Index

Last update: 6 march 1998.

Step by step assembly:

plateshr.gif 1. Cut all pieces of copperclad, and drill all holes.

top.gif The 22mm holes in top-plate "A" can first be drilled at a smaller size, f.i. 13 mm. Then widen the hole with a pointed grinding-stone in a table-drilling machine. Widen the hole until the diameter of the hole in the coppersurface is equal to the outer diameter of the central conductor. Then drill the other side of the hole in "A" to the same diameter. Turn plate "A" around and slowly widen the hole alternately on both sides until the 22mm-pipe just fits in the hole. Do not widen to much, as this makes soldering "A" to the central conductor "B" more difficult. You could also file the last piece of the fiberglass in the hole, so the plate fits tight, with the coppersurfaces nearly in contact with the pipe. Widen the holes for links "C" until the link just fits. Remove with a 4.5mm drill the copper layer at both sides of the holes near the big 22mm hole (insulation for the "hot" side of the link).

m.gif
Finish the sidelids "M", by filing the edges on the inside surface at 45 degr, to prevent contact between the sidewalls and the inside-surface of the sidelid. Only the outer surface can later be soldered to the sidewalls! Drill 12 small holes at 5mm distance from the edges in each lid. Solder a piece of wire (or rivets) in the holes, so the inner surface becomes connected to the outer surface only through those wires. Drill and tap M6 in bushings "D". Assemble the finetuning-bolts in them. Solder the assembled bushings "D" on the outside of the sidelids "M".

l.gif File all edges of the toplids "L" at 45 degr. to prevent contact with the sidewalls. Clean and spray with transparent paint.

2. Cut all central conductors from 22mm pipe. Saw the slits at the bottom ends with a thick sawblade. Smoothen the rims at the inside of the top end of "B" (not at the end with the slits).

3. Cut the tuning-rods.

4. Cut 7 pieces 3mm. 50 ohms teflon coax 1/4 wavelength long. Cut 1 piece 50 ohms teflon coax 1/2 wavelength long. Calculate the cable-lengths to the NOTCH-frequency of the cavity where the cable will be connected to.

Especially the 1/4 and 1/2 wave cablepieces connected to the antenna-outlet are important. They act as a frequency-dependent switch or circulator. After connecting the Rx-part and Tx-part of the filter together, the separation of the RX and TX filterparts, and the deepness of the notches depend on it.

Due to the severe mismatch on the notchfrequency, the 1/4 wave pieces between the cavities act as impedance transformers, decoupling here the interconnected cavities at their notch-frequency, avoiding mutual influencing. On the pass-frequency of the cavities, the cavities are matched to the cables. The cables have at the pass-frequency no influence.

Again: calculate all cablelengths for the NOTCH-frequency of the cavities to wich they are connected! The preciese length of the coaxpieces depends on the working frequency (US / EUR) and veloctyfactor of the coax (teflon is differend). Try to get the cable-lengths as accurate as possible. 1/4 wavelength = abt. 35cm teflon coax. 1/2 wavelength = abt. 70cm teflon coax.

Remove the outer insulation of the teflon coax to allow soldering the braid to mass.

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