Ham Radio → How tall is your mobile antenna?

I don't mean how long the antenna itself is but how high it stands above the ground mounted on your vehicle.

I did some searching on the best way to mount an antenna (dual band VHF/UHF) on my car (Prius) and found a couple of recommendations for the Diamond K412CNMO mount. There was another solution that I liked even better but I don't have the right tools to make my own mount.

What surprised me however was how low those hams mounted their antenna on the rear hatch. Almost half of the antenna is hidden behind the car when it is mounted so low. The same mount also fits near the top of the hatch which would give the antenna clear sky in all directions.

To maximize the effectiveness of the antenna I would like to mount it as high as possible. I'm however also having concerns about hitting low hanging objects overhead while driving. I haven't mounted the antenna yet (Browning BR-180 or Comet SBB224NMO) but attaching it near the top of the hatch would bring it to about 8ft above ground.

This brings me back to my question: how tall is your mobile antenna and did it ever cause you any problems being so high ?

The problem with high mounted antennas is garages, overhangs, trees, etc.

I have two antennas on my Jeep (three if you count the AM/FM antenna). The first is a 2m whip, I believe it is 1/4 wave. It sits on top of the roof.

My other antenna is a 102" stainless steel whip. It is mounted on the passenger's side of the body, about as high as the side of the tail light.

The Jeep is a 96 Grand Cherokee w/ a 4" lift.... if that says anything...

I used to have a Dodge Dakota with a 102" whip on the roof... Besides it looking like a 1:1 R/C Car... I hit everything with that damn thing. (Did I mention the Dakota was also lifted?) After I broke two fiberglass antennas, I went with the 102" whip.

102", that is 8.5 ft before you even attach it to the vehicle

However the 1/4 wave 2m whip on top of the roof is something I should probably consider since it would stick up less then 20 inches.
I wonder how the performance would compare to a 1/2 wave or 5/8 wave antenna mounted on the rear hatch ?
A shorter antenna without obstruction might perform better then a longer antenna partially hidden by the car.

From what I remember, at least as far as 11m goes, when you put the antenna at a corner (like my 102" whip), it makes the signal directional towards the opposite direction. (ie, my antenna is on the passenger's rear corner, so I am directional to the driver's front corner.) At 11m, you did lose some from the vehicle blocking part of the antenna, though. Not sure how this would affect a VHF signal like 2m. (I would suspect it would be worse.)

Mount it in the center as much as possible as it provides the best Omni directional coverage. If you go in fringe areas you will be disappointed if you mount it any place else. I use a 5/8 144/440 Larsen with NMO mount. I do have to remove the antenna when going into public parking and the garage at home. I keep a small wrench in the vehicle and only takes about 15 seconds to remove and re-install. No one has ever complained while waiting to enter the public garage. Placing a small hole in the roof is no big deal and can easily be repaired if you decide to dispose of the vehicle later on.

Having read a few of your post I know you will take your time and plan your power feed and antenna location/feed and not just jump in and do a hap hazard job. One suggestion I would make is to go with a power feed greater than the recommended minimum gauge in most equipment manuals. I prefer equipment that has a remote heard so I can mount in the main portion in the rear of my vehicle. Saves room up front and mounting problems and the rear is a bit more safe from theft.

It is funny you mention power since that is also very much on my mind

I bought the dual-band Alinco DR-635T (including the remote head kit) and already while testing it at home discovered that it is far more sensitive to good clean power then I would have liked in a mobile radio The radio behaved erratic on a 12V 20A switch mode power supply that should have been more then enough to provide it with power (it works fine on a 13.8V 30A power supply as well as on fully charged 12V battery).

Good 12V power supply is a challenge in the Prius where most of the energy is stored in the high voltage battery and the 12V battery has the size of a motorcycle battery. Wire sizes (for example to the 12V outlets in the front) are way too small as well.

At a minimum I need to ensure that the radio won't drain the 12V battery when the high voltage system is off. The better option is to install a battery dedicated for just the radio. There are good examples on how to do this inside the storage compartment underneath the rear cargo area (which conveniently is next to the existing 12V battery). The storage area is large enough to also use it for the radio and the charging electronics for the radio battery (I'm thinking deep cycle AGM batteries like Optima).

I have heard this before about the Alinco equipment. I currently use a Yeasu and it does not exhibit any sensitivity. I am not familiar with the Prius or its power system. I agree, if you have the options of placing a dedicated battery in the vehicle that may be the best option and still keep the Alinco happy.

I have the 12 volt outlets in the rear of my vehicle also, even placing a small load on them the IR loss is high. I don't use them for anything. I guess if your only interest is a cell phone charger they are adequate.

If your antenna system is good and installed properly you should not have any problem running low to medium power.

Does that battery 12v battery get charged by an alternator? How about regenerative breaking? Always wondered what challenges higher current DC accessories have on hybrids.

And for the antenna. I have a 19" 2m/70cm whip mounted on the suicide door on my pickup. This setup is terrible. It's directional, ugly, and high loss RG-174 feeding the fancy and expensive mount. »www.diamondantenna.net/k400.html Works on hatchbacks also.

I would love to drill and NMO in the center of the roof. But I always park in the garage. And that's too much hassle for me. Could probably get away with a 70cm 1/4 wave up there. That make fancy powered mounts too. But haven't heard too many reports about those.

Put yours in the center of the roof!

There is no starter motor and no alternator in a Prius.

The Prius has two electro motor/generators (50kW and 20kW) that can individually or jointly charge the high voltage battery (either with power from the engine or through regenerative braking). The "charger" (DC-DC converter) for the 12V battery is fed from the high voltage system and is capable of delivering about 1kW. As long as the high voltage system is turned on, drawing a high 12V current isn't that big of a deal. The small battery size matters when the high voltage system is turned off.

My present antenna on my ancient Chevy van hits a height of 15' 5" above the ground. It is a modified GS-3 screwdriver antenna. The installation may be seem on my web site at: »W5JGV.com/GS3_antenna/index.htm

My earlier antenna reached a height of 17' 10" above ground. Seen here at: »W5JGV.com/mobile_antenna ··· ndex.htm

It took out gas station overhead lights, tree branches, and telephone lines. It eventually met a tree branch that was stronger than it was, and it now lies in shattered pieces in my workshop.

The GS-3 antenna works great, and is a heck of a lot more convenient for me to use on the road. I did have to install a small spring above the loading coil because constant collision with tree branches fractured the whip where it was screwed into the top of the loading coil.

73,

W5JGV - WD2XSH/7 630 Meter CW/PSK31 beacon 476.300 KHz

Look up WB4APR as he runs equipment in a Prius (as well as being the guy who help develop APRS.)

»www.aprs.org/EV-charging ··· ere.html

With conflicting requirements I had to compromise a bit. I wanted a dual band antenna with good gain (meaning tall) mounted high for clear reception from all directions but I also needed to be concerned about the limited headroom in many parking structures around here.


Browning BR-180 on Prius

not mentioned yet:

in general, you want any antenna mounted in the center of the roof, for farthest omnidirectional coverage.

mounted in the center of the trunk lid will also give omnidirectional, but you will get blockage in the front direction from the metal of the roof, say 10% by spherical area. the lower trunk height will also reduce the distance you can send receive, again by about 10%.

in general, for simplicity and cheapness, you want just a straight whip. if the whip is too tall, you can get one of those gutter clips, so you can bend the whip over and clip the tip of the whip near the roof. of course, that ruins the reception/transmission, but you can undo it in a second.

in general, for an antenna with a coil, the more turns on the coil the more short the rest of the whip can be. so look for or construct a bigger coil.

I have a Subaru Forester and I find it rather easy to reach the center of the roof to remove the antenna when it has to be removed. If the coverage meets your needs then leave it as it is. But you also want to keep the ones that you are attempting to communicate with in mind. If it doesn't provide a decent signal into the repeater then you may just be creating unnecessary noise. Get some feedback from others on the repeaters that you want to work into and see what they say. I have seen several installations similar to yours and they have reliable/sufficient signal strength into the repeaters that they normally work into. Best wishes.

Before mounting the antenna on the hatch I was using a mag-mount in the center of the roof (only stationary, I didn't fully trust it for driving) and therefore I do have some experience of the ideal antenna performance. If the performance of the same antenna in the new location is much worse I should notice it. The difference in antenna cable (RG-58 vs. RG-316) will certainly also be a factor with the RG-316 being described as very lossy.

I haven't actually used the antenna since I mounted it since I'm still working on the mounting of the radio and power equipment. Right now I'm looking for an inexpensive source for a 2ft by 3ft aluminum plate (about 5mm thick: 3/16" or 1/4") that I want to use to attach all the hardware (with the side benefit of the panel acting as a heatsink).
I did find a local source for it but the price is far more then I was willing to spend (which is causing me to delay this project a little bit).

I also drive a prius gen 3 (same color as yours even) use a mag mount as well. The base cracked and a few times while driving it's blown off, can usually tell as the signal drops and you start hearing it "thwacking" around on the car. But it's easy to just pull over and stick it back on.

Thank you for confirming that my fears regarding mag mounts while driving are not completely unfounded. The antenna may very well stick to the roof even at high speeds but with the extremely poor road maintenance around here there are plenty of bumps in the streets that are severe enough to possibly knock it off.

Mine stuck fine until the base cracked. The magnet stays on the car just fine, but with the base cracked the actual plastic part comes lose as there is nothing holding it to the magnet. I've driven with mag mounts for 20+ years and as long as they're in good shape they're not gonna budge.