RadioReference on Facebook   RadioReference on Twitter   RadioReference Blog
 

Go Back   The RadioReference.com Forums > Topic Specific Forums > CB Radio Forum

CB Radio Forum Discussions regarding Citizens Band Radio (CB)

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1 (permalink)  
Old 10-08-2012, 7:28 PM
Member
   
Join Date: Oct 2012
Location: Columbia, SC
Posts: 5
Default problem calibrating swr meter

I have a cobra 29, and I cannot seem to get my swr meter to calibrate, to check swr. The radio has been tuned and peaked. I have 18ft of coax. The radio is double grounded(to the battery and a jumper to the frame). I have to antenna is grounded to the battery and to the cab of the equipment the radio is in. I have tried to calibrate with 2 swr meters, and I cannot get the radio to calibrate to check the swr. Help?
Reply With Quote
Sponsored links
  #2 (permalink)  
Old 10-08-2012, 11:15 PM
Member
   
Join Date: Dec 2006
Location: Oklahoma
Posts: 2,145
Default

Exactly what are you doing to 'calibrate' this radio?
- 'Doc
Reply With Quote
  #3 (permalink)  
Old 10-09-2012, 10:32 AM
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: Mar 2006
Location: Washington DC
Posts: 1,935
Default

You don't "calibrate" an SWR meter. Here's how you use it:

1. While transmitting, turn the control on the meter so the needle reads full scale with meter's switch in the "forward" position.

2. Turn the switch to the "reflected" position, transmit again and read the meter to see the SWR.

That's it, nothing more.
Reply With Quote
  #4 (permalink)  
Old 10-09-2012, 12:48 PM
Member
   
Join Date: Dec 2006
Location: Oklahoma
Posts: 2,145
Default

An SWR meter doesn't change anything, it only tells you what the impedance mismatch (SWR) is. You have to do the changing of that impedance mismatch to change the SWR meter's reading. That's usually done by adjusting the length of the antenna.
Anyone remember the thingy 'they' used to use for measuring a foot to see what size shoe you wore? That's what that SWR meter is like. It doesn't change the size of your foot, or the size of the shoe, it just tells you what you need to know to select the right shoe or impedance match.
- 'Doc
Reply With Quote
  #5 (permalink)  
Old 10-09-2012, 5:42 PM
Member
   
Join Date: Oct 2012
Location: Columbia, SC
Posts: 5
Default

Maybe calibrate is not the proper terminology, but when I push the transmit button on the mic, and turn the knob on the meter, it will not move all the way into the "set position" to flip the switch to give you your swr reading. The dead key has been set high enough to be able to support this, but to no avail.
Reply With Quote
Sponsored links
  #6 (permalink)  
Old 10-09-2012, 5:47 PM
Member
   
Join Date: Oct 2012
Location: Columbia, SC
Posts: 5
Default

I was using the term "calibrate" for a lack of better terminology. When I push the transmit on the mic, and turn the control knob on the meter, I cannot get the needle to climb to the proper position, so that I can flip the switch to give me my swr reading. I am aware of how to set the swr, I am having trouble getting my meter to "calibrate", in order to get my swr reading.
Reply With Quote
  #7 (permalink)  
Old 10-10-2012, 8:30 AM
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: Mar 2006
Location: Washington DC
Posts: 1,935
Default

Sounds as if your RF output is so extremely low that what's coming out of the radio is not enough to push the meter's reading to the end of the scale. I would say "bad meter" but you've now tried two of them so that's not likely the problem. A wattmeter would tell you how much the radio is putting out in RF.
Reply With Quote
  #8 (permalink)  
Old 10-10-2012, 10:14 AM
Member
   
Join Date: Dec 2006
Location: Oklahoma
Posts: 2,145
Default

The first thing that comes to mind is, has your radio been modified to 'improve' it in some way that is different from a 'stock' radio? Lowering 'dead key' seems to to be popular now. That's not always a good idea for several reasons, you may be experiencing one of them.
There are minimum as well as maximum power levels for all SWR meters. That 'normal' range of power handling assumes that the radio is 'normal'. That also assumes that the meter is properly designed and constructed. Lots of 'assuming' in all that, you determine which/where/who is being made an 'axe' out of.
- 'Doc
Reply With Quote
  #9 (permalink)  
Old 10-10-2012, 6:10 PM
kb2vxa's Avatar
Completely Banned for the Greater Good
  Amateur Radio Operator
Amateur Radio
 
Join Date: Mar 2005
Location: Point Pleasant Beach, N.J.
Posts: 6,127
Default

"I cannot get the needle to climb to the proper position, so that I can flip the switch to give me my swr reading."

Uh oh:
"The radio has been tuned and peaked."
There's your answer and the reason why I can't emphasize enough KEEP THAT GOLDEN SCREWDRIVER OUT OF THERE! I could tell you how to calibrate it against a 50ohm standard but an internal SWR meter is a logistical nightmare. The only practical solution is to use an external meter, just a cheap and dirty one without all the needless bells and whistles. Just be sure to use a SHORT jumper between it and the radio, they get fooled by the length of it.

Now you make me wonder what else got goofed up in there... <shudder>
Reply With Quote
Sponsored links
  #10 (permalink)  
Old 10-10-2012, 7:54 PM
Member
   
Join Date: Oct 2012
Location: Columbia, SC
Posts: 5
Default

Just an FYI, I absolutely, for no reason have even considered trying to tune and peak the radio myself. I had a professional do it, and they have done work on several radios for me and they turned out perfect. The thought that my "dead key" was set too low came to mind, but I was informed that the antenna set up could be what is causing the issue. What I did to resolve the issue is I took out the cobra, and put in a brand new galaxy 33hp2 that has 3 dead key settings. They were set at 3, 5, and 9 watts. The low setting would not "calibrate" on my external meter, so I moved to the medium setting and it would calibrate on the meter. Much to my dismay the swr was off the charts. ( I think it was around 5) I ended up taking off my 18ft coax and tried a 12ft coax, and it worked like a charm! On channel 1 it was almost flat line on the swr, channel 40 was about .2, and on 19 it was about .1. I sincerely appreciate everyone's input. Nice to see people willing to offer a hand!
Chandyman
Reply With Quote
  #11 (permalink)  
Old 10-11-2012, 11:49 AM
kb2vxa's Avatar
Completely Banned for the Greater Good
  Amateur Radio Operator
Amateur Radio
 
Join Date: Mar 2005
Location: Point Pleasant Beach, N.J.
Posts: 6,127
Default

Speaking of FYIs, there is NO reason to fiddle with the guts since they come aligned from the factory to meet FCC specs. Two valid reasons to keep so called "professional" hands out of it are:
1) Tampering automatically voids the guarantee of any device.
2) Tampering voids FCC certification automatically making the rig illegal.
Besides that any slight "improvement" you may get doesn't buy you an edge in communications effectiveness. I've seen a lot of snake oil out there, much of it laughable so don't fall for the "sales pitch" when you can benefit from vast collective knowledge and experience. There is wisdom in the age old phrase "If it ain't broke don't try to fix it."

As for your SWR "problem" it's like I said, length of the coax fools the meter. You can fool it back to looking good by adjusting it a bit at a time for the lowest reading on channel 20 which is the band center, everything else will fall in line. BTW, your figures are misleading and confusing being they should be expressed as a ratio, that is x:1 with 1:1 being a perfect match. May I suppose the highest you got was 1.2:1 on channel 40? If so leave it be, that's about as good as it gets.

"Nice to see people willing to offer a hand!"
That's what we're here for.
Reply With Quote
  #12 (permalink)  
Old 10-11-2012, 8:05 PM
Member
   
Join Date: Oct 2012
Location: Columbia, SC
Posts: 5
Default

New issue. My swr was off the chart again! And not in a good way. The radio is in a "knuckle boom" loader, used to unload log trucks at a paper mill. The loader in on a 24 volt system. We use power converters to change the 24 to 12 volt to power not only cb radios, but also for am/fm radios. Apparently, the voltage surges as well as the ground is not a constant for some reason. Does anyone know of a power converter/voltage regulator that offers both features to solve my issues? Or better yet, does anyone have knowledge on properly installing cb radios in equipment that are 24 volt?
Reply With Quote
  #13 (permalink)  
Old 10-13-2012, 5:05 PM
kb2vxa's Avatar
Completely Banned for the Greater Good
  Amateur Radio Operator
Amateur Radio
 
Join Date: Mar 2005
Location: Point Pleasant Beach, N.J.
Posts: 6,127
Default

First off your SWR problem is not power supply related. Your problem lies in the antenna and/or coax, something has jarred loose not being rugged enough to withstand shock and vibration encountered in such a hellish environment. Beyond that I can't help you except to say you need military grade equipment to stand up to that beast, any Army communications techs out there?
Reply With Quote
  #14 (permalink)  
Old 10-16-2012, 12:27 PM
Member
   
Join Date: Jul 2011
Location: GA
Posts: 170
Default

Quote:
Originally Posted by W2NJS View Post
You don't "calibrate" an SWR meter. Here's how you use it:

1. While transmitting, turn the control on the meter so the needle reads full scale with meter's switch in the "forward" position.

2. Turn the switch to the "reflected" position, transmit again and read the meter to see the SWR.

That's it, nothing more.
What?

My meter clearly says "calibration" over one pot and "cal" next to one of the switches. I use them to "calibrate" or to "turn the control on the meter so the needle reads full scale with meter's switch in the 'forward' position" the meter to the radio I'm using. Is my meter wrong or something?
Reply With Quote
  #15 (permalink)  
Old 10-16-2012, 12:30 PM
Member
   
Join Date: Jul 2011
Location: GA
Posts: 170
Default

OP remove all those extra grounds you have installed and try retesting it. You should only need the one ground supplied through the radio's power cable.
Reply With Quote
Sponsored links
  #16 (permalink)  
Old 10-17-2012, 7:15 AM
Member
   
Join Date: Feb 2012
Location: Reading, PA
Posts: 87
Default

Quote:
Originally Posted by kb2vxa View Post
Speaking of FYIs, there is NO reason to fiddle with the guts since they come aligned from the factory to meet FCC specs. Two valid reasons to keep so called "professional" hands out of it are:
1) Tampering automatically voids the guarantee of any device.
2) Tampering voids FCC certification automatically making the rig illegal.


Most radios are so badly aligned/tuned "from the factory" that most are not even on frequency...will they work, yes, but not efficiently. Tampering only voids the warranty if not done by a factory authorized repair facility...just because a radio is opened to simply repair it, doesn't void any certification. Even new-in-box radios aren't perfect, I just bought one...it was off frequency, receive was dead, and modulation was low; now its on frequency, receive is amazing, and still within its "4 watts".

While I don't agree with letting the typical truck stop hacknician in a radio to do his Super Hack Pack, repairs can be made that will improve performance without adding channels, clipping limiters, jacking up power, etc.. Most radios I have owned really benefited from just being adjusted to do what they should have left the factory doing...all changes still within FCC specs. It takes time to do that, and the factory worker is about production, not quality.

The hardest part is finding that one reputable and qualified shop that will do that kind of work (like searching for a needle in a haystack).
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 5:20 AM.


Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
All information here is Copyright 2012 by RadioReference.com LLC and Lindsay C. Blanton III.Ad Management by RedTyger
Copyright 2011 by RadioReference.com LLC Privacy Policy  |  Terms and Conditions