Topband: Series LC to notch AM broadcast ?

[donroden at hiwaay.net]

We had a 1550khz in town and a 1450khz moved 2 blocks away from 1550.

Yep.... mix products on 1650khz and 1350khz. ( and to some extent 
1500khz )

a simple 1550 notch on the top of the 1450 transmitter eliminated the 
mix products and didn't bother the 1450 transmitter.

Don W4DNR

On 2022-02-20 12:14 pm, Nick Hall-Patch via Topband wrote:

> Hello Jim,
> 
> Better, I think, is this notch, found at the IRCA Reprints:
> 
> <https://www.ircaonline.org/editor_upload/File/reprints/irca-reprint-index.pdf>https://www.ircaonline.org/editor_upload/File/reprints/irca-reprint-index.pdf
> 
> Look for Reprint A-063, An RF Notch Filter by VE6JY.
> 
> You really should only need to notch the carrier of the offending AM 
> station, as  that's where the bulk of the overload will be coming  
> from.  It's a pretty amazing device, in my estimation.
> 
> 73
> 
> Nick
> 
> VE7DXR
> 
> At 17:41 2022-02-20, 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
>> _________________
>> Searchable Archives: http://www.contesting.com/_topband - Topband 
>> Reflector
> 
> Nick Hall-Patch
> Victoria, BC
> Canada _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband 
> Reflector