Something for ELF interest

Instructions for the assembly of a BNC plug
to an ex-TV whip antenna. Ideal start for the Mcgreevy BBB-4 RX )

This is the endview of the brass section of the antenna.

Different angle showing area to be cut down. (brass)
This one has been filed down slightly before the scan
was made.

The antenna itself is 124 cm long, and has a diameter of 8 mm, it represents a fairly common whip antenna supplied with portable TV units. It comes in a plastic 'Y' holder with 2 of these whips installed. The flat view shows the part we are interested in which must be cut down to fit into the end of the BNC plug. First, cut the area with the hole off, straight across, leaving a 4 mm long stub, then cut into each side to a depth of ca: 3 mm, and then down into the cut from the top on each side until it looks like ......

The hole into the top of the BNC plug is 8.5 mm, at least it is on the one I have. This means you have 0.5 mm clearance, this will be taken up by a short length of 'shrink' material. Of all the parts shown for the BNC plug we are interested in ONLY parts 1, 5, 6. The rest are not used.

Parts supplied with BNC plug.

Once you have done the cutting you should have a square of brass 3 mm square and 4 mm long.
In the center of the square end on, center punch the position of the hole,(in the middle) and drill a 1.5 mm hole ca: 4 mm deep. This is the hole for the 1.5 mm stiff silver wire, or something like that. Solder a length of wire into the hole, say 10 mm long, you should have ca: 6 mm left outside the hole, see (end with pin) it's not that critical as you will be trimming to fit the BNC pin anyway. Drop BNC pin (5) into the BNC plug (1) and then ring (6). Try the antenna for fit, the silver wire should be dead straight. The silver wire pin should connect to the back of the BNC pin inside the BNC plug, you won't see it but you can feel it. Cut the silver wire pin down until you have a good part of the end of the antenna in the BNC socket.You should have a silver wire pin of about 3 mm long after trimming. When you are satisfied with the fit, take the BNC pin OUT of the BNC socket and stick it into a cork pad point down. Support the antenna with a third hand or whatever and solder the end of the silver wire pin you have trimmed onto the end of the BNC pin, ( make sure you have filed the silver wire pin flat on its end before you solder) You should now have something that looks like ......

Now take 14 mm of 'shrink' material and fit it over the antenna where it fits into the BNC plug, this will insulate the antenna proper from the case of the plug..(earth) leave about 3-4 mm visible above the top of the BNC plug. Shrink with heat carefully. Insert the pin and antenna into the BNC plug for checking fit pressing into the white ring inside the plug, not too hard, just enough to feel the play in the ring.

If good take out again. Using 2 component BISONITE glue, glue the white ring into the BNC plug, taking care NOT to get any glue in the hole where the BNC pin should be. Then coat the outside of the antenna, ( including the 'shrink' material) where it will fit into the plug and the threaded area inside the plug, don't use too much. When ready drop the antenna into the plug and twist a couple of times to spread the glue. Once firmly in the hole and the pin is in the correct position, wipe off surplus with a damp cloth and leave overnight to set.

If everything went well you have a very rigid BNC coupled antenna, just to check, use a voltmeter on ohms to check for shorts if any. Its a lot cheaper than $15-$19 that's for sure.

Note: I do not supply whip antennas, this description is general to antennas supplied with Japanese portable TV's sold in Europe. If the antenna with your portable is a different in size to above, you will have to find a way of adapting these instructions.