Ham Radio Antenna Questions

[DrDmoney]

thank you for the feedback. Can you help me understand why some people say I need a no ground plane antenna in this situation? (Either mounting to the side or rear of the Jeep?

Ideally the antenna would work best dead in the middle of a metal roof unobstructed 360 degrees but we TJ Owners don’t have that, you want to mount up high on the biggest chunk of metal with the least amount of metal in front, beside, or behind the antenna. That said behind the spare or low on the tub is not ideal the wheel in front of the antenna is worse, but....still better than a NGP for power. They are designed to use the NG coax for the ground, therefore you can’t cut the cable down. The tailgate is not solidly grounded neither is a carrier so if you mount to these add a good ground strap to the tub. This is what was told to me by a com officer at a Fire Department.

 

[DrDmoney]

From my understanding the gist is if the antenna or mount are attached to a properly grounded metal base.

If you’re drilling a hole in a hard top or similar - Non-ground. Any metal mount (Bumper, taillight mount, etc) - grounded. The caveat for the metal mounts being you need to grind away the painted coating between the antenna mount and the antenna.

CB antennas are similar for the grounding. For example the powder coated taillight mounts usually need a few spots ground down to expose the metal to ground to the tub: antenna mount and tub bolt.

X2 I ground the paint off where the screw heads made contact with the bracket as well as ran a tap in the threaded holes then painted it all black after mounting (I didn’t want to grind my paint on my tub) also I have a thin rubber gasket under the bracket and I rely solely on good contact from the two screws. My radio gets out great.

 

[rasband]

X2 I ground the paint off where the screw heads made contact with the bracket as well as ran a tap in the threaded holes then painted it all black after mounting (I didn’t want to grind my paint on my tub) also I have a thin rubber gasket under the bracket and I rely solely on good contact from the two screws. My radio gets out great.

I used a dremmel to grind off the area under the antenna mount point (terraflex tail like bracket), drilled through the tub and ground off the mount’s exterior bolt head area and the interior lock nut area. Total space compromised on my rig was pretty minimal- but I get the apprehension. My CB antenna was at a SWR of 1.1 or so, which is pretty solid (for those unfamiliar closest to 1 is best, meaning 100% of the transmit power from the radio reaches the antenna, 1.3 is 98.3%)

Better the ground plane better the reception and transmission.

 

[TJustin]

Thank you for the info. Still new to the ham thing. I understand that performance may suffer, but mainly looking for trail comms mostly.

So, as I understand it, technically if I have a good ground I could go with a 1/4 wave and get it to perform decent for trail comms. Anything I am missing?

 

[Mr. Bills]

. . . So, as I understand it, technically if I have a good ground I could go with a 1/4 wave and get it to perform decent for trail comms. Anything I am missing?

Nope.

With 2m ham you can get decent performance with a tail light antenna mounting bracket as long as the mounting bracket is well bonded to the body and frame.

Scrape away some paint on the back of the antenna mount bracket and the corresponding area around the bolt holes in the body to ensure a good metal-to-metal connection between bracket and tub. Also be sure that there is a good metal to metal connection between the the antenna mount and the antenna mount bracket.

For my antenna installation I sanded the paint to bare metal around the bolt holes on the inside of the tub as well the outside of the tub and ran a short lengths of 1/2" tinned copper braid from one antenna bracket fastener to an inconspicuous place on an inside surface of the the tub. I added two more grounding straps from tub to frame near each rear corner.

This article on bonding illustrates the theory and the process: http://www.k0bg.com/bonding.html You can purchase grounding strap on Amazon (called "Tinned Copper Metal Braided Sleeving") and use ordinary crimp-on ring terminals at each end. See: https://www.amazon.com/gp/product/B01BIBQ940/?tag=wranglerorg-20

I do not use "no ground plane" antennas or any special kind of coax . Neither are necessary in a jeep mobile installation if the antenna mounting bracket and antenna mount are properly bonded to the vehicle. (As mentioned above, NGP antennas are for fiberglass boats, etc. that do not have metal frames or other metal surfaces that can constitute a ground plane. Jeeps installations do have a ground plane, perhaps not the best of one when one mounts an antenna at a corner rather than the center of the hood, but a ground plane nonetheless.)

As I noted in post # 2 of this thread, a 1/2 wave 2m ham antenna is generally more forgiving of ground plane issues. However, I have used used 1/4 wave, 1/2 wave and 5/8 wave antennas on my current antenna mount without issue. [Photo in post #2.]

 

[fuse]

Can you help me understand why some people say I need a no ground plane antenna in this situation? (Either mounting to the side or rear of the Jeep?

I think there's some confusion here between electrical grounding, which you need to complete the circuit between the transmitter and the antenna, and the antenna ground plane, which reflects radio waves back upward.

https://www.electronics-notes.com/a...rthing/antenna-ground-plane-theory-design.php
If you don't mount the antenna on a flat sheet of metal (i.e. in the middle of your hood), and don't have radials extending from the base of the antenna, you need an antenna designed to transmit without a ground plane. That would be a "no ground plane" (NGP) antenna.

If you try to use a ground plane antenna on a Jeep, a good portion of the radio signal is going to be transmitted down into the Earth. That's a waste of good radio power.

Fortunately, NGP antennas are easy to come by and about the same cost as GP antennas. You just need to pick one tuned to the right band with the right impedance (and with other properties you like).

 

[DrDmoney]

Thank you for the info. Still new to the ham thing. I understand that performance may suffer, but mainly looking for trail comms mostly.

So, as I understand it, technically if I have a good ground I could go with a 1/4 wave and get it to perform decent for trail comms. Anything I am missing?

Nope you are on the right track!

In short, the NGP system (we call it a system because the antenna and coaxial cable are a matched set that may not be interchanged with other non-Firestik NGP antennas and coax assemblies) is a problem solver. If your vehicle does not provide sufficient ground plane for a regular GP antenna, the NGP system will solve the problem. Who should use an NGP system? Here are some probabilities. Those with ...

• Fiberglass or plastic vehicles
• Hot air balloons
• Wilderness back pack frames
• Fiberglass pick-up bed caps
• Aluminum and/or fiberglass boats and canoes
• Aluminum and/or fiberglass cab-over campers (antenna on camper)
• Aluminum and/or fiberglass travel trailers

The NGP systems are not "required" on metal vehicles. They will work but in most cases you are better off using a GP set-up if you have the reflective metal surface available. The ground wave field strength of a GP antenna on a metallic surface is about 15% stronger than a NGP system on the same vehicle in the same location. This is directly due to the way that the radio's power is delivered to the antenna via the special cable. There is some energy absorption within the cable assembly. However, and again we stress the specific purpose of the NGP system, it is better to have some energy absorbed in the cable assembly than it is to have no communications, or very poor performance with a GP set-up.

 

[Mud dauber]

I should have my call sign today! Posted on the FCC site.

I am KN4SMO

 

[fuse]

I am KN4SMO

Congrats! KM6WKE