Band stop-Notch Filter suggestions

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spareparts
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Band stop-Notch Filter suggestions

Post by spareparts » Sun Feb 18, 2018 9:22 am

I need a Band stop-Notch Filter to reduce ingress to an OTA MATV system. The offending TX antenna is co-located with MATV antenna, with approximately 1 meter vertical separation between OTA MATV and repeater antennas. Nothing I can do about the antenna location.

Offending TX is 468.3625000 . RX is 463.3625000. Max PO from the repeater is 25W, TX antenna is 0 db gain.

Any suggestions?

SP

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NECRAT
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Re: Band stop-Notch Filter suggestions

Post by NECRAT » Sun Feb 18, 2018 9:40 am

Contact Microwave Filter Corp out of Syracuse, NY.

They make and sell fantastic filters. (And yes, for UHF, VHF, etc. Despite the name, they aren't microwave only)
http://www.necrat.us

"Arguing with an engineer is like mud wrestling with a pig. After a couple of hours, you realize the pig likes it"

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RGORJANCE
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Re: Band stop-Notch Filter suggestions

Post by RGORJANCE » Sun Feb 18, 2018 11:25 am

Second that suggestion for U-wave Filter Co. Have used their product for FM receiver issue.

Fossil

spareparts
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Re: Band stop-Notch Filter suggestions

Post by spareparts » Sun Feb 18, 2018 12:01 pm

Email away - lets see what magic they can work

SP

wb9fhr
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Re: Band stop-Notch Filter suggestions

Post by wb9fhr » Sun Feb 18, 2018 1:23 pm

Besides Microwave Filter I used this guy out of Canada. Filters work for the need I had, notching out nearby FM that was preventing reception of my own signal. Sent him an e-mail with need and he gave me a quote for what he thought would work best. He has a full line of various use filters.

http://www.tinlee.com

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PID_Stop
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Re: Band stop-Notch Filter suggestions

Post by PID_Stop » Mon Feb 19, 2018 9:12 am

I love Microwave Filter, and we have a lot of their equipment here... but it isn't inexpensive, and the cost might be prohibitive for your application.

468MHz is just below over-the-air channel 14; one possibility you might explore is finding a used Blonder-Tongue CEF-750 channel elimination filter on channel 14, and adjusting the lower corner frequency downward to reject that repeater output. A spectrum analyzer would be helpful here, but given the application, you can probably get reasonable results by making careful empirical adjustments with a level meter.

Jeff
Last edited by PID_Stop on Mon Feb 19, 2018 11:09 am, edited 1 time in total.

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Deep Thought
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Re: Band stop-Notch Filter suggestions

Post by Deep Thought » Mon Feb 19, 2018 10:09 am

How much rejection is "good enough"?

I've had pretty decent luck getting strong FM signals out of EAS receiver antenna connections by using a simple quarter-wave open stub teed off the the coax near the receiver. If you use quality coax and an actual tee adapter (not a splitter) you should be able to achieve a 20-25 dB notch which may be enough to get the interference down to tolerable levels.

1/4 wave at 468.3625 MHz is 6.3 inches at 100% propagation velocity. Adjusting that for typical small coax (~66%) you'd need 4.2 inches, but I'd start long and trim off 1/4" at a time while watching the received unwanted signal levels. Once you find the "null" just tape the end, leaving it an open circuit.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

spareparts
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Re: Band stop-Notch Filter suggestions

Post by spareparts » Mon Feb 19, 2018 4:35 pm

Deep Thought wrote:
Mon Feb 19, 2018 10:09 am
1/4 wave at 468.3625 MHz is 6.3 inches at 100% propagation velocity. Adjusting that for typical small coax (~66%) you'd need 4.2 inches, but I'd start long and trim off 1/4" at a time while watching the received unwanted signal levels. Once you find the "null" just tape the end, leaving it an open circuit.
Will try the shorting stub. Already have a handful of LCOM 75 ohm "T" fittings.

The MATV antenna feed line is Belden RG-11, VF is .84 Connectors are T&B Snap & Seal.

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Deep Thought
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Re: Band stop-Notch Filter suggestions

Post by Deep Thought » Mon Feb 19, 2018 6:13 pm

Just to clarify...it's not a shorting stub. Leave the end open, since what you want is a 1/4 wave at the reject frequency and that'll reflect j0 at the tee.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

spareparts
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Re: Band stop-Notch Filter suggestions

Post by spareparts » Mon Feb 19, 2018 6:17 pm

Thanks - Need a proofreader for postings....

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