Fig. (1) diagram antenna tuner (PI network)

" with a PI network one can adapt each wet shoelace ", reads an old radio operator wisdom.
Now a clamp for such a cord is not intended, probably however with this weekend project two tidy BNC sockets. The challenge consists also of it, such a network, also Collins filters mentioned miniaturizing thus that it fits into a pharmacist box in accordance with the advertisement in (1), whereby the problem is the height of 18 mm (1.4") for switchable inductance. With the selected rotary switch and the amideon toroidal core it is so possible even.

The PI network is described and in fig. (1) represented in among other things (2).

Into the tablet box - as drops I would not like to define these pills - first the assembly holes for the BNC sockets, the telephone socket, the variable capacitors and the rotary switch are bored. In addition a HSS step drill worked satisfactorily, which is turned by hand, so that the necessary feeling is brought to the thin sheet metal.

The cover of the box is demoted to the rear side and experiences no handling.

The toroidal core is wound evenly with 36 turns cu enamelled wire (CuL) and soldered from the rear to the 12-stage rotary switch. Before one removes the lacquer isolation at the outer edge of the coil with a small file, so that the turns concerned can be tinned. Note: for stripping and soldering the CuL to be needed the switch does not stand long soldering times, those. The appropriate turns must be beforehand prepared thus. The wound toroidal core fits " sucking " between the 12 soldering irons of the rotary switch mentioned. If one regards the switch from down, then all 30° a soldering iron between those is to three or four turns to be accommodated can.

Now the elements are inserted into the box and wired according to fig. (1) to a pi network.
With the organization of the " front plate " a label even arranged is used. For this becomes file label with a laser printer prints accordingly, low-cut out and on the box adhesive.

Fig. (2) shows the finished device.

Components:

2 variable capacitor 50... 500pf
(squeezing he/small flat variable capacitor e.g. Conrad stock No.: 48 23 23-44)
1 step switch, 12-stage, for print assembly (e.g. Conrad stock No.: 70 97 43-44)
3 rotary button
2 BNC sockets
1 telephone socket
1 iron powder toroidal core Amidon T80-2 (red)
1 pharmacist box (Fishermans friend box, it may be an altoid box as well)
1 m cu enamelled wire (CuL) 0.5... 0.8 mm in diameter
1 file label (self adhesive)

Literature:

(1) FUNKAMATEUR Heft 9 1997 Seite 1023 (9/1997 page 1023)
FA-Ideenwettbewerb: "Wochenenprojekte in Dosen"
design competition "weekenders in doses"

(2) Rothammel, Karl: Antennbuch (Antenna book)

Pictures: