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 capacitors and high Q toroidal coils mounted on a two sided printed circuit board.
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.
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.
With the filter installed the station at 1460KHz is down 47 dB and the one at 1120KHz is down 50 dB.
. I retired in 2001 after working as an electronics design engineer/scientist for over 40 years at eight different companies. We then turned to consulting and are still involved in that.
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 meets my criteria for loss over the entire AM Broadcast Band while allowing full use from 1800KHz through 30MHz.
Ordering:
As of 02/15/2008 The base price of the filter is $185.00USD. Postage and handling is a flat rate of $10 within USA. International shipping is a flat rate of $25.00USD. Filters are sent USPS Priority Mail.
Sales Tax: For sales to customers with Missouri addresses we will add 7.4%.
Payment: Within USA; personal or company check, money order or Paypal. Paypal address is dougwill@dlwc.com
For customers outside USA we only accept Paypal.
Options: N connectors can be substituted for SO-239 connectors for $10 additional. Please specify on order.
