[CQ-Contest] Multi-Band Bandpass Filters

[Jim Brown]

On Wed,5/6/2015 10:33 AM, Joe wrote:
> This is similar topic.
> Could a "Filter" notch filter I assume. be made.
>
> Say you have a AM Broadcast station, 740 Khz,
> At night it drops down to a measly 6 watts,
>
> Could you possibly be able to make a filter good enough to be able to 
> while that is still transmitting it's 6 watts be able to operate on 
> 160 meters? 

I think you're asking if you could transmit and receive on that antenna 
while the broadcast station is on the air. If that's the question, the 
answer is yes, but the design is not trivial. :) The obvious part is 
knocking 740 kHz down to something that won't blow away your receiver. 
That takes a lot of filter.

The other parts are a network to allow both transmitters to feed the 
same antenna while also blocking either transmitted signal from reaching 
the other transmitter, where it could cause intermod. And, all of those 
networks must be disconnected when the station goes to its daytime power.

So -- while the answer is yes, it's a complex engineering problem.

73, Jim K9YC