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Will a 36” x 24” x 1/4” thick aluminum plate work ok for a ground plane for a 102” whip antenna?

63Sprint

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Joined
Mar 18, 2024
Messages
35
Hi everyone, I’m new here and I have a 102” whip antenna lying around.
From what I’ve been reading the bumper is not the best place for a 102” whip antenna.

Here are a couple pictures of what I’ve been thinking:
IMG_1864.jpeg

IMG_1865.jpeg
The aluminum plate is 24”W x 36”L x 1/4” thick. The cross bar is 4” x 2-1/4” x 1/4” thick Aluminum C channel. All aluminum is 6061-T651 heat treated stuff. It will hold any type of legal height road worthy antenna.


I know it’s not a large ground plane but, will it work better than putting it on the bumper.

The aluminum did not cost me anything.

I could be wrong, I read that it’s best to keep the antenna elevated from the floor. And, it’s best to keep it centered.

I’ve been thinking that this design can be slid from front to back on the bed.

I’m not worried about scratching the truck. It’s a work truck.

I do have a president 33” 1/4 wave antenna and I’m not pleased with the performance.
The SWR is between 1 & 1.1

IMG_1867.jpeg

Output on the President Walker ll is right at 4 watts.

I’m hoping that the 102” whip antenna with a barrel spring will give better performance than the 33” base loaded antenna.

I was also reading that aluminum is fine for a ground plane. Is this correct?

The height of the whip antenna will be right around 13 feet. I will have an insulated hold down clip when I have to go under low objects.

It looks like the base of the 102” whip antenna will be 22” below the roof of the cab.

Please let me know what you think.

Thanks
 
Last edited:

prcguy

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That's a very small ground plane for 27MHz, and elevated/isolated from any other large flat metal on the truck will probably not work very well. Some antennas will not match up and will not perform as good compared to lots more metal under them. Why not stick the 9ft whip in the middle of the truck bed? That's a lot of ground plane and the bed walls will add capacitance and help the antenna achieve a great match.
 

prcguy

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Aluminium and magnets never seem to get along...
i did drill on a station wagon years ago and had the 108 whip.
i received stuff that no one else could even hear.
drill the hole.
A triple or quad mag mount will work in the bed and you can improve the grounding with an 8" X 11" sheet of refrigerator magnet material covered with self adhesive copper foil, then a very short wide braid from the foil to the ground side of the mag mount then flop the magnetic sheet onto the truck bed. That will capacitively couple the ground so well it will work the same as if the mount was hard grounded to the bed, and it will be removable if needed.
 

63Sprint

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Joined
Mar 18, 2024
Messages
35
That's a very small ground plane for 27MHz, and elevated/isolated from any other large flat metal on the truck will probably not work very well. Some antennas will not match up and will not perform as good compared to lots more metal under them. Why not stick the 9ft whip in the middle of the truck bed? That's a lot of ground plane and the bed walls will add capacitance and help the antenna achieve a great match.
My first thought was to mount the antenna in the center of the bed but I load the bed up a couple times a week. Would you recommend a huge 4 magnet mount or drill and mount a connector with some type of disconnect. Do you think the connector can be installed just below the bed so a cap can be put in place to seal and protect the connector? Would a longer spring make up for the recessed connector?

So much to learn. I’m looking to get the best performance possible without going over 13’ 6”. Possibly look for a different roof mount antenna? If roof mount is best then I prefer permanently mounting it.
 

63Sprint

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Joined
Mar 18, 2024
Messages
35
A triple or quad mag mount will work in the bed and you can improve the grounding with an 8" X 11" sheet of refrigerator magnet material covered with self adhesive copper foil, then a very short wide braid from the foil to the ground side of the mag mount then flop the magnetic sheet onto the truck bed. That will capacitively couple the ground so well it will work the same as if the mount was hard grounded to the bed, and it will be removable if needed.
Have some things to think about. Thanks for posting. A quad magnet . Ok, this sounds good. I don’t quite understand the refrigerator magnet material covered with self adhesive copper foil.

Would a whip antenna mounted in the center of the bed outperform a better roof mount?
 

mmckenna

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I am a lineman for the county.
So much to learn. I’m looking to get the best performance possible without going over 13’ 6”. Possibly look for a different roof mount antenna? If roof mount is best then I prefer permanently mounting it.

Full 1/4 wave works well.
But I think the challenges of getting a good ground plane under it are the challenge.
Yeah, not ideal on the bumper since the ground plane is really lopsided, but it might work better than a 33" tall antenna. Kind of hard to trick a 33" tall antenna to act like 108".

A lot of people just mount off the bed rail and deal with it. I think most of the guys out there don't even consider a ground plane, yet they still have a good time with their radio.

Like I said, a 33" antenna is hard to make work like a 108".

I used to mount my base loaded CB antennas directly on the roof, dead center. Still not an ideal ground plane, but it's got other good stuff going for it.

I always ran a Larsen NMO-27, with a permanent mount NMO on the truck roof. Worked fine for what I was doing, and well under your 13'6" limit.
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
My first thought was to mount the antenna in the center of the bed but I load the bed up a couple times a week. Would you recommend a huge 4 magnet mount or drill and mount a connector with some type of disconnect. Do you think the connector can be installed just below the bed so a cap can be put in place to seal and protect the connector? Would a longer spring make up for the recessed connector?

So much to learn. I’m looking to get the best performance possible without going over 13’ 6”. Possibly look for a different roof mount antenna? If roof mount is best then I prefer permanently mounting it.
A ball mount on the rear quarter panel, outside bed wall 6" to 12" down from the top rail (as long as it angles outward as it goes down) has been a classic place to mount a 9ft whip on a pickup truck. The antenna actually has some ground plane and usually has a good match and it just works. My current truck and last truck has a CB/HF antenna mount on the inside bed wall, old truck about a foot behind the cab and new truck just aft of the rear wheel well. All antennas, CB whips, Hamsticks, big screwdriver HF antennas all work very well there.
 

KB4MSZ

Billy
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This may or may not be an option for you. I have my whip antennas mounted on a 12 gage galvanized rail that is bolted to the sides of my tool box behind the cab of my truck. The tool box in turn is grounded to the truck body. I have a solid stainless whip (tuned for 10 meters) on the passenger side and another mount which I use to switch out hamsticks for other bands on the driver side. It works quite well despite not being "symmetrical". (Yes, the spring is getting up in age).

IMG_20240324_102314471_HDR.jpg
IMG_20240324_102334571_HDR.jpg
 

KB4MSZ

Billy
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I use an antenna analyzer with a 17' telescopic whip that I put in place of the solid stainless whip when I am operating in a fixed location. The telescopic whip can be tuned on any band from 14 mhz and up. Having an antenna in the other mount does affect the "tune" of the telescopic whip, it causes an odd dip in the sweep pattern when tuning for SWR. I usually ignore it, sometimes I will remove the unused antenna since it's easy to do so. As to what the unused antenna does to my radiation pattern on a given band I haven't a clue. I never use both antennas at the same time, only one radio is in use. I do have a McKinley CB which is usually connected to the solid whip but not on when I'm using the amateur bands on the Hamstick. I'm VERY happy with the results I have with the setup. The ham rig is a Yaesu FT-891 with 100 watts out.
 

niceguy71

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Apr 28, 2023
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334
Location
Middleboro MA.
I know you already have the 102 inch Stainless Steel whip laying around... and I also know everyone say's they work really great... I never had good luck with one myself...... I heard many people having great luck with the tram 3500 magnetic antenna. I watched a video of a guy I trust getting 18 plus miles on a 4 watt CB and thought for the price I would try it.... it's been fantastic! I can talk several towns away most days on AM and on SSB I can talk skip all across the country..... Tram discontinued the 3500 but you can still find them fairly cheap... this one at walmart is $66 bucks with free shipping..... if it worked for you.... you could be done quick and easy for $66 bucks.

Robot or human?

I also have regular cab truck ( not a lot of metal on the roof to reflect the RF signal) I did do a lot of RF bonding so I don't know if it works so fantastic because of the great antenna or from my RF bonding.. but you could give it a try.


this is some of my RF bonding pictures.... truck install finally done
 

kb1fua

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May 14, 2009
Messages
71
Location
Stover MO
Full 1/4 wave works well.
But I think the challenges of getting a good ground plane under it are the challenge.
Yeah, not ideal on the bumper since the ground plane is really lopsided, but it might work better than a 33" tall antenna. Kind of hard to trick a 33" tall antenna to act like 108".

A lot of people just mount off the bed rail and deal with it. I think most of the guys out there don't even consider a ground plane, yet they still have a good time with their radio.

Like I said, a 33" antenna is hard to make work like a 108".

I used to mount my base loaded CB antennas directly on the roof, dead center. Still not an ideal ground plane, but it's got other good stuff going for it.

I always ran a Larsen NMO-27, with a permanent mount NMO on the truck roof. Worked fine for what I was doing, and well under your 13'6" limit.
😎👍perfect!
 

merlin

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Jul 3, 2003
Messages
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DN32su
An old buddy mounted his 102"/ball/spring in the center part of a diamond plate toobox, works great.
That's a very small ground plane for 27MHz, and elevated/isolated from any other large flat metal on the truck will probably not work very well. Some antennas will not match up and will not perform as good compared to lots more metal under them. Why not stick the 9ft whip in the middle of the truck bed? That's a lot of ground plane and the bed walls will add capacitance and help the antenna achieve a great match.
Maybe, but my truck I had a similar setup with a Wilson 1000M and talked all over the place, Match across the band was under 1.5:1
Bed was grounded so the whole truck was the ground plane.
 

slowmover

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Aug 4, 2020
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Fort Worth
“. . If roof mount is best then I prefer permanently mounting it . . . . “

It was the route I’ve followed.
7’ antenna choices keeps it well under 14’.

IMG_2345.jpeg

Not mine, but a similar Dodge I’m using as a model. Run power up starboard A-pillar. Radio to board epoxied to roof under headliner.

IMG_2010.jpeg

Getting back to finishing it in a couple of days.

.
 
Last edited:

slowmover

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“ . . I don’t quite understand the refrigerator magnet material covered with self adhesive copper foil . . . .”

Here’s a pic of his creation.

IMG_4199.jpeg
 

jhooten

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Mar 6, 2004
Messages
1,740
Location
Paige, Republic of Texas
From Antenna Myths

"A vehicle is not a ground plane for an HF antenna. Rather, it acts like a capacitor between the antenna, and the surface under the vehicle in question. That surface, whatever it is, forms the actual ground plane, albeit rather lossy." Spend some time on Alan's site. There is enough content there to keep you reading for a long time.


It doesn't matter where you mount your hf/cb antenna on a vehicle. There is NOT enough metal in a car or pick up sized vehicle to act as a ground plane for an HF antenna.
 
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