Two Meter Bandpass Filter

A year or so ago I found the need for a Bandpass Filter ahead of my two meter pre-amp. The following is what I came up with and seems to do the trick. Construction is simple and parts are readily available. The 3 dB Bandwidth is very close to 5 mHz, and the insertion loss is in the 0.19-0.2 dB range. Thanks to Al, W5LUA for the encouragement and for making the performance measurements on the unit. Build and enjoy.

Materials are as follows:

The outer shell is 3" ID copper pipe, 13" long, 1/8" wall.
The center conductor is 7/8" OD copper pipe 11" long.
Input & Output couplings are #12 copper wire spaced 1/4" from center conductor.
Connector center pins are 2.75" from the bottom of the filter.
The capacitor plates are 2.5" diameter copper or brass. Thickness not critical. I used .032" Hobby brass from Hobby Lobby.
The Top & bottom covers should be 1/8" thick. (thick enough not to flex)
Connectors can be UHF or Type N.
Screw is 1/4" brass, 3 1/2" long with the head cut off.

*The 1/4" screw should have threads as fine as possible. I used 1/4-20 and that is too coarse as it makes tuning difficult.
*To mount the top capacitor plate I soldered the 1/4" nut to the screw, then soldered the capacitor plate to the nut.
*Holes for the input & output coupling wires were drilled in the bottom plate, and the wires were made too long. They were soldered to the center-pin of the connectors. Then when the bottom cover was mounted the wires projected out through the holes in the bottom and were soldered to the bottom cover.
*Solder the bottom plate of the capacitor to the top of center conductor, then solder the center conductor to the bottom cover. Slide the center conductor assembly into the outer shell allowing the input/output coupling wires to go through the holes in the bottom plate. Solder the wires to the bottom cover and cut them off. Solder the outer shell to the bottom cover using a propane torch.
*Make the top cover, upper capacitor plate, and screw as an assembly, then insert them into the outer shell. Solder the top cover to the outer shell with a propane torch.

*The nut on the outside of the top cover was soldered in place after a hole to accommodate the ¼” screw was drilled in the center of the top cover.
*Above the nut soldered to the top cover, I put another nut on the screw to use as a jam nut.

Tune-Up:

If you have access to a network analyzer, then that is the preferred method. Initially I hung a 50 ohm load on one port and a MFJ analyzer on the other, and adjusted the capacitor for 1:1 SWR at the desired frequency. This will come very close to the optimum adjustment. Many of you have Noise Figure meters, therefore another possibility might be to adjust for minimum NF at the desired frequency.