Ham radio antenna relocation

[Captain Skip]

When I installed my ham radio in my JL I didn't want to put the antenna on the tailgate as it would create issues in transmitting capability. So, I found a side mount for the front fender and installed the antenna there on the left side cowl. After using it there for a year I wasn't really happy with my transmitting distance. My wife has a shorter antenna mounted on the roof rack of her Outback and we did a public service event a couple weekends ago where we provided radio communications for a marathon. I swapped out her short antenna to the same antenna that I have on the JL and her transmitting distance was much better than mine. That got me thinking....the way I had the antenna mounted on the JL, the base load coil, which is a very important part of the antenna was located below the plane of the hood by several inches. This created a situation where the radio signal would bounce off the side of the JL and limit my transmitting capability towards the right side of the vehicle.

I decided it was time to relocate the antenna to make sure that the coil was in the clear. Mounting on the center of the roof was a no go as I wouldn't be able to fit the JL in the garage with the antenna mounted there. Tailgate is out as stated earlier. I happened to notice an advertisement somewhere for light mounts that go over the cowl and that got me thinking. I found one brand, Hooke Road, that has a reasonably thick powder coated light mount at a reasonable price. I only needed the left side one but the only sell them in sets but for the price it didn't matter.

I installed it today and it's working out much better. I checked my SWR with my nanoVNA and the repeaters and frequencies I normally use are showing near perfect SWR. I then tried a couple test calls on the area repeaters. The two closest that I was having problems reaching from my driveway are no problem now so mission accomplished. I will admit, the mount location is not perfect. The center of the roof would provide a better ground plane - provided I attached some sheet metal either on the roof or inside - but as stated, that won't work because of height. All antennas are compromises anyway so at least now I've got good radio exposure to the front and both sides. I'll still have rearward exposure but not as good due to the windshield, A & B pillar, etc. But it definitely works better.

If anyone is looking to use these light mounts for an antenna here's a couple things I learned. They powdercoat the mount black but send stainless steel flat head bolts. And of course, being a Jeep the two bolts on the top of the cowl are 6mm while the ones on the side are 8mm...they couldn't make them the same size. Rather than go with the shiny stainless flatheads I got the right length button head bolts and sprayed them satin black. For the top ones I did use the stainless flathead bolts but put a plastic screw cap over them as figured water and snow is going to sit on top of the cowl on occasion. I may end up swapping the out for button head bolts painted black, haven't decided yet. I did drill out the forward light mount hole to fit the NMO antenna base which wasn't a problem. The only thing I found was that the antenna base would not ground to the body due to the powdercoating on the mount. I didn't want to scrape off powder coat and expose steel to rusting so I just added a 12ga wire to base of the NMO mount and ran it to a ground on the body. It's all bonded together now which I verified with a multimeter. Another thing I did was add some rubber spacers behind the flat areas that contact the body so the mount wouldn't scratch the paint. They include a few with the kit but I added more to be sure.

Any questions, fire away. I put the photo of the first mount below too for comparison to the new mount. Oh, by the way. If you're interested in these mounts Amazon has them that are sold by Hooke but you have to pay shipping. I got these on eBay from Hooke for a few dollars less than Amazon and free shipping included.

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[dstevens]

Your antenna placement looks good. I've got some polar charts for different antennas in different locations on my Jeep and the A pillar was very good. I placed mine further forward on the hood because I get sick off the antenna bouncing of the a pillar every 20 seconds. Center of roof was best and tailgate was the worst.

There was significant difference between different antennas (base loaded 1/2 wave) - up to 4 db. I had a 5/8 wave outperform all the 1/2 wave antennas by 1.5 db but at a certain point you start to go in circles - would the flatter donut from the 5/8 wave actually be worse in hilly terrain or if the Jeep was not level? Never tried 1/4 wave but I should as some people use them simply because they are smaller and fit in their garage. I image they do not perform well with no ground plane.

Your Larsen 02/70 tested ok on my Jeep.

Out of town today; I'll post the data tomorrow.

 

[dstevens]

Average signal by antenna. Highest signal is best (ie least negative).

770 = Diamond NR770HB
285 = Diamond M285S
2x4 = Comet CA-2X4SR
2/70 = Larsen NMO2/70B
1442 = Larsen B1442N

 

[dstevens]

Average signal by location. Again, highest signal strength number is best.

There were multiple antennas tested in each location, I moved some so that the above comparison is using the same antenna in different locations. So that is why some locations are duplicated and empty.

Tailgate sucks. A pillar is the best. Center of hood and center of roof was not that much better than the front cowl, but this is an average so does not tell the full story.

 

[dstevens]

Antenna signal strength in polar form. Antenna was located on the front left cowl. Highest number is best ie furtherest from center.

The antenna location makes some dead spots in the signal, notably at 8 o'clock and to a lessor extent at 4 o'clock.

Remember than 6 db is double or half the range. So you have well over double the range at 9 o'clock compared to 8 o'clock. Sorry I am mixing angles with clock numbers.

 

[Captain Skip]

Average signal by location. Again, highest signal strength number is best.

There were multiple antennas tested in each location, I moved some so that the above comparison is using the same antenna in different locations. So that is why some locations are duplicated and empty.

Tailgate sucks. A pillar is the best. Center of hood and center of roof was not that much better than the front cowl, but this is an average so does not tell the full story.

Very nice work! I’m retired LE and our radio tech always insisted on Larsen products….old habits are hard to break.

 

[dstevens]

Signal by location. Again highest number is best. ie furthest from center.

Note that tailgate is near 1/4 the range towards the front of the Jeep than the a pillar.

 

[Captain Skip]

Antenna signal strength in polar form. Antenna was located on the front left cowl. Highest number is best ie furtherest from center.

The antenna location makes some dead spots in the signal, notably at 8 o'clock and to a lessor extent at 4 o'clock.

Remember than 6 db is double or half the range. So you have well over double the range at 9 o'clock compared to 8 o'clock. Sorry I am mixing angles with clock numbers.

Fully understand, thanks again, you put a lot into the comparison.

 

[dstevens]

Very nice work! I’m retired LE and our radio tech always insisted on Larsen products….old habits are hard to break.

I mainly use a 1442 with good results. I would say that your 2/70 is not as good as the others in my test (sorry, initial post yesterday was from memory). But I could raise the mount by 4" like you did and it probably would all change.

And when I started to wonder about measuring signal by elevation as well as azimuth then I knew it was time to stop. I already had worn a circle in the backyard from walking round and round making measurements. I think it took 7 miles of walking to record the data.

 

[Captain Skip]

I got the 2/70 primarily from past Larsen experience on UHF trucked systems. I may have to revisit my options looking at all of this.

 

[Cllowe]

I have that mount that I used for a while but went back to the light bracket that mounts to the cowl. I couldn’t tell a huge difference. It’s hard to see with the snorkel.

 

[Captain Skip]

I set up my rig for ARES field operations from the back of the Jeep with my Go Box. It works well. I built a 2m Slim Jim antenna from 450ohm ladder line and enclosed it in a Sch20 PVC tube. I picked up a 20’ expandable flagpole from Harbor Freight and mount the antenna on the top when I use it. I welded up a drive on base that holds the flagpole in place. All in all it worked perfectly on the two events where I used it. But I wanted some better protection from rain so my wife, who’s also a ham, sewed a cover for the back by repurposing an RV cover that we had and didn’t use. It’s waterproof and covers the back for rain or sun. Just need to get a couple good tent poles for the corners. Being that I’m a cheap Yankee I built the Go Box using a large Home Depot tool box that I modified.

 

[Captain Skip]

I have that mount that I used for a while but went back to the light bracket that mounts to the cowl. I couldn’t tell a huge difference. It’s hard to see with the snorkel.

I did see a slightly better SWR moving up to the light mount position.

 

[Captain Skip]

Signal by location. Again highest number is best. ie furthest from center.

Note that tailgate is near 1/4 the range towards the front of the Jeep than the a pillar.

Just curious. When you talk about the A pillar location are you referring to where I mounted mine or actually mounting the antenna to the pillar itself?

 

[Cllowe]

I did see a slightly better SWR moving up to the light mount position.

Do you think where your mount has more metal so you get a little get a better ground plane?

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