Topband: Series LC to notch AM broadcast ?

[Jim Brown]

On 2/20/2022 3:33 PM, Grant Saviers wrote:
> Somewhat related was my effort to produce a pair of 80m notches so CW 
> and SSB could run 80m simultaneously on Field Day (separate antennas). 
> While the CW guys would be ok with 20KHz BW, not so for the SSB team. 
> Just below a Rx 40db notch was about the best I could do with a one db 
> loss Tx.

For CQP county expeditions, we've often run CW and SSB on 80 at the same 
time, also on 40, using K3 and KPA500, with nothing more than resonant 
half-wave dipoles carefully sited colinear, separated by 250-300 ft, and 
serious chokes at each feedpoint. The chokes are important -- they 
prevent feedline pickup from filling in the nulls.

For 7QP, we rig a 2-el 20M Yagi a few feet above a 40M dipole, with an 
80M inverted V just below that, also a pair of K3s, KPA500s, and 
carefully located double stubs to kill 2nd harmonic on CW. We also have 
W3NQN BPFs on both radios. They're part of W6GJB's contesting trailer, 
documented in these slides, but before Glen built the 2-el 20M folding 
Yagi. And we're rigging them closer now. k9yc.com/7QP.pdf  Again, chokes 
at the feedpoints are critical -- we forgot once (thankfully the day 
before in Glen's driveway), and it blew the isolation. And, of course, 
nothing will help passive IMD generated outside the RF chain.

73, Jim