5 Band Filter Board

Just like a bought one hey? This has been a while in the making and brings together many of the smaller project boards into one. We have 5 low pass filters, band pass filters, TX/RX switching, and + and – 20dB RF preamp. Low and behold, it actually all works right out of the box, no major issues, other than winding all those toriods is a nightmare LOL

In testing the losses were acceptable, 1/2 a dB on the low pass and 1.5dB on the band pass. With essentially 10 filters on the board, it was going to be interesting to see how much work they would require to bring into the correct band.

Most of the filters were actually just fine as you can see here with the 80m low pass filter. Only 1 low pass filter needs to have a turn taken out of each toriod to bring the corner frequency up a little so the corner is not in band, and 3 of the band pass filters need the same to move them up in frequency also.

I did my best to account for strays and variation in winding, but there is always going to be some error and fixing, especially in the band pass filters where I am using a specific value of inductance in the calculations for the filter and then using a turns calculator to get that inductance. These things are always rather hit and miss. With the low pass filters you can always set the corner frequency higher than needed, like with this 80m filter, our band here is from 3.5Mhz to 3.7Mhz, and I set the corner frequency to be 4Mhz, because if you end up with strays you always end up with more inductance and capacitance, not less and those lower the frequency response.

Anyway, thats it for me, I have another 6 boards to build now and I seriously hope that the receiver board is actually good, because if that works well enough to use, I will have a very useable and workable 5 band 50w transceiver. Wish me luck.


2 thoughts on “5 Band Filter Board

  1. Nice. Sometimes you can spread or compress the turns to get the inductance where you want it. I usually figure that out after the inductor is glued to the board!

    1. I did not even try that Tom, the ones that were out were substantially out and pulling a turn or 2 was the only real fix. Not hard to do just tedious. One of the filters was off by 1/2 a meg as an example LOL.

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