Test setup: an Elecraft XG3 signal generator into the BPF into a 50 ohm dummy load, with scope measuring the output pp and converting to dB. The double peak vanishes with the reduced value. Plotted filter response for two values of the coupling capacitor C3 (3pF and 1.2pF) - see attached files. Started with the 12m BPF kit and removed transformer primary turns until there was a well defined peak near the centre with both trimmers. Thanks to Chris WX5CW for sending a link to this useful video showing one way to wind toroids! The QRP Labs Low Pass Filters are designed to handle at least 10W power and the attenuation at the operating frequency should be very low. For example you may wish to use a Band Pass Filter after a mixer to eliminate unwanted mixing products above and below the wanted output.Īt a transmitter output always use a Low Pass Filter, whose purpose is to attenuate harmonics of the output frequency. It may be Ok to use the band pass filter in an early stage of a transmitter output signal chain where power levels are very low. And the lost power will be dissipated in the BPF as heat and also likely lead to failure. You will not want to be losing that much power from a transmitter output. In a receiver this is Ok but if you are using it in a transmitter, the higher voltage will exceed the rating of the capacitors and could lead to failure.įurthermore, the filters have around 2dB of insertion loss. As a result the voltage in the centre section will be higher. The double-tuned circuit with transformer match results in an impedance step-up from the 50-ohms input/output. The filters are designed for receiver input band pass filtering. Bandĭon't use these Band Pass Filters as a transmitter output filter! The following measurements indicate the behaviour that should be expected from this kit. Of course, you may vary the component values to change or experiment with the characteristics! The kits were constructed as shown in the above photographs and in accordance with the parts list provided in the assembly instructions. Note also that the filters have 50 ohm input/output impedance and could be cascaded together if required. So you can see, away from the passband the attenuation reaches 60-80dB in most cases. In the spectrum analyser photographs below the "height" of the screen is 80dB. This means that the filters are suitable for each whole amateur band, including CW, QRP and SSB segments. The components and suggested toroid turns etc have been designed for a -3dB bandwidth of approximately one tenth of the centre frequency, and an insertion loss of better than 2dB.
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Here's the full array of 10 BPF kits, one for each HF band from 160m to 10m.
Printed instructions are NOT supplied with the kit. You can download the kit-building instructions for your PCB from the links below.ĬLICK HERE to download the kit-building instructions for the BPF kit.įRENCH TRANSLATION Click Here, assembly guide in French, by Michel ON4LAU Please read the kit-building instructions (see below) for more details on the circuit, design trade-offs, construction, and adjustment procedures. It has a 50-ohm input and output impedance. The kit can therefore be used with our relay-switched filter kit. The Band Pass Filter kit is the same size as our LPF kit, 1.5 x 0.5 inches (38.1 x 12.7mm).
Designed for the relay-switched LPF kit, or your own projects! NP0 - near-zero temperature coefficient). The capacitors supplied with the kit are high-quality RF ceramics of the C0G type (a.k.a. The kit uses a high-quality double-sided PCB with silk-screen, solder-mask and through-hole plating. It uses the popular double-tuned-circuit which is reliable and easy to build, without needing access to any special equipment. This Band Pass Filter (BPF) kit is for receiver input filtering.