Showing posts with label electronic test equipment. Show all posts
Showing posts with label electronic test equipment. Show all posts

August 29, 2020

Repairing Portable Rotatable Dipole

For portable operations, we have been using a portable rotatable HF dipole from EmComm-Products (model RADS 9-11/A) since 2008.  The antenna provides HF (160m, 80m, 40m, and 20m) and a second VHF/UHF antenna on top of the dipole which is fed by a separate cable enabling concurrent operations of both a HF and VHF/UHF radio on one mast.

Activating Hatteras Island, NC

KC2VSR (Field Day at Fort Ord, CA) rotating the dipole by giving the mast a simple twist

When setting up the antenna for portable operations to teach the radio merit badge in 2018, we discovered that we could no longer tune up when using the 20m elements.  SWR was extremely high.  The was the first time we had an issue when using the antenna after a decade of use.  It was time to give the antenna some attention and bring it back to working order. 


Once back home, we brought out each of the elements and check them individually for continuity using a ohmmeter.  To perm this test, we placed one of the ohmmeter probes on one end of an antenna element and the other problem on the other end of the antenna element.

All the elements passed this basic test with the exception of one of the 20m elements.  The 20m element had no continuity indicating that the wire had a break somewhere along the fiberglass element.

I visually inspected the element for apparent damage and found none.  This suggested that something was amiss with connection between the wire and one or both end connectors.

Corrosion on the joint between the antenna wire and antenna connector

Using an X-acto knife I carefully cut a window in the shrink wrap at the junction between the antenna element wire and the end connector to inspect the connection.  This revealed corrosion on the junction.  Using the continuity tester, I checked for continuity between the wire and both end connections.  This showed continuity at the junction to the far end connector and no continuity to the near connector.  Ah ha!  We found the issue.  The corrosion was likely caused from a decade of operating near saltwater and in the rain.


A brass wire brush was used to remove the corrosion.  The connector was then resoldered to the wire along with a copper wire wrapped all the way around the connector to assure positive contact.  The connector was recovered with shrink wrap and relabelled as a 20m element.  This was a straightforward and easy repair.

Repaired 20m element


We setup a wilderness radio station to teach the radio merit badge at summer camp with the portable rotatable dipole as one of the antennas.

Portable rotatable dipole back on the air at summer camp near Truckee, CA

We setup the antenna with the 20m elements and it performed flawlessly all week while at summer camp.  We made numerous SSB contacts on 20m.

Several people have contacted me asking about buying their own portable rotatable dipole antenna.  Sadly, the manufacturer, EmComm-Products, is no longer in business.  It has been an outstanding antenna.

Good DX and 73,  

April 13, 2014

FCC Technician Exam Question Of The Day (T7D04)

Q) Which instrument is used to measure electric current?

A) An ammeter

NJ2X Notes:
An ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes (A).


October 4, 2013

Using your multimeter: Continuity Test

One of the most basic uses of a multimeter is to test if there is continuity in a circuit. Testing for continuity means to verify if a circuit, wire or fuse is complete with no open. A switch in the off position will be "open" and no continuity.  A switch in the on position "closed" and has continuity between its contacts.

Digital Multimeter

Audible continuity means the multimeter produces a tone that you can hear when a circuit is complete.  Audible continuity testing is very handy since it allows you keep your eyes on your hands and the circuit you are testing.  You can hear if continuity is present without looking at the meter.

Never try to test continuity with on a circuit that is energized.  The meter may be damaged and you risk injury.

The basic procedure for a continuity test:
  1. Make sure the circuit is not energized.
  2. Set your multimeter to continuity test.
  3. Touch the two probes together.  You should hear a tone which indicates the continuity test is working.  If you don't hear a tone then the multimeter you must stop and resolve the issue. Likely problems: the meter is not set to continuity test, the meter's fuse is blown, or the multimeter is damaged.
  4. Place the two probes across the two conductor you are testing for continuity.
  5. If you hear a tone, continuity is present.  If you don't hear a tone then the circuit is "open" and there is no continuity.
Typical uses in amateur radio:
  • Confirm there is no electrical connection (short) between the center conductor and shield on a piece of coax
  • Confirm that there is an electrical connection between the center conductors on both ends of a length of coax
  • Confirm that there is an electrical connection between the shield on one end to the other end on a length of coax
  • Testing DC power cable assemblies.
  • Testing fuses
  • Test if a switch is working properly
  • Test if the multimeter's own internal fuse has been blown
There are an endless number of uses for a basic continuity test and it is a great feature to have in a multimeter and on your bench.

Good DX and 73, NJ2X

Check out our other related articles on NJ2X.COM:
Quick Guide To Common Multimeter Symbols and Abbreviations

© Michael W. Maher and NJ2X.COM, 2013. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Michael W. Maher and NJ2X.COM with appropriate and specific direction to the original content.

September 27, 2013

Quick Guide To Common Multimeter Symbols and Abbreviations

Ever wonder what all the symbols and abbreviations mean on your multimeter?  Here is NJ2X's handy quick reference guide to help you decode some of the more common symbols and abbreviations appearing on multimeters.

AC Alternating current or voltage
~ Alternating current or voltage
•))) Audible Continuity
DC Direct current or voltage
Direct current or voltage
V Volts
mV Millivolts (1 x 10- 3 volts)
A Ampere (amps). Current
mA Milliampere (1 x 10-3 amps)
uA Microampere (1 x 10-6 amps)
nS Nanosiemens (1 x 10-9 siemens). Conductance (1/W)
Ω Ohms. Resistance
Kilohm (1 x 103 ohms). Resistance
Megohm (1 x 106 ohms). Resistance
Hz Hertz (1 cycle/sec). Frequency
kHz Kilohertz (1 x 103 cycles/sec). Frequency
mF Microfarads (1 x 10-6 Farads). Capacitance
nF Nanofarads (1 x 10-9 Farads). Capacitance
- Negative
+ Positive

Good DX and 73, NJ2X

Other related articles on NJ2X.COM:
Using your multimeter: Continuity Test
What is the schematic symbol for a ferrite bead?

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© Michael W. Maher and NJ2X.COM, 2013. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Michael W. Maher and NJ2X.COM with appropriate and specific direction to the original content.

December 28, 2012

Project: Anderson Powerpole Polarity Checker

Ward Silver's (N0AX) article, "Hands-On Radio: Experiment #120: Power Polarity Protection", in the January 2013 issue of QST included a circuit diagram for a 12v polarity checker.  Inspired by the diagram, we headed to workshop on a Friday evening to fire up the soldering iron and fabricate our own Anderson Powerpole polarity checker using junk-box parts.

Schematic of a polarity checker with a 1k Ohm resistor and two LED's one red and one green
Powerpole Polarity Checker Circuit Diagram
From Hands-On Radio: Experiment 120: Power Polarity Protection, January 2013 QST; copyright ARRL

We are big fans of Anderson Powerpole connectors and recabled our radio gear with the connector sometime ago.  A polarity checker would be a very useful item to have around the shack and in a go-kit.

Step 0: Round up the parts and tools

A well-stocked junk box and workshop will likely yield all the necessary parts needed to build the polarity checker.  A few minutes of scrounging around our workshop is all it took to find the parts for this project.
  • Green LED
  • Red LED
  • 1k Ohm resistor 1/4W
  • Pair of Anderson Powerpole connectors
  • Junk box plastic part to turn into an end-cap
  • Hot glue gun
  • Soldering iron
  • Shrink wrap tubing (small diameter)
  • Wire snips

Step 1: build the circuit on a solderless breadboard

We find it helpful to first build a circuit on a solderless breadboard prior to assembly and soldering.  This approach helps confirm the junk-box parts are still functional, the circuit works as advertised, as well as verifying the orientation of parts having polarity (e.g. the LED's in this project).  This circuit is very simple.  The key is to make sure the LED's are wired together in opposite polarity.

Anderson PowerPole polarity checker circuit being tested on a solderless breadboard prior to assembly.
NJ2X first built the polarity checker on a solderless breadboard as a test

Step 2: Prepare the end-cap

We found some sort of plastic cap in our junk box that would marry up perfectly to the back side of a pair of Anderson Powerpole connectors.  We drilled four small holes in the top of the cap to pass the LED's leads through.
Anderson PowerPole polarity checker cap - four holes being drilled for the LED wires to pass through.
NJ2X drills four holes in a small cap for the LED leads

 Step 3: Solder the components together

Insert the leads of the two LED's on the top of the cap.  Solder the leads and resister together per the wiring diagram.  Use shrink wrap tubing to insulate the leads from each other to prevent a short.  Solder a short red wire and back wire to the leads.  Again use shrink wrap tubing to insulate the connections.  Solder the Anderson Powerpole connectors onto the wire ends.  Be sure the Powerpole positive and negative are tied together in the correct configuration, "Red Right Up".  Test the circuit to confirm it is working before proceeding with final assembly.

Anderson powerpole polarity checker in a vice while be fabricated
NJ2X testing the soldered polarity checker prior to final assembly

Step 4:  Final Assembly

Fill the cap with a generous amount of hot glue.  You want enough glue to assure a solid mechanical connection and prevent the wires from moving or being stressed during use.  Press the wire and Anderson Powerpole connectors into the cap and hot glue.  Let the glue cool and harden.  Test again to confirm the circuit is functional with both correct and reversed polarity.  We used a label maker to add our call sign to the outside.

Fully assembled Anderson PowerPole polarity checker.
NJ2X's Anderson Powerpole polarity checker fully assembled

We shared a picture of the finished product with N0AX and he pointed out that it looked a little like a rabbit.  My son, KC2VSR gave the polarity checker a funny bunny face to really set off the effect.  We had a good laugh and decided to call the polarity checker, "Bunnicula".  Ham radio is really a wonderful hobby to share with kids.

fully assembled Anderson PowerPole polarity checker with a cat-face drawn on it for humor.
NJ2X's Homebrew Anderson Powerpole Polarity Checker

Voila!  There is our build of a very handy 12v Anderson Powerpole polarity checker.  Use the polarity checker before plugging into an unverified Anderson Powerpole connector.  This simple test may save your equipment from damage.  A lit green LED denotes correct polarity and lit red LED indicates reversed polarity.

There are at least a couple of potential failure modes that would cause the polarity to be reversed on a pair of Powerpole connectors.  One potential failure is that the red wire terminating at the power supply was accidentally connected to the negative terminal.  Another possibility is that the Powerpole connectors were snapped together with the incorrect orientation.

For example, when volunteering during an emergency and you need to recharge your HT's battery from the HQ emergency power via a Powerpole.  If you plug into it without checking polarity you may end up with a dead HT if the cable was wired incorrectly to the supply.

Not all cars are wired so the center of the cigarette lighter connector is positive.  If you use an Anderson Powerpole to Cigarette Lighter adapter on an unfamiliar vehicle you may be in for an unpleasant surprise when you connect your rig and the reversed polarity causes damage.

An additional use of the polarity checker is a quick power cable or connector continuity checker.  We plan to put our polarity checker to good use in the shack testing all new cables and Anderson Powerpole connectors that we build for mechanical contact, continuity, and polarity.  In the past, we have simply used a multimeter which didn't confirm that the connector makes proper electrical contact when connected mechanically to another Powerpole.

Good DX and 73, NJ2X

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© Michael W. Maher and NJ2X.COM, 2012. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Michael W. Maher and NJ2X.COM with appropriate and specific direction to the original content.

January 27, 2012

What can you do with an oscilloscope?

This is an oscilloscope:
Tektronix Type 422 Oscilloscope
An oscilloscope is a test instrument that displays a graph of voltage verses time which allows the user to visualize electronic waveforms. The vertical axis displays voltage and the horizontal axis is time. Modern oscilloscopes are either analog or digital. It is a must-have piece of equipment for experimenting or working on electronics and very useful to radio amateurs in general.

So what can  you do with an oscilloscope?
  • You can determine how the voltage of a signal changes with respect to time.
  • You can calculate the frequency and period of a waveform.
  • You can test for malfunctioning components causing signal distortion.
  • You can measure a DC voltage in a circuit.
  • You can find what component of a signal is direct current (DC) or alternating current (AC).
  • You can tell how much of the signal is noise and whether the noise is changing with time.
  • You can attach a transducer and measure all manner of phenomena.
  • You can create Lissajous figures.
  • You can measure the timing of events having very brief durations.
  • You can visualize signals.
  • You can build a scope clock.
  • You can check a DC power supply for AC leakage due to a bad capacitor.
  • You can test to determine if components in a circuit are functioning correctly (resistors, capacitors, inductors, and semiconductors).
  • You can measure the phase shift between two sinusoidal signals.
  • You can measure the RMS value of a noise signal.
  • You can use an oscilloscope as a very cool prop in a play or movie.
  • And so much more....

See related articles on NJ2X.COM:
Oscilloscope School
Soldering 101

January 24, 2012

Oscilloscope School

The New Jersey Antique Radio Club held an Oscilloscope School in March, 2011.  The club recorded this excellent 2 hr 21 minute program and provided an on-line textbook.

  • Part 1: History of Oscilloscopes, by Al Klase, Technical Coordinator for NJARC
  • Part 2: Basics of Oscilloscopes, by Alan Wolke (W2AEW), Application Engineer at Tektronix Corporation (begins at 15 min. 42 sec. into the program)
  • Part 3: A Brief History of Oscilloscope Tubes, by Nevell Greenough (begins at 2 hr. 13 min. 35 sec. into the program.)
This is a first rate presentation regarding oscilloscopes and we highly recommend it to anyone interested in this versatile piece of test equipment.

See related articles on NJ2X.COM: