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5 Pole high-pass CTCSS audio filter
For Two-Way Radio Applications

Model PLF-15

Click Here for schematic, installation, and set-up instructions.

Ordering instructions on bottom of page.

The PLF-15 is an affordable, professional audio filter.
 It's a steep-slope - high-pass filter to eliminate CTCSS tones in a two-way radio receive audio path. 

This product is used to filter out (reject) CTCSS tones below 260 Hz.

This product is all thru-hole to allow assembly and repair by the common technician.

Price $15.00 each - in kit form - unassembled - you put it together.
Also available assembled and tested - $25.00 each.


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Actual Size PLF-15 Top board photo.
(Click image to enlarge)

Description:
A versatile, high-performance circuit configured as a high-pass filter with a knee of 350 Hz to eliminate CTCSS tones. An external voltage source is necessary. A supply voltage of at least 10VDC is recommended. Maximum supply voltage is 30VDC. Regulation is not required, but recommended. Current draw at 12VDC is under 7mA for the filter, increasing slightly when passing audio. At 12V, no more than 10mA is consumed at load impedances of 600 ohms or more.

The frequency response was tested with an input level of 2.44Vrms, or +10dBm, which was well below the maximum, using a 12V power supply. The output level was exactly the same as the input level (i.e. unity gain) at 5 kHz, the middle of the pass-band. The distortion at this level was around 0.03%. The signal was considered unacceptable when it reached 1% distortion. With a 5V power supply, this occurred at about 0.6Vrms or 1.7Vp-p and the maximum output level was 0.9Vrms or 2.7Vp-p, but that had almost 5% distortion. Clipping occurred first on the negative peaks of the output waveform. With a 12V power supply, 1% distortion occurred at about 3.3Vrms or 9.6Vp-p and this was also the maximum output level. Clipping was symmetrical with higher input levels.

This filter has undergone several stages of optimization, performed by Robert W. Meister WA1MIK. Bob used his audio talents to choose the component values and prove the performance of this filter.
Originally - this filter was part of the "FL-10" series but got moved to its own product after some time.

The circuit board has been optimised for this particulal duty allowing the larger bias resistors to be mounted tight against the circuit board and eliminating the configuration jumper.

Be sure to read Bob's evaluation article, with response graphs!

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PLF-15 Options:

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Click Here for schematic, installation, and set-up instructions.
 

Email Kevin Custer for ordering information, order by check, and/or support of this exciting product.
 

Product of Masters Communications, all rights reserved.
Specifications may change without notice.
Images are property of Kevin Custer - Masters Communications
Filter optimization performed by Robert Meister - WA1MIK.
Board layout by Kevin Custer - W3KKC.
HTML December 1, 2020 W3KKC All Rights Reserved!