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How to Measure SWR on the AM Radio by Your Own?

Date:2021/3/15 12:29:00 Hits:



How to measure SWR? What equipment is needed? The following content will introduce you in details about how to measure SWR on your radio on your own!


1) AM Radio Trouble Shooting

You will need these: SWR meter, short jumper coax 3 foot.

Procedure:   

The SWR meter needs to be placed in line between the antenna and the CB. Connect the antenna (normally connected to the back of the CB ) to the connector marked “Antenna” or “Ant”  on your SWR Meter. Connect one end of the short jumper coax to the “transmit” or “Xmit” on the SWR meter. Connect the other end of your jumper coax to the CB.


Assuming you have a standard SWR meter the switches should read as follows: REF or SWR, FWD, and there should be a slide switch marked “set” or “Adjust”. If different consult your meter’s owners manual.


With the radio on the lowest channel (1 on CB) and the SWR meters switch in the Forward (FWD) position, depress the transmit switch (key up) located on the microphone. While holding the unit in this transmit mode, adjust the meter needle to the set position using the Set or Adjust knob on the meter. As soon as the needle is in alignment with the corresponding mark on the meter face, flip the switch to the Reference (REF) position. The meter is now showing your SWR on channel one. Note the value and quickly release the microphone switch. Record this reading.


Repeat the previous step on channels 19 and 40.


How to read your results:  

If SWR on channels 1, 19 & 40 is below 2.0, your radio can be operated safely.

If SWR on all channels is above 2.0 but not in the “red zone” (normally over 3.0), you may be experiencing coaxial cable reaction (bad quality, wrong length, etc.), insufficient ground plane, or have an ungrounded antenna mount.

If SWR is in the “red zone” on all channels, you probably have an electrical short in your coax connectors, or your mounting stud was installed incorrectly and is shorted. Do not operate your radio until the problem is found, serious damage can occur to your radio.

If SWR on the lowest channel is higher than it is on the highest channel, your antenna system appears to be electrically short. Your antenna length may need to be increased.

If the SWR on channel 40 is greater than that on channel 1, your antenna is considered to be “LONG” and reduction of physical height and/or conductor length will correct this situation.


Conclusion: 

A “bad” SWR can destroy a radio or amplifier in a worst case scenario, but in most cases it will just mean that your system isn’t working great and will sound like crap.

The standing wave ratio is exactly what its name depicts. It’s a ratio based on how much power can be delivered to your antenna VS the amount of power that is reflected by your antenna back down the coax to your radio.

A perfectly performing antenna would turn all the of wattage reaching it into signal and you would have no reflected energy going back down your coax. But many things such as a poorly tuned antenna, or any antenna of the wrong length, a badly grounded antenna, faulty coax, or any number of other things could cause a bad SWR reading.


2) SWR Reading Range Explanations:

Name

Range

Conditions

Suggestions

SWR

< 1

You might have a bad SWR meter, something wrong with your antenna or antenna connection, or possible have a damaged or defective radio.

If your SWR is below 1, please make sure you have a good SWR meter, and remember to 
1. Check your antenna by inspecting its quality or re-connect the antenna if it is not working well. 
2. If everything is OK but the reading range of your SWR meter is still below 1, make sure your receiving device (radio, etc.) is still well-working by checking whether it is damaged or become defective.

SWR

1.0-1.5

The ideal range! If your SWR is under 1.5, you're in great shape.

If you're at 1.5 and really, really want to drop down to closer to 1 it's likely possible to do with addition tuning, different equipment or a different mounting location. But the drop from 1.5 to 1.0 won't make a substantial increase in performance. It's not nearly as noticeable as, say, going from 2.0 down to 1.5.

SWR

1.5 - 1.9

There's room for improvement, but SWR in this range should still provide adequate performance.

Occasionally, due to installations or vehicle variables, it's impossible to get SWR lower than than this. You should try to get it lower, but performance should still be acceptable in this range. If you've tuned the antenna, SWR in this range is likely an issue of a less-than-ideal mounting location for your vehicle and/or an antenna that isn't ideal for the mounting location. To troubleshoot, see this article on problematic CB antenna mounting locations.

SWR

2.0 - 2.4

While not good, this likely won't damage your radio with casual use.

However, you should definitely try to improve it if you can. SWR in this range is usually caused by a poor antenna mounting location and/or a poor choice of equipment for your specific vehicle. To troubleshoot, you'll likely need to move the mounting location and/or use a more suitable antenna. It's by no means a good tuning job, but will function if you've exhausted all other troubleshooting possibilities.

SWR

2.5 - 2.9

Performance in this range will be noticeably decreased, and you might even damage your radio if you transmit frequently and for extended periods.

We advise you not to operate your radio in this range. SWR in this range is usually caused by a poor mounting location and/or a poor choice of equipment for your specific vehicle. To troubleshoot, you'll likely need to move the mounting location and/or use a more suitable antenna.

SWR

3.0+

Performance will be severely affected, and you're likely to damage your radio with extended transmission use.

You SHOULD NOT transmit with your CB at SWR levels above 3.0. If your SWR needle swings all the way to the right (off the charts) when getting your 3.0+ readings, you almost certainly have a major installation problem. This is almost always the result of a poor ground or incorrectly assembled stud, but on rare occasions can indicate a faulty coax, antenna, or incorrectly attached SWR meter.

Extra reading:

If the SWR reading on channel 1 is higher than the reading on channel 40, your antenna system is too short and you need to lengthen your antenna.

Alternatively, if the SWR reading on channel 40 is higher than channel 1, your antenna system is too long and you need to shorten your antenna system.
Please see our article for additional important information: How to Tune a CB Antenna


IMPORTANT NOTE: 

Radio damage will only occur when you're TRANSMITTING from an antenna with high SWR readings.  Leaving the radio on to receive signals poses no risk to your radio.


If you have already optimized your current antenna setup (similar readings on Channel 1 and 40) and you still want to improve your SWR readings, you can try a different antenna, a different mounting location, or, if you are setting up a dual antenna system, try utilizing only one of the antennas instead of both. Sometimes, you will get better performance from using one antenna instead of two.



Also read: 

What is Low Pass Filter and how to build a Low Pass Filter?

What is VSWR and how to measure VSWR?

How to DIY your FM Radio Antenna|Homemade FM Antenna Basics&Tutorials

How to Eliminate Noise on AM and FM Receiver

Simple and Budget DIY - How to Make An FM Transmitter?


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