Filter Specifications
- Maximum power rating: 200W CW or SSB
- Pass band loss: < 0.85dB (1.8 - 54 MHz )
- Stop band loss: > 40dB (1.7 MHz and below)
- Return loss: > 20dB (1.8 - 54 MHz)
- Nominal Size: 5"L x 3.2"W x 2.3"H
- Shipping Weight: 2 lbs
AM Broadcast Band Reject Brick-Wall High Pass Filter
FL1718 - AM Broadcast Band Reject Brick-Wall High Pass Filter -
This high pass filter is intended to be placed between a HF transceiver output and an amplifier or antenna tuner. It is optimized for a 50 ohm input and output impedance. The filter is a 9th order elliptic design that has a very sharp slope occurring between 1.8MHz and 1.7 MHz. The FL1718 effectively attenuates all AM broadcast band signals by at least 40 dB. The filter is packaged in a cast aluminum watertight (o-ring seal) case with standard SO239 flanged coaxial fittings. The components consist of high-Q high voltage NPO ceramic or mica capacitors and high Q toroidal coils mounted on a two sided printed circuit board.
Filter Performance
The model and spectrum plots of the filter showing the signal frequency Vs the amplitude response of the filter when connected to a sweep generator and an actual antenna are presented below.
Filter Model
This is a graph of the insertion and return loss calculated by the filter design model generated by the filter design tool.
The design is a 9th order elliptic filter that has the ability to provide a very sharp transition from passband to lossband.
Each null in the graph represents a high Q series resonant response from each of the four coil/capacitor sets.
These nulls can also be seen in the filter swept response depected below.
Filter Insertion Loss (Shown on HP3577A Vector Network Analyzer)
Broadcast band Spectrum - With No Filter Installed (Shown on SDR-14 Spectrum Analyzer)
The station at 1120KHz is running 50,000 Watts. The close-in 1460KHz station is only running 5000 Watts but uses a highly directional antenna to increase it's effective power toward my location (within 5 miles) and is showing a reading near 0 dBm.
Broadcast band Spectrum - With Filter Installed (Shown on SDR-14 Spectrum Analyzer)
With the filter installed the station at 1460KHz is down 47 dB and the one at 1120KHz is down 50 dB.
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