Freightliner antenna issue

Trucks antennas

Have the older antennas checked with an external s.w.r meter,not the one built into the radios,if they check high then by pass them,or try new antennas on the mounts,if the new ones show high its most likely coax issuses,the wilson 2k is an onmi-directionel antenna and will talk nicely for you,and it should talk father than 6 miles with ease depending on noise and channel traffic,good luck G.R.

A couple of things to consider.
If you can unwrap an antenna and have it work right as-is, you are very lucky! All antennas have to be adjusted a bit for them to work correctly. They have to be tuned, just like that engine in your truck. Your present antenna(s) may be just fine, but not tuned correctly. If you can't do that then find someone who can. That goes for new antennas too.
I can't think of any vertical or mobile antenna that is directional all by it's self. So, the quick-n-dirty answer to that question would be that they are omnidirectional (work in all directions). There are a couple of things that you have to consider though. One is where you mount the thing because an antenna's surroundings can make them directional to some extent. Antennas would rather be above metal rather than beside metal and don't like being under metal at all. So you do what you can to make them 'happy'. You can only take that so far and then the antenna just has to live with it, you know? And that's where tuning comes in.
I don't know why but the SWR meters in radios seem to never give an honest reading. An external meter is almost a requirement. Except for the more expensive meters all of them require adjustment/calibration to give a meaningful reading. And then, you have to know what that reading means so that you can make the necessary adjustments. Don't want to go to that trouble? Okay, not everyone does, so find someone who can do it for you.
- 'Doc

I'm not trying to 'talk down' to you! I certainly don't know it all, and that's how I would explain it to me too.

StormyNitesOnCB said:

Firestik Has a nice artical about semi-truck Coax
here it is: Pre-Wired Semi Coax

Click to expand...

There is some descent data in the group of articles that includes that one, and easy to read. I'll post a link to their article index...

Tech-Docs Index

The problem is there are also glaring errors, including the specific 18 foot length that is referred to in StormyNites link above and multiple other articles from their index page I linked to. Apparently they also think that SWR itself is a source of loss, and a 102" whip acts like a base loaded antenna and the low SWR point is also the resonant point of the antenna. I could go on...

Just know this, take any data that is given on the Firestick web site with caution. There are serious glaring and obvious errors in many of their "tech" articles that anyone who qualifies to be a "tech" should easily be able to discredit.

One of them, titled "Things Every CB'r Should Know" I did a write up for someone. It is seriously riddled with errors and should be ignored at all costs.


The DB

Try a ground wire from the door to the door jam, your hinges have nylon bushings.

Ground wire to door jam works. If you have a bar across the back of the cab/sleeper clamp antenna there. Run the coax down the back to the bottom then through the passenger door. Feed it through there. Be careful not to crimp it. Depending on the install. You may have to run it up the right side window post to the radio coby hole up top. For dash mount run the coax up the right side of the dash. Then across to the radio. You can use extra long bungy cords (the black rubber ones) to strap it there. I use 6' Fransis antennas most of the time. (Pilot Truck Stops.) Sometimes Wilson 5000`s. I have to slip seat alot so my radio is mounted to a plastic cutting board. (grocery store) I just put it on the seat. Get a good external speaker. (Texas Star. The one in the chromed metal case.) Don't be cheap on coax. You will not notice any difference in the antenna performance if it a little too long. 73's. Curly.

The DB said:

and a 102" whip acts like a base loaded antenna

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I suppose given that they both have the current maximum at the base of the radiating element then it has some validity.

And if they're having 18ft lengths of coax which is acting as "the missing half" then I guess because of the losses the SWR minimum could coincide with the resonant point of the antenna...

M0GVZ said:

I suppose given that they both have the current maximum at the base of the radiating element then it has some validity.

Click to expand...

All quarter wavelength antennas have their current node at the base of the antenna, including top loaded and continuously loaded antennas. So following your logic, Firestick's top loaded antennas also act like base loaded antennas. The current node being at the base of the antenna is a staple of the quarter wavelength antenna, shortened or otherwise.

M0GVZ said:

And if they're having 18ft lengths of coax which is acting as "the missing half" then I guess because of the losses the SWR minimum could coincide with the resonant point of the antenna...

Click to expand...

The pages on that tech site actually uses a different length for the other half of their no groundplane antennas. It is the only time that I saw them talk about using the outer shielding of the coax for the other half. This coax of theirs also has continuity, a small amount of resistance actually, between the center conductor and shielding with no antenna hooked up... Its right on their web site in those same tech articles...

Also, their theory of what happens at a half wavelength of coax isn't true... To quote Firestick directly...

Firestick said:

Because of the imperfect world, we almost always recommend 18' (5.5m) when our products are used. We do so with good reason too! At 18' the voltage curve has dropped back to the zero voltage point where the cable meets the antenna which reduces the reactance within the cable itself (a null cable if you would). It has been our experience that if the antenna location makes it somewhat out of sync with its surroundings, cable lengths that are not multiples of our 18' suggestion adds to the problem.

Click to expand...

Here is a link to their specific page that has that quoted text.

First off, they are apparently referring to a forward wave as they are talking about the voltage as it is on the line where the line meets the antenna. If they were talking about a reflected wave they would be referring to where the voltage meets the radio. In either case this information is wrong, the forward and reflected voltages (if the reflected voltage exists) are always changing at all points of the coax, including the radio and antenna ends. The only apparent relatively stable voltage on the coax is caused by the standing wave, and the standing wave waveform is a function of both the forward and reflected waveforms.

Second off, they have no concept of a velocity factor. Every transmission line has a velocity factor. This velocity factor is the change in the speed at which the waveform travels through the coax or any medium. Until they take the velocity factor into account they will never have anything like a "correct" length. Therefore this fictional "null" they are referring to is not where they think it is, and will be at different places for coax with a different velocity factors.

Third, they also have a fundamentally flawed view of reactance. There is no reactance in the coax itself. The actual reactance in the system is in the antenna and the matching network if one exists. The coax can transform the feedpoint impedance mismatch including feedpoint reactance into any number of values, but in the coax itself it is not reactance but simply a reflected waveform that interacts with the forward wave to create the standing wave.

All that for one a quoted paragraph, and the quote is only about half as long as the full paragraph it came from. I provided a link to the page so you can see I'm taking what is being said in context for yourself if you wish...


The DB

The DB said:

All quarter wavelength antennas have their current node at the base of the antenna, including top loaded and continuously loaded antennas.

Click to expand...

Err no. The idea of top loading the antenna is to distribute the current evenly across the full antenna length. It also increases Rr thus increasing the efficiency of the antenna.

Source, ARRL Antenna handbook, 2" thick, has lots of information about antennas and the theory. You should buy a copy. Very informative.

I have to agree with 'DB' that there are a lot of misconceptions or errors in the ideas on Firestick's site. Their 'how to's are almost 'how don't's. That's not new by any means, they've been there for a very long time.
Current distribution in an antenna is only important in that it 'shapes' the antenna's radiation pattern. Where it tends to 'put' the signal when it's radiated.
The importance of how an antenna is constructed mainly applies to convenience and radiation pattern shape. 'Convenience' in that depending on frequency, it may be shorter than 'normal', that pretty well describes any HF mobile antenna. That applies to the physical characteristics mainly, but physical characteristics always determine how an antenna will perform (along with it's location and environment).
The only good reason to 'load' an antenna (in any way you want to do that loading) is to make it more convenient to use, to make it smaller/shorter. It works the same way no matter if you are talking about a 1/4 wave length antenna or one of any other wave length. The 'catch' to that is that an antenna's physical size/length determines it's radiation characteristics, it radiation pattern. If you change that 'size' then you change it's radiation pattern, where it can put a signal. If it's a small'ish change then the pattern isn't changes all that much and it'll behave almost like a full sized antenna and that's good. But there are limits to that and if it's 'good enough' anymore. That 'good enough' is always determined by the user of that antenna.
And then there's the misconceptions about resonance and SWR. SWR has nothing to do with resonance, period. Resonance has nothing to do with impedance matching, other than that almost all resonant antennas are never 50 ohms therefore 1:1, the 'ideal' SWR. Equating the two is an absolutely sure way of being wrong. They can both be adjusted so that an antenna can be both resonant and have a good SWR. But, not by the 'common' way of 'tuning' an antenna (adjusting length alone).

This is getting to be longer than intended so I'll quit here. It isn't just Firestick getting things 'not right', most manufacturer's don't explain things, or at least their reasoning.
Have fun.
- 'Doc

M0GVZ said:

Err no. The idea of top loading the antenna is to distribute the current evenly across the full antenna length. It also increases Rr thus increasing the efficiency of the antenna.

Source, ARRL Antenna handbook, 2" thick, has lots of information about antennas and the theory. You should buy a copy. Very informative.

Click to expand...

I see where this complaint comes from, I mistyped something. I said...

The DB said:

Firestick's top loaded antennas also act like base loaded antennas.

Click to expand...

Where what I meant to say was...

The DB said:

Firestick's top loaded antennas also act like quarter wavelength antennas.

Click to expand...

For the record when I make a statement like this point it out, but also take the context of the post as a whole into account. If you did that you would have clearly understood that while it was in error, I clearly meant to say something else... This one just happened to get by my proofreading... I'll edit in a correction in on said post...

Actually, while in error what I said is still true, at least to a point. Any quarter wavelength antenna with a coil will act more like another quarter wavelength with a coil than a loadless, full length, quarter wavelength antenna. Raising the point where the load on the antenna is does change some things, but no matter where the load is the antenna will never be as efficient as a full length quarter wavelength antenna. You will also notice in that book you failed to adequately reference (more on that next) that they never once compared a loaded quarter wavelength antenna to a full length quarter wavelength antenna.

When making a reference to a source to me you need to be more detailed than just "read this book". That doesn't tell me anything. I need to know what version of the book and what page. I own all but four versions of the ARRL Antenna Book, and I have read them all. I can look pretty much anything that has been mentioned in said books up, but saying "read a book" doesn't help me, or anyone else, any. I also have a collection of books that goes beyond the ARRL Antenna Book line of books, so I may even have references to other sources. Even better, here's a thought, quote the source. That way everyone can see exactly what you are referring to. I have done this multiple times in the past, and will likely do so again.


The DB

EDIT: I said I would edit the previous post, however, the edit button for said post no longer exists so I cannot correct and note the correction.