Two Way Radio People - Cybertruck RF Noise

[BrockN]

This won't be of interest to most of us, but anyone with Amateur Radio gear or anyone needing a two way radio for backcountry travel or perhaps work, might find this relevant.

When I installed my VHF radio in the truck, I was initially happy with what I thought was a fairly quiet truck. I didn't hear any birdies I typically have come to expect from computers and inverters. But then I noticed that weaker signals often had noise on them... just a seemingly higher noise floor with random static. So I got out my trusty TinySA Ultra and sniffed around a little.

I did not see any obvious noise on the display, but then I set it to also show a waterfall. At that point I realized that I could cause seemingly random noise to appear when I turned on the 120 Volt outlets. This is what I saw:

The lower part of the waterfall (blue background) is with the outlets off. The upper area is with them on. Next step was to power my radio from a LiFePO4 battery, to take my 120 V power supply out of the equation. This video shows the radio powered by the battery, with nothing plugged into any of the sockets. Sockets are on at the beginning, get switched off and then back on again. Note the background noise that pops on and off with the sockets:

When I scanned around with the spectrum analyzer to find the VHF noise, I hadn't seen evidence of any significant noise on the lower bands, except for 10 meters (28 MHz). I was out on my rural property a few days ago and decided to see how HF sounded in a very low noise environment. The noise floor out there is about an S1 (!), which is heavenly... I bolted on the old screwdriver antenna I have, to the hitch assembly and grounded it to the truck body. Recognizing that the socket system is noisy, I powered my little FT-817ND from my trusty battery. Happily, the noise floor was almost non-existent, except for a regular 'tick' that might be the radio attempting to charge the non-existent internal battery. Or maybe the truck is the source, looking for a Bluetooth signal or something. Anyway, it was something I could live with. But then I unlocked the door and the big battery contactor engaged.... as in this video:

Definitely not good! S1 to S8 instantly!

What I haven't tried yet is to see whether the 48 Volt system also creates noise like the 120 V system does. I'm cautiously optimistic that it might not, given there's no AC waveform being constructed. But given the general noise emanating from the vehicle itself, maybe I'll be disappointed.

Has anyone else done any testing like this? If so, what did you find? And were you able to quiet it down at all? I don't think it's something that can be addressed by the owner - it's likely much more complicated than simply slapping some ferrites on cables (if you could access them safely in the first place).

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[FRUNK-IT]

I’m kinda curious to see what others have to say. I’ve been considering putting some gear in the truck and wondered what kind of experiences other users have had. Might throw my mobile ‘portable’ setup in there on the passenger seat and just try it out for a bit before I commit to actually mounting anything.

 

[CyberGus]

What I haven't tried yet is to see whether the 48 Volt system also creates noise like the 120 V system does.

Right, the 120VAC must always be generated via the noisy DC-AC converter.

When the truck is in standby (contactors open) then it is using the 48V battery exclusively, The DC-DC converter would still be employed periodically to top off that MV battery.

But when the truck is "on" and the contactors closed, I believe the 48V system is powered by the DC-DC converters full-time. You could probably even disconnect the MV battery (??) and would be fine until you stopped and got out

 

[Langestreet]

Thanks for this. I have an FT857. On U/V it is fine. For HF (40M stick) I also have the high noise floor. Unless I move to battery, I think I am stuck with it.

 

[BrockN]

Right, the 120VAC must always be generated via the noisy DC-AC converter.

When the truck is in standby (contactors open) then it is using the 48V battery exclusively, The DC-DC converter would still be employed periodically to top off that MV battery.

But when the truck is "on" and the contactors closed, I believe the 48V system is powered by the DC-DC converters full-time. You could probably even disconnect the MV battery (??) and would be fine until you stopped and got out

Yes, although I don't think 'standby' ever really happens until a while after you leave the vehicle and it locks itself. If I'm working around the truck or inside it, it takes a long time before the truck forgets about me and shuts down the screen, HVAC etc... I could hear the contactors release probably a minute or so after the truck locked. The HF noise disappeared at that point.

Oddly enough, the general noise of the truck being alive didn't seem to be a problem on VHF.... just HF.

I expect that the DC-DC converter could actually be as noisy, or almost as noisy as the 120 V inverter is. Unless, that is, Tesla was more aware of the potential for noise from the DC-DC device because it would always be alive when the truck is on. The 120 V is more of an option to run your fridge, etc., so might not have been tested as extensively by them.

 

[BrockN]

Thanks for this. I have an FT857. On U/V it is fine. For HF (40M stick) I also have the high noise floor. Unless I move to battery, I think I am stuck with it.

FT-857... hopefully you aren't suffering from the zebra stripe problem. I think that was the model that suffered that issue?

How are you powering it? And if from the AC system, have you tested VHF receive on a weaker signal? I had no trouble until the received signal strength started to drop. I really thought I was going to be fine until I drove out of town a ways and realized the signal sounded pretty bad!

How/where have you got the 40 meter stick mounted? Always looking for ideas...

 

[Langestreet]

I added a well grounded cross members to mount antennas to my rack. I Duplex in the radio side and on the antenna side so that only one feed transitions from inside to outside.

Power is a normal bench supply secured with the body of the radio within the added center console. I have holes drilled for wiring an heat vent.

HF performance is poor. I think this is the inverter generated noise, though it could be the computers, compressors, heating and cooling of cab and/or batteries, etc

 

[BrockN]

I added a well grounded cross members to mount antennas to my rack. I Duplex in the radio side and on the antenna side so that only one feed transitions from inside to outside.

Power is a normal bench supply secured with the body of the radio within the added center console. I have holes drilled for wiring an heat vent.

HF performance is poor. I think this is the inverter generated noise, though it could be the computers, compressors, heating and cooling of cab and/or batteries, etc

So your HF experience fits with mine. How critical have you been with VHF performance? Do you ever get into a location where the receive signal is getting weak? Between inactive repeaters and mostly staying within the solid coverage footprint of the repeater, many of us rarely hear a challenging signal...

I ended up mounting my radio control panel to an aftermarket underscreen shelf. I added a little steel plate above and below the shelf to stiffen the shelf and transfer load from the bolts, then attached a small tripod ball head to the bottom. That allowed me to connect the control panel and tip/twist it to a position that works for me...:

I tried the whole radio in that position, but the weight made things a bit bouncy and I decided I didn't like that. The body of the radio is now under my seat and I have a LiFePO4 battery in the yacht floor area between in front of the console. I'm watching for a storage solution in that area that would accommodate my battery, but it isn't small (50 Ah).

 

[Langestreet]

I have decent U/V performance, but enjoy good repeaters in my area.

Batteries will give better HF performance sice the noise floor drops when the truck is "sleeping."

Your mount approach is a good choice. There aren't enough hard points identified that I am comfortable with using a RAM ball mount and carrying the weight of a radio. It hurts to think of drilling into the co sole.

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