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Old May 1st 04, 09:58 PM
PDRUNEN
 
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Default fm trap

G'M group,

I recall you could make a fm filter trap using a 300 ohm ribbon cable at some
length and put a cap on the end.

I am looking for something like this but would be more for channel 8/9. Or
would I be just as well to put a parallel L/C ?

What bandwidth and db rejection would I get with one L/C network? Would need
like 10MHz of BW.

de KJ4UO.
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Old May 1st 04, 10:28 PM
JGBOYLES
 
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I recall you could make a fm filter trap using a 300 ohm ribbon cable at some
length and put a cap on the end.


An electrical half wavelength with a shorted end or an electrical quarter
wavelength with open end are effective traps. Their bandwidth is rather
narrow.
What bandwidth and db rejection would I get with one L/C network? Would need
like 10MHz of BW.


For that type of bandwidth, I would think a single section L/C would not work.
Probably need multiple sections.

73 Gary N4AST
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Old May 2nd 04, 11:39 AM
Richard Fry
 
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Getting a decent amount of rejection across one or two TV channels takes a
multi-pole filter. You might check out the 5KV series from Microwave Filter
Company http://www.microwavefilter.com/multichannotch.htm . They are well
made and not too expensive.

RF

Visit http://rfry.org for FM broadcast RF system papers.


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