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DLW Associates

AM Broadcast Band (BCB) 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 over 40 dB. The filter

is packaged in a cast aluminum (o-ring seal) case

with SO239 flanged teflon dielectric 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. The

PCB and coils are conformal coated. All mounting

hardware is stainless.

We offer modifications to this basic filter model that can enhance performance for difficult user applications. These modifications are

provided at no additional cost to the user as long as housing and PCB remain common to the design. Changes usually consist of

moving a stop band or pass band endpoint and placing a filter null over an interfering frequency. Call or email for a free consultation

on your particular interference problem.

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

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 pass band to loss

band.

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

depicted 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.

About Us

I retired in 2001 after working as

an electronics design engineer for

over 40 years at eight different

companies. We then turned to

consulting.

However, I thought that with the

technology available today it might

be feasible to design, develop and

market one or more of my own

products. The filter presented on

this page is my first product.

I have been an amateur radio

operator (present call sign AB0SA)

since 1952 and I designed and built

my first single sideband exciter in

1956.

In my present location I am less

than five miles from a highly

directional 5,000 Watt AM radio

station. My transceiver front end

was being blocked by the strong,

near 0 dBm signal at 1460KHz on all

the low HF bands. My receiver S

meter only displays to 60dB over S9

which is -13dBm.

I could not find a commercial filter

for sale that had a significant loss

over the entire AM band, especially

at the upper end (1700KHz) without

effecting the use of the 160 meter

band starting at 1800KHz.

The filter presented here was

developed in 2006 and meets my

criteria for loss over the entire AM

Broadcast Band while allowing full

use from 1800KHz through 54MHz.

Ordering:

The base price of the filter is

$195.00USD. Postage and handling

is a flat rate of $10 within USA.

Filters are shipped via USPS

Priority Mail Service.

International customers should

email us for a shipping/handling

quotation tailored for their specific

location..

Sales Tax: For sales to customers

with Missouri addresses we will add

7.45%.

Payment: Within USA; personal or

company check, money order or

PayPal.

For customers outside USA we

only accept PayPal.

Options: N connectors can be

substituted for SO-239 connectors

at no additional charge.

Contact

DX Engineering

stocks standard FL1718 filters