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Old 07-02-2015, 08:20 PM
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CB electrical resistance

Hello everyone,
I am trying to tune my CB set up. SWR is dreadfully high - around 3:1, so I am trying to trouble shoot. I got the antenna base grounded to the body (checked), but then I measured the resistance between the antenna base and the active (upper) part of the antenna, thinking it should be completely isolated. To my surprise, the resistance was very much measurable - around 4.7 kOhm. I started digging through the connection points in my setup and found that resistance, when measured between the central pin and the outer casing of the antenna input of the CB radio itself, was that same 4.7 kOhm. Has anyone ever tried to measure that resistance value? Am I dealing with a faulty CB unit or is this a proper resistance reading?
Thank you!

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Old 07-02-2015, 08:32 PM   #2
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Hey, try posting it here: Communications and Electronics - Jeep Wrangler Forum
You might get faster feedback.

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Old 07-03-2015, 02:55 PM   #3
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Hello everyone,
I am trying to tune my CB set up. SWR is dreadfully high - around 3:1, so I am trying to trouble shoot. I got the antenna base grounded to the body (checked), but then I measured the resistance between the antenna base and the active (upper) part of the antenna, thinking it should be completely isolated. To my surprise, the resistance was very much measurable - around 4.7 kOhm. I started digging through the connection points in my setup and found that resistance, when measured between the central pin and the outer casing of the antenna input of the CB radio itself, was that same 4.7 kOhm. Has anyone ever tried to measure that resistance value? Am I dealing with a faulty CB unit or is this a proper resistance reading?
Thank you!
If you are down near Fort Lauderdale go see RAVEN or SCREWDRIVER at bella CB. They have MFJ swr readers and pour antenna might be off. Also swr is normally calculated from the Antenna through a coax cable.

Get a decent rg8x cable, check your antenna's swr by putting it on somebody's else Jeep.

Ultimately if you are near south Florida hit BELLS CB on commercial.

Problem solved!
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Old 07-03-2015, 02:56 PM   #4
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I also have a free firestick Antenna for you if you need it...
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Old 07-04-2015, 07:25 AM   #5
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What antenna mount are you using? I have the Teraflex one and had to grind off all of the powder coating to get a good ground and good readings. Doesn't make sense that they sell it that way if that's the result.
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Old 07-04-2015, 07:34 AM   #6
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@Phase2
I have the teraflex. What did you use to grind it off? I have a dremel and nothing yet so far has made much of a difference.
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Old 07-04-2015, 08:58 AM   #7
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I used a Dremel and I ground off some powder coat where the new bolts went into the tailgate. Wish I had a pic. But basically the bolt head is contacting bare metal. Once I mounted it I repainted around the bolt so you can't even tell. And it will prevent rusting. I also ground down to bare metal on the underside of the mount where the coax meets the antenna/connector. I ended up with great swr readings.
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Old 07-04-2015, 03:12 PM   #8
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@Phase2 I have the teraflex. What did you use to grind it off? I have a dremel and nothing yet so far has made much of a difference.
I just used an electric sander with 80 grit sandpaper. I did the entire mount just to be sure. Only downside is that now it's all rusty.
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Old 07-06-2015, 08:34 AM   #9
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I just used an electric sander with 80 grit sandpaper. I did the entire mount just to be sure. Only downside is that now it's all rusty.
Nobody cares BC I can ear you from space!
Whoever think using paint is good idea is not totally aware that certain paint contains lead and other metals that can affect reception and TX...

You are better off with your bare mount. Really.
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Old 07-06-2015, 08:47 AM   #10
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Nobody cares BC I can ear you from space! Whoever think using paint is good idea is not totally aware that certain paint contains lead and other metals that can affect reception and TX... You are better off with your bare mount. Really.
Yep - I can't see the mount anyway, so I'm fine with the 1.1 SWR readings I have. 😀
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Old 07-06-2015, 08:51 AM   #11
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Im using a firestik 4ft no ground plane setup on my JK and it works perfect. Im getting 1.2 on my meter with a Midland 75-822 radio.
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Old 07-06-2015, 09:15 AM   #12
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If you are just measuring the resistance of the antenna from bottom to top (removed from mount) I think you should have very low resistance if any at all.

I had a problem a while back and it turned out to be where the copper wire that wraps around the antenna from top to bottom, was corroded at the base and needed to be cleaned and re-soldered to the base of the antenna.
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Old 07-07-2015, 11:47 AM
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I also have a free firestick Antenna for you if you need it...
Thank you, Higgy, for the help links and antenna offer. I'm not in Florida though. I am using a brand new Firestik antenna, 5 ft.
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Old 07-07-2015, 11:49 AM
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What antenna mount are you using? I have the Teraflex one and had to grind off all of the powder coating to get a good ground and good readings. Doesn't make sense that they sell it that way if that's the result.
I don't recall who made that thing, but a good ground is not an issue in my case - I measured the connection from the mount to the Jeep body, it's solid.
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Old 07-07-2015, 11:52 AM
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If you are just measuring the resistance of the antenna from bottom to top (removed from mount) I think you should have very low resistance if any at all.

I had a problem a while back and it turned out to be where the copper wire that wraps around the antenna from top to bottom, was corroded at the base and needed to be cleaned and re-soldered to the base of the antenna.
The resistance I am concerned with is not in the antenna, but in the CB radio unit itself - from the center pin to the outer casing of its antenna connection plug.
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Old 07-07-2015, 12:07 PM   #16
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It seems like everyone is answering him but ignoring what he said in his post.

What you are seeing is normal. You can't do that measurement with the coax attached to the radio. Your seeing the resistance of the CB radio's RF amplifier and other associated electronic parts. This is a meaningless measurement. You need to disconnect the coax from the radio and remove the antenna when checking for resistance or continuity in coax.

With the coax disconnected from the radio and the antenna removed from the mount (but the coax still attached to the mount), you should see the following on your multi-meter set for ohms or continuity.

- An open circuit between the coax center conductor and coax shielding
- An open circuit between the coax center conductor and the mount
- An open circuit between the coax center conductor and vehicle ground
- Zero ohms between each end of the coax center conductor
- Zero ohms between the coax center conductor and the mount's center conductor
- Zero ohms between the mount itself and chassis ground

If all of those are met, you have a properly installed mount and coax, and none of it is chaffed or broken. Happy day. A failure of these tests can easily result in very high SWR. But is not the only cause of SWR. With a reading of 3 on an SWR meter, that is more likely to be an antenna tuning issue.
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Old 07-07-2015, 03:37 PM
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It seems like everyone is answering him but ignoring what he said in his post.

What you are seeing is normal. You can't do that measurement with the coax attached to the radio. Your seeing the resistance of the CB radio's RF amplifier and other associated electronic parts. This is a meaningless measurement. You need to disconnect the coax from the radio and remove the antenna when checking for resistance or continuity in coax.

With the coax disconnected from the radio and the antenna removed from the mount (but the coax still attached to the mount), you should see the following on your multi-meter set for ohms or continuity.

- An open circuit between the coax center conductor and coax shielding
- An open circuit between the coax center conductor and the mount
- An open circuit between the coax center conductor and vehicle ground
- Zero ohms between each end of the coax center conductor
- Zero ohms between the coax center conductor and the mount's center conductor
- Zero ohms between the mount itself and chassis ground

If all of those are met, you have a properly installed mount and coax, and none of it is chaffed or broken. Happy day. A failure of these tests can easily result in very high SWR. But is not the only cause of SWR. With a reading of 3 on an SWR meter, that is more likely to be an antenna tuning issue.
Thank you for the insights. I did, however, already make those measurements. Everything is fine. And I did disconnect the coax from the radio when I measured the described resistance - it was still present, so it's not due to a faulty coax or the mount (both of those are fine). But from what you said, it sounds like a non-zero measurement between the center pin and the outer casing of the radio is normal.
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Old 07-07-2015, 03:49 PM   #18
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Good. So it sounds like at the very least it is installed properly. A simple antenna tuning should fix the SWR.
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Old 07-07-2015, 04:22 PM
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Good. So it sounds like at the very least it is installed properly. A simple antenna tuning should fix the SWR.
So my Firestik is the adjustable kind, but in the entire range of the screw's motion (including completely taking the screw out) did not really change SWR much - it went from around 3.4 with the screw stretched out, to around 3.2 with the screw all the way in, to around 3.1 when I removed the screw. Not sure how else to adjust it. From what I've read this situation might be related to some wiring issues. The only one I can think of is the power connection of the radio. I haven't traced where the wires are connected to (it's not directly to the battery and I wasn't the one wiring it).
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Old 07-07-2015, 04:55 PM   #20
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when measured between the central pin and the outer casing of the antenna input of the CB radio itself, was that same 4.7 kOhm.
That sounds about right for the power amplifier inside the radio.

Follow what Pedals2Paddles said and you should be good. You just need to tune the antenna or find someone who can. There's usually some kind of CB shop around major truck stops. They can tune your antenna for you pretty easily.

I have personally found that the adjustable tip antennas don't have enough adjustability. I go with the regular firestick and trim back the end of the wire a hair at a time until I get my SWR in a good range.
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Old 07-07-2015, 05:57 PM
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That sounds about right for the power amplifier inside the radio.

Follow what Pedals2Paddles said and you should be good. You just need to tune the antenna or find someone who can. There's usually some kind of CB shop around major truck stops. They can tune your antenna for you pretty easily.

I have personally found that the adjustable tip antennas don't have enough adjustability. I go with the regular firestick and trim back the end of the wire a hair at a time until I get my SWR in a good range.
That seems to be the case for me as well (unless something else is causing the issue). If so, what other ways of adjusting SWR do I have left?
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Old 07-07-2015, 06:22 PM   #22
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That seems to be the case for me as well (unless something else is causing the issue). If so, what other ways of adjusting SWR do I have left?
Honestly, I'd suggest buying a different antenna. It's the easiest piece in the equation to change.

I found that when I had a spring mount on my firestick I had to trim back more than if I mounted the antenna directly to the mount with no spring. The total length from the mount to the tip is what affects SWR. Adding a spring changes the effective length of the antenna and therefore your SWR.
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Old 07-07-2015, 06:39 PM   #23
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I solved a similar problem using an extra grounding strap from the tailgate to the tub. You can test if this would help by trying to tune the antenna with the tailgate open. Apparently the grounding is improved when there is stress on the hinges..worked for me. Got my SWR down below 2 on all channels.
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Old 07-07-2015, 08:08 PM
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I solved a similar problem using an extra grounding strap from the tailgate to the tub. You can test if this would help by trying to tune the antenna with the tailgate open. Apparently the grounding is improved when there is stress on the hinges..worked for me. Got my SWR down below 2 on all channels.
Interesting, thanks for the advice, everybody. Maybe I need a thicker wire or a strap. Although when I tested SWR without any ground it wasn't appreciably different...
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Old 07-08-2015, 07:16 AM   #25
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So my Firestik is the adjustable kind, but in the entire range of the screw's motion (including completely taking the screw out) did not really change SWR much - it went from around 3.4 with the screw stretched out, to around 3.2 with the screw all the way in, to around 3.1 when I removed the screw. Not sure how else to adjust it. From what I've read this situation might be related to some wiring issues. The only one I can think of is the power connection of the radio. I haven't traced where the wires are connected to (it's not directly to the battery and I wasn't the one wiring it).
Sounds like you are still a little too long. Is your antenna mounted direct, or are you using a spring or quick disconnect?
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Old 07-08-2015, 11:37 AM
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Sounds like you are still a little too long. Is your antenna mounted direct, or are you using a spring or quick disconnect?
It's a 5 ft antenna, so I'm using a spring with it.
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Old 07-09-2015, 10:23 AM   #27
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It's a 5 ft antenna, so I'm using a spring with it.
First that spring only makes the physical length of your Antenna longer.

Second are you sure you have all the correct parts on your Antenna stub? They throw your swr or impedance readings of if they are not right.

Make sure you strip all paint from parts touching each other.

Check your coax and or buy a rg8x for improved performance

Go to a Cb store or ham club and ask them for an antenna analyser... Test all ways

Try a braided strap 30inches is enough and see how that goes.

Keep on working... It will get fixed maye!
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Old 07-09-2015, 11:41 AM
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First that spring only makes the physical length of your Antenna longer.

Second are you sure you have all the correct parts on your Antenna stub? They throw your swr or impedance readings of if they are not right.

Make sure you strip all paint from parts touching each other.

Check your coax and or buy a rg8x for improved performance

Go to a Cb store or ham club and ask them for an antenna analyser... Test all ways

Try a braided strap 30inches is enough and see how that goes.

Keep on working... It will get fixed maye!
Thanks, will try!
First, I will remove the spring to see if SWR is affected or not.
As to the connections. I checked the continuity from the bottom nut of the antenna (the one below the base) to the grounding point on the Jeep body, it's good. Also, the top of the antenna was checked for connection with the bottom - they are insulated from each other, as they should be. The coax is testing ok as well.
Testing the antenna itself (not sure what exactly they test for) may be a good idea at this point.
On the grounding. It is still unclear to me why a regular, 14 (I think) gauge wire is not enough and people use straps. Doesn't really make sense to me. This should only matter if we're dealing with significant currents passing through this connection. With a 4W CB and a 50 Ohm coax I just don't see how high currents can be generated to the ground. For the voltage drop across the wire to be appreciable the resistance of the wire needs to be comparable to the coax one, but it's not, it's far smaller than 50 Ohm, so going with a thick strap won't change much. But I might be wrong - it's possible, I guess, there are spikes of current to the ground happening, but they need to be very intense for the grounding wire's resistance to make any difference.
Cheers.
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Old 07-09-2015, 11:46 AM   #29
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I run something like 20 or 22 gauge wire between my antenna base and a ground point on the body. Seems to work just fine for me. In the group I wheel with, I'm usually the only one everyone can hear.
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Old 07-09-2015, 01:16 PM   #30
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As to the connections. I checked the continuity from the bottom nut of the antenna (the one below the base) to the grounding point on the Jeep body, it's good.

On the grounding. It is still unclear to me why a regular, 14 (I think) gauge wire is not enough and people use straps. Doesn't really make sense to me. This should only matter if we're dealing with significant currents passing through this connection. With a 4W CB and a 50 Ohm coax I just don't see how high currents can be generated to the ground. For the voltage drop across the wire to be appreciable the resistance of the wire needs to be comparable to the coax one, but it's not, it's far smaller than 50 Ohm, so going with a thick strap won't change much. But I might be wrong - it's possible, I guess, there are spikes of current to the ground happening, but they need to be very intense for the grounding wire's resistance to make any difference.
Cheers.
I had continuity between the antenna mount and ground on the Jeep before installing a ground wire, but I still had SWR issues. When I added a 10 AWG stranded ground wire I could get the SWR below 2 on all channels on both my 3 and 4 foot Firefly antennas. Apparently it is not to do with the existence of a circuit per se, but whether the connection makes the antenna "see" the rest of the Jeep metal as a ground plane....

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