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Bearcat 980SSB Continuity

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LAC-777

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First Post,

I have continuity between center of SO-239 (F) and outer threads on back of radio...is this normal? Because of this I have continuity between hot and ground throughout the whole antenna setup...effectively, I think, making this an NGP antenna. Does this radio force NGP from the factory? I took the radio to a CB shop and the owner said it was fine...but this goes against everything I know. There should be no continuity between Hot and Ground, Center and Shield, Radiator and Reflector...

Furthermore, my SWR reads 1:1 throughout the entire band on the built-in SWR meter. I'm running 8' of LMR240 to a Firestik 4'

I'm confused,
Thanks for the help.
 

RFI-EMI-GUY

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It is likely, and good design that there is an RF choke from the center pin to ground inside the radio. It bleeds off static that might otherwise damage the radio. It has nothing to do with antenna ground plane. All antennas need a counterpoise or ground plane to work. The vehicle body provides the ground plane.

Sent from my SM-T350 using Tapatalk
 

mmckenna

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First Post,
Welcome.

I have continuity between center of SO-239 (F) and outer threads on back of radio...is this normal?
As RFI-EMI-GUY said, yes, normal. Remember, you are looking at DC continuity. That's different than RF.

Because of this I have continuity between hot and ground throughout the whole antenna setup...effectively, I think, making this an NGP antenna. Does this radio force NGP from the factory?
"No Ground Plane" is a term sometimes used for half wave antennas. The radio can't change your antenna.

I took the radio to a CB shop and the owner said it was fine...
He's probably correct.

but this goes against everything I know.
Your background is probably in electrical systems, DC, AC, etc? That's O.K. RF is different.


There should be no continuity between Hot and Ground, Center and Shield, Radiator and Reflector...
No, not always the case. Many antenna designs are "DC Grounded". 5/8th's wave antennas are. Many base station antennas are. It's actually a good design, especially for base stations where having the DC ground can help with lightning and static dissipation.

Furthermore, my SWR reads 1:1 throughout the entire band on the built-in SWR meter. I'm running 8' of LMR240 to a Firestik 4'
Couple of things:
1. Don't trust the built in SWR meters. They are useful, but about as useful as a warning light on your car. It might suggest there is something wrong, but you still need to check with the right test equipment. I'd recommend testing with a known-good SWR meter external to your radio.
2. SWR isn't the be all/end all measurement for radio antennas. Especially on setups like this.
3. A perfect 50Ω dummy load will show 1:1 SWR, and it won't radiate worth a dang.


I'm confused,
Thanks for the help.
Understood, and we are happy to help un-confuse you as best as we can.
 

LAC-777

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Hey guys,

Thanks for all the great feedback.

So, How can I test that I haven't inadvertently created an NGP. Will the SWR skyrocket on an 8' feedline?

Also, the owner of that CB shop said I needed to buy RF cable (for CBs) in 3 foot sections. He specifically said that an 8' cable shouldn't be attached to a CB antenna. I've always understood that the shorter the cable the better to help eliminate loss in the feedline?

Also, on the firestik 4' antenna, there's a small jumper cable that comes out of the bottom near the connector. I cut this off assuming that connecting that jumper to the antenna bracket would ground out the RF to the cable shielding. Am I correct in that assumption or should I have used that jumper?

Actually, I'm mistaken, it's not a firestik, it's a Wilson 305-4FD. I guess, looking back and reading the specifications of the antenna it looks like that jumper is for static reduction and not for grounding the RF to the shielding...I may have answered my own question.

But that still doesn't explain why 3' sections is the 'rule'
 

chief21

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To simplify... The no-continuity rule only applies when the coax is isolated from the radio and the antenna. Even some types of antennas will show DC continuity between the center and shield of the connector.

John
 

jonwienke

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Also, the owner of that CB shop said I needed to buy RF cable (for CBs) in 3 foot sections. He specifically said that an 8' cable shouldn't be attached to a CB antenna. I've always understood that the shorter the cable the better to help eliminate loss in the feedline?
The owner is massively uninformed. 3 feet has no relation to CB wavelength, even considering the velocity factor of the coax. It's utter nonsense. Use the shortest length of cable necessary to go from the radio to the antenna.

I'm not sure about the model of antenna you have, but in general it's a bad idea to cut off wires that are part of the antenna design unless you KNOW exactly what you are doing. Post a photo of what you cut off and where it connected.
 

LAC-777

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Uniden Bearcat 980SSB Continuity

The owner is massively uninformed. 3 feet has no relation to CB wavelength, even considering the velocity factor of the coax. It's utter nonsense. Use the shortest length of cable necessary to go from the radio to the antenna.

I'm not sure about the model of antenna you have, but in general it's a bad idea to cut off wires that are part of the antenna design unless you KNOW exactly what you are doing. Post a photo of what you cut off and where it connected.
Attached is what looks like a stock photo. But you can see the pigtail/jumper at the bottom of the antenna. It's doesn't seem necessary for antenna operation, but I may re-attach to see if there is a performance difference. I'm not experiencing any abnormal static or engine noise; i think that's what it's designed to reduce. I had snipped it originally because I incorrectly assumed it was designed to make the connection to a matched cable length in order to create a No Ground Plane antenna.
 

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RFI-EMI-GUY

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Apparently that lead is some sort of gimmick capacitor the way it is wrapped on the antenna. And it appears their "no ground plane required" antenna actually requires a ground plane. Although I can't find anything on their website, the solution is an un grounded counterpoise wire looped through the vehicle to couple the common mode current which normally flows on the coaxial cable.


The "Wilson Way"...
https://www.bellscb.com/products/antennas/wilson/Wilson_Antenna_Floating_Ground_Kit.htm

A better way....
http://img.photobucket.com/albums/v604/IBTJn/Antenna Info/mobile_dipole-drawing.jpg

The best way: Drill a hole in center of roof, drop in an NMO-27, tune for best VSWR and call it a day.

http://i154.photobucket.com/albums/s280/casimon77/DSC00493.jpg
 
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mmckenna

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Hey guys,

Thanks for all the great feedback.

So, How can I test that I haven't inadvertently created an NGP. Will the SWR skyrocket on an 8' feedline?
You can't "create" a no ground plane antenna. The antenna is either designed to operate without a ground plane or it isn't. Nothing is going to change the antenna design, unless you do something silly like start modifying it….

Also, the owner of that CB shop said I needed to buy RF cable (for CBs) in 3 foot sections. He specifically said that an 8' cable shouldn't be attached to a CB antenna. I've always understood that the shorter the cable the better to help eliminate loss in the feedline?
I'm sure that CB shop has a bridge they can sell you along with a nice plot of swamp land.
Apparently it doesn't take any knowledge at all to open a CB shop. I'd avoid that shop at all costs. The owner is absolutely clueless. Makes me wonder how someone can make a living without some basic understanding of the products they are selling.
Or, he's 100% full of crap and he's just trying to get you to purchase stuff you don't need.

Here's the issue with his line of thinking:
As Jon said, 3 feet of cable means absolutely nothing to CB. Might as well say 3 inches, 3 yards, or 3 miles.
You can use very specific lengths of coax cable to hide SWR issues. It doesn't fix anything, it just hides the issue from the CB. Not sure why CB'ers got on this kick, but it's a major disservice. If anyone tells you that you need a specific length of cable to make your CB work, and it's any more or less than the length between your CB and your antenna, walk away.
These length claims do not take into account the velocity of propagation of the cable. Again, clueless CB'ers at work. Ignore them.

The shortest reasonable length of 50Ω coaxial cable of decent quality is exactly what you should be using. "Magic" lengths are just B.S. LMR-240 is excellent cable for mobile use. Better than 99% of the CB/hobby/amateur grade stuff sold. You did good there. As for the length, if one end connects to your radio and the other end connects to the antenna, and you don't have a bunch rolled up somewhere, then it's the correct length for what you are doing. Using magic cable lengths will hide SWR issues. The antenna will show good, but it'll radiate horribly. Some CB'ers seem to think this is a good setup, but it isn't.
What you have is correct, don't change it.

Also, on the firestik 4' antenna, there's a small jumper cable that comes out of the bottom near the connector. I cut this off assuming that connecting that jumper to the antenna bracket would ground out the RF to the cable shielding. Am I correct in that assumption or should I have used that jumper?
Why?
Maybe if you explained to me why you would take a new antenna and start blindly modifying it, I could understand how to best answer that question.
No, you should not have modified it.

Wilson says: "Unique Ground Lead to Help Insure Reduced Static and Ignition Interference".
So, it's intended by the antenna manufacturer to be grounded.
Explain to me why you chose to cut that off again? I'm not following your logic.

Actually, I'm mistaken, it's not a firestik, it's a Wilson 305-4FD. I guess, looking back and reading the specifications of the antenna it looks like that jumper is for static reduction and not for grounding the RF to the shielding...I may have answered my own question.
Yep, always a good idea to read the directions first.

But that still doesn't explain why 3' sections is the 'rule'
Because the CB shop owner doesn't have a clue what he's selling. His "rule" is to BS customers so they'll buy stuff they don't need. Probably how he stays in business.
Lemme guess, all the local CB'ers claim the guys a genius?
 

LAC-777

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Uniden Bearcat 980SSB Continuity

Apparently that lead is some sort of gimmick capacitor the way it is wrapped on the antenna. And it appears their "no ground plane required" antenna actually requires a ground plane. Although I can't find anything on their website, the solution is an un grounded counterpoise wire looped through the vehicle to couple the common mode current which normally flows on the coaxial cable.


The "Wilson Way"...
https://www.bellscb.com/products/antennas/wilson/Wilson_Antenna_Floating_Ground_Kit.htm

A better way....
http://img.photobucket.com/albums/v604/IBTJn/Antenna Info/mobile_dipole-drawing.jpg

The best way: Drill a hole in center of roof, drop in an NMO-27, tune for best VSWR and call it a day.

http://i154.photobucket.com/albums/s280/casimon77/DSC00493.jpg
Ok, so since I deleted that lead, and grounded the bracket to the vehicle, I should be ok. Because I don't need a No-Ground-Plane antenna. If I attached the lead where it says in the diagram, I would effectively be turning the RF shielding into an emitter...as the second addition to the 'dipole'? And the cable length would have to be resonant with the antenna...since my SWR isn't through the roof, I think I've avoided creating the NGP by snipping the lead and grounding the mount bracket to the vehicle.
 

LAC-777

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You can't "create" a no ground plane antenna. The antenna is either designed to operate without a ground plane or it isn't. Nothing is going to change the antenna design, unless you do something silly like start modifying it….



I'm sure that CB shop has a bridge they can sell you along with a nice plot of swamp land.
Apparently it doesn't take any knowledge at all to open a CB shop. I'd avoid that shop at all costs. The owner is absolutely clueless. Makes me wonder how someone can make a living without some basic understanding of the products they are selling.
Or, he's 100% full of crap and he's just trying to get you to purchase stuff you don't need.

Here's the issue with his line of thinking:
As Jon said, 3 feet of cable means absolutely nothing to CB. Might as well say 3 inches, 3 yards, or 3 miles.
You can use very specific lengths of coax cable to hide SWR issues. It doesn't fix anything, it just hides the issue from the CB. Not sure why CB'ers got on this kick, but it's a major disservice. If anyone tells you that you need a specific length of cable to make your CB work, and it's any more or less than the length between your CB and your antenna, walk away.
These length claims do not take into account the velocity of propagation of the cable. Again, clueless CB'ers at work. Ignore them.

The shortest reasonable length of 50Ω coaxial cable of decent quality is exactly what you should be using. "Magic" lengths are just B.S. LMR-240 is excellent cable for mobile use. Better than 99% of the CB/hobby/amateur grade stuff sold. You did good there. As for the length, if one end connects to your radio and the other end connects to the antenna, and you don't have a bunch rolled up somewhere, then it's the correct length for what you are doing. Using magic cable lengths will hide SWR issues. The antenna will show good, but it'll radiate horribly. Some CB'ers seem to think this is a good setup, but it isn't.
What you have is correct, don't change it.



Why?
Maybe if you explained to me why you would take a new antenna and start blindly modifying it, I could understand how to best answer that question.
No, you should not have modified it.

Wilson says: "Unique Ground Lead to Help Insure Reduced Static and Ignition Interference".
So, it's intended by the antenna manufacturer to be grounded.
Explain to me why you chose to cut that off again? I'm not following your logic.



Yep, always a good idea to read the directions first.



Because the CB shop owner doesn't have a clue what he's selling. His "rule" is to BS customers so they'll buy stuff they don't need. Probably how he stays in business.
Lemme guess, all the local CB'ers claim the guys a genius?
I chose to cut it off because I didn't read the directions and assumed it was for creating the "dipole", effectively eliminating the need for a good vehicle ground plane. Since I didn't want to cut the feedline length to match the resonance for 11M, I deleted the lead, and grounded the bracket.

That was my thinking; I think I was off-base.

This is where, I think, CB'ers get the idea that they need a certain length of coax. because an NGP antenna needs a specific length of cable because the shielding becomes an emitter as the 2nd part of the 'dipole'.

However, I don't believe this antenna was ever intended to be used in an NGP configuration. So really, I cut it for no reason.
 

mmckenna

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I chose to cut it off because I didn't read the directions and assumed it was for creating the "dipole", effectively eliminating the need for a good vehicle ground plane. Since I didn't want to cut the feedline length to match the resonance for 11M, I deleted the lead, and grounded the bracket.

That was my thinking; I think I was off-base.

This is where, I think, CB'ers get the idea that they need a certain length of coax. because an NGP antenna needs a specific length of cable because the shielding becomes an emitter as the 2nd part of the 'dipole'
No, not necessarily.
While the outer shield can act as part of the dipole, it's not necessary. No ground plane antennas, like a half wave, don't need a ground plane, hence the name. Again, in this case, the ground plane portion of the antenna system is different than DC ground.

As for the cable length, it's not just the measured length. Each type of coax has a velocity of propagation. That's the speed at which the signal travels through it. It's not exactly the speed of light, it's slower. That needs to be taken into account when doing these "magic length" tricks. CB'ers seem to ignore this and just stick with the 18 feet thing, and that's not going to be correct in every installation. There's some math involved in doing it right.
But again, it's not something for free. Your coax has loss, so if you run more coax than you need, you are just adding losses to the antenna system. And, by using these magic lengths, all you are doing is hiding the real issue, often an antenna that is not properly tuned. While it may trick the radio into seeing what it wants, and thus allowing it to work more efficiently, if the antenna is not set up correctly, it's sort of wasted effort. Unfortunately all CB'ers often focus on is SWR and power output. Nothing more. Making sure the antenna is actually tuned correctly would make a bigger difference.

So, I get it, I understand making mistakes like that. Just be careful about what you listen to from the CB crowd. While many of us got our own start on CB, there's centuries of experience on this site, and we're happy to help you out. We're not trying to sell you anything, so there's no pressure for us to tell you anything but the truth. Always happy to help out however we can.
 

RFI-EMI-GUY

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Ok, so since I deleted that lead, and grounded the bracket to the vehicle, I should be ok. Because I don't need a No-Ground-Plane antenna. If I attached the lead where it says in the diagram, I would effectively be turning the RF shielding into an emitter...as the second addition to the 'dipole'? And the cable length would have to be resonant with the antenna...since my SWR isn't through the roof, I think I've avoided creating the NGP by snipping the lead and grounding the mount bracket to the vehicle.
I don't think the pigtail is necessary if you are getting an effective ground from the vehicle. I have not seen any other antenna made with such a gimmick. There were some HF antennas with a flying lead to tap a particular band, but this is not the same case.

It is a misnomer to think that an antenna does not require a counterpoise or a ground plane, regardless of the wavelength fraction. For a handheld, the radio and your body are the counterpose. For a vehicle antenna the current flows through the vehicle chassis if the antenna is properly grounded or follows the feedline if it isn't. In the case of the feedline, this is probably where all of the "magic" cable length old wives tales originated.
 

kf4eyr

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i have in my antenna pile a firestick antenna that is 4 foot long ,, it was gave to me by a neighbor who had bought a big honda bike,,, it was on a bracket with no insulated washers,, the coax was connected to a clamp looking thing that looks like it would move up and down for adjustment,,, figured it was for some kind of no ground plane use,, since it was on a bike,,,


as to the length of coax i have always used what it takes to get where i am needing it,,, in my ranger i have 9 feet of belden rg 213 to my amp behind the seat then to the radio 6 feet of belden rg8x that is just the lengths that i needed ,,no formula or any thing,,,,now on my blazer i have a wilson 5000 hard mounted on the roof in the middle,,, and have the coax under the headliner and down a post then under the floor mats to the front passenger seat where i have about 6 feet coiled up,,,,the length is 18 feet with the mount and ends that came with it,,,, swr 1,2 across the whole band and 10 meters is 1.5
 
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