neazoi
Advanced Member level 6
For my **broken link removed** I want to build a 40m LPF using a PVC pipe as a coil former. Note this transmitter has an auto transformer to match higher impedance antennas (wires, no feedline).
A problem I had with a LPF was that I thought could only be designed for 50R I/O impedance. But see this design of mine attached. It uses lots of poles but one value of capacitors and coils only. The coils are exactly 6T on this coils former 32mm. Apart from the great harmonics attenuation, this LPF can work satisfactorily at any I/O impedance, as long as the input impedance is the same as the output. This means that I can plug even higher impedance antennas to it and also tap it in the higher impedance tap on the transformer and the filter will still operate fine. See the diagrams, I provide for each impedance, two photos, one for the pass frequency and one for the second harmonic.
What do you think of it?
I am also thinking of building this onto the same PVC pipe instead of splitting the coils. Now I know it is better for the coils not to couple energy between them, but if they are far apart, even on the same pipe, it may not matter. I do not know how far apart though.
Also, I am thinking of winding near-by coils in different winding phase (direction). This should cancel the coupling between them, even if they are wound on the same pipe. Shouldn't it?
A problem I had with a LPF was that I thought could only be designed for 50R I/O impedance. But see this design of mine attached. It uses lots of poles but one value of capacitors and coils only. The coils are exactly 6T on this coils former 32mm. Apart from the great harmonics attenuation, this LPF can work satisfactorily at any I/O impedance, as long as the input impedance is the same as the output. This means that I can plug even higher impedance antennas to it and also tap it in the higher impedance tap on the transformer and the filter will still operate fine. See the diagrams, I provide for each impedance, two photos, one for the pass frequency and one for the second harmonic.
What do you think of it?
I am also thinking of building this onto the same PVC pipe instead of splitting the coils. Now I know it is better for the coils not to couple energy between them, but if they are far apart, even on the same pipe, it may not matter. I do not know how far apart though.
Also, I am thinking of winding near-by coils in different winding phase (direction). This should cancel the coupling between them, even if they are wound on the same pipe. Shouldn't it?