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

[Fmiser]

hershey wrote:

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.

So using your theory, we can just stick a coat hanger in the back of the cb radio and we're as good as we can get when it comes to transmissions???? Maybe move it to the roof for a better view?
I'm being sarcastic I know but, I don't think your theory is accurate.

The principle is accurate. There are thousands of radios and antennas in use right now that are demonstrating this principle. A longer antenna is better than a shorter one, but let's stick to your coathanger idea.

If you were to just stick a coathanger wire out the back (but make sure we have a connection to ground too), the SWR would likely be very high and the radio would be "unhappy". Since we are stuck with the coathanger, let's add an antenna tuner. This is a inductor and/or capacitor network that changes the impedance that the radio sees and thus can keep the radio "happy". So now our SWR is 1:1, the radio is happy, and the antenna is no better or worse that it was before. Changing the SWR had no effect on the energy leaving the antenna.

The conclusion - get a better antenna or better location if you want better signal strength. SWR is the wrong rabbit to chase.

[MrWizard]

SWR of 1:1 on mid band is the MAX that can be achived
larger numbers are bad

SWR is term it means Standing Wave Ratio

or 'reflected power', power reflected back to the transmitter, power NOT going out

the 'capactance' and 'reactance' of the antenna circuit determines SWR

adjusting aka tuning the antenna circuit is done to minimize this reflection
and get max efficiency aka watts out the antenna and hence transmit range

all of this is affected by terrain

the best place to 'tune' the antenna is the middle of an open field
not always easy to find, a large empty stadium parking lot can be a good place

[hershey]

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.

So using your theory, we can just stick a coat hanger in the back of the cb radio and we're as good as we can get when it comes to transmissions???? Maybe move it to the roof for a better view?
I'm being sarcastic I know but, I don't think your theory is accurate.

[Cloud_Dancer]

OK, I'm back.

At one point I was ready to purchase a Firestick antenna, fiberglass roof mount model. It comes with a dedicated/mandatory 17 ft cable (do NOT modify). I gave up on this idea after I found out where and how Newmar ran the original coax cable (it was trapped, does not budge, can't access it).
Went back and reviewed everything I had read and learned (kinda) from y'all and from all the googling, plus from the Cobra manual.
I ran into an explanation about why there's no need to tune the antenna further, after you achieve 1.5 SWR on channels 1 and 40. It sounded good, so I went back and reviewed Squelch, DynaMike, RF Gain, etc. After playing with the radio adjustments, I started hearing truckers talking on channel 19 (they were on I-10, which is 4 miles away). THAT was good enough for me, so I quit.
I now believe my problem was my own ignorance regarding which way to knobble the knobs. I don't think there was anything wrong with the antenna.
Just another case of "the school of hard knocks".
I thank you again for your patience, and for all your help.

[SCVJeff]

RoyB wrote:
---snip---
Always another project to get things like you want them. I used to get to listen to all of the local POLICE/RESCUE SQUAD frequencies but most of them in VIRGINIA now has gone to the digital mode... All I hear now is a loud BRRRRR when they transmit... geesch... Those scanners cost $400-$500 so I guess I won't be doing that anymore...

Roy Ken

If you ever do decide to dive in and buy an APCO25 scanner, make sure that the comms you want to listen to are not encrypted. If that's the case you'll be right back where you started and -$500 poorer..

[Cloud_Dancer]

I apologize!
I composed a long explaination, and got in a big hurry checking spelling and screwed up and deleted my draft. I'll try later 'cause right now I gotta go do something else. Sorry

[RoyB]

I run the ICOM 706MKII with a TARHEEL HF screwdriver LIL-TARHEEL and two Comet SBB-7 top rear door mount 2M/440 on each side of the F150 truck for the ICOM VHF/UHF portion and another Kenwood 2m/440 rig in my console. I use two of those Kenwood KES-5 mobile speakers mounted in my drivers door side pocket. All sounds great right next to my knees... My LIL TARHEEL screwdriver didn't work all that well mounted to the top of the bed rail up close to the rear window. I added a pretty good flat braided ground strap to it its connector and grounded down at the frame which helped alot.

My remote ICOM head and the other 2m/440 remote head are mounted at a angle in on of the BLACK DESIGNER SPECIALTY three gang switch plates (LOWES). Got it velcroed at an angle down where the bottom of the upright truck console meets the console between the two captain seats in the truck. Perfect spot for my radio control heads.. My two remote microphones are hanging on the console between the two captain seats next to my right leg... Must be a good install as no complaints for mommabear yet. Also no holes in the roof on this install hehe...

I am tore plum up however from radio RFI coming from the trucks electronics on some of my favorite bands... Never have attemped to solve that noise yet... The FUEL TANK sender will be the first RFI mod I will do...

I have a nice small console mounted FWD/REVERSE RF power meter for the ICOM and my screwdriver tunes up great on the HF bands from indoor remote tuning switch...

Always another project to get things like you want them. I used to get to listen to all of the local POLICE/RESCUE SQUAD frequencies but most of them in VIRGINIA now has gone to the digital mode... All I hear now is a loud BRRRRR when they transmit... geesch... Those scanners cost $400-$500 so I guess I won't be doing that anymore...

Roy Ken

[wa8yxm]

By the way.... Not a CB but a ham rig (kenwood TS-2000) I occasionally have transmit issues due to a broken wire on the mic plug.

I just replaced the entiere plug with a much improved model.. (NOTE this plug likely won't fit your CB, I mean it's 8 pin, most CB use 4 pin but broken wires happen on 4 pin as well).

Then I went to work on the dash radio in the RV.. I'm 99% sure I got it's problem too.. Will know for sure in a couple of months after running over many bumps and rail road tracks and the like.

[RoyB]

Just keep in mind what you are working with..

With the 11-meter band it really doesn't matter much what you do to your antennas for tweaking this and tweaking that as you will still only be able to get two or three miles down the road. It is just the nature of the frequency being used.. When the skip is in on those frequencies then the 3-4 WATTS RF output may reach around the world but won't go more than two to three miles down the road.

Have dual antennas on the RV motorhome side mirrors works great like the truckers do. Finding a good groundplane spot on the roof is almost impossible. Their is no metal on most of the RV roofs...

Since the CELLPHONE ERA has come out now full force most all communications now between family members is using cellphone or amateur radio going through the repeater systems...

Just my take on the subject...
Roy Ken

[Cloud_Dancer]

I'm encountering obstacles such as this one:

This is a quote from the Firestik.com website.

"TESTING CONTINUITY

Checking your CB antenna system for continuity, shorts and opens is a MUST process and should always precede SWR checks and settings. Exception: Cable supplied with 'No Ground Plane' antenna kits will have continuity between the center lead and ground."

Surely they're not saying that the signal wire in the center is grounded? What am I missing?
On mine, the center wire in the coax ONLY has continuity to itself.

[WyoTraveler]

SCVJeff wrote:
I don't think anyone is going to install a 102" whip on a Motorhome, let alone build a mount to hold it that won't tear off the roof. It's just 11 mtrs

You are right about that. However, I was pointing out a 102 inch whip puts out more. Putting one on may be a problem to overcome. I have a 20 meter whip mounted 18" off my MH ladder. Just trying to point these guys in the right direction. Of course all amateurs should read K0BG web site about Mobile antenna matching. SWR is kind of old school. Technology has changed over the years. I've been mounting mobile antennas since about 1956. The CBer needs to find a good ham neighbor or go to CB shop that understands why the antenna isn't doing what it is designed to do. If it worked before it may be as simple as a bad coax because of moisture or a corroded lead. Like posted prior by another amateur. I can put a quarter wave short across my line, get a 1:1 match and nothing into the antenna. JMHO

[SCVJeff]

I don't think anyone is going to install a 102" whip on a Motorhome, let alone build a mount to hold it that won't tear off the roof. It's just 11 mtrs

[wa8yxm]

IDeally SWR should be 1:1.... Most CB radios are designed to work with antennas that are slightly out of tune.. like LESS THAN 3:1 SWR.

Your Owner's manual will give you the cut off

NOTE: that performance degrades as SWR rises.

[Cloud_Dancer]

old guy wrote:
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

I think "No-Ground models" is referring to antennas which are designed to be mounted on fiberglass roofs, like mine. A metal ground plane is not available.
However, the metal sheath on the antenna cable is grounded to the metal framework of the MH body, upon which the fiberglass roof rests.
I'll check the quality of this ground (for the third time).