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Saturday 16 January 2021

New 13cm pipe end cap filter

Components RG402 semi rigid, piece of FR4, SMA connectors, 3-22mm pip cutter (to score the shield before removal), Brass M3 nut and bolt (should be M4 but don't have to hand).

Holes are 3mm (initially, filed out to have a tight fit about RG402 sheath. 16mm apart.

It's a 1" copper end cap. So much larger than the 10GHz ones you might have seen using the 1/2"/13mm end caps. But the principal is the same.

The RG402 make up isn't hard.

You take one end and strip off the teflon insulator and trim the centre conductor to about 4mm and fit a pin over.

Then solder on the other part.

Then solder into the FR4 (the shield remains below). I'll trim the probes to about 8mm before filling the cap.

You then solder on the end cap, first soldering the brass nut on the central hole so the brass bolt can be screwed in and out and secured by the second nut, I might add a red locking liquid (nail varnish works if the XYL has some she will not miss!). You tune by advancing this bolt. The more you advance the higher in frequency the filter tunes.

The soldering of the brass nut and pipe end requires considerable heat, I have a small precision (bit of an oxymoron when talking about a blow torch!) blow torch I use this this work.

I will make up and add the NanoVNA 3GHz scan image here, basically when tuned it will allow the 2.4GHz signal to pass and block frequencies either side, like mixing products. 

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