Building a simple hi-pass filter

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N2UJZ

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I'm getting a bit of interference from a local MW station (probably related to the W3GV repeater conspiracy, lol) on my SDR. It's a Soft66LC2 so its kinda cheapo (but worth the low price IMO) I see plenty of instructions online but have a few questions.
1) If I want the cutoff to be 2500khz what value capacitor do I need?
2) I have a few 3.3µH inductors- will these work?
3) would a 3 pole filter at 2500khz work? the station is on 990khz & not very close, its just a cheap radio.
4) is it best to put it by the antenna or by the radio, and if at the antenna end, before or after the "un-un?" I'd rather do it at the radio end because the R75 shares the antenna. I don't often listen that low but I'd like to at least be able to with the Icom.
If you can answer any of these I'd appriciate it. Oh & the Soft66LC2 only goes down to 2500khz, so I wouldnt be missing anything 73 -Justin (aka oar9fi)
P.S. if you don't get the W3GV reference its kind of an inside joke on #wunclub. W3GV is the source of ALL radio interference, especially with cheapo radios :)
 

mm

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The 3.3 uh's will work just perfect if you make a PI filter with two shunt 3.3 uh inductors and one series 620 pf to 680 pf capacitor.

On the filter input side you have a 3.3 uh to ground then a series 620- 680 pf capacitor then an output 3.3 uh inductor to ground.


With this 3rd order high pass butterworth filter you should get around 27 to 30 db of attenuation at 990 KHz.


Mike
 

N2UJZ

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Thanks- Thats just what I needed to know. How about location on the coax & in relation to the matching transformer? Any ideas for construction I could put it in a case with connectors etc. but if you (or anyone)have a better/easier idea let me know. (trying to be cheap & lazy here, lol) -Justin
 
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