dipole on a big rig swrs

[Marconi]

Don't worry about your posting in this thread 71. I just looked closer and discovered the thread is from last year, and I posted a similar model back then.

If you guys (NB for sure) see any difference between my models then and now...just mark it up to me currently taking more time to check out the details for better accuracy and improving the best I can for the mobile object I used as a mount in this case.

71. the model you see here is a V-type antenna fed in the center. I saw this setup installed on Bill's Big Truck years ago when he stopped by on a trip in this area. The model is different to be sure, but it was none-the-less similar and a dipole of sorts. As I recall the truck was also all metal back then, and that too affected the antenna in some ways I can't explain, but there are many out there that will tell you, categorically, such antenna setups will not work being so close to metal.

For my first 10 years in the radio hobby, I ran a mobile on a Chev P/U truck. I put a variety of antennas at several locations over time, but I always ended up with a 102" ss whip on the back bumper...even with the tailgate in the way. I never had a problem with the initial setup and that whip operated best for me.

 

[rabbiporkchop]

For what it is worth I saw about 36 ohms with this particular antenna

 

[222DBFL]

Would be cool to try a setup with 2 antennas placed like an L above the mirror, or just above the cab line with the lower L antenna and the other being vertical. I know horizontally has been done, but has anyone tried this way? I am not a big rig owner so I could not do this. Heck it may have already been done, but just curious how it would work that way. Either with it as an L setup or having the 2nd whip be at about just below being an L. I might be headed in the wrong direction so don't flame me fellas. Just thinking of other ways to make a dipole type setup is all. Any replies would be much appreciated and tell me if I am just way off base and that it won't work if it won't. But just don't flame me please as like o said, never been a big rig driver so don't know if it would work this way or not. To all have a great day.

 

[Riverman]

For what it is worth I saw about 36 ohms with this particular antenna

rabbi,
How did the performance of this setup compare to the vertical alone without the radial?

 

[Marconi]

71, I posted my model of the 1/4 wave radiator alone near the middle of the truck sitting at the rear of the cab as noted here:

dipole on a big rig swrs

 

[Marconi]

71, I posted my model of the 1/4 wave radiator alone near the middle of the truck sitting at the rear of the cab as noted here:

go back to my post #44 and open up the PDF file

I posted it there. You must have missed it. If you check it out, it will show you what the model predicts for the match per your request.

 

[Riverman]

Thanks, Marconi.
But was wondering about an actual performance comparison from rabbiporkchop with and without the extra antenna.

 

[rabbiporkchop]

rabbi,
How did the performance of this setup compare to the vertical alone without the radial?

The vertical was useless.
The body of the truck had voltage running through it.
Awful truck. Impossible to ground due to something wrong with wiring shorting to body somewhere.
Dipole was very acceptable under the circumstances but nowhere near as good as this...

 

[Riverman]

Have never seen that setup on a truck before. Am surprised more drivers don't use it.

 

[rabbiporkchop]

The idea has been there from the 70"s when we had them "al-u-minium mirrors" I guy I worked with quit his job as a Teamster driver and opened up a radio shop, go figure,
His was called the Rooster Booster and it came in two flavors, one was one 5 foot francis with an insulator in the bracket facing up and one 5 foot francis facing down with out the insulator facing down to make it "cold". The other was a custom block with one up and two short legs pointing down at 45%. There were a couple of others made.

I still drive and slipseat daily with Volvos, Freightliners, and Macks ,glass trucks and experience all the problems.
While I can't quote theory, I do know what works in trucks. My vertical dipole you can hold out the window in your hand and still have a 1.5 swr so it works, however it doesn't out perform my Wilson 5000, with a short ground strap to the cab.
Here's one that I made:
View attachment 19580

Here's a link to an article that may help you.http://www.hamuniverse.com/cbstrongtie.html

How do you attach that Vise grip mount to the truck without grounding either element to the truck?

 

[Sarasota Slim]

How do you attach that Vise grip mount to the truck without grounding either element to the truck?

I assembled a vicegrip mount for dipole use (have not yet used it, though), for my spare radio system. My wife and I, occasionally, have to go pick up a tractor to drive back to the yard, so I keep a spare system on the truck.

What I did with the vice grips, was I painted the jaws with liquid tape. I did several coats, so that it would be nice and thick. One could also keep a square of rubber sheeting on hand (like those dash pad things that you lay on top of your dash, that you put your phone or sunglasses on, to keep them from sliding around); wrap that around whatever you're clamping the bracket to, to act as an insulator.

And, of course, if I'm picking up a Volvo, the mirror brackets are painted, anyway, and also aren't grounded very well. Or, I could use the grab bar, on the rear, too. 18' of coax will just barely make it back there.

It's not a completed project, yet, but I'll probably just fit it with matching Francis antennas. I'd prefer the 4' ones, but for storage reasons (and the fact that they won't see but a couple of days use, annually ) I'll probably use 3' antennas.

 

[StrangeBrew]

How do you attach that Vise grip mount to the truck without grounding either element to the truck?

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.

 

[rabbiporkchop]

I assembled a vicegrip mount for dipole use (have not yet used it, though), for my spare radio system. My wife and I, occasionally, have to go pick up a tractor to drive back to the yard, so I keep a spare system on the truck.

What I did with the vice grips, was I painted the jaws with liquid tape. I did several coats, so that it would be nice and thick. One could also keep a square of rubber sheeting on hand (like those dash pad things that you lay on top of your dash, that you put your phone or sunglasses on, to keep them from sliding around); wrap that around whatever you're clamping the bracket to, to act as an insulator.

And, of course, if I'm picking up a Volvo, the mirror brackets are painted, anyway, and also aren't grounded very well. Or, I could use the grab bar, on the rear, too. 18' of coax will just barely make it back there.

It's not a completed project, yet, but I'll probably just fit it with matching Francis antennas. I'd prefer the 4' ones, but for storage reasons (and the fact that they won't see but a couple of days use, annually ) I'll probably use 3' antennas.

I used plastic washers as insulators to isolate everything from chassis ground. This thing can clamp directly to bare metal on the truck but the plastic washers isolate everything from DC ground.

 

[Sarasota Slim]

I used plastic washers as insulators to isolate everything from chassis ground. This thing can clamp directly to bare metal on the truck but the plastic washers isolate everything from DC ground.
View attachment 21638

If I'm looking at that pic correctly, it looks like you've got your ground half at a 90 degree angle to your "radiant " half. Wouldn't that lend a more directional quality to your signal?

 

[rabbiporkchop]

If I'm looking at that pic correctly, it looks like you've got your ground half at a 90 degree angle to your "radiant " half. Wouldn't that lend a more directional quality to your signal?

I ended up mounting the ground element at a 45 degree angle which still allowed me to open my door and the ground element had a couple inches of clearance so it wouldn't rub on the hood of the truck when I open the door. I didn't notice how directional it might have been. I haven't used that setup since 2014 and I only used it for about 6 months