Projects Banner

Building a 2-element Tape Measure Yagi

During the March 22, 2018 meeting, Dave Joseph W1AMX discussed how to construct a simple 2-element direction-finding yagi for 2 meters. The antenna can be made with about $12 in materials, all of which are readily sourced at the local hardware store, and common hand tools.

Parts List
  • inches of inch schedule 40 PVC pipe
  • 1- inch schedule 40 cross connector
  • 1- inch schedule 40 T-connector      
  • 1-  inch schedule 50 cap
  • 1  inexpensive tape measure (a 1 inch wide tape is recommended)
  • 4  feet of coax cable with a connector on one end (UHF, BNC, SMA, etc.) and the other end prepared for soldering
  • 4  #12 (11/16 inch to 1 1/4 inch) hose clamps 
  • 5  inch piece of solid wire for hairpin tuning component (14 to 18 gauge will work)
Tools required
  • Hacksaw or PVC pipe cutter
  • Soldering iron or gun
  • PVC cement
  • Electronic solder
  • Wire cutter
  • Hot glue gun
  • Tape measure
  • Tin snips
  • Black indelible marker
  • Metal file
  • Flat blade screw driver or 5/16 inch nut driver (to tighten hose clamps)
Step 1

Cut a 3 inch length of PVC pipe, and another that's 6 1/2 inches. The 3" length will be used to form the boom between the director and driven element, and the 6 1/2" pipe will be used to form the handle, so you can hold the antenna from the rear. Optionally, you may use an elbow to angle the handle downward, but this depends on preference. Before cutting the pipe,  measure and mark the length using a black indelible marker.

Step 2

Cut two lengths of tape measure to 18 5/8", which will be used for the driven element, and another length of tape measure to 37 3/16", which will be used for the director. Once cut, round off the corners of the outside edges of the tape measure elements and cover them with electrical tape, for safety. Then, sand and tin the other ends of the driven elements, so it will make good electrical contact with the feedline.

Step 3

The time to tin the driven elements is BEFORE you connect them to the PVC pipe, so the extra heat required to do so won't melt the plastic pipe.  Next, form the 5" wire into a "U" shape, with the two legs about 3/4" apart. Tin the ends of the hairpin to make it easier for soldering later.

Step 4

At this time you can pre-assemble the PVC boom, connecting the cross and T, which will support the tape elements. PVC glue is not required, since the pipe will press in securely to the fittings, but you can use it if you choose to. When assembled, the cross and T will be 4 inches center to center.

Step 5

Finally, use the stainless steel hose clamps to secure the tape measure elements to PVC fittings as shown in the diagram.

2 Element Yagi

More information about this, and other RDF projects can be found at the links below:

Radio Direction Finding RDF Projects - WB2HOL
Tape Measure Beam Optimized for RDF - WB2HOL

Dave W1AMX also calculated measurements for the same antenna, but for use on 440 MHz. See below:

441 MHz 2 Element Yagi

Numbers are rounded off for ease in measurement.
No hairpin match needed.

Driven: 2 X @ 6.5"
Director: 11.70"
Spacing: 3.3"

Forward Gain: 3.78 dBd (7.112 X input power)
Front to Back: 8.52 dB

Calculated SWR @ 441 MHz: 1.07:1
1.5:1 VSWR Bandwidth: 20.053 MHz.
2.0:1 VSWR Bandwidth: 39.411 MHz.

Be sure to keep the spacing between the driven elements to about 1/4"-3/8".

HT Tricks for Radio Direction Finding

Use 'Body Shield/Fade' to get fade on signal.  Direction to travel will be behind you.

When the null gets shallow..use one, some or all of the following with 'Body Shield/Fade' technique...
- Rotate radio 90 degrees for ~20 dB attenuation.
- Slip tin foil 'glove' over antenna.
- Radio in VFO mode - tune 5 kHz off frequency.
- Use paper clip for antenna.

If direction suddenly changes bearing - you've been following a reflection.
Try to stay away from metallic objects (fences/buildings etc.)

If no null disconnect antenna and look for signal using body.  If signal found - you may have 'arrived'.  Start looking around.

Easy Loop Design

Here's an easy method to make a loop for any frequency, courtesey of Dave Joseph W1AMX.  You'll need some 75-ohm coax to make a transformer to match to 50 ohms.

VHF Loop (146 MHz)
Length of wire/tubing = 1005/146=82.603"
Loop diameter will be: 26.31" - or -
A square with 20.65" sides. Feed square at one corner.
Use RG-59 cable for matching transformer.  Length will be the same as one side of loop (or 1/4 the total length of wire/tubing), minus the velocity factor.  i.e. 20.65" X .66 (velocity factor) = 13.63" -  that's the length of your 75-ohm cable.
Use your favorite connector at end of 75-ohm cable to connect a 50 ohm jumper to the radio. (BNC, UHF, etc.)

UHF Loop (445 MHz)

Length of wire/tubing = 1005/445=27.1"
Loop diameter will be: 8.63" - or -
A square with 6.775" per sides. Feed square at one corner.
Use RG-59 cable for matching transformer. Length will be the same as one side of loop (or 1/4 the total length of wire/tubing), minus the velocity factor. i.e. 27.1"/4 = 6.775" X .66 (v/f example) = 4.472" - that's the length of your 75-ohm cable.
Square Loop Antenna diagram

Use your favorite connector at end of 75-ohm cable to connect a 50 ohm jumper to the radio. (BNC, UHF, etc.)
With either loop design, an insulated square/rectangle with screws to mount loop ends and holes to ty-wrap the coax to works well. Then some kind of handle to that.

Use 1005/F(MHz) plus 1/4 of that for 75 ohm matching cable (+velocity factor reduction) for any frequency you want.

Building a 2 meter Copper Dipole

Recently, we built one of the K1RQG-designed 2m copper dipoles, and construction is quite simple. All that's required is some 1/2" M Series copper pipe, a small piece of PVC, some tees and end caps, and a chassis-mount PL259 connector (to connect the coax). Its possible to omit this and solder a split piece of coax directly to the antenna, but for durability purposes, its recommended to use the connector. 

All material is 1/2" M Series copper pipe, except 1/2" X 1 1/4" PVC (noted).

The tees are 1/4" apart after assembly.

The  18 1/2" subsections are 2" apart C/L to C/L.

Feedline is fastened (52 ohm coax) to the points A and B on the 18 1/2"sections.

Materials needed:

10' of 1/2" M Series copper pipe
4 tees
4 caps
1/2" OD X 1 1/4" PVC pipe

2mcd1  2mcd2   2mcd3

After cutting the pipe to the lengths shown in the diagram, lay it out on a large, flat surface, and fit it together. Its recommended, however, to leave some extra length on the 38 1/2" sections (the two longest sections), in case the material is needed during tuning. Once everything fits up nice, sand both ends of each joint with either a 3M pad or fine grit sandpaper to prep it for soldering.

2mcd4  2mcd5   2mcd6

When you're satisfided with the fitment, sweat the joints, and don't forget to put the PVC spacer in place before soldering. Once this is complete, attach the PL259 connector, as shown (above right). Now its time to attach some coax and hook it up to an analyzer for final tuning. If trimming is required, make the cuts as needed and solder on the end caps. Finally,  mount it up on a mast and begin transmitting.

2m Copper Dipole Schematics

Click here to download a high quality PDF of the diagram shown above.

Installing Optional Filters in the Yaesu FT 857

Recently I decided to upgrade my Yaesu FT 857d field radio with accessory filters (available through W4RT Electronics). The ones I opted for are the 300-Hz (for CW) and 2.3-kHz (for ssb) Rockwell Collins mechanical filters. Installation is relatively easy, but there are a few things to look out for.

The first step is to disconnect any power source, and then to remove any mobile brackets (if used). Next, we'll remove the 7 screws that attach the top cover (4 on the sides and 3 on top). Be sure not to unscrew the speaker screws, as this is unnecessary. Once the screws are out, the top cover slides off in the direction of the faceplate. The first thing to be careful of is not to damage the speaker wire, which will still be connected. This wire can be detached from the board, but it should be long enough to be able to set the cover on its side and out of the way.

   Filter 1   Filter 2   Filter 3

The filters plug into the front right of the main board (if looking at it from the control head). The spaces on the board are labeled FIL1 and FIL2 respectively, allowing up to two filters to be installed at any given time.

If you look closely at the filter slot, you'll notice that on one side (LHS) there are 3 pins, and on the other side (RHS), there are 4. When the filter is oriented properly, these should line up perfectly with the female receptacles on the filter. Simply align the filter (writing side up), and press into place. Press it gently, however, to be sure not to bend any of the pins.

At this point, your work is almost done. Slide the cover back in place, secure it with the 7 screws, and reconnect to a power source. There's one more step involved to begin using your filters. Press the B button (in Multi Function Row 'n') to activate the optional filter installed in FIL1 (in my case this was the ssb filter), and Press C to activate the filter installed in FIL2. In some cases, you may have to change the setting in Menu Mode No-086 to "FIL1" or "FIL2" as well to activate one or the other.

After doing some preliminary tests, I'm astounded by the performance of these. The CW filter, especially, makes a huge difference. It has excellent frequency response, with very sharp skirts, and no noticeable distortion.

CW With Your HT 

Our CW With Your HT project is to build a simple device that can be used with any handheld tranceiver to send modulated CW. It is basically an audio oscillator and keying circuit which acts as an interface between a cw key and a handheld radio. Modulated CW is nothing more than audio tones keyed on and off and fed to your transceiver's audio jack. The circuit design, including speaker and 9V battery are small enough to fit inside an Altoids tin, or similar enclosure, so it can easily fit in your pocket or be stowed with your HT. Please find the schematics below, (drawn by Roger Pience, N1XP), as well as a detailed parts list. As we build these over the next several weeks, we'll post images of the construction process.

    cw_oscillator1   cw_oscillator2   cw_oscillator3

CW With An HT Schematic

    cw_oscillator4   cw_oscillator5   cw_oscillator6

Parts List

R1, R2

C1, C2




10k0 / 1/4W Resistor  (10,000 Ohms, Brown, Black, Orange)
47k0 / 1/4W Resistor  (47,000 Ohms, Yellow, Violet, Orange)
100k Potentiometer (100,000 Ohms, Marked 104)
100k / 1/4W Resistor (100,000 Ohms, Brown, Black, Yellow)
2k2 / 1/4W Resistor (2,200 Ohms, Red, Red, Red)
1k0 Potentiometer (1,000 Ohms, Marked 102)
5k0 Potentiometer (5,000 Ohms, Marked 502)

0.01 uF / 50V Capacitor (Marked 103)
220 uF / 16V Electrolytic Capacitor
0.1 uF / 50V Capacitor (Marked 104)

NE-555 Integrated Circuit

3.5mm phone jack, mono
3.5mm phone jack, stereo

Speaker, 7 Ohm, 22mm-round

Switch SPST
Additional Parts:

Bread Board or Holey-Toids Board (available at
Battery Leads
8-pin IC Socket


Circuit Diagram (Image)

Carbon Composition Trimmer Potentiometers

Aluminum Electrolytic Capacitors

Building a Miniature Code Practice Oscillator

At November's club meeting, Roger Pience N1XP, supplied kits of his own design, and helped members build miniature code practice oscillators. The kits are relatively easy to build and only require a battery connector, 100k resistor, .50 uF capacitor, a couple of transistors, and a small solderable bread board. It's also recommended that you include a couple of leads or posts to attach a straight key.

Parts List

  • 9V Battery Connector
  • 100k Resistor
  • .50 uF capacitor
  • 3904 Transistor
  • 3906 Transistor
  • Bread Board

   cw1   underside    assembled  
cw oscillator design

  Thom, Dave, and Roger    Dakota, Charlie, Rory    Dakota and Rory  

If you look at the picture of the underside of the board, you'll see that we also added some wire to complete the circuit, however most of the contacts can be made by using the leads of the individual components, bent over and soldered in the appropriate place. The best way to start is by positioning a few components on the board, pushing their leads through, and soldering them to the board, leaving their leads long. As you add components, simply fold the leads over the back side and begin to form the circuit, then do a final solder, adding wire where necessary, and trim the excess material. After you complete this, plug in a battery and a key, and you'll be making sound!

If you're interested in a kit, complete with all the parts necessary, please contact Roger Pience at:

A Band-Pass Filter for Field Day

Field Day, for multiple transmitter categories, presents interference problems not normally associated with single-station setups. Unwanted harmonics and receiver blockage are not only a nuissance, but can potentially cause damage to your receiver as well. The solution are these relatively inexpensive band-pass filters, which provide for higher-power handling, increased reliability and greater frequency attenuation than other designs. Our filters are based on the Chebyshev 3-resonator design, as presented by Ed Wetherhold, W3NQN in the 1998 QST article, Clean Up Your Signals with Band-Pass Filters.

bpf1   bpf2   bpf3

The performance of these filters is obtained by employing the three-resonator configuration, using inductors wound on powdered-iron or phenolic torroidal cores, and series-parallel connected, high-voltage, low loss NP0 ceramic capacitors. If you're a contester, especially one who's involved in multi-transmitter activities such as Field Day, these filters are what you need!

The materials you'll need to get started are enclosures (we recommend ones sized 5 1/4" X 3" X 2"), torroidal cores (T-130-17, T-130-6, T-130-0, T106-0), copper-clad laminated sheets, ceramic disc capacitors (15pF/4KV 10%, 110pF/2KV 10%, 30pF/3KV 10%, 220pF/1KV 5%), 18g, 16g, and 15g magnet wire (for winding) and PL259 chassis connectors. For a complete list, as well as detailed instructions, please refer to the following articles:

            Clean Up Your Signals With Band Pass Filters            Clean Up Your Signals With Band Pass Filters (Part 2)

bpf4    bpf5   bpf6

(Assembly process shown) - Note that the copper-clad sheet is riveted to the floor of the enclosure, and PL-259 connectors are mounted.  Next, a piece of braid or wire is used to ground the chassis connector to the copper sheet, then the wound torroid is soldered, along with appropriate capacitors, to create a 50W tap. The core bodies are attached to the copper sheet with hot glue to prevent wire-to-ground contact.

 bpf7    bpf7    bpf9        
Our filters were modified, assembled, and tuned by Roger Pience, N1XP. Note, that since we use a slightly larger enclosure than the one recommended in the original QST article, the torroidal cores can be arranged in an orderly fashion with less chance of passband loss caused by the proximity of the other cores or the enclosure.

Building a Pneumatic Antenna Launcher

In the Summer of 2012, WSSM members built pneumatic antenna launchers, under the direction of Steve Freeman K1MV, who built the original prototype. The launchers are constructed using 3" and 1-1/2" pvc piping, and air gage, schrader valve, and a fishing reel. With about 40 pounds of air, they are capable of launching a weighted plastic slug several hundred feet - perfect for putting up that next wire antenna!

Parts List

  • 3" PVC pipe X 13" long
  • 3" PVC pipe dome cap
  • Step flange (3" down to 1 1/2" pipe)      
  • Total of 24" long X 1 1/2" rigid non-metal conduit
  • valve for 1 1/2" pipe
  • Fishing reel
  • 2 hose clamps 
  • 1 Schrader valve
  • 6" of 3/4" PVC pipe (to be cut in half for slugs)
  • 4  3/4" dome caps (for slugs)
  • Eyelet (for attaching fishing line to slug)
  • Fly line
Tools required
  • Hacksaw 
  • PVC cement
  • Tape measure
  • Black indelible marker
  • Metal file
  • Electric drill
  • Flat blade screw driver or 5/16 inch nut driver (to tighten hose clamps)
    parts  looking over the launchers  keeping it reel

Begin by  cutting your pipe to the sizes shown below, then file rough edges and prefit. The open/close valve should be located about 4 - 1/2" from the air chamber. Be sure to prep the areas to be glued, and allow adequate drying time before applying any air pressure. I mounted the shrader valve in the small pipe section, between the open/close valve and the flange, and the pressure gage (optional) was mounted on the air chamber section itself. Its a good idea to add a pressure gage, unless you have an accurate one on your compressor or air tank, because this is what determines distance when firing the slug. It is not necessary or recommended that you fill it with any more than 40 pounds.

                      antenna launcher blueprint
Mounting the fishing reel is relatively simple. Any open reel will do, and its personal preference whether to mount it on the top or bottom of the pipe. As far as the slug goes, its just 3/4" PVC pipe, cut to about 6" long and capped on both ends. Before assembling it, cut a small piece of scrap wood for the inside for the eyelet to screw onto, and its a good idea to fill the slug with sand so that it has enough weigh to drop down the other side of that tree you'll be firing at. Another good practice is to either paint it a bright or flourescent color, or wrap it in a bright tape to make it easier to locate.

    launcher, completed  reel  slug

Firing the antenna launcher is pretty easy, but it takes a steady hand. Once air is pumped into the chamber, be sure not to point it at yourself or anyone else as the projectile comes out very quickly. Its also a good idea to wear safety glasses. The idea is to point it just slightly above the tree that you're aiming at and quickly open the valve, to release all the air in the chamber at once.

Building a 3-element Tape Measure Yagi

In the September / October 2011 newsletter we discussed how to construct a transmitter that can be used  for radio direction-finding. But there is another piece of equipment you'll need to consider before heading out to the field for a transmitter hunt - an antenna! For reasons of simplicity, and because they are relatively inexpensive to make, we chose to build a "tape measure" antenna. Below, you'll find directions on how to build your own 2 meter direction-finding antenna.

Parts List
  • 3  feet of inch schedule 40 PVC pipe
  • 2- inch schedule 40 cross connectors
  • 1- inch schedule 40 T-connector      
  • 1-  inch schedule 50 caps
  • 1  inexpensive tape measure (a 1 inch wide tape is recommended)
  • 4  feet of coax cable with a connector on one end (UHF, BNC, SMA, etc.) and the other end prepared for soldering
  • 6  #12 (11/16 inch to 1 1/4 inch) hose clamps 
  • 5  inch piece of solid wire for hairpin tuning component (12 to 18 gauge will work)
Tools required
  • Hacksaw or PVC pipe cutter
  • Soldering iron or gun
  • PVC cement
  • Electronic solder
  • Wire cutter
  • Hot glue gun
  • Tape measure
  • Tin snips
  • Black indelible marker
  • Metal file
  • Flat blade screw driver or 5/16 inch nut driver (to tighten hose clamps)
Step 1

Cut an 11 inch, and two 7 inch pieces of PVC pipe. Before cutting the pipe,  measure and mark the length using a black indelible marker.

Parts Tools Measuring

Step 2

Assemble the cut lengths of pipe as seen in the drawings to create the boom of the antenna.  Begin by connecting a T-connector  to one end of your 11 1/2 inch pipe, and a cross connector to the other. Then add one of the 7 inch pipes to the cross connector. Glue the remaining cross connector to the end of this pipe and connect the last pipe to this cross connector. Make sure that you align the cross connectors. The easiest way to do this is to place them on a flat surface and twist them to be flat with the surface. Finish this step by adding the cap to the open end of the last pipe.

Step 3

Cut four pieces from the inexpensive tape measure: 41 3/8 inch, 35 1/8 inch, and two lengths of 17 3/4 inches. Be careful not to cut yourself on the sharp corners or ends. Use your tin snips to carefully round off the sharp edges.

Step 4

Now attach the longest (41 3/8 inch) piece of tape to the cross connector closest to the end with the cap. It will be helpful to mark the center point (20 11/16 inches) with your black indelible marker. Position the tape over the cross connector, so the curve of the tape is similar to the curve on the cross connector. Center and secure the element with hose clamps on each side. Next, attach the next longer element (35 1/8 inch) to the T-connector at the opposite end of the boom in a similar fashion.

Cutting the pvc Partially Assembeled hot glue

Step 5

The next step is to take the 5 inch piece of wire and bend it into a "U" shape about 3/4 inch wide. Then tin the ends of the wire. This will be used to make the “hairpin match.” Scrape or file about 1/4 inch of paint off the back side of one of the ends of the two remaining pieces of tape. Tin the bare areas, then attach the hairpin match and coax wire with solder as shown in the diagram.

Step 6

Next attach this assembly to the boom using the two remaining hose clamps. The soldered joints are then covered with hot glue to seal and help waterproof it. For a balun,  4 or 5 turns of the coax feed wound round the boom should do the trick. Now your antenna is ready for use.

Hairpin Match Side View Fully Assembled

Tape Measure Antenna Schematics

For more information on tape measure yagis, check out the following links:
ARRL Q&A "How to Build a 2m Tape Measure Yagi"
Radio Direction Finding Antenna for VHF -
RDF and Hidden Transmitter Hunting - VE3RRD
Cheap & Light Portable 2m Yagi - M0RUN
The 2 Meter Tape Measure Antenna - K4IVE 
Tape Measure Beam Optimized for RDF - WB2HOL

Building a Direction-Finding Transmitter

One of the most enjoyable projects that we tackled this summer was constructing a pair of transmitters for radio direction-finding. Of the two that we built, one is a modulated-CW beacon, like the ones used for International ARDF competitions, and the other is a "voice" beacon. While researching for this project, we discovered Bob Simmons' (WB6EYV) boards that could be used in their construction. We chose the MicroHunt and SqwakBox transmitters.

The MicroHunt transmitter produces about 50 milliwatts of FM-modulated CW on 2-meters on a board measuring 0.9 X 1.2 inches. It comes partially assembled, and the PIC micro (that generates the CW message an ID at regular crystal-controlled intervals) can be pre-programmed before shipping. What we find upon delivery is a tiny board with mounting points for power and an antenna.

ardf 1 ardf 2 ardf 3

The MicroHunt is intended for competitive transmitter hunts, where multiple transmitters operate sequentially on a single channel. For this reason, crystal timing is essential to prevent transmission overlaps. It can also be used as a DF "homing beacon" on free-flight balloons. It uses a PIC 12F675 micro for supervision as well as a strap programmable, crystal-controlled PLL synthesizer chip. Ground range, depending on antenna, is typically well over a mile.

Its sister, the SqwakBox, also produces 50 milliwatts of FM-modulated RF on 2-meters, but its assembled on a slightly larger board, measuring 0.9 X 2.4 inches, and includes a voice record/playback chip with 60-second recording capacity, and an integrated electret microphone to record a message.

ardf 4 ardf 5 ardf 6

The SqwakBox makes use of a PIC 16F84 micro for supervision, ISD2560 for voice record/playback and an ICS525 PLL CPU clock generator chip. Messages can be recorded by pressing a "record" button and speaking into the integrated microphone. Its mostly intended for recreational 2-meter transmitter hunts.

The first step regarding assembling these transmitters is to find an enclosure. Just about any electronics enclosure would work. We wanted something that was small, lightweight, and had a good surface to mount an antenna, and on/off switch. Checking several options online, we decided on plastic enclosures with removable tops, and room enough to mount the necessary 9-volt battery. Believe it or not, it was less expensive to purchase these from their manufacturer in Poland and ship them, than from the US distributor. The antennas we chose are Nagano 2 meter HT "flexi" ducks. We added an on/off switch so we didn't have to worry about disconnecting the battery when not in use. Besides the enclosure and switch, the only other parts required to assemble them were BNC chassis connectors for the antenna, some wire, and 9-volt battery connectors. 

For more info on the parts used in this project, please visit:
Doppler DF Instruments
Electronics Enclosures

Restoring the EL-Key

The EL-Key is an important paddle in the history of amateur radio. This single lever design was the first commercially manufactured paddle offered to ham radio operators. They were made by R.E. Poucel (W2AYJ) and Sid Shore (K2FC) doing business as "Poucel Electronics," a division of Shore Mfg. Co., of Long Island NY, starting in 1959. Today they are very scarce, and sought after by collectors.

El-Key Before  before  Disassembled

While searching for an EL-Key, we were looking for two important qualities - a key which had all the components intact, and one which still had the all-important name plate attached and undamaged. Everything else could be restored.

The first step in any restoration process is to decide what needs to be done. This one was in obvious need of new paint on the base, and the lever, upon initial inspection, didn't function as it should have - It was frozen and had no springing action. To begin, we would need to remove all of the components from the base. Before disassmbling anything, however, its a good idea to take pictures and to draw diagrams of how everything is attached and wired.

The main carriage comes off with just two bolts, allowing removal of the swing arm assembly. A flat head screw driver is the only tool that is required. The rest of the components are simple upright posts which act as electrical contacts, spring holders, or stops. They all remove with a single machine screw, threaded from the underside of the base.

Base Before   Sanding   Polishing

Once everything is removed, the base can be sanded and prepped for paint. We used two different grits of sandpaper with a sanding block. The first was 220, followed by 320, making sure to smooth out all the chips and scratches. Then the base was cleaned with solvent and set aside for painting. Our base was painted by our good friends at Moody's Collision Center, in Scarborough, Maine. We chose Volvo paint code 019, which is a solid black, closely resembling the original color.

Lever Assembly   Reassembled   Bottom

The rest of the components were cleaned and polished, and much of the stripped or worn hardware was disgarded and replaced. For the plastic paddles, which were yellowed and scratched, we used Mothers Plastic Polish, which removed almost all of the surface scratches and yellowing. Then we gave it a finishing coat of Zymol Concours Glaze. The metal components were polished with mag and aluminum polish, then finished with Zymol. We discovered that the problem with the side-to-side motion of the lever assembly was a missing spring, and a badly bent center bolt.  With these replaced, the left side motion was restored.

With all the components repaired and polished, and the base back from the body shop, we began the reassembly process. Consulting our photographs and wiring diagram, the process went smoothly. The wiring was straight forward, but required a few connectors to be soldered to the wires, and to each other, to match the original layout. On removal, some of these just fell apart. The finishing touch was to reapply the EL-Key nameplate, which was done with a two-part epoxy called J-B Weld.

Mixing  Applying the emblem Finished El-Key

So there you have it - a fully restored 1959 EL-Key, ready to get back on the air and make some QSO's!

Constructing a 20 meter Dipole

Tim (KB1HNZ), Charlie (W1CPS), and Thom (W1WMG) work together on building a 20 meter dipole  Rory (KB1PLY) in the foreground, while Thom, Tim, and Charlie work on the antenna

What is a Dipole Antenna?

We chose to build dipole antennas for our field activity because they are cheap to produce, very efficient, and easy to construct. But why are they effective? Let’s take a closer look, as we examine just what a dipole is...

A dipole is a balanced antenna. It consists of two haves, which extend in opposite directions from a feed point at the center. It is commonly called a “half-wave dipole” since the entire antenna is - wavelength long at the desired operating frequency.

Why do we start here? In its simplest form the dipole is very dependable. It’s easy to construct, tune, and to install, but it is also the building block for other, more complex antennas. Once you understand the techniques involved in making the dipole, they can be applied to any type of wire antenna including the “Full Sloper,” “Inverted V,” “End-Fed Zepp,” “Folded,” and “Trap” varieties of the dipole.

For our example, we will construct a simple, center-fed dipole for the 20 meter band. To do this we need the following materials:

1 spool of 14 gage copper-strand wire (for the radiated elements)
1 spool of lamp cord, or “zip line” (for the center feed line)
2 commercially available plastic end insulators
1 Center insulator
Nylon Rope
The following tools are also required:

Wire Cutters
Soldering iron
Wire Strippers
Electrical Tape
Zip tie

The first step is to determine the total length of the antenna. We do this (for frequencies up to 30 MHz), by using the following formula:

Length of half-wave antenna in feet  =     492 X 0.95 / f(MHz)    =     468 / f(MHz)
A half-wave antenna for 14.200 MHz  =   468 / 14.200 = 32.96 ft.  Divide this number by 2 to get the length of each leg, and we have 16.48 ft. Keep in mind that it’s a good idea to cut the wire a few inches longer than the calculated length, since some of the resonating area of the wire will be lost when it is tied back onto the insulators.

After this is done, cut a length of feed line. We used what is commonly called “zip cord,” which is simply the electrical cord used on lamps or other appliances. Cut a length of about twenty-five feet, and strip the ends (about three inches on the end that will connect to the center insulator). Although there are many ways to connect the feed line, we chose to use a commercially available insulator made of plastic. This could also be made from PVC tubing, wood, or even a scrap of Lexan. The commercially made insulator has a fat round center with grooves in it, and holes drilled on the ends.  Secure the feed line to it by wrapping it tightly around the center grooves and securing it with a plastic tie, leaving enough of the stripped wire to loop around and eventually connect to each leg. 

Dipole Schematic

Similarly, attach the antenna legs to the center insulator, by looping each end through the holes, and wrapping it around itself several times. Then, connect one side of the stripped feed line to  a leg of the stranded antenna wire, and repeat with the other side. Do a good job of soldering the antenna and feed line connections. When you’re finished soldering, and it cools, wrap the connections with electrical tape for water-proofing.

After this is completed, attach the end insulators in a similar fashion, looping each end through a hole on the insulator, but don’t solder just yet.

The antenna is nearly complete. Raise it to a working height, and check the SWR at several frequencies across the band. Most dipoles require a little pruning to raise the resonance the desired frequency. Remember to trim each end equally. When you’re satisfied with the SWR, lower the antenna and secure each end with solder, and when it cools, tape the connections to waterproof.

There’s a few things to consider about how to connect the feed line to your radio. We simply soldered a PL 259 connector to the zip cord and plugged it in directly to the radio, but it’s probably a good idea to use a balun if the dipole is fed with coax. The disadvantages of coax are increased RF loss and low working voltage, but sometimes it can’t be helped. The most efficient way to feed a dipole is with 450 ohm ladder line. Ladder line has extremely low loss, and although zip cord has a little more, they both can stand very high voltages (SWR).

Now you’ve done it. You made a dipole. Go tell the world!

One advantage of the dipole is that its takes up little space, when compared to a yagi, and  doesn’t require a tower to get it up. Simply put it in a tree, or if none is available, set up a mast or two, and you’re on the air. They can be made of almost any wire or tubing, and can be set up in an infinite number of configurations. The dipole is popular because of its simplicity, and the fact that it can be erected quickly in emergency situations. They are the choice of EmComm operators and dx’ers alike. During our field operation on September 18th, we put up three dipoles for the 20, 40, and 80 meter bands in just 15 minutes, and made nearly fifty contacts in just a few hours.


Facebook Google + Twitter Email
Wireless Society of Southern Maine, P.O. Box 6833, Scarborough, ME 04074