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Non-metallic body – ground plane issues
I have a portable XM Radio receiver that I move between my cars so that all have a small magnetic antenna (about 1.5″/40mm) on them. In addition I have CB radios I use with the cars. One CB antenna is a magnet mount K40. I can fabricate steel plates for these but will the frame of the Aptera provide a sufficient ground plane?
- This discussion was modified 1 year, 5 months ago by
bbelcamino.
- This discussion was modified 1 year, 5 months ago by
- 27 Replies
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Non-metallic body – ground plane issues
updated 9 months ago 14 Members · 27 Replies -
Is that much different than the grounding requirement for all the other electronics in the Aptera?
Also we leaned then belly will be aluminum for the skin cooling system.
( Of course the attached picture of the beta mule has much more metal components that will not be in the production unit)
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The belly pan will be aluminum. It may already be DC grounded. For maximum performance run a braided bonding strap from the chassis of your CB radio to the belly pan. This should allow sufficient RF capacitive coupling to ground. The XM ought to be fine.
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Ground planes, when referring to an antenna, is not the same thing as an electrical ground!
In the case of a non-metallic vehicle, you would probably need to have a special antenna with its own ground plane built in. The size of the ground plane changes depending upon what frequency the antenna uses. Higher frequency, smaller ground plane (think VHF/UHF for satellite) and CB is HF and requires a much larger ground plane. To learn more, look into ham radio related websites.
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Correct. I was thinking of getting the tow package and use it as the base for creating a steel platform for the XM & CB magnetic antennas.
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The XM/Sirius antenna may do well on the dash, preserving the aerodynamics…
As far as Amateur Radio VHF/UHF antennas, the ground plane needs to be ≈ 48cm for VHF and ≈18cm for UHF. Antennas not needing ground planes are usually half wave antennas.
In roofs of non-metallic materials, I have applied stainless steel tape to build a ground plane. This would be problematic with the solar cells on the roof of the Aptera.
Not having received my Aptera, I can only suspect that a lip mount antenna with metallic tape under the lip may have to suffice for a ground plane that may be adequate but directional due to the nature of the less than ideal ground plane. Reflected power may also be a consideration.
The addition of an external antenna will adulterate the aerodynamics. Could an accommodation be made for public safety/amateur radio/specialty antennas within the structure of the vehicle?
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Correct. The CB band in these United States has a nominal wave length of 11 meters or 36.09 feet. So those real large CB antennas you sometimes see on Jeeps, pickups are 9 feet or 1/4 wave length. My tunable K40 antenna is 1/8 wave length and the CB splitter I have on my Miata’s stock radio antenna makes it a 1/16 wave length. Thus the need for a ground plane. I’m hoping that the metal framework with the tow hitch attached will be sufficient.
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You DON’T need a ground plane.
Use a NGP antenna.
I use a window antenna for the UHF in my van. It is a film with wiring in it that sticks to the window.
No hole drilled in the car for cable. No ground plane. Stick it on a surface in a logical spot and you are done.
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You are aware that antenna is set for 477MHz? Just because that frequency is the 17.55th harmonic of 27.185 MHz (Ch 19 mid-point of the 40 CB channels 26.965 – 27.405 MHz) doesn’t mean it will work. Besides, I have my trusty K40 bottom-loaded whip antenna. Mounted on a flat horizontal plate from the tow hitch, the magnetic base & load coil will be slightly below the tail so only about 48″ of the 3/16″ diameter stainless steel whip will be sticking up in the airflow. How much drag will that add?
Oh, that 477MHz is the 4.9th sub-harmonic of the 2338.75 MHz middle of the XM radio frequency band. Again, that doesn’t guarantee it will work with the XM satellite signals.
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yep. It was an example.
Use any other non-dipole that will suite the application and you don’t need a ground plane.
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Sense the Aptera body shell is not metal the antenna could be placed inside. This would also eliminate the air drag that it would cause. Sticking things on the outside of the Aptera that might disturb the air flow around it could be considered an insult to its designers.
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Again, I’m curious as to how much drag will be induced by a 3/16″ stainless steel whip.
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That whip has a base and haven’t you seen the whips get bent by the air flow while driving. It may increase the total air drag by 10% as it will not be part of the intended air flow.
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The base will be lower than the license plate so it will only affect the underflow. Besides it will be BEHIND the Aptera body so the airflow will have left the body already. Of course there will be turbulence caused by the whip but I don’t think it will add that much to drag. On other vehicles the K40 would either be in the middle of the roof or at the middle of the front edge of the trunk lid on a convertible. I think those positions would cause way more drag for those vehicles.
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having a stiff non moving antenna can also function as was for people to see the outer parts of wheel cover, and it should be placed at wheel driver is not near to so he can see it and place it when driving properly. a camera at the top end of it would also allow preserving momentum around a turn or around lanes, looking over most SUV towering in front of you, behind you etc. itd aldo help for parking this big car.
one reason people buy SUV is for visibility like this. another reason for SUV is assumption that they need all the space when in reality they almost defintly could just use roof rack for unusual times when they could justify need for more storage space. the other reason is precived safetey:youtube channel called “apteras owners club ” did video on crash saftey… its not as simple as “big car= safer because big people and animal and big things generally more durable”, aptera could convince people its just as safe.
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I have a ham license but do not presume to know what I am talking about here. But couldn’t the aluminum heat sink above the belly pan serve as an adequate ground plane for an antenna one could mount inside the cab? Does the antenna need to be in contact with the ground plane? I’m thinking a little whip antenna like I use on my handheld. Not a big 12 footer.
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Yes, it can. The belly pan will be likely aluminum itself. It doesn’t matter if it is wrapped or painted. As long as you run an RF braid (not DC wire) from the transmitter to the belly pan you’ll have a good capacitive coupling to ground. However, if you mount the antenna fore or aft of the belly pan, you can expect a wonky propagation pattern.
If you mount the antenna inside the cab, it will be partially shielded by the copper backing plates of the solar cells.
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I don’t like that, I also wish there was an embedded magnetic plate on top of the roof center with a mass bond to the rest of the metallic features of the battery and case and chassis.
Another alternative would be to drill a hole and install a bots antenna, which isn’t exactly pretty to look at.
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An antenna is essentially a wire of the proper length and a few components for impedance matching (sometimes). How about adhering a wire in the back window on the inside? Add a connector and some coax cable and you are good to go.
Is there a heater in the back window? That might be an obstacle to this approach.
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There may not be a back window if the purchaser ordered the hatch solar cell option as I did.
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Well, curses… You are quite correct. The solar panels contain a lot of metal connections which form an RF shield so an antenna inside won’t work.
The solar panels might be a decent ground plane except for the fact of having to drill a hole through the panels to mount the antenna.
Some aircraft are made of fiberglass. They found a way to add a folded dipole antenna into the structure using wire or copper foil then cover with a thin layer of fiberglass and epoxy. It might be an option in the door. This technique does not work with a carbon fiber panels since carbon is partially conductive. I am new to Aptera so I am not sure what material they are using. If I were designing the car, I would use carbon fiber. It is unlikely my idea would work. Well, curses…
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what if i can place the antenna in one of the three wheel arches or maybe i. the lamps in front or behind, if there were to be a 3rd brake light Similar to the Ford F150 Lightning electric pickup? if this could be a possibility then you can use a 3-d print to create an adapter board in order to be able to mount a bracket for one or two antennas, what do you think?
if Aptera would get a 3rd brake light then I would like to be able to solve this in order to be able to mount an antenna according to the instructions.
- This reply was modified 9 months ago by
Martin Waldispühl.
- This reply was modified 9 months ago by
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Will carbon fiber conduct electricity? To a limited degree. So, will the larger size of aptera body panels make up for it, allowing use of body panels for ground return of current like on metal body vehicles?
It turns out that carbon fiber does conduct electricity, but not as well as metal. If you have carbon fiber woven cloth, the fibers touch each other and will conduct current. However, liquid resin impregnates the cloth and tends to separate fibers reducing conductivity.
Carbon fiber SMC is not made of woven carbon cloth. Its fibers are short strips of fiber and contact each other less.
There would also be the issue of making good electrical contact of a metal wire to the carbon fiber. Special connectors may have to be employed to insure contact to many fibers, not just a few.
Also, the carbon fiber body panels would be glued to each other and the glue would not be a good conductor.
In short (not a good term to use when discussing electricity) the carbon fiber SMC may conduct electricity, but it does not look like a good conductor.
However, you do not know if the carbon fiber panels would conduct electricity well enough until experiments are performed. If Aptera Motors has panels glued up, it would be easy to make a simple conductivity test
What are your ideas on the subject? It would be very convenient if they did conduct.
- This reply was modified 1 year, 5 months ago by
Harry Parker. Reason: Removed double text - This reply was modified 1 year, 5 months ago by
Gabriel Kemeny.
- This reply was modified 1 year, 5 months ago by
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As shown on Aptera’s wiring test bench video, the wiring system is not like other vehicles and doesn’t use the body as an electrical conductor. It is a networked system with three wires going to every control module, the three wires are power, ground and data. The HV and solar systems are of course different.
I have not seen an antenna in any info, they may be depending on your cell phone for Wi-Fi connection.
The only thing that could serve as a ground plane would be the belly pan.
Having the body as an electrical conductor is a hazard in the case of an active power wire falling on the vehicle, possibly causing you to be electrocuted when truing to exit or enter it.
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Well, I’ll need a ground plane to work with my XM and CB radio antennae. Since there is a tow package being offered, that will have to have a lot of steel, so maybe there will be enough for a ground plane.
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You might be able to use a metalised wrap, and Earth bond that?
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It’d depend on how much carbon fibre they added, but in my opinion it’d be very close to being an insulator, since the resin is non-conductive. Probably just enough conductance to reduce static electricity, but that’s all. Nowhere near enough to use it as a ground plane.
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No, a CF layup will not conduct electricity. It is a very weak Faraday cage, nothing more. Why do you want conductivity? There are many composite aircraft that are shielded for lighting, but I have never heard of that being used for cars.