High pass filter


Rolf Ekstrand
 

Greeting y'all,

Suddenly I have a new broad band QRM here centered on about 3.5  Mhz  S9 - 40++.    Looks like switcher or  perhaps more likely a high power grow light nearby.   I guess until I have located the source, I need to put an effective high pass filter at 4 - 6 Mhz ahead of the Kiwi if I like to receive anything on 7 Mhz and up as it goes onto constant OV.   I most certainly could  build something,  but is there anything commercially available out there that will work? 

73 and a happy thanksgiving 

Rolf K9DZT 


Jim Lill
 

Consider using a simple single freq. notch

On 11/24/21 12:14 PM, Rolf Ekstrand wrote:
Greeting y'all,

Suddenly I have a new broad band QRM here centered on about 3.5  Mhz  S9 - 40++.    Looks like switcher or  perhaps more likely a high power grow light nearby.   I guess until I have located the source, I need to put an effective high pass filter at 4 - 6 Mhz ahead of the Kiwi if I like to receive anything on 7 Mhz and up as it goes onto constant OV.   I most certainly could  build something,  but is there anything commercially available out there that will work? 

73 and a happy thanksgiving 

Rolf K9DZT 


Glenn Elmore
 

Rolf
While the qrm you see may be coming in from what you consider to be the antenna it may actually be sourced by ground currents or common mode sources.
If it's the latter, increasing symmetry through increasing CM impedance with better balance may be worth much more than hpf filtering after the problem has already achieved ingress via conversion to a differential mode.

If you are using an unbalanced antenna then noise current in the image plane will get in even earlier just like real near-field noise in any antenna. Neither baluns nor filtering will fix that, only position and polarization or directivity will likely help.
But near-field coupling does drop much faster than inverse-square so small changes in locatiin may help a lot.

On Nov 24, 2021 10:14 AM, Rolf Ekstrand <rekstrand@...> wrote:
Greeting y'all,

Suddenly I have a new broad band QRM here centered on about 3.5  Mhz  S9 - 40++.    Looks like switcher or  perhaps more likely a high power grow light nearby.   I guess until I have located the source, I need to put an effective high pass filter at 4 - 6 Mhz ahead of the Kiwi if I like to receive anything on 7 Mhz and up as it goes onto constant OV.   I most certainly could  build something,  but is there anything commercially available out there that will work? 

73 and a happy thanksgiving 

Rolf K9DZT 


Rolf Ekstrand
 

Thanks Glenn,  

I will dive into it after the holiday  

73 and happy thanksgiving.

Rolf K9DZT