to noise 
ratio. 

I mostly use Beverages to feed my 2nd RX. I'm using the very 
excellent DX Eng preamp, and on some band/antenna combinations I 
need an attenuator between the preamp and the rig to prevent the COR 
from operating. 

You can sometimes find precision attenuators at hamfests, and you 
can build your own non-precision attenuator with a few resistors. 
Impedance matching is not a big deal -- anything that is in the 
ballpark will work fine. It goes in line between the RX antenna and 
the RX antenna input. 

To roll your own for 10 dB, use something like 82 ohms across the 
antenna, 68 ohms in series, and 47 ohms across the RX antenna input. 
For 20dB, use something like 56 or 68 ohms across the RX antenna, 
470 ohms in series, and 47 ohms across the RX antenna input. 
Resistor values are not critical, but keep leads short and don't use 
wire wound resistors. :)

73, Jim Brown K9YC