Paul Maciel, AK1P and I decided to create some interest and fun in the NorCal meetings, and perhaps give the guys a reason to show other than just to visit. We decided to do a "Kit of the Month" with the rule being that the selling price of the kit could not be over $5. We just want to recover cost of the parts and provide some seed money for the next month's kit.

Our first kit was the Pipsqueak Regen Receiver, designed by Paul Harden, NA5N, and published in QRPp several years ago. That was a popular kit, and the idea was well received, so we decided to continue it this month with an RF Probe designed by Monty Northrup, N5ESE. Monty has all of the details on how to build the probe on his website at http://www.io.com/~n5fc/rfprobe2.htm If you decide to build one of these probes, be sure and visit Monty's site for all the info.

I gathered all of the parts during the holidays and bagged them into kits. Originally we were going to sell them for $3 each, but Paul suggested that we give them away to the brave members who showed up at the meeting today even though the swap was rained out. So, we did.


Parts Kit for N5ESE Ball Point Pen RF Probe

The parts needed are shown above. From left to right, top to bottom they are: 5" x ¼" piece of double sided pcboard, 2 banana plugs, 1/8" shrink wrap, ¼" shrink wrap, 24 inches of RG174 (or other suitable shielded cable), 3" dissecting pin, 1N34A Germanium Diode, 4.7 Meg resistor, .01uF capacitor, alligator clip, #24 insulated stranded hookup wire, 1 Bic Round Stic Pen.

Ok, now it is time to start building. The first step is to cut through the top layer of copper, being careful to just go through the copper. You want to make 3 separate pads to solder to. I used a small hacksaw to do mine, but you may wish to use a dremel, fret saw, etc.


The pcboard after it has been cut into 3 "islands"

Next, take a nibbling tool, or a file, and cut a slot out for the germanium diode. Use the diode as a gauge.


The pc board with the slot cut out for the diode.

Next take the straight pin, and with a pair of strong pliers, cut off the head. Be care to shield your eyes. Next, solder the pin to one end of the pcboard, on the same side as the slots.


Close up of straight pin after it has been soldered onto pcboard. (The red is flux)

The next step is to solder the .01 capacitor to the pcboard as shown.


The board with the capacitor soldered in place.

Now we will solder the resistor in place.


The resistor is in place.

Now find the Germanium Diode. Be very careful with it, as it is somewhat fragile. Do not make a sharp bend in the leads near the body, or you will break the diode. Note that one end has a band on it. Place it as shown so that it solders to the same side of the pc board as the capacitor and resistor.


The banded end of the diode is soldered in place.

Now, flip the pc board over and solder the other lead of the diode to the ground plane side of the double sided pc board.


The other end of the diode is soldered to the ground plane side of the board.

We are just about finished. It is starting to look like a probe!! Next, prepare the ink pen body. Take the pen apart by pulling on the ink tip. When you get it out of the pen body, pull off the ink tube. Next take something to push out the pen tip, leaving just the plastic body. You will need to hold the pin tip under a faucet to rince out the ink left over. You will need to drill a 1/16" hole in the side of the pen to accommodate the ground wire and a hole just large enough to pass the RG174 cable in the end. I used a 1/8" bit for this.


The pen tip and tube after separation.

The next step is to solder the banana plugs on the RG174. Carefully peel the insulation back about 3", and unwind the shield around the center conductor. Place a piece of shrink tubing over the shield, and then connect each wire to a banana plug. Now take the other end of the RG174, and remove ½" of insulation and separate the center conductor and the shield. Solder the center conductor on the same side as the resistor, and the shield to the ground plane side as shown.


Center conductor soldered to resistor side of pc board.


Braid soldered to ground plane side of pcboard.

Next, take about 10" of insulated wire and connect it to the ground side of the pcboard by the probe tip. This will be threaded through the hole in the side of the barrel of the pen and then hooked to the alligator clip.


The ground lead for the alligator clip soldered on the ground side of the pcboard.


The completed probe.

Monty suggests that you use shrink wrap to cover your probe, then use either copper tape or the shield from RG-58 cable to shield the inside of the probe. Details are on his web page. One word of caution. This probe is only to be used in transistor circuits, NOT tube circuits!!

Enjoy.

72,