Notch Cavity TWNC-0408
This tool evaluates the performance of the Notch RF Cavity for low-band RF site design. It calculates the rejection at the specified frequency to be blocked and the insertion loss at other frequencies operating on the site.
How to Use It
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Input the frequency to be blocked. Up to 4 reject frequencies can be entered if multiple cavity branches need to be analyzed.
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If multiple reject frequencies are entered, click the radio button next to the frequency you want to evaluate.
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Input up to 8 other site frequencies to determine the notch cavity insertion loss at each frequency.
Advanced Engineering Principles of Notch Cavity Filtering and Deep Rejection Tuning
In dense co-located Land Mobile Radio (LMR) or public safety networks, an adjacent high-power transmitter can easily desensitize a nearby receiver, even if they operate on different frequencies. While band-pass filters isolate a tight window of operation, band-reject cavity filters—commonly known as notch cavities—provide an alternative, highly efficient tactical solution. A notch cavity targets a hyper-specific, problematic interference frequency and drops it deep into an electrical null while allowing adjacent operating channels to pass with minimal disruption.
Sizing Notch Depth and Analyzing Passband Performance
The primary engineering challenge when deploying a structure like the TWNC-0408 is balancing notch depth attenuation against passband insertion loss constraints. A perfectly tuned notch loop can provide over 30 dB of absolute rejection to eliminate a specific transmitter's intermodulation product or wideband noise sidebands.
However, as the frequency of an active site channel sits closer to that sharp rejection notch, the shoulder of the attenuation curve introduces unexpected loss. This calculator models these exact interaction characteristics, allowing field technicians to plot up to four multi-cavity reject branches and view precisely how a high-attenuation null influences neighboring operational frequencies.
Protecting Receiver Front-Ends from High-Power Transmitters
Maximizing site efficiency requires monitoring the insertion loss of up to eight co-site frequencies simultaneously. If a system designer relies on a notch cavity to resolve an interference conflict but fails to map the insertion loss across the rest of the combined system, overall coverage area will suffer due to unintentional signal drop.
By utilizing this multi-frequency matrix, network integrators can accurately evaluate physical cavity tuning adjustments. This workflow guarantees maximum protection for highly sensitive receiver preselectors, minimizes desensitization risks, and maintains robust link budgets across complex low-band spectrum layouts.