451 shielding problem (Re: RFI and cruise control)

[Kermit]

Holy snikes! We've got some serious RF frequencies here. A lot of people have problems with their garage doors opening and closing on their own. I'm still on the fence about what to choose for my next cruise unit. Then again, there is of course just adding a little shielding.

[SmartieParts]

Sorry, but I really have to disagree with the use of the terms "The 451 forum is all abuzz with this" and "problems with aftermarket devices [...] And this only affects the 451 Cruise Control".

The sole discussion relating to this on the Area 451 forum was started by a guy named "Buzz" (so perhaps you were being coy?) and it generated limited discussion and really it seems to me it is largely unsubstantiated anyway.

Since the wiring from the ECU is exposed and is no more or less shielded than the cruise module, the car's electronics in general are just as susceptible to RF interference as the cruise is. So something generating those kinds of problems are going to affect more than just aftermarket parts.

The cruise control uses ABSOLUTELY NO radio receivers or transmitters.

I'd have to see it to believe it. I just can't get behind the idea that radio waves are affecting the cruise control in any way but especially in the manner you're describing. Actually I'm not clear on what it is you're describing when you say "throttle control loss". Is your pedal going dead? Or does your cruise stop working? Or??

It just seems to me that if driving by a tv station cuts your throttle out that we'd have reports of it all over the place. I drive by a pretty massive relay every day and it certainly never happened.

Color me skeptical, but if I can assist by all means let me know. We can swap your unit out for another one.

Double check your wiring too.

[SuperGeek]

Originally Posted by SmartieParts

It just seems to me that if driving by a tv station cuts your throttle out that we'd have reports of it all over the place. I drive by a pretty massive relay every day and it certainly never happened.

Agreed. I can't imagine Smart creating a vehicle for 10 years with electronics that would be susceptible to a CB antenna or anything less than 1.21 Gigawatts with a flux capacitor. The FCC has regulations to limit the amount of interference between devices, and I doubt they'd allow a car on the road as sensitive as appears to be described. That means, by design - if there are a few that are in fact that sensitive, that's a problem with individual units.

Aftermarket cruise - If the 451 uses no transmitters/receivers, I fail to see how common radio waves would interfere unless another connection is flaky. Has the OP tried disconnecting the 451 to prove it's the triggering device, or just not activating it?

[Old smart]

Whatever smart has been doing for the 10 years, this is what is in the OpMan says about some relatively high power transmitters:

“The transmitting power of the telephone or radio must not exceed the following maximum values.

Frequency range (band) - Maximum transmitting power (Watts)
Short wave (<50 MHz) --- 100
2 m wavelength ------------ 50
0.7 m wavelength ---------- 35
0.25 m wavelength ---------10

“Warning!
Radio transmitters can interfere with the vehicle's electronic system, endanger the operating safety of the vehicle and thus your own safety, if -
• there is no external antenna
• the external antenna is not low-reflection
• the external antenna is incorrectly installed
Excessive electromagnetic radiation can damage your health and that of others. Using an external antenna addresses and considers the concerns currently being discussed in scientific circles about the
health hazards possibly posed by electromagnetic fields.”

Interestingly, my low power Nokia cellphone instructions contain, in part, the following:

“RF signals may affect improperly installed or inadequately shielded electronic systems in motor vehicles such as electronic fuel injection systems, electronic antiskid (antilock) braking systems, electronic speed control systems, and air bag systems.”

The cellphone’s 900MHz mode (0.333 m wavelength) puts it within smart’s frequency sensitivity range thought not at the noted powers. It will cause my computer’s speakers to hum if within about 6”.

[SmartieParts]

Hi again. I got hold of Craig that led the design team of the Area 451 cruise.

It is not impossible for the cruise control or any other aftermarket or OEM component of the car to be affected by RF signals, but it is doubtful.

I think the question is "does our cruise control have adequate shielding for its operating environment?". I suppose that is relative to what the operating environment is. Typically, the answer is a resounding "yes" simply because it functions within the confines of the car and the vehicle's body is all the shielding it needs. This is on par with every other non-radio component in the car and as you pointed out the car's main wiring harness is unshielded in the same location the cruise sits.

The design exceeded DOT standards for automotive electronics including tests for rf signal absorption.

Could we have used more shielding? Sure at a cost. But I can't see how it should have been designed for the tiny percentage of people operating a radio station from their car to the cost detriment of the rest of those that do not. In any "normal" operating environment, the cruise control is more than adequately shielded.

If you are concerned your cruise control is being affected by RF signals and you can't fix the source of the problem (there should not be that much RF inside your car) then you can add shielding to the cruise. If it is simply shutting off then it is probably the long switch cable that is picking up the interference. Cut that wire and splice it in with a 3-wire shielded cable (24AWG or larger). If the symptoms are something else then you should shield the cruise box. There are various paints, fabrics, foils and other materials on the market for this purpose. Many of the cheaper ones appear to be selling to the "aliens are trying to get us" market so it is up to you to determine what would work and what's full of it.

If the RF is coming from a source in the car and it is cutting out throttles, etc... I think I'd also be concerned about shielding my brain and... ummm... other "sensitive" body parts.

- Steve

[nscaler]

Originally Posted by SmartieParts

Actually I'm not clear on what it is you're describing when you say "throttle control loss". Is your pedal going dead? Or does your cruise stop working? Or??

At first it was a 10w 2M signal burst from something sitting on my dash. Later it was a 50W 2m transmission from a Larson glass mount 2M/440 antenna on the windshield (limited spots for antenna on cabrio).
Throttle loss means "push pedal - car no go" - just idles.
And you are correct. I did not actually check the 451 forum myself. I'm going on what was told me by a fellow smart owner I know (the one whose throttle would stop working near a certain big antenna). On Sunday, when I have more time, I will try the 50W 2M radio again with the 451 CC removed (module removed and bypass plug installed) and see what happens. This will give a more definitive answer.
I am in no way blaming the 451 Cruise Control. I use it quite often and am very pleased with it. Highly recommend it to my fellow smarties out there. I just happened to get the wrong combination of conditions and got a surprise.

If it is not the 451 module or the cable running up to the stalk, I will let you know here. I may just need to add a RF choke on the wire to the switch to stop it acting as an antenna.
I am sorry to have started this small little mess and will try to be fair.

Mostly I'm trying to help any others that could possibly (but I really doubt this happens that often) have this same problem.
Besides, I think you would like to know if the 451 is the culprit or not, correct?

[SmartieParts]

Absolutely. I'm not going to say I'm not curious!

But I think it is clear that it isn't the cruise control even if it is the cruise control... if that makes any sense. What I mean is it isn't fair to say "my cruise is defective" rather than "my cruise doesn't like the interference put out by my radio setup". The former is an unfair portrayal of an unsuspecting product (in my opinion) while the latter serves as a warning to other radio enthusiasts.

I'm trying to think of an analogy... ok, let's say you have an aftermarket stereo with an LCD screen. It works perfect and everything is just great about it. But you happen to live in an area that gets to -45 degrees Celsius in the winter and the screen starts to misbehave (it happens). Can you blame the product? Not really... blame the weather. It just happens to be your situation that you're using it outside of a normal operating temperature range. So here, it would seem that you are operating the cruise (and every other component in your car including your internal organs?) outside of normal RF range.

I know next to nothing about radio so am I off base?

Maybe I should put it another way: If you discover it is in fact the cruise and only the cruise misbehaving when you blast it with your mobile broadcast fascility... what, if anything, should we do about it? I suppose at the least we can acknowledge it with a warning on the A451 website. Open to suggestions.

- Steven

[nscaler]

Originally Posted by SmartieParts

Maybe I should put it another way: If you discover it is in fact the cruise and only the cruise misbehaving when you blast it with your mobile broadcast fascility... what, if anything, should we do about it? I suppose at the least we can acknowledge it with a warning on the A451 website. Open to suggestions.

- Steven

You are absolutely correct. It is the combination of situations. Just trying to help anyone else that could (and a slim chance at that) have this happen to them.
And 50W is safe as long as you are not standing right next to the antenna. The "radiation" comes out straight from the antenna and does not radiate that much energy below or above the antenna.
Usually most hams have a metal roof on their vehicle which acts as a ground plane and helps direct all the energy from the antenna away from the occupants. No such luck with the smart. Cabrio or hard top (being polycarbonate) give no ground plane. The Larson antenna is designed to function without a ground plane. Designed to be installed on a window - and it does warn you not to install on windshields because of thicker glass there. There is a coil on the inside (shielded on the inside I presume) that radiates through the glass to another coil which connects to the antenna on the outside. Could be some leakage there too.

I will let you know Steven.

David

[nscaler]

Steven,

I was able this afternoon to test my 451 CC as you suggested. I unplugged the 451 module and the switch wire. I plugged in the jumper plug (putting the car in "stock" mode) and started the car. Keyed the Ham radio @50W on 2m using the Larson glass mount antenna. The throttle functioned fine.
Turned off the car, removed the jumper and plugged the module back in. I purposefully left the switch wire unplugged from the module. Started the car and keyed the radio.
No throttle response. Yellow triangle came on on the dash (this happened last time too. The reason I took the car to the dealer the first time).
Test shows that the module can be interfered with by RF.
The switch wire does not act as an antenna (disconnected in test).
35W @ 2m causes no problems. 50W is not used that often - 5W is fine most of the time.

I just remembered something my friend told me though. He said the original wiring for the smart has a "twisted pair" of wires that go into the ECU that are two of the wires switched out when installing the 451 CC. The twisted wires are to help remove possible interference from RF. So this could also be the culprit except the throttle still worked with the jumper installed.

Still, as you so wisely commented, this is only due to a strange combination of circumstances.

Next I will try some shielding so I can use my radio at full power if need be.

Another observation I noticed is that the Radio -10 display fades out during the 50W test also. Another reason to not use the radio at full power much.

Any other ideas out there?
Besides not using the radio at 50W?

David

[John_H]

Semiconductors (active electronics) are subject to RF interference of high enough amplitude. The normal P-N or N-P junctions in bipolar junctions rectify the RF energy and provide voltage offsets that are particularly annoying to analog signals. Most of what I've seen are discussions about interfaces to the circuits; in the case of the Area451, I would imagine most of the energy would be on the wires.

A clamp-on choke that attenuates at the right frequencies without affecting the risetime of the signals would help keep that energy out. Too aggressive and the intentional signals are attenuated in bad ways.

The bulk-cable clamp-on chokes may work okay since the ground also goes through the same cable bundle, cutting out the common-mode "noise" while keeping the differential clean. If the bulk-ferrite approach doesn't work so well, some guidance as far as which individual lines to filter and what ferrites to try could be helpful from those who know the signals.

If the twisted pair was one of the items of interest, a ferrite around just those two signals might also help.