Gareth, interesting results. I had noticed that the ends don't seem to affect the filter itself but didn't think about external interference entering that way. In that case adding metallic tape to the end plugs might be worth it.
I have such terrible mobile coverage here that I doubt I would notice anything.
The length of the ends should not be too critical.
My finding about the brass screws seemed to be quite repeatable. There was only a small difference but the brass screws always produced less loss. Toolstation do M4 * 20 brass in a bag of 100 for £5.
Colin.
Filter hacking for 2395 ISS TV
Re: Filter hacking for 2395 ISS TV
If the distance from the input/output to the first/last resonator is similar to or less than the distance to the ends, then they are obviously going to need covering, but that will impact the impedance. If the distance from the input probe to the end is much more, I suspect it won't make much difference to the match, but it is still possibly a good idea.
These dimensions produce a cut-off frequency of around 4 GHz. The calculator Tom, WA1MBA developed indicated a loss at 2.39 GHz of about 560dB/metre. That's a lot but if it were to be say 5cm, it would be only 25 dB of loss - assuming you can scale it that way, which might not be the case. While 25 dB is still a lot, it isn't compared to what we are expecting from the filter, so best either make it long enough or make it a short circuit.
Aside:
In the filter I have, the distance to the end of the guide is double the distance between the resonators, so it isn't going to impact the matching, but I suspect it will be a problem for 5G/6G.
The cut off of the waveguide is ~4 GHz. As well as signals above 4 GHz getting in, the second TX harmonic will propagate in the waveguide. While hopefully, any harmonic energy won make it through the filter, (it might) it will make it out of open ends, regardless of how far the spacing is. So, if the filter is also intended to prevent TX harmonics escaping, it isn't likely to work very well at that and they will come out of the filter, not the antenna.
For 13cm, the significant harmonics are probably the 2nd and 3rd, 4.6-4.8 GHz, 6.9-7.2 GHz. 4.6-4.8 GHz is used for aviation and military applications and also targeted for 6G mobile. 6.9 - 7.2 GHz is planned for 6G mobile and Wifi. Interference to either isn't a good idea, so, a) use a low pass filter after the PA and b) it is probably best to cover the ends, especially if you plan to put the filter up on the mast.
Mike
These dimensions produce a cut-off frequency of around 4 GHz. The calculator Tom, WA1MBA developed indicated a loss at 2.39 GHz of about 560dB/metre. That's a lot but if it were to be say 5cm, it would be only 25 dB of loss - assuming you can scale it that way, which might not be the case. While 25 dB is still a lot, it isn't compared to what we are expecting from the filter, so best either make it long enough or make it a short circuit.
Aside:
In the filter I have, the distance to the end of the guide is double the distance between the resonators, so it isn't going to impact the matching, but I suspect it will be a problem for 5G/6G.
The cut off of the waveguide is ~4 GHz. As well as signals above 4 GHz getting in, the second TX harmonic will propagate in the waveguide. While hopefully, any harmonic energy won make it through the filter, (it might) it will make it out of open ends, regardless of how far the spacing is. So, if the filter is also intended to prevent TX harmonics escaping, it isn't likely to work very well at that and they will come out of the filter, not the antenna.
For 13cm, the significant harmonics are probably the 2nd and 3rd, 4.6-4.8 GHz, 6.9-7.2 GHz. 4.6-4.8 GHz is used for aviation and military applications and also targeted for 6G mobile. 6.9 - 7.2 GHz is planned for 6G mobile and Wifi. Interference to either isn't a good idea, so, a) use a low pass filter after the PA and b) it is probably best to cover the ends, especially if you plan to put the filter up on the mast.
Mike