Topband: NCC-2 antenna pattern?

[Rick Kunath]

OK Kenny. I understand now. Not all of the TX will be under control of 
the transceiver at the operating position that is using the in-band 
antenna, so you need RF protection while also receiving in-band. I think 
your phased vertical idea could work. But, a pair of flag antennas would 
also work well. And they're ground independent too.

You would want endfire arrays here. As was mentioned, about 100-foot 
separation is a good starting point, and that's inline of course. In the 
case of either the 2 vertical array or the 2 flag array you could use 
coax sections cut to the appropriate length considering the velocity 
factor of the coax to get the pattern that you want. One other thing 
about the flag option is that the antennas can be either unterminated, 
and the pair will give you a really deep null at low elevations, or you 
can add VACTROL termination and adjust it on the fly. In your case with 
the TX going on I think I'd install the VACTROLs, tweak the terminating 
resistance to the best values, and then measure it and replace the 
VACTROLs with a several watt non-inductive combination of fixed 
resistors that give you that same value. No TX worries then. Terminated, 
the flags will give you a deeper back null than the verticals will.

The flags don't need to be huge. You didn't specify the bands of 
interest but a 10-foot by 25-foot flag with the bottom wire 3-feet off 
of the ground works well from mediumwave to over 40 meters, maybe 
higher. I have a pair of these in an inline configuration and 
unterminted I can sweep a null from horizon to horizon. Terminated I can 
deepen the null and swing the max null angle some against the horizon.

I have my flags setup so they're moveable. I used 4 5-gallon plastic 
buckets and put a 3 foot PVC pipe with a cap centered, bolted the cap to 
the center of the bucket bottom, and then filled the buckets with 
concrete. I can move them and they stay put even in high winds. I have a 
10-foot piece of PVC in a PVC coupling on top of the bucket cemented 
pipe section and on each end that supports the antenna loop. The flags 
are fed in the lower corner via twisted-pair transmission line and that 
is back to the shack where any transformation or preamping is done. And 
then on to the SDR. The termination is at the opposite corner. I modeled 
and tested corner feed vs center side feed and termination and I did not 
notice any difference in performance.

You could do something similar with a KAZ or Superloop and that would be 
longer but need only one support at the center.

Just a few more thoughts for you to consider...

Rick Kunath, K9AO