SWR readings-what does this mean?

[Bert2006]

Finally got around to take some SWR readings after completing the Marshal mod last month and here is what I get:

 

Channel 1 - no reading

Channel 20 - got 2.5 once then nothing

Channel 40 - nothing

 

Repeated readings 3 times with chan 20 giving a reading only once. Tried with bike engine on and off.

 

Also noticed that the push to talk button on the passenger armrest does not seem to work, so had my son sit on bike and push the talk buton on the bars while I took readings in the back.

 

When I transmit and am on FWD, I can calibrate but when I then switch to REF the needle buries itself to the left with no movement. Is my antenna too short? I have the 36inch Francis mounted on a fold-down, then the base and then a 90deg to the cb cable. Seems like 4ft units would be way too long.

 

The meter I am using is a Workman Model:SWR -2T,

Impendance 52 ohms,

Acuracy 5%,

Min power for SWR frequency range - 27MHz

 

Any ideas?

 

Thanks

 

[MikeWa]

SWR is Standing Wave Ratio. It is a measurement of how well the transmitter is matched to the antenna. An SWR of 1 is ideal. To high or to low can damage the transmitter. it is adjusted by adjusting the length of the antenna. The readings you are getting are not right. The Workman is an ok unit so I will go back and check the instructions on mine and get back to you.

 

Mike

[MikeWa]

The stock antenna has a loading coil in it to simulate a longer antenna. At only 36 inches your antenna also need some sort of loading coil. Does it have one? If not it is back to the drawing board.

 

Seems like your proceedure is correct but here it is again for those who don't know.

 

Mike

 

ADJUST YOUR SWR on your CB radio

Equipment needed: 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.

[Bert2006]

I am using the same type of antenna for the radio also. Went out and switched the antennas and I now get these readings:

 

Channels 1 to 3 - no readings

Channels 4 to 7 - intermittent readings of 1.5

Channel 8 - 1.5 consistently

Channel 20 - 1.7 consistently

Channel 40 - 2.5 consistently

 

Also noticed that when I try to use the passenger transmit button I get a Cb error message.

 

I took these last readings in my garage and will check again tomorrow with the bike in the open to see if it makes a difference.

 

This is the antennas I am using:

 

http://www.francisantennaonline.com/francis_antenna_3_foot_hot_rod_cb_antenna.html

 

[videoarizona]

I am using the same type of antenna for the radio also. Went out and switched the antennas and I now get these readings:

 

Channels 1 to 3 - no readings

Channels 4 to 7 - intermittent readings of 1.5

Channel 8 - 1.5 consistently

Channel 20 - 1.7 consistently

Channel 40 - 2.5 consistently

 

Also noticed that when I try to use the passenger transmit button I get a Cb error message.

 

I took these last readings in my garage and will check again tomorrow with the bike in the open to see if it makes a difference.

 

 

 

Interesting readings. Where are you connecting the SWR meter? So you swapped antennas and the readings changed. One antenna should be optimized for CB and one not. The CB antenna should have a loading coil on it and a way to adjust the length... Make sure that is the antenna you are using for the CB.

david

Edited August 2, 2014 by videoarizona
spelling...misread post

[Bert2006]

Interesting readings. You said you are using same antenna for both radio and CB. Where are you connecting the SWR meter? Never mind my question...so you swapped antennas and the readings changed. One antenna should be optimized for CB and one not. The CB antenna should have a loading coil on it and a way to adjust the length... Make sure that is the antenna you are using for the CB.

david

 

Essentially when I did the Marshall mod I removed the original antennas and the cb one was center loaded. I replaced them with the 3ft Francis CB antennas. They do not make an am\fm antenna so I used a matching cb antenna for am\fm. The Francis antennas are fiberglass with internal winding. And yes, I had the SWR meter connected properly..

 

[Condor]

Essentially when I did the Marshall mod I removed the original antennas and the cb one was center loaded. I replaced them with the 3ft Francis CB antennas. They do not make an am\fm antenna so I used a matching cb antenna for am\fm. The Francis antennas are fiberglass with internal winding. And yes, I had the SWR meter connected properly..

 

Sorry gotta ask. Did you use a pigtail between the radio and the SWR, and have the antenna connected to the SWR. The reason I ask is that with out putting a load on the radio you will blow the finals, and that's what it sounds like you've done. The finals are gone and you're not putting out a signal... hence... 0 readings...

 

[Bert2006]

Sorry gotta ask. Did you use a pigtail between the radio and the SWR, and have the antenna connected to the SWR. The reason I ask is that with out putting a load on the radio you will blow the finals, and that's what it sounds like you've done. The finals are gone and you're not putting out a signal... hence... 0 readings...

 

 

I connected the cable from the cb to the transmiter input on the meter and a short cable from the meter antenna output to the antenna. I think that is right, never transmitted without the antenna connected in line.

 

Also noticed that when I would be taking readings the tx would not appear on the cb when transmitting. Once I removed the meter and reconnected everything the tx now shows. Weird.

 

[billmac]

pretty sure the readings will be all over the place if your trying to do it in the garage. need to be in the open and away from overhead wires.

[Bert2006]

pretty sure the readings will be all over the place if your trying to do it in the garage. need to be in the open and away from overhead wires.

 

Agree, but the first time it was out in the open and got nothing. The second time was in the garage and asside from not getting readings for the lower channels I was getting some more normal ones as the channels went up. Will try again tomorrow in the open to see what I get.

 

[videoarizona]

I replaced them with the 3ft Francis CB antennas. They do not make an am\fm antenna so I used a matching cb antenna for am\fm. The Francis antennas are fiberglass with internal winding.

 

Understood...

Then I'm curious how you can adjust the SWR with a Francis antenna? There has to be a way to shorten or lengthen, physically or electrically, so you can adjust the swr?? Is there a tiny tip that is adjustable?

 

And the "input" of the swr meter should have the antenna connected...the output of the meter goes to the CB input. The swr meter is electrically between the antenna then the CB. The swr meter should be labelled "ant" and "cb". If that is what you did then you are good to go. If not, reverse. In other words, the antenna should plug in directly to the swr meter...no other connections. The output of the meter needs a small cable to connect it to the cb.

 

Hmm...hard to visualize without images...but lets see how the above fits with what you did...

 

david

[videoarizona]

BTW, I've done swr readings in garages or out in the open. The meter reads electrically between two hard wired points....the garage may change the pattern of the radiated signal, but I don't "think" the swr meter will reflect that. But I'm not an expert...just did some antenna theory/practicals while in radio and tv broadcast.

 

I changed my antenna last week on my VR and did the readings in the garage. Got good readings...so I left it that way. Seems to work very well...

 

FWIW,

david

[Bert2006]

Understood...

Then I'm curious how you can adjust the SWR with a Francis antenna? There has to be a way to shorten or lengthen, physically or electrically, so you can adjust the swr?? Is there a tiny tip that is adjustable?

 

And the "input" of the swr meter should have the antenna connected...the output of the meter goes to the CB input. The swr meter is electrically between the antenna then the CB. The swr meter should be labelled "ant" and "cb". If that is what you did then you are good to go. If not, reverse. In other words, the antenna should plug in directly to the swr meter...no other connections. The output of the meter needs a small cable to connect it to the cb.

 

Hmm...hard to visualize without images...but lets see how the above fits with what you did...

 

david

 

The connection points in the back of the meter I have are labelled 'ant' and 'trans'. When I took my readings the cable coming out of the CB box was connected to the 'trans' and then a jumper was used from the base of the antenna to the 'ant' connection. This would place the meter in-line so I think I did that part right.

 

Thanks

 

[Bert2006]

BTW, I've done swr readings in garages or out in the open. The meter reads electrically between two hard wired points....the garage may change the pattern of the radiated signal, but I don't "think" the swr meter will reflect that. But I'm not an expert...just did some antenna theory/practicals while in radio and tv broadcast.

 

I changed my antenna last week on my VR and did the readings in the garage. Got good readings...so I left it that way. Seems to work very well...

 

FWIW,

david

 

Ok, thanks for that. I got better readings after switching the antennas but took those in the garage. Should be ok.

 

Still do not understand why channels 1 to 6 dont give readings consistently though. Is it possible for a CB unit to stop transmitting on some channels? Also, the PO never used it, is it possible that the unit may be lazy after not being used for so long-sorry this last one may be a stupid question-

 

[Flyinfool]

If the CB is working correctly you should get readings on all channels. My guess is that there is a problem in the CB on those lower channels.

 

When you connect up your SWR meter. Do not use a separate coax from the meter to the antenna base. Use the same coax that will be used to connect the CB to the antenna, just remove the connection from the CB and put it right onto the SWR meter, then you will need a short coax to go from the CB to the SWR.

[Bert2006]

If the CB is working correctly you should get readings on all channels. My guess is that there is a problem in the CB on those lower channels.

 

When you connect up your SWR meter. Do not use a separate coax from the meter to the antenna base. Use the same coax that will be used to connect the CB to the antenna, just remove the connection from the CB and put it right onto the SWR meter, then you will need a short coax to go from the CB to the SWR.

 

Ok, thanks for that. To clarify, on the 2nd gen and as per the Marshall mod, the cb outputs through a Motorola plug that has a Pl-259 at the other end of an 18inch long cable to connect to the antenna. You cannot connect to the cb with a different cable due to the Motorola plug issue. So I connected the meter in-line using the Pl-259 end of the cable from the CB. Then using a short 16 inch cable with Pl-259 connectors on both ends I connected to the antenna base.

 

[dacheedah]

I have a pair of short test cables cable with a motorola plug on one end and the pl259 connector on the other to connect to the swr meter. I don't thing the connection matters much as long as you have short runs and the swr is connected correctly.

 

Remember to put the trunk back in place and load it as you normally would.

 

Best to go outside, no overhead power lines . . .

 

The antenna you are using is supposed to be "pre tuned" and all I can say is tuning to your application will give better results.