Best Moblie Antenna for OTR Truck

[The DB]

I think I already have above.

What he is describing is more accurately called "self resonance", which is more of a special case, even though many people, especially on the CB band, think that is all their is to it.

One way to describe resonance is the point where inductive reactance is in balance with capacitive reactance. The description you quoted is incomplete because the way he describes achieving that balance is not the only way to do it. There is another way to achieve balance, to induce it, if you will, and the guy he called his "friend" told us all about it in his writings. If the antenna feed point is presenting, say 92 ohms of inductive reactance, what happens if the signal being fed to the antenna is presenting 92 ohms of capacitive reactance? You have balance, and by extension resonance, and you have it on an antenna that is not a so called "resonant length". Every antenna system that includes some form of matching network uses this principle to match the feed point to the feed line, it doesn't matter is it is a gamma match, the Maco ring style match, a coaxial stub, or an antenna tuner elsewhere in the system, or whatever they all do the same thing in the exact same way.

Hey, I stated that above...

So to put it another way, lets say an antenna presents 100 ohms of inductive reactance at its feed point. If you use a matching systems to to counter that reactance with 100 ohms of capacitive reactance, you have balance, and by extension resonance. It doesn't matter where that matching system is, as long as the antenna is provided an equal amount of reactance of the opposite type than its its feed point presents. This is the basis of all matching networks, at least as far as reactance is concerned.

Oh, and him wondering where the word "resonance" comes from? It is used with all types of waves, mechanical, electrical, ect. It is fundamental to any application of wave theory, no matter the type wave in question, as well as other words we commonly use, like impedance and SWR. If you want to understand what is actually going on you cannot disregard any of these terms, even if you are just talking about ripples on a pond that were caused by throwing a rock...


The DB

 

[HARDROCK]

Thanks you hit it with the matching. I took the matcher off and retuned for lowest swr.

The signal dropped, Also the pre amp on the amplifier did not work..... had to be
a mismatch issue.

I was talking to a base unit 45 miles out. when i took the matcher off and retuned the lowest swr.
This is when the preamp was garbled and . he said the signal dropped .

Put it back like you had it he stated.
I put the matcher on and retuned. His reply was leave it be it is on the money now.

So it has to be the conjugate match.

I noticed CTR stated most AM broadcast towers are non resonant lengths although they match at the base.

The matching equates to a matched resonant system.
Even though the antenna has a 2.1 swr and a flat match at the radio side it works better than just tuning for lowest swr with no matching.

Thanks for your time Db . I do value little o me...... The problem with a lot of the professional engineer experts is they dont have time or patience with the CB crowd.
Fact is they look down on Cbers because of the widebandwith / bleedover and nasty signals.
which i can understand.

So i do value and appreciate you.

 

[338_MtRushmore]

I think I already have above.

What he is describing is more accurately called "self resonance", which is more of a special case, even though many people, especially on the CB band, think that is all their is to it.

One way to describe resonance is the point where inductive reactance is in balance with capacitive reactance. The description you quoted is incomplete because the way he describes achieving that balance is not the only way to do it. There is another way to achieve balance, to induce it, if you will, and the guy he called his "friend" told us all about it in his writings. If the antenna feed point is presenting, say 92 ohms of inductive reactance, what happens if the signal being fed to the antenna is presenting 92 ohms of capacitive reactance? You have balance, and by extension resonance, and you have it on an antenna that is not a so called "resonant length". Every antenna system that includes some form of matching network uses this principle to match the feed point to the feed line, it doesn't matter is it is a gamma match, the Maco ring style match, a coaxial stub, or an antenna tuner elsewhere in the system, or whatever they all do the same thing in the exact same way.

Hey, I stated that above...



Oh, and him wondering where the word "resonance" comes from? It is used with all types of waves, mechanical, electrical, ect. It is fundamental to any application of wave theory, no matter the type wave in question, as well as other words we commonly use, like impedance and SWR. If you want to understand what is actually going on you cannot disregard any of these terms, even if you are just talking about ripples on a pond that were caused by throwing a rock...


The DB

Hook ,line and sinker. They got your number, and you cant fix stupid. Good luck on your battle...

 

[543_Dallas]

The magic matcher was making the preamp in his pos amplifier work properly. Keeps getting deeper.

What steps were taken to ensure common mode current didn't skew your test results? When you say matcher youre still talking about the 2:1 balun right?

 

[StrangeBrew]

Please let this thread die already. ....

Sometimes it's best to let threads like this go, it keeps it all contained so it doesn't spill over into other threads.

 

[HARDROCK]

https://dxengineering.wordpress.com...etter-efficiency-with-your-hf-mobile-antenna/

 

[Sarasota Slim]

Wow. This thread is filled with information to sift through. When I have more time, I will start sifting.

In the meantime, I'll just post what I've done in regard to antennas on my rig; it's relevant to the original post, and seems to be working well, although I could probably tweak things further for even better results.

I took the big coil K40 "super-trucker" antenna (as I call it; I bought it for the height. It's a rather silly device, otherwise) that I already had, and mounted on my mirror bracket, insulated from the rest of the truck. Then I bought a 3ft K40 fiberglass whip, and mounted that right next to the first antenna, upside down. I then took a short piece of coax with a pl259 connector on one end, and screwed the pl259 to the end of the fiberglass antenna.

I stripped the other end of the coax to the center conducter, and crimped an "eye" to that. I attached that to a bolt on the mounting bracket of the big coil antenna. In effect, the fiberglass antenna acts as an artificial ground, or counter-poise.

I tuned the antenna set up (I monkeyed with both antennas) until my SWR readings were equal across channels 1, 20, and 40. In my case, I was getting 2.5. I then hooked a Zetagi MM27 matcher in the line, and it dropped my SWR down to a little over 1.

Set up is as follows : Uniden 980 to RM KL 203-P to Valor VLPF-30 (low pass filter) to Astatic PDC-2 SWR/Power meter to Zetagi MM27 to antenna. All this, within a 2017 Volvo tractor; tall sleeper that pulls dry and reefer.

I make no claim that my setup is optimal or superior, only that this is the most productive setup that I have tried, by far. (As far actual results; ie. the ability to actually have conversations that last longer than 10 seconds while moving.)

I don't even know that the OP continues to monitor this thread. I post for posterity, this time, lol.

 

[338_MtRushmore]

Wow. This thread is filled with information to sift through. When I have more time, I will start sifting.

In the meantime, I'll just post what I've done in regard to antennas on my rig; it's relevant to the original post, and seems to be working well, although I could probably tweak things further for even better results.

I took the big coil K40 "super-trucker" antenna (as I call it; I bought it for the height. It's a rather silly device, otherwise) that I already had, and mounted on my mirror bracket, insulated from the rest of the truck. Then I bought a 3ft K40 fiberglass whip, and mounted that right next to the first antenna, upside down. I then took a short piece of coax with a pl259 connector on one end, and screwed the pl259 to the end of the fiberglass antenna.

I stripped the other end of the coax to the center conducter, and crimped an "eye" to that. I attached that to a bolt on the mounting bracket of the big coil antenna. In effect, the fiberglass antenna acts as an artificial ground, or counter-poise.

I tuned the antenna set up (I monkeyed with both antennas) until my SWR readings were equal across channels 1, 20, and 40. In my case, I was getting 2.5. I then hooked a Zetagi MM27 matcher in the line, and it dropped my SWR down to a little over 1.

Set up is as follows : Uniden 980 to RM KL 203-P to Valor VLPF-30 (low pass filter) to Astatic PDC-2 SWR/Power meter to Zetagi MM27 to antenna. All this, within a 2017 Volvo tractor; tall sleeper that pulls dry and reefer.

I make no claim that my setup is optimal or superior, only that this is the most productive setup that I have tried, by far. (As far actual results; ie. the ability to actually have conversations that last longer than 10 seconds while moving.)

I don't even know that the OP continues to monitor this thread. I post for posterity, this time, lol.

So you made a verical dipole with a k40 and a 3' whip? Is that Volvo all fiberglass, because I guess that would make sense. It would be interesting to see the resonance, if nothing else.

 

[HARDROCK]

FS measurements

The formula is 2*L*L divided by the wavelength where L is the length of
the mobile antenna in feet and the wavelength is 984 divided by the
frequency in MHz. For instance, for an 8.5 ft mobile antenna on 27 MHz,
984/27=36.4 so the far-field starts at 2*8.5*8.5/36.4 = 4 ft.
For a 120 ft dipole on 4 MHz, the far-field starts at 117 ft.

4 to 6ft distance from the antenna should be suffiecient on mobile antenna
to check peak on FS meter.

 

[Sarasota Slim]

@338_MtRushmore:

I referred to that set up as a "vertical dipole", when I was speaking to my HAM cousin, the day I did it, and he questioned the accuracy of that term. I'm kind of learning things, still; I don't know what to call it, I just know it's working, lol.

But, yeah, the Volvo is mostly fiberglass, and poorly grounded. There are other antenna set ups that I could try, if I owned the truck. But, it's a company vehicle, so I have limits on what I can do.

My next step, I think, is to cophase dual "dipoles", because the flaw that I expected manifested the other day, when I passed the guy that I was talking to. The passenger side of my truck has a big "deaf" spot. But, as I said, I expected that.

As to the resonance, I want to see that, myself. An antenna analyzer is on the top of my wish list. Two of them are, actually. There is an MFJ model that I want, mainly because it seems to be a very widely trusted brand and model. But, I also want the "Mini60" Sark100 clone with Bluetooth. The various graphs and all look fun; and the technology of the thing appeals to my inner geek, lol.

 

[222DBFL]

You might also want to look at one of the Rig Expert analyzers as well. Supposed to be pretty good ones. The AA-30 would be one to look at. Just some food for thought. Be safe on the road. Good evening.

 

[Sarasota Slim]

@222DBFL :

I'll have to look into the Rig Expert. I haven't heard of them, before. Thank you for the tip.

Also, 'tis always the plan, to be safe on the road, lol. Thank you.

 

[HARDROCK]

I have the aa-30 rig expert. I like it.
I also like the dipole idea.

Also be sure and read all of CTR posts.

He is the designer of the Ameritron amps.
Also he is the sharpest knife in the drawer.



Tony 73

 

[HARDROCK]

Hardrock, I have a question for you. Are you talking about HF antennas in general, or are you taking general HF knowledge as ham would need it and trying to apply it to a CB antenna?

In the real world, if you are using something like a 40 meter ham radio antenna in a mobile environment, the data you like to quote is fine. However, if you are trying to apply it to CB specifically, you are reading to much into it. If you have a CB antenna of reasonable length and you get an R of "20 or less", then you have a problem with the CB antenna.

In one case you are shortening a CB antenna to, lets say for comparison purposes, about 50% of its optimal (resonant) length, and in the other, to get an antenna of the same physical length and tune it to the 40 meter ham radio band (a frequency band in the ham radio spectrum commonly used for mobile work) you are looking at closer to 15% of its optimal length.

Which of these antenna is going to have more of an effect on R at resonance than the other? Which antenna will take a much bigger hit to coil efficiency?

Also, do you think coil efficiency is the only loss you have to worry about in a mobile environment that adds to the R variable? Set up a full length CB antenna that has no loading coil on a car and see what R is, it will be higher than you expect. You can take a magnet mount antenna and move it around the vehicle and see changes in R, and that will happen weather or not there is a loading coil on the antenna. Thinking that a loading coil is the only thing that will raise R on your antenna analyzer is a dangerous and incorrect assumption.

Also, as far as a vast majority of CB antennas are concerned, if you have more than one or two ohms of loss on an antenna that is five feet long or longer, then you have a problem, much less 25 ohms. To make this determination, however, you would have to separate said loading coil from the antenna and measure such things separately, as when it is on the antenna, as I mentioned above, it isn't the only thing that affects R in that way.

And for information purposes, the more you shorten a given antenna, comparatively speaking, the more additional losses you will see. To explain that, lets use an example. Lets say you have a full length resonant antenna (no loading coil) and decide to shorten it by 10%. There will be some loss in the loading based on that 10% of shortening. Then you decide to shorten it again taking another 10% of its original size off. The total losses in the antenna will increase yet again, but this time, even though you took the same length away again, the loading will add even more losses. Do this a third time and you have even more losses added than the second time. Each time you take away a given percent of antenna length losses go up more than the last time. Another way of saying this is as you physically shorten an antenna losses increases exponentially.

What does this mean in the real world? There is an effective limit to efficiently shortening your antenna, and depending on how it is shortened, that limit is between 40% and 50% of original length. You get beyond those numbers and performance significantly drops off due to the exponential growth of losses in efficiency.

Now lets add this to the CB/40 meter comparison above. In one case we are at 50% of the resonant length, it is on the edge, but still relatively efficient, and its effects on R, both the lowering of R due to antenna length, and raising R due to losses in the coil, will be visible but minor.

In the other case the antenna is near 15% of its resonant length, you will have a much larger effect on R from both shortening the antenna and additional losses, and the antenna will be far less efficient.

One thing to note in both of these situations, you will see far more of an effect on R from shortening the antenna than you will see from the added loading losses, but like I said above, coil losses are not the only thing in a mobile environment that will increase R.


The DB

I am speaking of a 5ft cb antenna.
If the analyzer is used at the feedpoint and tuned for lowest swr 1.1 r 50
When the analyzer is adjusted just above that point is when you will see swr 2.1 r 23 and X = 0 This is the resonant point.
This is explained by K0BG and G3TSO.
I simply added a matcher at the feedpoint to give the radio a flat 1.1 swr and the feedpoint is a true 50 ohms.
Current and voltage are now in Phase and the system is resonant.

What you stated above makes sense about shortening the antenna and loosing effieciency.

Also the fact of losses in the matching added.
I need to take time and measure the antenna with FS meter .
Until then i am interested in your comments

 

[rabbiporkchop]

I am speaking of a 5ft cb antenna.
If the analyzer is used at the feedpoint and tuned for lowest swr 1.1 r 50
When the analyzer is adjusted just above that point is when you will see swr 2.1 r 23 and X = 0 This is the resonant point.
This is explained by K0BG and G3TSO.
I simply added a matcher at the feedpoint to give the radio a flat 1.1 swr and the feedpoint is a true 50 ohms.
Current and voltage are now in Phase and the system is resonant.

What you stated above makes sense about shortening the antenna and loosing effieciency.

Also the fact of losses in the matching added.
I need to take time and measure the antenna with FS meter .
Until then i am interested in your comments

Got any pics of the matcher at the feedpoint?