CB Radio re SWR question...ANSWERED (update)

[Cloud_Dancer]

Back in 2003, MH came with optional CB antenna installed (no ground plane model). I installed a Cobra 29 LTD Classic radio, and as per usual didn't bother to read the manual.
It never had more than a couple of miles of range. I mostly used it as a walkie talkie, in conjunction with a handheld Radio Shack CB radio, for instructions when backing up.
Recently, after a long period of NOT using the CB, I turned it on and it would not transmit. I read the manual, and started trying to learn about tuning the antenna. I first checked the antenna for shorts and opens. Then, using the procedure as per the manual, I went through the motions of shortening and lengthening the antenna such that I finally achieved 1.5 SWR on channel 1 and 1.5 on channel 40. However, on channel 20 the SWR is "off the scale" (about minus .5).
On the road, the range of use for me is channel 9 to 19, both of which show a SWR of less than 1. In fact, the range of channels with 1 or less SWR is channel 8 through 26.
So, the main question I have is: Are these SWR readings good enough for normal operation, or is there something wrong with the antenna system?

BTW the no TX problem that I started out with was that the knob settings were messed up. I finally learned what each knob is supposed to do, and got it to work like it used to work (short range, walking distance). Now, I'd like to know the answer to my question because I now would like to optimize the TX/RX range on the highway.
Thanks

[WyoTraveler]

Fmiser wrote:

Cloud Dancer wrote:
Back in 2003, MH came with optional CB antenna installed (no ground plane model).
Recently, after a long period of NOT using the CB, I turned it on and it would not transmit.

What do you mean by "would not transmit"? When you push the button, the red "transmit" light doesn't turn on? Or you can't hear any audio on a receiver? Or it won't break the squelch on a receiver?

I first checked the antenna for shorts and opens.

Just the antenna? Or antenna and cables? Typically a no-ground-plane antenna will show infinite ohms when tested with an ohm meter.

Then, using the procedure as per the manual, I went through the motions of shortening and lengthening the antenna such that I finally achieved 1.5 SWR on channel 1 and 1.5 on channel 40. However, on channel 20 the SWR is "off the scale" (about minus .5).

This suggests the radio will transmit, since setting SWR involves transmitting.

SWR is "standing wave ratio", and is a measure of how much of the signal sent out by the transmitter is reflected by an impedance mismatch at the antenna. If 100% of the signal goes out and zero is reflected, the SWR is 1:1. So "minus 0.5" would mean the antenna transmits more signal than the radio puts out - which is impossible. *smiles*
On most meters, an SWR of 1:1 will be almost no meter movement. So if the meter hardly moves then it's a good thing.

On the road, the range of use for me is channel 9 to 19, both of which show a SWR of less than 1. In fact, the range of channels with 1 or less SWR is channel 8 through 26.
So, the main question I have is: Are these SWR readings good enough for normal operation, or is there something wrong with the antenna system?

Absolutely. The goal is an SWR of less than 1.5:1. But there could still be something wrong with the antenna system.

BTW the no TX problem that I started out with was that the knob settings were messed up. I finally learned what each knob is supposed to do, and got it to work like it used to work (short range, walking distance). Now, I'd like to know the answer to my question because I now would like to optimize the TX/RX range on the highway.
Thanks

Ah. Got it. So it is transmitting. A significant point - SWR has almost nothing to do with transmit or receive range. The reason we care about SWR is to keep the radio happy. So if you are perusing range, SWR is the wrong rabbit to chance. The efficiency of the antenna is where to look.

So, with a good SWR, you won't damage the radio. But to get good range, the cable and antenna need to be doing a good job of getting the signal in the wire into the air. The best way to test this is by measuring field strength - which can be coarsely done with just another receiver - like your handheld radio.

Not totally true. First most transmitters are 50 ohms. Most mobile antennas are 25 ohms. most mobile transmitters have a 2:1 SWR. Whoa, mine has an SWR of 1:1. Yes, but! You most likely have a transmitter that is 50 ohms, an antenna that is a 25 ohm resistive load and a either an inductive or capacitive reactance impedance of 25 ohms. Still a 2:1 match. Your finals in the transmitter like it. You like it but the facts of life are it is still not really a 1:1 SWR. Sorry to bust your bubble. First you have to know what is the true resistance of the antenna. Then what is the reactance and in which direction. Once we know that we can make the transmitter happy by adding either capacitive or inductive reactance to make the transmitter happy. So 1:1 may be better for the transmitter and may make you feel better but it still isn't getting the power to the antenna. I know, pretty deep stuff for CB but still very interesting to know what is really going on. If your antenna is capacitive by a high amount you can add inductance. if your antenna is inductive by a high amount you can add capacitance. You buy these magic cans or wind coils yourself to make things look better at the antenna. The solution? Get a better antenna. On CB get a full 102 inch whip. You will be putting more signal out there and not just think all is OK. JMHO.

[old_guy]

lack of proper ground is your problem. back in the old days I had that problem and a friend of mine cleaned up the ground and I blew the doors off the truck with power and distance. I know you said you had the no ground model of antenna but that is still your problem

[Cloud_Dancer]

Thanks for all the replies, kinda makes me feel like I'm back in school.
Let me first say that the SWR meter that I'm using is NOT high-quality. It's the one that's built-in, on the front panel of the radio. It's rectilinear with vertical needle. It's small, .410" x 1.185". It has 3 horizontal scales; SWR, RF, SIG. The "green" of the SWR scale goes to 3, and the remainder is "red".
In the off position the needle is at .062" less than the start of the "green", which is 1. On the S/RF mode, when main switch is turned ON the needle does not move, but you can make it start moving by cranking up the RF Gain knob past about 65%.
OK, I realize that the above info might not mean anything, but I find it odd that the needle goes below 1 (in SWR mode).
Anyway, after reading all your replies up to this point, I will probably decide to experiment further, like adjusting the antenna to 1.5 SWR on channel 14, and then do some more field testing.
Also, I will now Google KOBG, and see about learning some basics on antenna installation and technical design points.

I'll report back when I have something. Thanks again

[Fmiser]

Cloud Dancer wrote:
Back in 2003, MH came with optional CB antenna installed (no ground plane model).
Recently, after a long period of NOT using the CB, I turned it on and it would not transmit.

What do you mean by "would not transmit"? When you push the button, the red "transmit" light doesn't turn on? Or you can't hear any audio on a receiver? Or it won't break the squelch on a receiver?

I first checked the antenna for shorts and opens.

Just the antenna? Or antenna and cables? Typically a no-ground-plane antenna will show infinite ohms when tested with an ohm meter.

Then, using the procedure as per the manual, I went through the motions of shortening and lengthening the antenna such that I finally achieved 1.5 SWR on channel 1 and 1.5 on channel 40. However, on channel 20 the SWR is "off the scale" (about minus .5).

This suggests the radio will transmit, since setting SWR involves transmitting.

SWR is "standing wave ratio", and is a measure of how much of the signal sent out by the transmitter is reflected by an impedance mismatch at the antenna. If 100% of the signal goes out and zero is reflected, the SWR is 1:1. So "minus 0.5" would mean the antenna transmits more signal than the radio puts out - which is impossible. *smiles*
On most meters, an SWR of 1:1 will be almost no meter movement. So if the meter hardly moves then it's a good thing.

On the road, the range of use for me is channel 9 to 19, both of which show a SWR of less than 1. In fact, the range of channels with 1 or less SWR is channel 8 through 26.
So, the main question I have is: Are these SWR readings good enough for normal operation, or is there something wrong with the antenna system?

Absolutely. The goal is an SWR of less than 1.5:1. But there could still be something wrong with the antenna system.

BTW the no TX problem that I started out with was that the knob settings were messed up. I finally learned what each knob is supposed to do, and got it to work like it used to work (short range, walking distance). Now, I'd like to know the answer to my question because I now would like to optimize the TX/RX range on the highway.
Thanks

Ah. Got it. So it is transmitting. A significant point - SWR has almost nothing to do with transmit or receive range. The reason we care about SWR is to keep the radio happy. So if you are perusing range, SWR is the wrong rabbit to chance. The efficiency of the antenna is where to look.

So, with a good SWR, you won't damage the radio. But to get good range, the cable and antenna need to be doing a good job of getting the signal in the wire into the air. The best way to test this is by measuring field strength - which can be coarsely done with just another receiver - like your handheld radio.

[Fmiser]

Cloud Dancer wrote:
Back in 2003, MH came with optional CB antenna installed (no ground plane model).
Recently, after a long period of NOT using the CB, I turned it on and it would not transmit.

What do you mean by "would not transmit"? When you push the button, the red "transmit" light doesn't turn on? Or you can't hear any audio on a receiver? Or it won't break the squelch on a receiver?

I first checked the antenna for shorts and opens.

Just the antenna? Or antenna and cables? Typically a no-ground-plane antenna will show infinite ohms when tested with an ohm meter.

Then, using the procedure as per the manual, I went through the motions of shortening and lengthening the antenna such that I finally achieved 1.5 SWR on channel 1 and 1.5 on channel 40. However, on channel 20 the SWR is "off the scale" (about minus .5).

This suggests the radio will transmit, since setting SWR involves transmitting.

SWR is "standing wave ratio", and is a measure of how much of the signal sent out by the transmitter is reflected by an impedance mismatch at the antenna. If 100% of the signal goes out and zero is reflected, the SWR is 1:1. So "minus 0.5" would mean the antenna transmits more signal than the radio puts out - which is impossible. *smiles*
On most meters, an SWR of 1:1 will be almost no meter movement. So if the meter hardly moves then it's a good thing.

On the road, the range of use for me is channel 9 to 19, both of which show a SWR of less than 1. In fact, the range of channels with 1 or less SWR is channel 8 through 26.
So, the main question I have is: Are these SWR readings good enough for normal operation, or is there something wrong with the antenna system?

Absolutely. The goal is an SWR of less than 1.5:1. But there could still be something wrong with the antenna system.

BTW the no TX problem that I started out with was that the knob settings were messed up. I finally learned what each knob is supposed to do, and got it to work like it used to work (short range, walking distance). Now, I'd like to know the answer to my question because I now would like to optimize the TX/RX range on the highway.
Thanks

Ah. Got it. So it is transmitting. A significant point - SWR has almost nothing to do with transmit or receive range. The reason we care about SWR is to keep the radio happy. So if you are perusing range, SWR is the wrong rabbit to chance. The efficiency of the antenna is where to look.

So, with a good SWR, you won't damage the radio. But to get good range, the cable and antenna need to be doing a good job of getting the signal in the wire into the air. The best way to test this is by measuring field strength - which can be coarsely done with just another receiver - like your handheld radio.

[Fmiser]

Cloud Dancer wrote:
Back in 2003, MH came with optional CB antenna installed (no ground plane model).
Recently, after a long period of NOT using the CB, I turned it on and it would not transmit.

What do you mean by "would not transmit"? When you push the button, the red "transmit" light doesn't turn on? Or you can't hear any audio on a receiver? Or it won't break the squelch on a receiver?

I first checked the antenna for shorts and opens.

Just the antenna? Or antenna and cables? Typically a no-ground-plane antenna will show infinite ohms when tested with an ohm meter.

Then, using the procedure as per the manual, I went through the motions of shortening and lengthening the antenna such that I finally achieved 1.5 SWR on channel 1 and 1.5 on channel 40. However, on channel 20 the SWR is "off the scale" (about minus .5).

This suggests the radio will transmit, since setting SWR involves transmitting.

SWR is "standing wave ratio", and is a measure of how much of the signal sent out by the transmitter is reflected by an impedance mismatch at the antenna. If 100% of the signal goes out and zero is reflected, the SWR is 1:1. So "minus 0.5" would mean the antenna transmits more signal than the radio puts out - which is impossible. *smiles*
On most meters, an SWR of 1:1 will be almost no meter movement. So if the meter hardly moves then it's a good thing.

On the road, the range of use for me is channel 9 to 19, both of which show a SWR of less than 1. In fact, the range of channels with 1 or less SWR is channel 8 through 26.
So, the main question I have is: Are these SWR readings good enough for normal operation, or is there something wrong with the antenna system?

Absolutely. The goal is an SWR of less than 1.5:1. But there could still be something wrong with the antenna system.

BTW the no TX problem that I started out with was that the knob settings were messed up. I finally learned what each knob is supposed to do, and got it to work like it used to work (short range, walking distance). Now, I'd like to know the answer to my question because I now would like to optimize the TX/RX range on the highway.
Thanks

Ah. Got it. So it is transmitting. A significant point - SWR has almost nothing to do with transmit or receive range. The reason we care about SWR is to keep the radio happy. So if you are perusing range, SWR is the wrong rabbit to chance. The efficiency of the antenna is where to look.

So, with a good SWR, you won't damage the radio. But to get good range, the cable and antenna need to be doing a good job of getting the signal in the wire into the air. The best way to test this is by measuring field strength - which can be coarsely done with just another receiver - like your handheld radio.

[gotsmart]

Here are tuning instructions, and a video:

http://www.rightchannelradios.com/tuning-cb-antenna-adjusting-swr

[WyoTraveler]

The problem could be more than just swr. If you don't understand swr you can't possibly tune your antenna. Your cb xmtr is 50 ohms. You need to know the resistive load of the antenna. Does it have XL or XC as part of that load? A good place to start is google K0BG. His web page has a lot of real good info on tuning mobile antennas. His info applies to all antennas not just ham antennas. You need to be able to measure the resistance and reactance of the antenna to totally understand what is happening.

[TucsonJim]

Actually, if your range of use is 9-19, set the CB to channel 14 and tune the antenna for an SWR of 1:1. The other channels (frequencies) will deviate from 1:1 due to the wavelength of the frequencies. Unless you have an automatic tuner for the antenna, there is nothing you can do about that. I'd just optimize 14 and leave it alone. It should be acceptable for use from there.

Jim - KC6AHF

[Dyngbld]

I have built several antennas over the years. I would tune the CB antenna for best SWR at 27.20500Mhz (ch 20) and not mess with it from there.

Sounds to me like you have other issues, what is the output power of the radio?
Keep in mind technically 5watts is all that is legal for a CB. Not seeing your setup I really am not much help. Find a Ham Radio operator locally they should be able to help you out.

[n7bsn]

Something is wrong, just what I don't know. But be advised that SWR is not the final answer, if I position a short in a coax "just so" I can get an SWR of 1:1

I'm not certain what the "minus" SWR really means, since SWR is a ratio and a "minus" reading is, well, frankly nonsense.