5 Pole high-pass or low-pass audio filter
For Two-Way Radio Applications
Model FL-10 Click Here for schematic, installation, and set-up instructions.
Ordering instructions on bottom of page.
Now available in three frequency configurations - 350 HP, 4kHz LP and 15 kHz LP.
This filter can be used to low-pass filter ultrasonic content from a USB radio adapter like the RA-35.
Available in two low-pass cut-off frequencies, 4 kHz and 15 kHz.
This filter can be used (by itself) to high-pass filter (reject) CTCSS (PL) tones below 350 Hz.
This product is all thru-hole to allow assembly and repair by the common technician.
Price $10.00 each - in kit form - any configuration of the available three.
Also available assembled and tested - $20.00 each.
US shipping and handling $7.50 in small quantity.
PayPal accepted - order below.
Actual Size FL-10 Top board photo.
(Click image to enlarge)
A versatile circuit board allows the filter to be configured as high-pass or low-pass. As a high-pass, it's commonly used (by itself) as a CTCSS reject filter with a knee of 350 Hz. In low-pass, it's used as a splatter/ultrasonic content filter for the RA-35. There are two options for this configuration. One with a knee of approximately 15 kHz, and one at 4 kHz - depending on your application and needs. The FL-10 will run from 5 VDC, but it severely limits the P-P output capability. The RA-35 should be configured for an external voltage source and the supply voltage be at least 10 VDC. Maximum supply voltage is 30 VDC.
Use the FL-10 with the RA-35 as a low-pass filter - NOT a CTCSS reject filter.
CTCSS filtering is done in the AllStar application and therefore the FL-10 isn't required for use with the RA-35 to filter PL tones.
Current draw at 12VDC is under 1mA for the LPF and under 7mA for the HPF, increasing slightly when passing audio.
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 each 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.
These filters have undergone several stages of optimization, performed by Robert Meister WA1MIK. Bob used his audio talents to choose the component values and prove the performance of each filter. Be sure to read Bob's evaluation article available from the "docs" page.
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Click Here for schematic, installation, and set-up instructions.
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 February 17, 2016 W3KKC All Rights Reserved!