I was wrong when I said this:
? ? "You need a low pass filter, not a high pass filter."
You are both sort of right.
The title of this thread is about FM broadcast, for which we should use a low pass
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But VU3ONX is having trouble with an AM broadcast station.
Since the ubitx operates above the AM broadcast band, he wants a high pass filter.
And the two filters I pointed him to were both high pass.
I just got a couple words mixed up.
Hopefully, he doesn't also have a nearby FM broadcast station.
Jerry, KE7ER
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On Mon, Dec 23, 2019 at 03:38 PM, Keven Pittsinger wrote:
The FM band is 88-108 MHz, IIRC.? The HF frequencies are 29.7 MHz on down for us.? You wanna stop the FM broadcast freqs, so you wanna use a low pass.
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On Mon, Dec 23, 2019 at 4:01 PM Martin Potter <
ve3oat@...> wrote:
Jerry wrote :
"You need a low pass filter, not a high pass filter."
No, high pass is correct.? Pass high frequencies, but block low frequencies.? Pass the HF stuff and block the lower frequency BC stuff.
The filters pointed to in the links are mis-labelled.? They are high-pass.? Capacitors across the top pass the high frequencies and block the lower frequencies.? Inductors going to ground drain off the low frequencies, letting the higher frequencies pass by.? High-pass, not low-pass.
If the interference is truly from the FM BC stations, and not their AM-band counterparts, then a low-pass filter would be appropriate.
73,
... Martin? ?VE3OAT
