| Author | Message | ||
     Ned Connolly (Roverned) Member Username: Roverned Post Number: 66 Registered: 10-2002 |
I'm installing my 4' Firestik II using their Jeep Bump Stop kit (bracket and coaxial). It's pretty much straight-forward, with the exception of a few things: 1. it looks like the bracket comes with a grounding screw and there is a hole on the bracket that this screw could go through, but there are no instructions/pictures about this part of the install. 2. How do you tune your antenna? | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 472 Registered: 06-2002 |
You only need to run a ground from the antenna mount if it is not attaching to something that is grounded. Forinstance, I mounted mine to my brush bar and it is powder coated so it did not ground when I attached it. I had to run a ground from the mount and drill into the brush bar and secure it with a screw to gound it. As for tuning it, you need an SWR meter to tune the antenna lenth for optimum performance. You can get one for cheap from Radio Shack and the instructions come with the tuner. Check out this website for information. http://www.firestik.com/Tech_Docs/Setting_SWR.htm http://www.firestik.com/Tech_Docs.htm | ||
| George Clayton (Offcamber) Member Username: Offcamber Post Number: 85 Registered: 09-2002 |
   Just had to drill a couple of holes in the tire carrier, used the mount I got with the Firestick Kit. No grounding necessary. HTH | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 474 Registered: 06-2002 |
Antenna location is key as well. If you have a 4', it should be OK on the tire carrier like the above pictures. If it is shorter, and wont stick up much over the top of the car, or you have a rack and frequently load it, it will cut you ground plane down to nill and get poor performance out of the radio. Again, those web addresses well talk about this and alot of other things you need to know. | ||
| Ronnie McKinney (Ronnie) Member Username: Ronnie Post Number: 63 Registered: 08-2002 |
Eric, do you have any pictures of your mounting/grounding? I am also running a firestick on my tjm front bumper and can't seem to get a low swr reading. Some sort of ground wire and set screw might help my situation and I'm looking for ideas. | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 476 Registered: 06-2002 |
I will get some pictures Teusday as it is dark now. There are a number of reason that could be causing a high SWR. Poor ground plain, poor location, not tuned properly, short in the cable or improper lenth, no ground on the antenna or bad ground, bad meter, bad radio, etc... Check out this site. http://www.firestik.com/Tech_Docs/swr-trblshoot.htm Basiclly, I ran a 2", 12 guage wire, terminated on both ends with a round type end, from the ground point on the mount and drilled into the brush bar with a screw. Verified grounding with a meter for continuity. | ||
| Reed Cotton (Reedcotton) Member Username: Reedcotton Post Number: 68 Registered: 01-2003 |
Proper cable length is a good place to start. It needs to be a proper harmonic of the CB frequency band. (I forget the exact demensions) Radio Shack premade CB antenna cables used to be pretty good. Go to a local truck stop and ask around for their CB guru, that person could make one up if you can't. Without the right length cable, no amount of tuning on the antenna trimmer will bring it into range. With the right size cable tuning will be minimal. Equally important as mentioned above is a well grounded ground. A ground that is not properly grounded is often called an antenna, and may cause problems beyond antenna trimming.) As mentioned above, use a continuity meter to check this. While doing this also check the antenna wire on the cable, a poorly soldered, or broken one of these is useless. Once the above is established, then use an SWR meter to tune the antenna. The one Radio Shack sells is good enough, and has instructions on how to use it. Ideally you want to mount the antenna where it will radiate the same in all directions. Unless you put it on the center of the roof, this will be pretty impossible. For most trail use of a CB, you can put the antenna about anywhere that will satisfy the above requirements and won't get it snatched off by a passing tree. | ||
| Rob Davison (Nosivad_bor) Senior Member Username: Nosivad_bor Post Number: 240 Registered: 02-2003 |
it says right on the package of the firestick II to use 18ft of cable. rd | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1321 Registered: 02-2002 |
Proper cable length is not at all critical for a properly installed antenna. One cannot make a blanket statement as to cable length due to variations in velocity factor of the dielectric material. Foam has a very different velocity factor than polyethylene, as a result, the electrical lengths of these wires will be different for a given physical length. The ground plain is not dependent upon the height of the antenna above the vehicle. Positioning can cause capacitive coupling effects and will dramatically affect radiation angle which is already poor for short distance communications using vertical antennas. Inability to tune for low SWR is caused by many things, including the proximity of the person doing the tuning. SWR is also affected by the movement of the antenna when underway as the orientation of the antenna to the vehicle changes in less than predicatble directions. Ground all of your antennas using the shortest stoutest cable you can, use the shortest physical length of cable that you can, and mount it as high as you can. Peace, Paul WD9HRP Extra Class amateur prior to April 15 | ||
| Rob Davison (Nosivad_bor) Senior Member Username: Nosivad_bor Post Number: 241 Registered: 02-2003 |
Firestik blatantly recommends 18 feet of cable. This recommendation is printed in english on the outside of the package in plain site. I would tend to heed this advice as it is from the manufacturer and it is not only reasonable from a common sense perspective but it is also prudent if you want to getting the most out of the antenna. or you can read it on their web site: http://www.firestik.com/FAQ.htm | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1322 Registered: 02-2002 |
If it were considered to be that important, they would include a wavelength for the cable to be, not the physical dimensions. Did they provide a material of construction for the dielectric? If not, depending upon the coax, the electrical length could be quite a bit different from the physical length. As it is, the 18 foot length would be for a specific segment of the band, and likely too short to matter. In a single antenna system (non-phased) fed with non-radiating feedline (coax in this case) the feedline length will have little to no impact on SWR, merely attenuation of incoming signal-this is why feedlines should be as short as possible to reach from transmitter to radiating element. I continue to stand by my earlier statement. BTW-I checked out the website you indicated. There are numerous fallacies in their statements, including the dangers of coiling unused feedline. Other antenna manufacturers include instructions on just how to make that coil to improve the common mode rejection of RF on the outside of the feedline. http://www.hy-gain.com/man/pdf/DB-1015A.pdf illustrates the assembly of just such a choke. Much more exhaustive discussions on feedlines can be found at http://www.arrl.org/tis/info/pdf/49470.pdf, along with SWR. You'll notice that all of the discussions deal with far longer runs of coax than what would ever be encountered in a mobile situation, but you get the idea. Peace, Paul | ||
| Rob Davison (Nosivad_bor) Senior Member Username: Nosivad_bor Post Number: 242 Registered: 02-2003 |
i dont follow the use of the word 'dielectric' in this context. so i am not sure what you are talking about but i can assure you that if i have three thousand feet of cable wrapped up in the back of my truck that it's going to make a difference comparted to a nice 18 ft length. rd | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1324 Registered: 02-2002 |
Dielectric is the insulator between the shield and the center conductor. If you check out the secondlink,velocity factor is described. Essentially, electrons and RF do not move at the same speed through a shileded conductor that they would in free air. As a result, the electrical length of a feedline is not the same as its physical length. As a result, if one were to be concerned about the lengths of his feedline (where's Merv when you need him?) one would be concerned about the fraction of a wave they were trying to achieve with that length of feedline, rather than giving an absolute length. As for the 3000 feet, that's not exactly realistic, whereas as short as possible is. THe biggest impact of that long a feedline would be due to RF resistance (attenuation) rather than anything else. At a few dB per 100 ft' length, you'd have a great attenuator. To make matters worse, 1/2 wavelength pieces of coax can in fact act as stub attenuators reducing the response at the resonant frequency dramatically. To get back to the issue at hand, place your antenna as high as you can, as far from metallic objects as you can, ground with the shortest piece of big wire you can, and feed it with the shortest piece of coax you can. Peace, Paul | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 478 Registered: 06-2002 |
Paul sounds like he really knows what he is talking about. I don't know nearly as much as him about radios and RF signals BUT, in this case we are dealing with citizen band frequencies with little power and I don't know if it is different but I will go with what Firestik says to do anyday. They are the best made CB antennas so they have something going for them. I would imagine they know what they are talking about as well. Here are pictures of my setup. I have an SWR of 1.20 at CH 19 and it is at 1.5 on CH 40 and CH 1 respectivly. That is a very good SWR for a CB and I followed Firestiks directions to the tee.     | ||
| david summers (Texmoto) New Member Username: Texmoto Post Number: 37 Registered: 12-2002 |
Eric, I just installed my Firestik on the spare tire carrier ala Expedition Exchange. My SWR blows on all channels. I'm going to improve my gound first, but if that doesn't do it, then I may try moving it to the front. How long a length of coax did you end up using? How much tuning needed to be done? | ||
| Ronnie McKinney (Ronnie) Member Username: Ronnie Post Number: 64 Registered: 08-2002 |
Just so everyone knows, I do know how to read the outside of the package and I am using the recommended 18' of cable. And yes, they do recommend a specific insulating material to use although I don't recall what it is right now. Again, I think my problem is probably the ground. Eric, thanks for the pics. My bumper already had a fixed/welded antenna mount on the brush bar so I don't think I need that grounding wire now that I see what you're talking about. My entire bumper is powdercoated so I may need to use the dremel to get down to bare metal where the stud mount is. What's everyone's opinion on that? | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 479 Registered: 06-2002 |
I used 12' I believe and it was just right. Very little tuning was done. A few things to remember: 1) It is recommended that you choose a cable length in 3' increments. 18' is standard. 2) Tune your antenna with the cap on. In other words you have to take cap off, make adjustments to antenna, put cap back on and check SWR. One thing David might be incountering is a leap in SWR as a result of the antenna being close to the body causing high impedence. You should not have more that half the antenna within 12" of vehicle or poor performance can be expected. Many people have this setup and it generaly works fine but may not be getting real distance or performance on transmit. Remember that most of us will be using the CB on trail and don't need maximum transmit distance. An SWR of 2 is OK and some may say if it works, and people can hear you, leave it alone. The only thing you might be aware of is a very high SWR (over 3) could result in damage to the radio. | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 480 Registered: 06-2002 |
Ronnie, yes you would have to get to bare metal to guarentee a good ground. If you can, double check it with a meter. | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1326 Registered: 02-2002 |
Gentlemenn: I do not mean to demean or insult anyone. I similarly do not wannt someone to put an 18' piece of cable on their radio and think that will fix all. Regardless of the length of cable you wish to use (clearly I have no ability to compell someonee to use something do not wish to), the other issues are far more important for an efficiently radiating signal. Ground your antenna base Use the shortest length of cable that will reach from transmitter to antenna Use the longest antenna you can use Put it as high and as far away from other metallic objects as you can. Now start tuning for resonance. Peace, Paul | ||
| Ned Connolly (Roverned) Member Username: Roverned Post Number: 68 Registered: 10-2002 |
Wow, don't check DiscoWeb for a few days and blammo: 19 posts! Just an update on my situation (4' firestik II mounted to the spare tire mount, 18' of firestik-supplied coax connected to a Cobra 75 something or other under my driver's seat...): I have borrowed a friend's SWR meter and adigital multimeter volt checker thingamabob and plan on checking things tonight. My friend thinks, more than anything, I may have a short because I can only hear garbled conversation on all the channels. Soldering's not my strongsuit so he may be right. And he said, regardless of SWR readings, I should be "receiving" decent audio on most channels. Anyway, wanted to bring that to some of the other CB newbies, like myself, who may be overlooking the obvious problems of their CB install. | ||
| Ronnie McKinney (Ronnie) Member Username: Ronnie Post Number: 65 Registered: 08-2002 |
Eric, you said to doublecheck everything with a meter. What sort of meter checks continuity? Sorry, most of my toys have been beaters in the past so I've never heard of/used one of these. As a matter of fact, this is the first cb I've ever owned. | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 482 Registered: 06-2002 |
You would be looking for a setting that would beep or alarm when the two sensors are touching; this is on an electrical multimeter. It is usually between the the AC and DC settings. If you put one end on a known good ground, like the chassis, and the other on the bottom part of the antenna, the portion of the antenna that the cable connects. This will tell you that the antenna is grounded to the chassis and, viola, you are golden! | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 483 Registered: 06-2002 |
 This is the area I am talking about. Try both bottom and top. I thought about it and I can't be for sure it is the bottom, so try both. | ||
| david summers (Texmoto) New Member Username: Texmoto Post Number: 39 Registered: 12-2002 |
Help! I have been trying to tune my Firestik, but still have SWR readings of just to just over 3. I have tried mounting on the spare tire carrier and the bull bar. I have changed cables. I have checked and found no faults in the coax cables or the mount itself. I have been following this tread and have read Firestik's SWR trouble shooting list. Any suggestions? (other than throwing the CB in the trash) | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 485 Registered: 06-2002 |
David, what kind of antenna and CB do you have? Where is the antenna located? | ||
| david summers (Texmoto) New Member Username: Texmoto Post Number: 40 Registered: 12-2002 |
The CB is a Cobra 75 (new) and a 4 ft. Firestik. The first location was the spare tire carrier (DII) with 18 feet of cable. The second location was the ARB bull bar with 12 ft of (different) cable. Before moving the antenna to the front, I tried tuning it by removing one wrap of wire (per the instructions) and replaced the tip. This had little effect on the SWR readings. | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 486 Registered: 06-2002 |
Well, it sounds like you have the kind without the tuning screw. Those are harder to deal with, but in my experience, one wire wrap will not do a whole lot for SWR at first. You have to do one at a time until you see it coming down and be patiant. Verify the gound on the antenna and start again. Antennas are not so expensive so I always recommend the Firestik with the tuning screws, way easier to tune. (Firestik II of Firefly) I have the Firefly and it took me 10 min to tune it up. Another thing to consider is how and where the cable is run. If you install the antenna on the bull bar, you could run it into the engine compartment and that could cause some RF interference. I ran mine up the gap where the hood comes down, between the body and rubber and through the door arch and into the vehicle. | ||
| david summers (Texmoto) Member Username: Texmoto Post Number: 41 Registered: 12-2002 |
Thanks for the input. I will try peeling and cuting more wire off the antenna. I have already tried another SWR meter and the results were the same. | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1348 Registered: 02-2002 |
Before you cut anymore, determine the resonant frequency, or at least if it is above or below your desired operating frequency, otherwise you don't know if the antenna is too long or too short. To raise resonant frequency, you cut, but to lower, you must lengthen the antenna. Also, it sounnds as though neeither of your mounting locations is giving you a good return path to the transmitter. Run a ground from the antenna mount to the chassis and see if this changes anything. | ||
| david summers (Texmoto) Member Username: Texmoto Post Number: 42 Registered: 12-2002 |
Here's an update. Cut off many coils of wire (did this before I saw Paul's last message). SWR went from 3+ to 2ish. But, before cutting this time SWR on channel 40 > 1, but now 1 > 40. SO, for no reason what so ever I placed a spring beween the mount and the quick disconnect. Vola! SWR less than 1.5 in channels 1, 19 and 40. Maybe not great, but what the hell. I will take it for now. I am going to hook up an additional ground wire today. To everyone, thanks for all the help. David |
