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QRP Dual Band Low Pass Filter For 3.5 and 7 MHz | 80 / 40m Band RF Low…

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작성자 DX Explorer 작성일21-04-25 00:00 조회5회 댓글0건

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Since lately I started learning a lot for my amateur radio exam, I decided to also start preparing a lot of QRP equipment that I could use. Why QRP for a beginner ? Because everything it's simple, and it's easy to build my own equipment while learning and improving my knowledge in amateur radio and radio constructions.

In this video I made this simple dual band QRP low pass filter for the 40 and 80 meter bands ( 3.5 and 7 MHz ). These are two of my favorite bands, that's the reason I decided on what filter to build. I tried keeping it as small as possible, and also as cheap as possible, using mostly recovered parts.

For the testing, it would be ideal in the first place to have an LC meter to measure the inductances value. As you will see at the end of the video, I tested the filter in a simple way. Since from my knowledge the filter was calculated to cancel de harmonics ( for example for 3.5 MHz the first harmonic would be 7 MHz ), it was better if I would transmit on 3.5MHz and see if I could listen and hear the harmonic on 7 MHz. At least this is what my logic tells me to do as that's why the filter it's meant for.... to cut out the harmonics. Anyway... an oscilloscope would be an excellent tool to actually check the efficiency of the filter, but I don't own such thing just yet... it's too expensive for my budget at the moment. Also the capacitors I used were ceramic ones, with lower voltages at around 100 volts, so for transmit please use some good quality silver mica capacitors rated for a higher voltage over 1 kV.

Also I apologize for my dirty hands in the video, but I just couldn't get rid of the dirt left over, after sanding the aluminum sheet )).

The dual band filter was inspired from one of the videos made by @Amateur Radio VK3YE
https://www.youtube.com/user/vk3ye

If you need more info, feel free to leave a comment and I will help as much as I can, but keep in mind that I'm no expert... I'm also learning as well.

Link to the schematic of the filters ( switch not included ):
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https://tinyurl.com/80-40-QRP-Low-Pass-Filter

Wishing you all an amazing week and happy DX-ing... 73 DE YO6DXE !

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