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The Toolman 01-16-2012 03:03 PM

CB Radio Basics: HOW TO Adjust your SWR
 
I just posted this in another thread helping someone, but thought I would create a how to thread for future reference to help everyone out.

Here goes.....

For Jeeps, etc... I am going to suggest getting a good SWR meter from Radio Shack. (There are much better, much more expensive meters out there, but the Radio Shack meters ARE reliable & won't break the bank.)

First Off, for those who are new to this, having a good Standing Wave Ratio is a vital key in your rig, if it is not set right you will end up killing some key components in your radio. ( final transistors, resistors, AM regulator, etc. usually the finals will be the ones to go, that is, if your radio is turned up, which I do not recommend) Then you will have to send your radio off to be repaired do reflected power back to it's components causing a strain on them. "Why?" You may ask, well, SWR indicates the quality of the match between your coax & the antenna's feed point ( Where you connect the coax coming from your radio to the antenna )

SWR (Standing Wave Ratio), is also a measurement of how efficiently your antenna system will radiate the power available from your radio. In simple terms, your radio would like to radiate all of its power, but can only do so if the other components cooperate. Bad coax and mounts, or inefficient antennas and ground plane can cause kinks in the radiation of RF power. The easiest way to understand the concept is to think of it in the flow of fluid through plumbing. That is, if you put a one inch reducer/bushing on a two or three inch main feed pipe, your potential output will be restricted by the one inch outlet which will cause backpressure & a considerable strain on the pump that is pumping the water ( With a radio, think of your final transmitting components as the water pump ) & the overrall result is less flow out of the other end of the pipe due to the restriction. So goes with antenna systems. Setting your SWR of your antenna will reduce the reflected power that puts a strain on your radio's / amp's components( think of reflected power as the back pressure I mentioned above ) & of course, the restriction of radiated power. Another thing is that the length of your antenna has ALOT to do with SWR, considering the antenna length resembles a portion of the wavelength of the frequency you are talking on & if it is resonate to that frequency, but we can get into antenna length vs. wavelength in another thread.

Having an SWR of 2.0:1 or less is a MUST for decent transmitting (Also, some will say it can burn up your radio, but if your radio is legal & hasn't been "turned up" your radio should live :thumb: ). Having an SWR of 1.5:1 or less is considered optimal for best transmit & recieve.


What You Will Need

GOOD SWR Meter

GOOD Coax Jumper ( a 3' jumper is usually sufficient )

Tools to adjust your antenna ( crecent wrench, allen wrench set, wire cutters, even some screwdrivers maybe, depends on the antenna )

Adjusting SWR

To start off with, you really can't put a whole lot of trust in your radio's internal SWR meter. ( if it has one ) They work & are fairly accurate for the most part. The best thing to do is get an external SWR meter, & don't get one of those that you see in the truck stops, they aren't worth a dime in my opinion, I have personally tested them against a Bird & Palstar meter.
You can usually find a decent meter for around $50 nowadays and yes, the Radio Shack meter is decent for checking SWR but that's about it. The watt meter is questionable in those. As you get into the hobby more, you will want a better meter that gives accurate RMS (Root Mean Square, or average power) and PEP (Peak Envelope Power) power reading along with reflected power. Bird directional watt meters are the best and most accurate. The Palstar & Daiwa meters are also darn good meters as well. The ultimate in antenna tuning is an antenna analyzer that can check the antenna's resonate frequency or impedance. For now, we just need an SWR meter.

Step #1 ) Find a place that is clear of trees, buildings, other obstruction and other antennas that could give you false readings. The areas should be clear of objects by 50 feet or more in all directions.

Step #2 ) Place the meter inline between the radio and antenna using your coax jumper.

Step #3 ) Hook the jumper from radio to the TX or transmitter side of the meter and antenna to the ANT or antenna side of the meter.

Step #4 ) Turn the radio on and set it to channel 1.

[ Special note: If you will only be broadcasting on the CB bands & if your radio has SSB ( Single Side Band ) &/or is an export, make sure the selector knob is ine the "AM" position & the frequency display ( if your radio has one ) on Channel 1 shows 26.965 Mhz / Channel 20 Shows 27.205 Mhz / Channel 40 Shows 27.405 Mhz ]

Step #5 ) Turn the adjustment knob to the minimum or full counter clockwise position. Set the meter to the CAL or calibrate position.

Step #6 ) Key the mic and turn the calibration knob so that the needle moves to the CAL mark on the scale.

Step #7 )Set the meter switch to the SWR setting without touching the calibration knob.

Step #8 ) Key the mic and record the SWR meter reading.

Now repeat steps 5-8 on channel 40.

Also, just for reference, repeat steps 5-8 on Channel 20 ( which is the center of the 11-meter CB Band )

If the SWR is lower on channel 1 than channel 40, your antenna/whip is too long. If the SWR is higher on channel 1 than channel 40, your antenna/whip is too short.
Adjust your antenna in inch increments. Some antennas have a set screw that allows you to adjust the height of the whip and others must have some of the whip cut or ground off to adjust the SWR. Many of the whips are stainless steel and very hard to cut. A hacksaw, cutoff wheel, or bolt cutters will be necessary to cut these antennas.
After you make an adjustment, repeat steps 5 through 8 until your SWR is the same at both channel 1 and channel 40.
The goal is to get the lowest SWR possible. If your SWR is below 2.1:1 you are ok, 1.5:1 or less is what I would recommend . If you have or plan on getting an amp, you need an SWR of 1.3:1 or less. If you have tuned the antenna but still have a high SWR reading, you may try moving the antenna to another location on the vehicle or you may need to add ground straps to the vehicle for better bonding. Grounding & bonding is dicussed in another thread.

Here's some info on adjusting SWR on a few different antennas.

ADJUSTING LONG ANTENNAS

If the SWR on channel 40 is greater than that on channel 1, your antenna is considered to be a little "TOO LONG" and reduction of physical height and/or conductor length will correct this situation. Depending upon antenna model, this entails screwing down the tunable tip on a Firestik II & similar antennas, or, removing the tip, making short slits in the plastic covering and unwinding and clipping off wire on a Firestik 1 & similar antennas. Most coil & whip style antennas require loosening the allen screws and lowering or raising the metal whip.

ADJUSTING SHORT ANTENNAS


If SWR on channel 1 is greater than that on channel 40, your antenna is considered to be "SHORT" and increasing the physical and/or electrical length of the antenna is required to correct this situation. Because we make our antennas extra long, readings which indicate "Short" normally stem from ground plane deficiency (lack of vehicle metal surface for the antenna to reflect its signal rom). This condition is often corrected by adding a spring and/or quick disconnect to increase the physical height. Ground plane deficiencies can also be compensated for by using dual (co-phased) antennas or special no-ground-plane antenna kits.

NOTE: The shorter the antenna, the more sensitive it is to adjustments. For example, removing two wire turns on a 4 foot antenna might move the SWR by 0.3; the same amount removed from a 2 foot antenna may move the SWR by 1.0. Make smaller adjustments on shorter antennas.

DUAL ANTENNAS


Measurements and determination of proper antenna length are the same as the single antenna procedure. However, when tuning co-phased antennas, if you adjust one antenna, it is advisable to adjust the other in equal amounts to keep them in perfect balance.

Firestick I (And similar) Antennas

If you take the cap off of the top, there will be some "wire" coiled in the top. This is what you trim to tune these antennas. Make sure you do not trim too much at at time. :thumb:

OregonRubicon 01-16-2012 03:10 PM

1 Attachment(s)
Thanks for the detailed thread! Great write up on it.

Was just looking at the CB combo on Quadratec. Says it is pre tuned for Jeeps.

That or drive down to the truck stop like a lot of folks recommend.



Attachment 90296

1SAS 01-16-2012 05:02 PM

Awesome post!!! Thanks for taking the time to write it up. It will help a lot.

Take care,

The Toolman 01-16-2012 08:09 PM

Quote:

Originally Posted by 1SAS (Post 1927771)
Awesome post!!! Thanks for taking the time to write it up. It will help a lot.

Take care,

No problem at all, I felt like this section needed it. I'll do one on wiring up the CB & properly installing antenna mounts here soon when I have the time to be very detailed.

Ageless Stranger 01-17-2012 06:15 AM

Sticky. :cool:

Good thread Toolman. :thumb:

The Toolman 01-17-2012 07:31 AM

Quote:

Originally Posted by Ageless Stranger (Post 1929757)
Sticky. :cool:

Good thread Toolman. :thumb:

Thanks, Communications is my other hobby :thumb:

KrzyMoke 05-20-2012 02:31 PM

I would like to add if you are adjusting a Firestik II antenna, after each adjustment, put the plastic cap back on. I WILL matter. I just found that out today adjusting mine. It will keep you from chasing your tail :doh:

dabolt55 06-05-2012 08:33 PM

Thanks Toolman...
 
This helped me with videos.. Installation Resources

stans1stjeep 09-07-2012 04:27 PM

So... Today I got my Midland 75-822 CB and a Little Wil magnetic mount antenna. I mounted the antenna in the middle of the hood, directly behind the hood tie down loop. Radio power is from the power outlet inside the arm rest, which is direct to the battery. The antenna cable, runs to the passenger door and into the passenger compartment. Attached my SWR meter and adjusted the antenna, up, then down, then up again, then I cut off a quarter inch of the antenna and adjusted it up down and all around. No matter how I adjusted it, the SWR readings were centered on 2.0. Finally left it at 2.1, channel 1; 1.9, channel 40. I'm calling it done, just looking for an affirmation that this is acceptable to use. Going on a cruise to an off road park tomorrow, and want to listen to the chatter.:confused:

reade 01-19-2013 08:08 PM

Hi, I finally got my CB installed today and tried to set the SWR. I borrowed an old SWR meter and I'm unsure about it. This is what I got, after I calibrated it I could only get just the lowest SWR reading on CH 1 and nothing on 40. I tried a few thing and after lengthening the screw on my Firestick I finally got some reading on both CH 1 and 40 but it was very faint. I can hear some people talking very far away but I haven't found anyone near so I don't know if I'm transmitting or not.

Is there a good chance I'm not grounded well and that is keeping the SWR so very low and also effecting my transmit?

stans1stjeep 01-19-2013 08:37 PM

Quote:

Originally Posted by reade (Post 3250751)
Hi, I finally got my CB installed today and tried to set the SWR. I borrowed an old SWR meter and I'm unsure about it. This is what I got, after I calibrated it I could only get just the lowest SWR reading on CH 1 and nothing on 40. I tried a few thing and after lengthening the screw on my Firestick I finally got some reading on both CH 1 and 40 but it was very faint. I can hear some people talking very far away but I haven't found anyone near so I don't know if I'm transmitting or not.

Is there a good chance I'm not grounded well and that is keeping the SWR so very low and also effecting my transmit?

What readings did you get? You want to be below 2.5

reade 01-19-2013 09:28 PM

It was 1 or less. The SWR meter is old and may not be right. ? I can hear but what I'm hearing is skip from all over the country. There seems to be no locals talking tonight so I don't know if I'm transmitting or not.

Jeepnolan 01-19-2013 09:46 PM

Chances are you've done everything correctly. I just I stalled a Cobra 148 and a 4' Wilson antenna solely for the purpose of the sideband on the lower side of 38. Even with a stock radio and decent antenna, with the right conditions you should be able to skip. My SWRs' were pretty low from the start.

stans1stjeep 01-19-2013 09:56 PM

Quote:

Originally Posted by reade (Post 3251105)
It was 1 or less. The SWR meter is old and may not be right. ? I can hear but what I'm hearing is skip from all over the country. There seems to be no locals talking tonight so I don't know if I'm transmitting or not.

I don't think you can have an SWR less than 1. Are you setting the meter correctly before you take a reading?

reade 01-21-2013 05:58 PM

As I said, the meter is old and I'm unsure of what I have with it. I did order a new one on ebay and will see what I get with it.

On another note, I did talk to a trucker today who was driving near me, he said I sounded very clear and all seemed to be working great. I'll be interested in seeing what the new SWR meter says.

LHC30 02-09-2013 03:14 PM

Thanks for this writeup. The SWR instructions failed to mention checking between Ch1 and CH 40... I was able to balance the SWR reading to <1.5 on both CH1 and 40 (after these pics). When I checked CH 20 it was near 1! I hope that is good..here are the three channel SWR readings (CH1, CH20, CH40):

http://www.riverdavesplace.com/forum...lery&type=full

http://www.riverdavesplace.com/forum...lery&type=full

http://www.riverdavesplace.com/forum...lery&type=full

The Toolman 02-09-2013 07:15 PM

Quote:

Originally Posted by LHC30 (Post 3344372)
Thanks for this writeup. The SWR instructions failed to mention checking between Ch1 and CH 40... I was able to balance the SWR reading to <1.5 on both CH1 and 40 (after these pics). When I checked CH 20 it was near 1! I hope that is good..here are the three channel SWR readings (CH1, CH20, CH40):

http://www.riverdavesplace.com/forum...lery&type=full

http://www.riverdavesplace.com/forum...lery&type=full

http://www.riverdavesplace.com/forum...lery&type=full

Not bad at all really, could it be better .... sure, but for a CB radio that is transmitting at +/- 4 watts; those are REALLY good readings, so you should be good to go :thumb:

You're welcome by the way, lol ;)

benjamin.allen 03-09-2013 08:44 AM

so i tuned my swr and i have 1.6 on both channel1 and channel 40 from what i read this is ok can i get some confirmation that this is acceptable for a reading.

stans1stjeep 03-09-2013 11:38 AM

Quote:

Originally Posted by benjamin.allen (Post 3480838)
so i tuned my swr and i have 1.6 on both channel1 and channel 40 from what i read this is ok can i get some confirmation that this is acceptable for a reading.

You should be fine at 1.6.

KX6D 06-18-2013 12:43 AM

Most of this was accurate. The parts you got wrong won't hurt anyone, but either you didn't explain it right, I misunderstood you, or you don't fully understand antenna theory.

I was excited to see that you got the part right about the SWR being a relationship between the feedline (coax) and the feedpoint (antenna mount). Most people don't get that right.

As for the person having issues getting below 2:1 SWR with his hood mounted magnetic mount antenna, it has to do with the capacitance in the ground system (or lack there of) with your antenna. Will it work...SURE! Everything works! But you could do better with a better antenna set up!

Don't skimp on your antenna system people! Its the best money you will spend on your radio set up!!!

Matt2001TJ 08-09-2013 12:48 AM

Quote:

Originally Posted by The Toolman (Post 1929918)
Thanks, Communications is my other hobby :thumb:

Mine too,..73

Benjy 06-29-2014 09:36 AM

Will obstacles (trees, buildings) cause the SWR to peg no matter what? I'm troubleshooting my setup and the SWR is pegged past the cal point. I tinkered with the adjustable tip on my Wilson Flex with no luck. Tried on my installed Cobra75 and an old Realistic TRC-410.

psouza 06-29-2014 08:14 PM

Quote:

Originally Posted by Benjy (Post 11639266)
Will obstacles (trees, buildings) cause the SWR to peg no matter what? I'm troubleshooting my setup and the SWR is pegged past the cal point. I tinkered with the adjustable tip on my Wilson Flex with no luck. Tried on my installed Cobra75 and an old Realistic TRC-410.


Obstructions within the "near field", 36 feet will not have any serious effect on your VSWR reading. Certainly not enough to peg your meter. With meter readings like that, a shorted antenna mounting is most likely, followed by a faulty antenna cable connector, especially if you have a "Fire Ring" at the antenna end.

Phil

Benjy 06-29-2014 10:50 PM

To add a bit, my CB worked last summer during a Jeep jamboree on day 1, then wouldn't work on day 2. Before that, the cobra75 worked for a couple years with no issues. I hooked up the two radios to power (no antenna on the TRC-410) and could hear myself on the other CB. I'm north of Houston 2 miles from I-45 and never heard anyone else on scan mode.

I started my testing just 10' or so from the house, then reading further about the obstructions, I moved about 30' away from the house. No change in the SWR readings. I've tested everything to see if it's grounded correctly and so far, I can't find anything wrong.

Is it possible that the circuits are bad on both radios, therefore I can't get a good SWR, but they'd still work within a short range of one another? Next chance I get I'll redo the grounds. Right now, I'm grounded to the body, not the frame, which was per the guy I bought it from who also tuned it the first go around.

psouza 06-29-2014 11:30 PM

Quote:

Originally Posted by Benjy (Post 11654426)
To add a bit, my CB worked last summer during a Jeep jamboree on day 1, then wouldn't work on day 2. Before that, the cobra75 worked for a couple years with no issues. I hooked up the two radios to power (no antenna on the TRC-410) and could hear myself on the other CB. I'm north of Houston 2 miles from I-45 and never heard anyone else on scan mode.

I started my testing just 10' or so from the house, then reading further about the obstructions, I moved about 30' away from the house. No change in the SWR readings. I've tested everything to see if it's grounded correctly and so far, I can't find anything wrong.

Is it possible that the circuits are bad on both radios, therefore I can't get a good SWR, but they'd still work within a short range of one another? Next chance I get I'll redo the grounds. Right now, I'm grounded to the body, not the frame, which was per the guy I bought it from who also tuned it the first go around.


It is not possible for a radio malfunction to cause the VSWR to change. I have had the same symptom (higher VSWR) when my coax cable got water in side it, last spring. But since Texas doesn't get rain... If the antenna is a fiberglass whip, I would suspect the antenna has broken the wire inside the whip. A cable or antenna problem are equally possible. In my case, the traditional cable check by ohm meter did not reveal a problem, but you should test it any way. Recheck all aspects of the mount, cable, and antenna. Don't bother tuning until you get the VSWR back to reasonable levels. Swaping components might be easier than doing any testing. (faster...not cheaper)

Phil

KX6D 07-01-2014 03:17 PM

Quote:

Originally Posted by Benjy (Post 11639266)
Will obstacles (trees, buildings) cause the SWR to peg no matter what? I'm troubleshooting my setup and the SWR is pegged past the cal point. I tinkered with the adjustable tip on my Wilson Flex with no luck. Tried on my installed Cobra75 and an old Realistic TRC-410.

Near by obstacles will affect your SWR, but NOT peg it. Driving down the road affects your SWR (bending of the main element), but will NOT peg it.

The first place to look is at your cable and where the cable connects to the mount/antenna. Usually that is the cause.

As for your other issues, you can hear yourself on another CB if they are close to each other, even if you don't have an antenna connected to either radio.

Do a quality installation with quality components and you will be very happy with the results. If you can't do it, get someone who can. Would you do heart surgery, or get a professional?


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