| Author |
Message |
    
Blake Luse (Muddyrover)
| | Posted on Monday, September 30, 2002 - 10:41 pm: | 
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I have a cobra 40ch cb thats small but worked
i mounted it on my disco's brush guard
i bought this
NGP-1 Everhardt RV/ Boat/ Fiberglass Trucks/ Vans 'No Ground' CB antenna kit. With all the fiberglass now being employed on cars, mini vans, motor homes, light and heavy trucks, it has become necessary for CB systems to create their own electrical 'ground plane' in order to work efficiently. The NGP-1 is available with a Black or White 4 foot fiberglass antenna that receives the weather bands, 18 feet of factory pre-tuned cable and a 3 way fiberglass mirror mount
on this websitehttp://www.alfenterprises.com/noground.htm
what should i do , i don't think that i can tune the swr on this one or anything
i'm new at this please help
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Matt Collins (Njdisco)
| | Posted on Monday, September 30, 2002 - 11:05 pm: |
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Blake,
There should be some tuneing available on the antenna. Is there a small set screw at the top of the whip? If there is this can be adjusted and dialed in so that you get much clearer reception by moving the tip of the whip in or out. Also it would not hurt to find a friend or a CB shop w/ a tuner. You can buy these at Radioshack, but once you tune in the radio you really never use it again. So it wouldn't hurt to find a CB shop and they can tune your radio in perfect and maybe your antenna as well
-Good Luck
Matt |
Blake Luse (Muddyrover)
| | Posted on Monday, September 30, 2002 - 11:23 pm: |
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its a fiberglass antenna
I pulled off the rubber top to see but i don't think it had anything
i'll check in the morn
how do you check and when you check how do you change the swr |
Al Oliveira (Offroaddisco)
| | Posted on Monday, September 30, 2002 - 11:39 pm: |
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Changing the SWR is antenna dependent. Most have a set screw. Some require you to cut a section of the antenna or the cable that runs to the radio.
An NGP antenna is more or less a resonant antenna (1/2 wave). There needs to be some way to adjust the SWR on the antenna system. I can't help you how to do that since I don't know the antenna. It could even be something as crude as trimming the cable.
Also check that the cable isn't shorting out somewhere. A common place for a short is at the point where the antenna mounts to the base. There should be an insulator of some type. Make sure that it's properly installed. |
Blake Luse (Muddyrover)
| | Posted on Tuesday, October 01, 2002 - 01:19 am: |
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the coax wire was installed to the mount by the company.
It has a screw on top to adjust |
Jerry Crawford, 98 D-I
| | Posted on Wednesday, October 02, 2002 - 12:06 pm: |
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Mounting antenna's on brush guarda and bumpers is a fairly good way to insure marginal quality of your CB communications. I realize SOME might work OK but most will not give you the good results. One source of solid data and info about antenna is on the FireStik site at Firestik Home page and look at the tech page. It tells you a lot of why your radios don't work well. Proper and solid grounding is a big culprit and that's one of the easiest problems to fix. The reason NGP mounts were invented was for the reason you stated - nonconductive body's on modern auto's and motor homes but you don't need an NGP antenna on a Disco if you know how to incorporate a grounding strap into your mounting system. |
Al Oliveira (Offroaddisco)
| | Posted on Wednesday, October 02, 2002 - 12:29 pm: |
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Jerry, I don't know if it was you or someone else who posted that Firestik site before but I still don't get the need for a "ground." I do understand the need for a ground plane or counterpoise. Now I'm no antenna guru but I would think a brush bar on a bumper would offer an "okay" ground plane to get you a good SWR if the antenna was properly mounted to the bumper. The bumper would work like a single radial. But the signal wouldn't be uniform since it wouldn't have a forward/backward radial. But since he said he has a NGP antenna the antenna itself is resonant and shouldn't need a ground plane. |
Paul T. Schram (Paulschram)
| | Posted on Wednesday, October 02, 2002 - 01:04 pm: |
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Grounding, grounding, grounding.
But, and a big but it is, he made the statement that he isn't receiving well. Most of the issues that have been raised here while somewhat related to reception, are much more transmission related.
I would look first to see what happens when he just plugs a piece of wire into the antenna connector and see if the reception doesn't improve.
At this point, I'm betting there is a kink or other problem with the coax that is causing it to be shorted to ground.
Blake:
Is it transmitting well? Do you have any test equipment? Field strength meter, or SWR meter? Do you hear ignition noise, or is the receiver dead completely?
I'll bet you're not transmitting any better than you are receiving.
Look to the Coax first.
Paul |
gp (Garrett)
| | Posted on Wednesday, October 02, 2002 - 01:08 pm: |
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this may have been mentioned, but i am not reading all this. my issue was that i had lost the bushing (insolator) in between the mount. there must be a bushing in there or you can do damage to your unit. (sorry no pun intended) but this took care of my issue. just had forgotten to put a new one back on when i busted my old antenna. |
Blake Luse (Muddyrover)
| | Posted on Wednesday, October 02, 2002 - 01:22 pm: |
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this antenna is for a no ground mount so i shouldn't need a ground
it picks up and i've talked to people close by
some say i "need to put some fire in my wire" the exact truckers words
i have my cb plugged into my cig lighter using an adapter
if i directly wired it to my battery would i get a better signal? |
Paul T. Schram (Paulschram)
| | Posted on Wednesday, October 02, 2002 - 02:10 pm: |
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Blake:
Just because it says you don't need a ground doesn't mean you don't need one. Do you have the chassis of the radio grounded, other than through the lighter socket? I suspect that if you look in the manual for the radio, it will make reference to the necessity of a good ground, both DC and RF.
Wiring to the battery will only get you less ignition noise.
If the mount has a metal bracket, try running a wire from that bracket to a metal part of the truck,like where your bumper bolts to the truck.
The supposedly groundless antennas are a serious compromise and I'm afraid you have discovered the effects of this compromise.
We all have to compromise somewhere in life, it is up to each of us to decide where, when, and what to compromise on. If you wish to hear better and be heard better, you will need a different antenna.
It is only my opinion, regardless of how much radio theory it may be backed up by. You can take someone's suggestions or not.
Paul |
Blake Luse (Muddyrover)
| | Posted on Wednesday, October 02, 2002 - 02:28 pm: |
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i don't have the radio mounted yet
its just sitting in my seat right now
that may be it huh |
Al Oliveira (Offroaddisco)
| | Posted on Wednesday, October 02, 2002 - 02:49 pm: |
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Paul and others.... if a ground (RF) is really needed and I'm talking ground here not counterpoise then how do hand held (HT) radios work? I know that HF and CB just suck on HT's. But that's because it's hard to fit a resonant antenna onto a small package.
Take a frequency close to 462mhz and you only need a 12" antenna to have a 1/2 wave antenna that needs no counterpoise that works very well in that frequency. Most will use a 1/4 wave 6" antenna with no real ground TXing at 4 or 5 watts. I've seen base antennas installed inside attics with no ground at all other than a counterpoise and they work very well.
But this is all moot since his antenna is a NGP (no ground plane) antenna like those often used on fiberglass boats.
So my question still stands. Why do you really need a RF ground and not a ground plane? And don't say just because. 
Blake, The cig lighter adapter is really bad. You should get a direct connection to the battery if you can. Even if you just run some temp wire into your cab to test it out. Check out www.gmrsweb.com and click on the message board link for additional help on the radio. |
Paul T. Schram (Paulschram)
| | Posted on Wednesday, October 02, 2002 - 03:11 pm: |
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Counterpoise and groundplane are synonymous. In each case, they are providing a mirror of the radiator.
An RF ground is a ground that will conduct radio frequency at the frequency you are using (non-resonant). A resonant ground will place a voltage peak at 1/4 and 3/4 wavelengths, a current peak at 1/2 wavelength and full wavelength.
A DC ground may be an RF ground, but not all DC grounds will work as RF grounds.
Handy-talkies use either the chassis of the radio (as is the case with such as Motorolas which have a very hefty metal chassis), or, they have a corresponding coil of wire as the groundplane, or the antennas are tapped at a point somewhere between the feedpoint and a ground (another of those times where I wish I knew how to do those cool graphics everybody else knows how to do). There may even be a counterpoise etched onto the circuit board next to the output network. Handy-talky output networks are also designed such that they can withstand extremes of SWR with no damage to the unit, nor impact on reception/transmission.
I suspect that Blake is suffering from his antenna being detuned by the close proximity of such a large metallic object (his truck). If his truck were fiberglas like the boat for which his antenna was designed, there would not be such a huge chunk of metal in one place to detune the antenna. Also, his not having the radio mounted (grounded) means that he has no ground reference, other than that which he has by virtue of the lighter power supply ground.
He may also have a problem with his SWR as the antenna can be tuned for use on a fiberglas boat and work well in most mounting configurations on a boat, once you put it on a vehicle, the SWR will change as the antenna is moved about the vehicle.
A few years ago, I was having an awful time with my amplifier not wanting to tune up, in spite of my knowing I had a resonant antenna and robust groundplane (stake in the ground and many radials). As I wold tune up, the plate current would begin to oscillate something terrible. Fearing I was destroying my tube, I decided to go over every component with a fine tooth comb... Everything in the shack was good, so outside I go. My ground had become detached from the common mounitng point, the ground stake. Hooked it back up and away I went. |
Al Oliveira (Offroaddisco)
| | Posted on Wednesday, October 02, 2002 - 03:39 pm: |
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Thanks Paul.... that's what I was looking for. But wouldn't then properly mounting the antenna to the front bumper be a sufficient groundplane even if the bumper isn't well grounded to the vehicle? Wouldn't the bumper act as a radial? |
RJ Clayton (Tozovr)
| | Posted on Wednesday, October 02, 2002 - 03:43 pm: |
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You can also change your SWR by moving the coax around. Did you coil the coax up (the slack)? This is a NO NO. Any excess coax should be rolled like a yarn Skein, ot layed out in a wandering path away from other electrical sources.
HTH
RJ |
Paul T. Schram (Paulschram)
| | Posted on Wednesday, October 02, 2002 - 04:37 pm: |
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RJ:
Where did you hear that? Time to run the flag up the pole! Coiling one's coax allows it to act as a common mode choke cancelling out some forms of interference.
Also, moving the coax should have no impact on the received or transmitted signal.
Coax should only be rolled in loose coils with fairly large radii. Rolling it too tightly can cause the inner conductor to contact the outer shorting it out-a bad thing! Same thing with bending it too tightly or allowing it to kink.
Al:
Yes and no. It all depends upon what the antenna "Sees" as its counterpoise. It might see the bumper as a big capacitor or a big inductor, depending upon how well it is electronically connected to the frame. This is why we see things like pieces of braid running from the hoods of American cars to the body, or frame. Think about it, why would the hood need to be grounded if it wasn't for fear of it becoming resonant at some frequency that might interfere with either radio reception, or the electronics of the car. In this situation, I would run a stout wire from the antenna mount to the bumper and another from the bumper to the frame, each of them as short as they can be.
I know I'm not the only ham on this board, where the hell are my brethren to help me out on this? |
Al Oliveira (Offroaddisco)
| | Posted on Wednesday, October 02, 2002 - 05:03 pm: |
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Thanks Paul, Maybe it's time for me to get my ticket. I wouldn't mind getting my GMRS radios and MURS radios tuned to the 2meter and 70cm frequencies. I never really liked the idea of trying to fit a 102" antenna for CB into a 3 or 4 foot space. By comparison GMRS seems so much easier to setup even though the principles are the same. |
Tate (Tate)
| | Posted on Wednesday, October 02, 2002 - 06:11 pm: |
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The coiling of the coax strikes me as very strange. If you look at the math of how the field travels in a coax wire, the beauty of it is that all the energy travels in the insulator between the inner and outer conductors. There should be little to no field outside of the wire. Lemme know if you want me to did up the math supporting this. |
Brian Friend (Brianfriend)
| | Posted on Friday, October 04, 2002 - 01:21 pm: |
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I think the problem is probably the cigarett lighter thing. I tried that and got no where. Hooked it up to the batter and fixed all my problems. I'm no wizz here but it worked for me. Also.....antena is mounted to my bumper. |
Paul T. Schram (Paulschram)
| | Posted on Tuesday, October 08, 2002 - 10:21 am: |
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Tate:
Think about signals flowing along the outside of the coax. Each rotation places the following sine wave 180' out of phase, thus cancelling any induced interference. It is so common that most beam antenna manufacturers suggest it be done on every installation.
Paul |
Hank (Disco_Tex)
| | Posted on Tuesday, October 08, 2002 - 12:58 pm: |
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Radio and antenna must be grounded. Setting the SWR's will also improve the reception and transmit signals.
My .02 |
Al Oliveira (Offroaddisco)
| | Posted on Tuesday, October 08, 2002 - 02:28 pm: |
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I found this interesting.... might help a little...
http://www.signalengineering.com/ultimate/index.html |
Paul T. Schram (Paulschram)
| | Posted on Tuesday, October 08, 2002 - 02:40 pm: |
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An even better site is
WWW.Radioworks.com
Check out Jim's Notebook. He is somewhat opinionated about some particular styles of antennas, but he knows his stuff and explains it pretty well.
Paul |
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