435MHz cavity notch filter, home made.
 ver: 05 04 30  20150121



English construction text including pa0nhc comments for connection as 70cm repeater duplexfilter.



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Important notices!

As the mass-contact and screening of N connectors is better than the contact and screening of BNC connectors, do use N connectors in  a repeater duplex filter. The maximal obtainable RF-insulation between TX and RX will prove to be far better using N-connectors (up to 30dB), especially after some time.

Do only use a combination of silver plated, gold plated, tin plated, bare aluminium or stainless steel connectors of a well prooven manufacturer ! Avoid cheap nice shiny nickel plated from unknown source. They cause INTERMODULATION caused by to big difference in electro valention.

    So use:
- N
- best quality for your money.

    Tight budget?
Used, a bit oxidated silver plated connectors from second hand markets are cheap and well suited. Silver oxide conducts as well. The black colorization on older silver plated surfaces does not have a negative electrical effect!

For simplex use, like in an ordinary amateur radio station, this all is not as critical. For most simplex stations you can use BNC, and those nice shining connectors, without noticeable degradation.
On the other hand, if you experience inter modulation, despite the use of good (extra selective) VHF filtering, you could try to change to silver plated N-connectors all over.

In general construction: do not use copper in direct contact with aluminium. Again to big difference in electro valention.

This will inflict corrosion, and possibly inter modulation, due to the difference in electro potentials of those materials, especially in salty environments.

Uncoated copper and silver surfaces can corrode, especially fingerprints.
SPRAY them with CRC5.56, a surface covering oily fluid, which drives moisture out, loosens corrosion, en prevents re-corrosion. Well prooven in years of service in a home made 145MHz duplexfilter made of copperclad.