Is it possible to get an SWR reading BELOW 1.0?

[High_Speed]

I need some help on my latest mobile install. I've installed a Uniden Bearcat 980 in a Ford Explorer. I've placed a Wilson 500 mag mount on the roof, dead center. After checking the SWR, I was originally setting at 1.15 on channel 1 and around 1.75 on channel 40. I began trimming the bottom of the whip in very small increments (approximately 1/8 of an inch each time) until I've finally landed with an SWR reading of 1.0 on channel 1 and 1.43 on channel 40. These are all from my radios internal diagnostics meter, however I have confirmed them all with an external analog SWR meter. With the external meter, channel 1 shows more like 1.05 maybe while 40 appears to be more like 1.5 (with the analog needle meter). Channel 19 reads 1.12 with my radios meter, and looks like 1.2 with the analog meter.

My question is if I continue to trim a little bit off the bottom, will the higher channels come down a little more while channel 1 stays at 1.0? Or, will channel 1 drop BELOW 1.0, while the higher channels come down a little more? OR, will channel 1 begin to go back up, while the higher channels come down to meet it?

Secondly, I have done nothing special as far as grounding or bonding. I did run 10 gauge power leads directly to the battery terminals, but I've done no other "grounding." Should I look into bonding straps anywhere?

[Deleted User 14541]

You can't get lower than 1:1. The numbers you have now are great. If you get the swr equal on ch 1 and 40 you will get the lowest reading on ch 19 since it is the center frequency of the band...channel 20 is close enough but 27.185 (ch19) is the center of the 11 meter band.

Picture swr on a graph having a v shape. When you tune it for the center of the band swr on 1 and 40 will be the high points of the V. Swr on 1 and 40 is equal and the highest reading. Ch 19 will be the lowest point of the V. When you trim the antenna you are moving the whole V up or down in frequency.

Firestick has some good antenna tuning info. Some of it isn't true but most is good stuff for a beginner. [Please login or register to view this link]

[milkman21218]

The 1:1 is flat. And you can't any better than flat!

[The DB]

There are any number ways of calculating SWR depending on the information available to you. The easiest way to try and explain it is it is a measure of forward power and reflected power, and is displayed as a ratio. The so called "perfect" ratio is some amount of forward power (however much it may be), and no reflected power. As you can't have a negative amount of reflected power, you cannot have an SWR of under 1 : 1. Get SWR to a certain point and be done with it. Don't fret if you have a 1.5 : 1 SWR, and typically 2 : 1 SWR is acceptable unless you are dong something like overdriving and overvolting an amplifier... In the real world you will never notice the difference between a 1 : 1 SWR and a 2 : 1 SWR.

There are a lot of things people will say about SWR, and most of it is incorrect. Don't get overly hung up on it, if you do and you progress to the point of using an antenna analyzer, it will hold you back. You will note that above I mentioned the 'so called "perfect" SWR'. Contrary to populat belief, very rarely does the strongest signal at a given frequency happen when the antenna is tuned to the lowest SWR...


The DB

[High_Speed]

Thanks for the info. So I know 1.0 is as low as it's going to go, so I'm going to leave this antenna alone from here. However, that leaves me curious for the sake of curiosity.


My question remains that if I were to continue to trim a little bit off the bottom, will the higher channels come down a little more while channel 1 stays at 1.0? OR, at 1.0 on channel 1, have I reached a crossing point where the higher channels is not going to get any lower without adversely raising the SWR on the lower channels? Thus would channel 1 begin to go back up, while the higher channels come down to meet it?

[1206FL]

Yes you can keep trimming. Keep it at 1/8" increments. You are now tuned to the lower portion of the cb band. You can take a bit more off and vswr should come down as it seems this is the progression your have already made. Trimming what you did got you down to 1.0 at 1 and what it channel 19? Should be about 1.22 or around there. 40 is 1.43 currently. Keep cutting of you want. The readings you have aren't bad. But you can most likely achieve a lower vswr reading across the entire band with a bit more trimming. 1/8", no more than that at a time. If for some reason channel 1 starts rising trim until 1 and 40 are close. Hope this helps. But as others have stated its not all about VSWR. There are other factors. But for GP yes you can cut a bit more off and get 40 down some I would think. JMO. Good day.

[MDYoungblood]

Once you get the center frequency (for CB it's channel 19, 27.185.0) to 1:1 continuing to trim the whip will move the resonance higher, luckily the Wilson gives you enough playroom on the whip to fine tune if you cut too much. Most antenna manufacturers make their antennas long because they don't know it's application, the location, desired frequency, etc., it's easier to trim to length than to add to it.
I was one of those that believed a low SWR was what you needed until I bought a antenna analyzer, now I agree with DB and adjust to resonance.

3's

Greg