Cavity Filters
Bird Technologies - The RF Experts


20-37-02, 144-174 MHz, Series-Notch Cavity Filter passes a relatively wide band of frequencies while rejecting a very narrow band of frequencies. It is equivalent to a series-tuned circuit. Notch depth is variable from 15-25 dB. Pass and notch frequencies must be known so that the optimum loop assembly can be used. This is the best filter for very close separations (200-400 KHz) in UHF applications.

  • Various Low-Loss High-Rejection Models to choose from.
  • All Loop Plate/connector assemblies are silver-or Alballoy®-plated for low IM.
  • Welded cavity construction and silver-plated tunable probe and loops give superior pass and reject characteristics.


Cascading Filters
All cavity types mentioned above may be cascaded to achieve an arithmetic sum of individual filter attenuation. Up to 6 dB of additional attenuation can be achieved when the proper length of cable is used to interconnect the cavities. (This additional 6 dB does not occur in the filter passband but only at frequencies where moderate to high attenuation occurs.) A TX RX system specialist can assist you in ordering the proper length of interconnecting cable for your frequencies.

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product specifications:

Item No20-37-02
Item Name144-174 MHz, Series-Notch Cavity Filter
Frequency Range144-174 MHz
Insertion Loss vs Frequency Separation

(with dual cavity, notch depth @ 34 dB)
<2.0 dB @ 100 kHz
<0.6 dB @ 250 kHz
<0.5 dB @ 500 KHz
<0.4 dB @ 1 MHz

(with dual cavity, notch depth @ 44 dB)
<3.6 dB @ 100 kHz
<0.8 dB @ 250 kHz
<0.5 dB @ 500 KHz
<0.4 dB @ 1 MHz

Impedance Ω50
VSWR1.5:1 max.
Max Power60 W @ 100 kHz
250 W @ 250 kHz
350 W @ 500 kHz
350 W @ 1 MHz
Cavity Length - Electrical1/4λ
Temperature Range-30 to +60 °C
Cavity Diameter6.625"
Number of Cavities2
Cavity Height26", w/ tuning rod extended, 38" max.
Weight34 lbs.

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