Topband: Series LC to notch AM broadcast ?

[Joe]

I will try if you are or anyone is interested getting the design of this 
filter we use on a AM radio broadcast antenna when we use it on 160 Meters.

This is NOT just a matching unit to match the antenna for us to use on 
160 meters. BUT also a pass band filter for 160, a High pass filter 
blocking anything below 160 meters, AND a notch filter tuned to the AM 
Transmitters frequency.

WHY? The Notch?  Because we use this WHILE THE AM TRANSMITTER IS STILL 
TRANSMITTING!!!

Yes we have played on 160 meters with this magic box while the AM 
station is still on the air.

Talk about isolation!

Joe WB9SBD / W9ET

On 2/20/2022 11:41 AM, jim.thom jim.thom at telus.net wrote:
> Has anybody tried using a simple series L-C to notch out ONE offending AM
> broadcast station ?  I'm talking about wiring from hot side of coax...to
> chassis / ground....like via a T connector etc.
>
> On paper, it should work. Did some minor research, and one comment was that
> by using higher values of L would result in  higher Q..and a deeper notch.
> Another comment stated to use some initial values, like what spits out on a
> L-C  online calculator for practical values..... then  multiply one value
> by the other...then take the square root of the result.   Then you ended up
> with 2 x numerically equal values of L + C..... and supposedly the greatest
> notch depth.
>
> On software, I tried several values..from one extreme to the other, and
> they all resonate on the same freq.   Also tried in software,  using 2 x
> numerically same values..and it too, also resonates on the same freq.
>
> The rationale behind all of this is... in some cases, there is only one
> offending AM broadcast station.  Typ  HP  filters offer little rejection
> towards the top end of the AM broadcast band..... like  1200-1710 khz.
>
> I would like to try it, but am still confused as to which combo (using
> practical values) will result in the deepest notch.  It would have to be
> wide enough to remove the 20 khz wide AM signal.  A fixed coil + variable
> cap, or padded variable cap could be used to fine tune the notch freq.
>
> Perhaps   2 or more LC filters could be used in parallel, to notch out 2 or
> more offending stations ?
>
>
> Jim   VE7RF
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