Model 21-520A

This piece of Micronta Test Equipment is designed for use with CB and Ham Transceivers. It will be very helpful in determining if your transmitter and antenna system are operating properly.


RF Power:0 to 10, 0 to 100, 0 to 1000 Watts
SWR:Calibrated from 1:1 to 3:1
Impedance:For 50/52 ohm systems only
Frequency Range:3 to 30 MHz (Useable at 144 MHz)
Connectors:Coaxial SO-239 (accepts PL-259)
Dimensions:3 3/8" X 8 1/4" X 4 1/2" (HWD)
(8.5 X 21.0 X 11.5 cm) (HWD)
Weight:29.3 oz (830g)

POWER Function -

There are three ranges of power: from 0 to 10 watts (for CB) and 0-100 and 0-1000 for Ham and business-type transceivers. The 3-position switch between the Meters selects the power range.

NOTE: The Power Meter readings will be accurate only with 50/52 ohm antenna systems (or 50/52 ohm dummy loads).

SWR Function -

Standing Wave Ratio (SWR) measurements are very important for any transmitter-antenna system. SWR is a measurement of mismatch between the transceiver and the antenna system. For maximum efficiency, the SWR must be as low as possible - this means that all of the power from the transmitter is being radiated from the antenna. A high SWR means there is a mismatch and that some (or even most) of the transmitter's power is not being radiated by the antenna, but is being "returned" to the transmitter.

You can read SWR directly on the SWR meter. It is calibrated from 1 to 3, with a red line above 3. When the meter reads 1, the antenna system is perfectly matched to the transmitter and you have an SWR of "1" - or to be more accurate, 1 to 1 (SWR is a ratio). If your reading is more than 3, you should correct the mismatch between the transmitter and antenna system.

You'll note a second set of numbers directly below the SWR value - these are the "percentage of reflected power" values. Since SWR is the direct result of mismatch, which produces "reflected waves" (not all the power is radiated by the Antenna - some of it is reflected back to the Transmitter) this will give you an idea af the actual efficiency of your system.

For example, an SWR of 1.5 (more accurately we shculd say "SWR of 1.5 to 1") means 4% of the power is coming back and only 96% of the available energy is absorbed by the Antenna. An SWR of 2 to 1 means 11% is reflected; and 3 to 1 is 25% reflection.

There are no "percent reflected power" markings on my meter.

NOTE: If you are interested in learning more about SWR, we recommend that you spend some time in your local public library in the technical section (the ARRL HANDBOOK is particularly helpful).


Connections are very simple.
  1. Disconnect the Antenna cable from the back of the Transceiver.
  2. Connect the Antenna cable to the ANT connector on one end of the Pick Up Box.
  3. Use a short piece of coaxial cable and connect between the TRANS connector on the other end of the Pick Up Box and the back of your Transceiver.

NOTE: A "jumper" coax cable such as noted above can be obtained from your local Radio Shack store.

IMPORTANT NOTE: POWER and SWR readings will be accurate only when used with antenna and transmission lines which have an impedance of 50/52 ohms.


When connections are made as noted above, you are ready to use your Tester. Be sure each connector is tightened securely and that your cables are good.


For CB you'll just leave the 3-position switch set to 10 and read watts output (from the Transceiver) dividing Meter reading by 10 to obtain 0-10 reading. If you have a Ham rig or are working with a business band transceiver (or other higher powered unit), place the 3 position Switch to 100 and read directly on the meter, or set to 1000 and multiply the Meter reading by 10.


To measure Standing Wave Ratios, set CAL/SWR switch to CAL position. Press the Push-to-talk button on your Mic. Adjust the CAL control for a reading to the SET mark on the Meter. Return the CAL/SWR switch to SWR position and read your SWR on the Meter.

If you have a reading of 1.5 or lower, you have a very efficient antenna system. If the reading is between 1.5 and 3, you may want to try lowering it (although in most cases, an SWR of 3 or less will be acceptable). lf you have a reading of over 3, you should check your antenna system and make adjustments as required to obtain a lower reading.

Adjustments for reducing SWR will depend entirely on your antenna system. We can only give you a few general pointers. Be sure you are using a 50/52 ohm antenna system and cable. Be sure all connectors are secure. Be sure your cables are good (no shorts or deterioration of the cable). If your antenna can be adjusted (see the instructions which come with the antenna), adjust it in small increments. If it is a mobile installation, check to be sure all mechanical connections have been made correctly. Make sure the antenna is vertical; move it away from metal bodies (if possible). For mobile installations, sometimes just a minor change in the positioning or location of the antenna can greatly improve the SWR.