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

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.