Making A High Power 70cm Low Pass Filter - This is so cool!

Nice one

No real need for PTFE at these kind of power levels and frequency range. Loss is lower with PTFE but I doubt that anyone would care that much.

👍👍👍👍👍

Hey Mat, love the videos – especially the QO-100 content! Really appreciate the effort you put in. Just a small video production tip I thought you might find useful.

I've noticed that when you pause in your narration, the audio level in your videos drops to absolute zero. On some home audio setups (mine uses SPDIF optical), that total silence can cause the system to enter a kind of "sleep" mode. As a result, when you start speaking again, the first word or two can get cut off while the audio connection re-establishes itself.

It's not really your fault – it's just how some audio systems behave. A common workaround used by video producers is to include a very low-level "silent" audio track in the background, so there's always some signal, even during quiet moments. Kind of like a squelch tone in radio – not meant to be heard, just there to keep the line open.

There's actually a similar practice in broadcast TV: producers avoid full black screens because automated systems can interpret them as signal loss or a cue to insert ads. Instead, they use "almost black" to avoid triggering those systems.

Anyway, just thought I’d share in case it helps. Keep up the great work!

73 de VE3INP

Bravo again Matt! Thanks again for reminding us of the importance of having clean signals, and that it is not difficult to achieve. -- Wayne K3WM

Regarding the soldering of the N-Types - isn't it the other side of the board that needs the good ground connection to the N-Type, as that is the other plate of your capacitors?

Flux!

Flux is your friend when soldering those nuts. Recommend some Kester liquid solder in a little plastic bottle.

I've not had much luck with uhf low pass filters but I did make 4 cavity filters for a 70cm repeater using old gas bottles. Worked extremely well. Your project looks extremely interesting. I've seen those modules for sale on Ebay. Cheers from old George

very cool Matt

the value of those coils is a bit lower than perfect. Push the windings of each coil a bit tighter, this way the cutoff frequency will go lower, and the filter will be better. Also try to loop the ends of the coils on the terminals of the sockets before soldering, for added mechanical and electrical stability.

Great new toy! The filter looks interesting - I'm intregued why clockwise/anti-clockwise winding is relevant? I'm definately interested in seeing the amplifier build. I think you need to solder the N-Type connectors to the non-etched side of the PCB as thats part of the groundplane I think?

Super interesting. Subbed here!

Generally it's a bad idea to make inductrors have same axes (even if wound in differenct direction). Even if winding direction is different, they still couple, only with face shift of 180 degrees.
Inductors near each others are always best to be in 90 degrees to others. (a sideways or up/down inductor couples much less than parallel inductors).

I don't have a CNC but I do have a 3D printer. It should be possible to print a single layer of plastic onto a PCB and then etch it… kind of like photoresist but without any of the messing about with UV or lithography. Maybe I'll give that a go to build a filter like this.

Another thing you can add to low pass filters is stubs - shorted (or open for a notch) lengths of coax suitably tuned. Obviously use good low loss coax suitable for the power needed.

What 432MHz insertion loss did you end up with? Should be Sub 0.5 dB.