Question on mounting 2m antenna on plastic big rig

[W5BRM]

Been having a helluva time trying to install a 2m antenna on my Freightliner Cascadia. I know we got a few current/retired drivers here hopefully can help

What I have is basically a plastic truck. It's all composite materials or outright plastic. As it is a company truck, I cannot make holes or modify the truck in any way. There are no West Coast mirror frames so I am using a Wilson (https://www.amazon.com/Wilson-305500-Antenna-Freightliner-Cascadia/dp/B00JKOEFVW) mount to attach to the plastic foldover mirror frame. This frame is all plastic and has no bonded connections in it anywhere to help make an antenna work right. there is nothing to bond to inside the frame and the rest of the door is composite material. This poses a problem.

What can I do to mount a 2m antenna? So far, I've tried Hustler SF2 5/8w antenna with no luck. Tried a Half Wave with no luck. Both failed due to needing grounding/bonding to the truck, which I can't do

I have been trying to look into "no groundplane 2m antennas" but can't find any info on whether they will work on a plastic truck. I know the theory but can't find any sort of explanation or construction history on how these work.

When the term Ground Plane is used, are they speaking of having a grounded bonded connection to the body/frame of the truck? or are they speaking of having an actual ground plane attached to the antenna? Will a "No groundplane" antenna actually need no groundplane or any sort of grounding/boding to the truck to work? If not, then what is the idea on how they work? To me, the term "No Groundplane Antenna" is an antenna that will work in free space without any sort of grounding, bonding or connection to any sort of metals.

As it looks like most of these type of antenna are 1 piece units, How do they balance out? Is the coax shield the other half of the antenna or is something else at work here? If so, does this mean I have to use a "tuned" piece of coax to provide the counter to the main antenna? Half wave at 146mhz is about 39 inches and thats a way short piece of coax to use in a mobile instance.

Help would be appreciated. My GoogleFU is weak today.

Thanks

[PA5COR]

Everyone of those antenna's needs a groundplane, one wire of about 50 cm running at a 180 degree angle will do, otherwise the coax will be used as ground plane.
That is less good, so if it is possible at the antenna feedpoint to connect a 50 cm wire do try so.

What we did in plastic top cars was glue in a 50 cm x 50 cm square aluminium foil and use that as ground plane but you can
't drill holes in it, so that is out.

[WZ7U]

Ohh, I gotta noodle that one for a while. I bet there is no way to have a dangly piece of wire as a counterpoise, is there?

Off to think about this....

[PA5COR]

Look for a wire with isolation in the colour of the mirror, tape it with same colour tape to the mirror frame.
That way it won't be a real eyesore, needs to be only a thin wire anyway, so you are making an open dipole with it with the wire acting as 2nd half of the dipole.

[N8YX]

Does your cab have an air dam overtop it and the sleeper?

[WØTKX]

Can you use this antenna on your rig? (http://www.arrowantennas.com/osj/j-pole.html)

http://www.arrowantennas.com/gfx/dbj-2.gif

http://www.arrowantennas.com/inst/igif/ijpole1.gif

[W5BRM]

Does your cab have an air dam overtop it and the sleeper?

I drive a "condo". I have a dome but not an actual hollow air dam. Wish I did as I could just wind counterpoise all over it...lol.

I think I'm going to try COR's suggestion and try to add counterpoise on the actual mirror housing frame.

[W5BRM]

Can you use this antenna on your rig? (http://www.arrowantennas.com/osj/j-pole.html)

http://www.arrowantennas.com/gfx/dbj-2.gif

http://www.arrowantennas.com/inst/igif/ijpole1.gif

Unfortunately, the mount style I'm stuck using is too small and oriented 90° the wrong way. Plus the jpole needs space around it and it would be right next to tge cab so it wouldnt work. The tuning stub would ne the issue

[W7XF]

FreightShakerCascadia? Dunno about that one, due to the ground (?) being all about non-existant. The best attempt I'll guess is to mount it to the frame rail on the left corner of the back of the cab. At least you'll some semblance of a ground. Of course, YMMV.

[WØTKX]

Yea, too bad. I have that Arrow antenna, and it kicks ass.

Build a twin lead jpole and stuff it in some PVC pipe?
I've built/elmered these for new hams
Suspend it inside of PVC with some fishing line.

http://www.qsl.net/wb3gck/jpole.htm

http://www.qsl.net/wb3gck/jpole/jp-fig1.gif

[W5BRM]

Update: Double checked all my measurements. 39.5 inches stainless steel whip, 19.25 inch 14ga wire counterpoise attached to mount. 10ft rg58au coax. Tested continuity on the coax. No shorts. Mfj-259c shows swr of 12. Impedance is R=153 X=217 AT 146MHZ. Coax loss is 0.7db.

Checked other frequencies for resonance. Have swr 1.1 r=47 x=3 at 73.0mhz.

Cannot figure out why this wont tune. Half wave antenna with counterpoise and not a point of resonance anywhere near the desired frequency. Don't think the mount is bad or wouldn't get resonance at 73.0mhz.

Frustrating!!

[PA5COR]

1/2 wave on 2 is a 1/4 wave at 73 MHZ....
Is the matching network at the feed point still alright? high impedance on 2 meters for a 1/2 wave....

[W5BRM]

1/2 wave on 2 is a 1/4 wave at 73 MHZ....
Is the matching network at the feed point still alright? high impedance on 2 meters for a 1/2 wave....

This is where my theory gets fuzzy. As the antenna is not a "shortened" or otherwise modified antenna, there shouldn't need to be a matching network?? I could see that if I were trying to make a half wave with a non resonant shorter whip . Add a coil, tap it, and I'd be in business. I don't get why a proper length balanced antenna won't tune. Obviously I'm missing something but what....

[PA5COR]

Feeding a half wave dipole at the end is feeding it at the high voltage point i.e. high impedance as you can see in your measurements.

http://www.ked-wireless.com/documents/High%20Efficiency%20Antennas%20for%20HT%27s%20-%20QEX.pdf

Just as with the 5/8 verticals you need to match that high impedance point to 50 Ohm, mostly done with an added coil.
See PDF, that will answer most of your questions ;)

[K0RGR]

For use as a groundplane, it needs to be 1/4 wave, or about 19.5 inches on two meters. A standard jpole is a halfwave antenna, too - the whole point of the 'J' part of it is to act as an impedance matching device. I'm surprised 39" isn't too high on your truck.

On his fiberglass tonneau cover for his pickup, a friend of mine uses metal tape on the underside of the fiberglass as a two meter ground plane. I've done this trick, too, and it works.

[W5BRM]

Feeding a half wave dipole at the end is feeding it at the high voltage point i.e. high impedance as you can see in your measurements.

http://www.ked-wireless.com/documents/High%20Efficiency%20Antennas%20for%20HT%27s%20-%20QEX.pdf

Just as with the 5/8 verticals you need to match that high impedance point to 50 Ohm, mostly done with an added coil.
See PDF, that will answer most of your questions ;)

Thanks! That does indeed! Much appreciated!

[KC2UGV]

Another solution: Mount a vertical dipole for 2M. They're not too big, and doesn't need a ground plane.

You can get creative with the mounting. I figure a host clamp somewhere will work.

[PA5COR]

http://home.planet.nl/~gmwan000/jwx.html
antenna to clasp on your windew, scroll a bit down from the top
http://home.planet.nl/~gmwan000/jwx3%20Antenne%20test.pdf
PDf with piccies and test.

[W5BRM]

Got it all working. Bought a Diamond NR770ha. Took about 30 seconds to tune it. Got the swr at 144.5 at 1.6. Ohms were a bit high at 73. 146.0 swr 1.3. Ohms at 60. 147.9 swr 1.5. Ohms at 71.

Not sure what to do about the ohms. Im using 50ohm coax. Tge antenna is tilted a bit forward so that may be the problem. No time left for today to experiment.

Listening to 146.52 in Columbus Ohio. Madhouse. Have about 7 or 8 hams mobile and base working. Nice to hear the activity.

Had a brief qso with n8ymt i think was the call. (Didnt write it down). He gave good audio report and strong signal about 4 miles away..

Still got some things to do to get the radio situated.

All in all, nice to be active again.

[WZ7U]

That is great! I wouldn't sweat the ohm readings, the impedance is close enough to be effective. Go enjoy it man, you earned it :clap:

[PA5COR]

an open dipole is 73 Ohms, not 50.
The reason why with a Ground Plane 1/4 wave you see the radials at an angle to bring down the SWR to 1:1 or 50 Ohm.
On a car roof you see thee same, adjust length of radiator to get o a good swr.
Personally everything under 1:2 is good enough for me, or lss as 10% loss.