• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

dipole on a big rig swrs

RF seems to have a way of finding "the path of least resistance".

It's not particularly relevant, but that statement reminds me of a lecture that I once received on a jobsite, from an older coworker, many years ago, on the nature of electricity. I don't recall everything he said, but he did say something along the lines of "electricity likes to take the path of least resistance". He went on to explain that this was so, "because electricity is lazy."

This guy gave many lectures, so this one probably wouldn't have made quite the impression, except that, as soon as he said that electricity was lazy, he climbed up a ladder, stuck his head in the dropped ceiling, and his head hit a junction box that was hanging loose, and open, with stripped, live wires hanging out of it. Those wires hit the steel ceiling beams, and sparks began to rain down in abundance, atop my coworkers head.

We figured that electricity took offense to the implication that it was lazy, and made a rebuttal, lol.
 
At one time when I used to slip seat I had a vice grip mount with a 108" insulated wire hooked to the ground side, I would just run that wire in the window and spread it out on the floor. No effort was made to isolate the mount from the mirror. Worked good enough for a simple highway info setup. RF seems to have a way of finding "the path of least resistance".

While the antenna system may be the most important part for peak performance when peak performance isn't required you can be pretty damned far from perfect and still be good enough.



PS: The phrase "the path of least resistance" is in quotes for a reason, it's a metaphor. Please don't post to tell me it's actually the path of least reactance/capacitance/whateverance. Thank you for your cooperation.;)

Its actually not the path of.... oh nevermind, you said please
It's not particularly relevant, but that statement reminds me of a lecture that I once received on a jobsite, from an older coworker, many years ago, on the nature of electricity. I don't recall everything he said, but he did say something along the lines of "electricity likes to take the path of least resistance". He went on to explain that this was so, "because electricity is lazy."

This guy gave many lectures, so this one probably wouldn't have made quite the impression, except that, as soon as he said that electricity was lazy, he climbed up a ladder, stuck his head in the dropped ceiling, and his head hit a junction box that was hanging loose, and open, with stripped, live wires hanging out of it. Those wires hit the steel ceiling beams, and sparks began to rain down in abundance, atop my coworkers head.

We figured that electricity took offense to the implication that it was lazy, and made a rebuttal, lol.
Lol, and that reminds me of how many journeyman electricians have no idea how a safety ground is supposed to function. I used to do a lot of ground rod resistance testing for remodels of schools and hospitals. I only saw 2 electricians check for current in the ground before unhooking it. I've heard that more electricians are killed by the safety ground than anything else, and I believe it.
 
Its actually not the path of.... oh nevermind, you said please

Lol, and that reminds me of how many journeyman electricians have no idea how a safety ground is supposed to function. I used to do a lot of ground rod resistance testing for remodels of schools and hospitals. I only saw 2 electricians check for current in the ground before unhooking it. I've heard that more electricians are killed by the safety ground than anything else, and I believe it.

Heh. My theory has always been that electricians die because they get cocky and lose respect for electricity. Much of the reasoning behind my theory is the great frequency in which I have witnessed electricians do stupid or thoughtless things. And, I'm not picking on electricians, here. Carpenters, drivers, heavy equipment operators, etc.; I see professionals do dumb things in all fields. Indeed, I have had my own embarassingly brainless moments.
 
With the dipole, one side is the HOT side and the other is the RF ground side. Obviously you would use the HOT side as the top vertical section of the dipole. You can use MFJ -347 dipole mount or make your own as long as the HOT antenna uses the insulator bushing and the RF ground does not.

As long as you weren't mounting the antenna on the exhaust stack grab handle on a Pete, I wouldn't worry about what little metal is left around the antenna.

You SHOULD use equal lengths antennas to do this correctly. However 2 full size 1/4 wave whips will be too long at being over 18 ft with mounts. Even using just one 1/4 wave whip mounted to the lower mirror bracket arm on a Freightliner or Volvo or any truck with upper and lower mirror posts will exceed 14 ft.

You would be better off using loaded antennas of the same brand and lengths, either 4 or 5 ft. fiberglass or steel ones. Most fiberglass antennas these days are 5/8 wave but that doesn't really matter. I believe the Francis antennas are still 1/4 wave so I would use two 4 1/2 ft antennas for this project.

There is one point to consider, Since a dipole is a balanced antenna, it is not 50 ohms. Even using 2 full size 1/4/ wave whips in this manner will have an feed-point impedance around 75 ohms, not 50 ohms, so the SWR will not be flat if that's what you were hoping for.

With 2 loaded antennas matched for 50 ohms and even using 50 ohms coax, I would expect your feed-point impedance to be even higher around 100 ohms. This can be verified easily if you have an antenna analyzer one or know a real CB shop that has one.

This is a easy fix using a 2:1 balun. A balun is a transformer device used to balance an unbalanced feed-line for feeding a balanced antenna, Hence the name BAL-UN. At a 2:1 ratio, this means it will cut the feed-point impedance down at 100 ohms in half to 50 ohms which should give you a nice flat SWR match. 50 ohm coax cable is an unbalanced feed-line.

You could also use a mobile antenna tuner which will be easier. But antennas tuners don't really tune an antenna, they just match your radio to a mismatched antenna.Your antenna will still have a higher SWR from the impedance mismatch, but at least your radio will see a near perfect match.

Good luck with your project!


I may not get too far with this project (Spot Mirror Mount), but a 2:1 balun makes some sense to try. Used an antenna tuner last time.

Thx

And, with the rest of the thread, maybe enough thrashing around to drive off the irritation of having an $85 antenna stolen yesterday.

Have an MFJ-347, and can also use two small mounts on a bar. No end of mobile CB antennas.

Vertical, Horizontal ? Hell, who knows. Maybe It’ll be as much fun as when RWB tried stringing dipoles on a Longhorn.

.
 
Last edited:
  • Like
Reactions: Handy Andy
Boy, this sure wasn’t the year for brand-new projects. Got behind on the several started the last year. From no toilet paper to stay home until you accept communism, 2020 was a year of aggravations AND increased expense.

I say this as this thread is pretty well the most fun I’ve had at this site in wanting to try something zany.

Maybe Big Truck Di-Pole 2021.

.
 
Came across a dipole with mount by BOBS CB to be used as an NGP antenna for motorhomes and the like to be mounted on the roof access ladder.

By special order, with 55’ Hustler center-coil whips. Upright “hot” and down-angled “cold”.

40297ED0-D33D-4B55-A347-6A1EC4342CCD.jpeg

.
 
  • Like
Reactions: HomerBB
FWIW. Tried the vertical dipole thing with 2ea. Firestick 4 footers off the passenger door of a Freightshaker. Copied a MFJ237 using the nylon bushings from stud mounts, so it was electrically isolated from any chassis ground. Best SWR was 1.8 to 2. Checked with a MFJ259 it was resonate below 26.965. Removed the lower whip and it didn't change the 259 reading (??). Ran it for a while and worked just ok, nothing any better than a single whip. Suspected that the bottom whip (shield side) probably coupled with the door sheet metal. The pattern had to have been oddly skewed. Had much better success with a 7' Firestick on drivers side mirror well grounded with a 1" wide copper strap, was the best setup I had. Good on AM and worked well for SSB when the band was open.

73
 
  • Like
Reactions: Slowmover
FWIW. Tried the vertical dipole thing with 2ea. Firestick 4 footers off the passenger door of a Freightshaker. Copied a MFJ237 using the nylon bushings from stud mounts, so it was electrically isolated from any chassis ground. Best SWR was 1.8 to 2. Checked with a MFJ259 it was resonate below 26.965. Removed the lower whip and it didn't change the 259 reading (??). Ran it for a while and worked just ok, nothing any better than a single whip. Suspected that the bottom whip (shield side) probably coupled with the door sheet metal. The pattern had to have been oddly skewed. Had much better success with a 7' Firestick on drivers side mirror well grounded with a 1" wide copper strap, was the best setup I had. Good on AM and worked well for SSB when the band was open.

73

Appreciated.

I can’t get it out of mind as one night I was running a dozen miles behind a driver on IH40 in Oklahoma said he was running a dipole off the rear fairings (flatbed). Nothing special as to radio (dual final export).

He (easily) was in the same league (audio punch & clarity) as most Billy Big Rig cattle haulers with a pair of Predators and a TX STAR 500.

He had to pull over to check load securement before we hit the AR scales at the line. I was running close to late with a load to Ft Smith. To this day, I’d rather have been a little late versus having been a good boy that night.

My best setup (a few months later) was a pair of 7’ Skipshooters on a FL Evo door mirror base. Could hear them, they could hear me.

But there’s no way to duplicate that on this 579. No clearance once doors are opened. No way with fab skills and tools I don’t have.

Up from the fuel tank frame extensions; or from behind rear fairings is how I see it (dipole arrangement). Truck attachment point is the bug-a-bear.

I did try a vertical pair from the Evo mirrors with a Francis set. Ridiculously bad.

Lack (overall) of a good antenna mount position (ground-coupling) drives the desire to want something better than the OEM mounts above the A-pillars.

.
 
The linked pic mount with a pair of 4.5’ antennas would mean an extension to set that mount between 8-9’ above-ground so that the “hot” whip didn’t quite touch 14’. That’d leave plenty of room beneath it for the “cold” whip.

FWIW, my travel trailer has an approximate 9’6” clearance. While I don’t have a ladder (would be a custom fit special order), that magic 14’ GP clearance would work well (remove whips for travel). But I’ve not the problem of inadequate ground plane with my trailer design & materials, so that’s moot.

I already have a pair of MFJ-947 mounts from my earlier attempt (even tried one on the 579 from the passenger door mirror; NOPE!), but I’m not sure about how well they would stand up to extended high-speed travel.


The mount linked looks useful enough to get a pair.


BOBS (TGT-DPB-SS) in stainless.
$24.95/ea

(Mount only; whips part of separate package)

E011489D-EFF5-4A58-92F6-C5F582AD728A.png

.
 
Last edited:
You going to run this on the rear cowl fairing?

I hope so, otherwise you'll poke the DOT Inspector eyes out...if you decide to run it out on the sides, on the front, it'll make you look like you've got eyelashes...

This is a variant of the "Hand rail" or outdoors railing method of use. This is the mobile variant of a workaround for an HOA issue.

  • If you want to skip the rest of this message, I'll just say, you're throwing money away - that Trailer is your problem. The Flatbed doesn't have the issues you've got because they don't have that near field effective signal killer the trailer really is so their setup is far easier to breathe their signal out to the ether than yours.

I had discussed this to some length in coffee klatches with other drivers I got together with, and talked about a method of using a rain visor of some type, to make the 8 foot space between the doors more useful.

Some cabs use a metal box framework with such a rounded metal ring already up there to attach the aero-sleeper 2nd story up there, but above that there is very little present to protect or otherwise reinforce the upper portion of that sleeper cab.

Newer ones seem to be all one piece, which then takes away your ability to use your 8 foot distance as a space for your stuff and your counterpoise.

You may have a metal support ring, but you need to bond your antennas and your shelf to them. Each any every one of the cabs I've had the pleasure to yank cables thru, all of them, the drivers pretty much used the inner cubby center shelf. The one in the upper console, as their resting spot, not a mounted bracket it just rested there with velcro or sticky dual sided (ugh) tape- just to raise the knobs past the plastic trim to gain and have access to the radio - the bracket in many were never mounted to bond the RF to that deck.

You say you've done that, well then there's more

As far as construction​
  • - so if they riveted, well then there's the bolt you can use once the rivets' drilled out, but if you say you have a strong seam, then the problem is more of the antennas outward position away from the ring - tends to force the signal to front and back from the cab, but the trailer is the biggest reflection a problem with sleepers, they put the whips at a "resonate" 8 - 10 foot rear reflector dead spot - works for some, but not all.
  • Since load constraints take precedence over CB SWR, the main saddle as well as the tandems being able to slide, don't provide much room for length, and for many, the load pretty much forces them to keep their antennas close to the sweet spot of resonance on the trailer - and the enemy is just that - your trailer.
  • Flatbeds - you have the trailer, but it's BELOW the main image, think of this as a raised ground effect kit and ground skirt
So some are looking into using those stainless steel rain / shade visors to help their image, although looks fancy, not a simple nor cheap way to use them - especially if you rent the cab. It's more for the dedicated and self purchased. They can take the cost and expense and have the real-estate expanse to have it permanently added to their truck.

If you're thinking about running that "duck vane" - not the best option - you'll look like a pincushion. What the Visor does, allow the RF floating about in the frame and cab to work on the visor as a metal element added to the elements still radiating in the cab - which may not be in the most ideal spots to direct your signal nor are they the QUIETEST because -they too- support the electrical returns much of your faraday cage of a cab, has embedded in it.

It's amazing those PC - Emission, and DTC diagnostic agnostics that equipment is, can still function and not conflict with each other.

I just wish nearly everyone that owns one, didn't destroy their limiter in their Galaxy's radios just to chat - for the limiter can be "fixed" and yet take out your noise picked up by that cord, from getting tangled up and mixed in, with the rest of the receive.
 
Last edited:
Just to have been able to eyeball HOW that driver affixed his R/L dipole pair would have been worth a lot (to me).

The suggestion of the rear fairings is that they’re composite material versus being metal. The hot side is in the space between tractor and trailer plus several inches outward. The cold side (angled in this instance; or vertical using the MFJ-247 mount) is the one gets nearer metal.

I get it (well as I can) your strong caution that a 53’ van is a genuine problem.

I also “get it” about the steel sheet across the top of the windshield
being the effective advantage on which to capitalize.

The image of “eyelashes” (spreading V) is dammed funny. No ones gonna much buy I got a clue I go that route. My name would have to be Cebik, Severn or Rauch to pull that off. “Hi, kids, Walter Maxwell here in another installment of . . .”

And,
I’m in a one-piece composite-body Ultraloft 579 versus what I’d prefer: the joined cab & sleeper with a large airfoil atop as was the single choice until about two-years ago (579 intro’d in 2012).

Had one of the road-test units camo (literally) flaged REVISED 579s parked near me a couple of days ago. Taller and narrower radiator, enlarged side air intakes; and projector headlights for low & high beam. Even more composite material according to a press release.

If I’m reading you correctly: best use of effort is (will be) that cab-forward steel shell of firewall, A-pillar and “shelf” across the top of the windshield (console inner frame). That the trailer presents too much trouble to get near it (unless no other options exist.

If nothing else, guess I’ll have to figure out how to get to the door mirror attach points to affix RF Bonds thereon and inwards to the door hinge bonds already in place.

Modern manufacturing is great for noise (rattle) reduction. But it’s a bitch (almost impossible) to get to the originating attachment point of interior parts.

.
 
Last edited:
I just wish nearly everyone that owns one, didn't destroy their limiter in their Galaxy's radios just to chat

Amen to that. But they just can't help themselves, can they? If anybody tells them how they'll GET OUT, yank goes the limiter. Kinda sad.

73
 
  • Like
Reactions: Slowmover
To sum this tangent up, I wish or hope there is a way to Unitize the body for your antennas, not so much of the doors. The crux of many of the trucks having the noise and flex problems are due to that mirror mounting right at the door hinge, on top of the fact they wish to "hide" that hinge using composite plastics to be the "Grommets and barrier" to keep out that creeping rust corroded crud.

The trailer is what it is.

  • It's amazing to see how many trucks arrive to the shop with their antennas "tuned too wrong" when they show up as a bob-tail - once the main reflector is gone, so is the problem - the radio gets out like a banshee. It's when they park back under the load, does that SWR light begin it's the blinking, winking process...all over again.

Plastics, as they don't rust - act like effective rustproofing until it's eventually dried out overheated and broken in two - by then the companies replacement will be something else you have to buy a new truck around in order to replace it as OEM.

Daffy Duck did it best...
upload_2021-1-16_15-7-33.png
The Stupor Salesman WB
You know, some of the Saddle grease used, one of it's main components was to use Graphite - would like to think they still do. Graphite works in ALL conditions and temperatures - it's pure carbon, can't reduce it any more than that. Seen several Synthetic blends causing issues of static generation when they run Reefer connected under them.

One of their many tricks and solutions was to use more graphite on the weight bearing saddle..

Why the concern? Because Graphite can conduct...

Wondering if static as a noise problem you don't have a good conductive layer of a conductive grease on your saddle...
 
Last edited:
  • Like
Reactions: Slowmover
I've been bouncing around the internet and have found that vertical dipoles seem to be a great idea to use on a big rig due to lack of metal in big rigs today. however I wonder wouldnt what little bit of metal that is on a big rig effects swrs of said dipole? I'm thinking of using a 108 whip as the main element and the Radio Shack with the fiberglass base load and 50 something inch stinger as the counter poise. Thanks in advance for answers and comments.

Use Two equal length antennas & you will get better results.Also there is only One SWR not any SWR's unless you have more than One antenna & not connected together but Two different antennas on a seperate piece of coax.SWR = Standing Wave Ratio.No Standing Wave Ratios.

SIX-SHOOTER
 
  • Like
Reactions: Slowmover
To sum this tangent up, I wish or hope there is a way to Unitize the body for your antennas, not so much of the doors. The crux of many of the trucks having the noise and flex problems are due to that mirror mounting right at the door hinge, on top of the fact they wish to "hide" that hinge using composite plastics to be the "Grommets and barrier" to keep out that creeping rust corroded crud.

The trailer is what it is.

  • It's amazing to see how many trucks arrive to the shop with their antennas "tuned too wrong" when they show up as a bob-tail - once the main reflector is gone, so is the problem - the radio gets out like a banshee. It's when they park back under the load, does that SWR light begin it's the blinking, winking process...all over again.

Plastics, as they don't rust - act like effective rustproofing until it's eventually dried out overheated and broken in two - by then the companies replacement will be something else you have to buy a new truck around in order to replace it as OEM.

Daffy Duck did it best...
View attachment 42545
The Stupor Salesman WB
You know, some of the Saddle grease used, one of it's main components was to use Graphite - would like to think they still do. Graphite works in ALL conditions and temperatures - it's pure carbon, can't reduce it any more than that. Seen several Synthetic blends causing issues of static generation when they run Reefer connected under them.

One of their many tricks and solutions was to use more graphite on the weight bearing saddle..

Why the concern? Because Graphite can conduct...

Wondering if static as a noise problem you don't have a good conductive layer of a conductive grease on your saddle...

I learned BEFORE I ever drove a big truck that proper 5th lubrication is a vital component of steering control.

So I am one of the rare truck drivers you’ll see re-greasing the fifth wheel with every trailer loaded or to be loaded.

That said, graphite as a grease component hasn’t been a concern. I’ve been meaning to buy grease in bulk, so am glad that’s been put off. I’ll look into it. Even if I have to mix it in.

Spent today disassembling the passenger door to try to get to the mirror bolt base from the interior and run a strap. Not happening, was that result. The door has two separate steel sheets (inner & outer) and acres to the back side of the outer is nigh on impossible.

My bonds at the door hinges were attached to that outer sheet, so it’s “done”.

As to attempting a dipole, I’ll pass on it.

.
 
Last edited:
  • Like
Reactions: Handy Andy

dxChat
Help Users
  • No one is chatting at the moment.
  • @ AWP:
    Is it possible to be on a lake and have a homing directional beam being emitted from the shore so a person could navigate to that beam's source? For example at night to a jetty.
  • @ BJ radionut:
  • @ wavrider:
    sea que sea que,
    +1