HF Mobile - Noise

[cockpitbob]

I'm just about done installing my FT-857 in my Isuzu Trooper. I used a lip mount half way up the rear door, bolted the body of the radio to the side wall in the rear area then ran the seperation kit cables to the front seat where the radio's face is. Today 14M was fairly quiet and with the engin off, but all accessories on I had very little noise (S-1 ish). With the engine running the noise reads about S-3. The noise does not vary with engine speed and doesn't sound like alternator whine or spark plugs. No change with the heater fan or headlights.

I have a lot of driving to do this week and was hoping to enjoy some contacts but they'll have to be pretty strong with the current noise situation.

Any ideas for what I can try to reduce the noise?

 

[Madball13]

What kind of antenna?

 

[KMS]

Everything grounded?

 

[cockpitbob]

The antenna is just an MFJ Hamstick (for now). I have 8 turns of coax in a 9" diameter loop in the feed line.

As far as grounding goes, there's probably room for improvement. The antenna's lip mount did cut through the paint and is grounded to the door. The radio is grounded to the car's body. But, I don't have braid bonding any of the doors or hood to the body.

 

[jpm]

I assume you tried a filter on the power lines to the radio already?

 

[n1oty]

I'd start by bonding the doors to the car frame with good, wide braid. Second, be sure to bond the exhaust system well.

 

[cockpitbob]

I assume you tried a filter on the power lines to the radio already?

Even better, I ran it off a gel cell, so it had no connection to the car's power system. No improvement, but thanks!

- - - Updated - - -

I'd start by bonding the doors to the car frame with good, wide braid. Second, be sure to bond the exhaust system well.

OK, I'll move that to the top of the list. I never would have thought of bonding the exhaust system.

 

[KMS]

I had the same issue on my Dakota,I used braided ground wire on every body connection twice over.I did not do the exhaust but it worked for me.

 

[Madball13]

I have a ATAS-120A for my truck with a breedlove stake pocket mount and i grounded the mount to the bed of the truck. I have some noise but it doesn't seem as bad as what i have in the house. I need to get it out away from everything to see how it really is.

I think bonding might be the key. Worst case is you bond everything good and tight and you may be able to slap on an 40 or an 80 meter stick and find out those work also.

 

[cockpitbob]

I had the same issue on my Dakota,I used braided ground wire on every body connection twice over.I did not do the exhaust but it worked for me.

Was it really noisy before you bonded everything with braid?

 

[n1zfg]

Don'tcha just hate the fact that car electronics are basically exempt from Part 15 emissions limits?

Oh yeah the manufacturers have their own standards that have strict quiet zones around the
broadcast bands, but outside of that, not so much.

I assume you tried a filter on the power lines to the radio already?

--This.

BTW: My favorite for this is a garden variety AC line filter like a Corcom 10EB3 with a hefty cap
in parallel, just for good measure.

If you have a spare battery or some independant power source you can temporarily hook up with,
you can try isolating the power to see if you really are dealing with radiated EMI.

 

[cockpitbob]

If you have a spare battery or some independant power source you can temporarily hook up with,
you can try isolating the power to see if you really are dealing with radiated EMI.

Tried that with a spare battery and it didn't help :-(. The thing that bugs me the most is that the noise doesn't change with engine RPM. You're probably right about it being the (non-Part-15) electronics. I would imagine the computers are running even when the engin is off, but I bet things like the fuel pump, injector power and a bunch of other stuff is off.

If it addis insight, I have a 20M hamstick mounted and when I tune the radio to 30M the noise is way down and on 40M it is basically gone.

 

[Realtor MA]

I'm having the same issue on 6 and 10 meters. At some point I plan to try and figure it out. For now the squelch knob is doing an admirable job. I suspect it's the injectors or something like that.

 

[n1zfg]

Some fuel pumps do sit in the gas tank, but those will often start running the instant the ignition switch hits the "run" position. The engine control system(s) these days have sensors on just about everything, but I'm not even sure that's the problem. The CAN bus, which is the network standard used for the car electronic systems, has a data rate of 1Mbit/s. That's a factor of 15 away from where you're complaining.

That's not to say that the bus isn't the cause. Baseband (e.g. not modulated) computer networks really like having a usable bandwidth several times their data rate. It makes for sharper transitions on the waveform and therefore better bit detection at the receiver. And the squarer the waveform, the more harmonics to potentially radiate (at just about every multiple of the data rate).

One spectrum analyzer trick is to use a small antenna and wave it around at suspected sources to see which thing produces the best signal strength. Put an improvised antenna on the end of a good length of coax, (the 20M stick may be a little ungainly for this exercise) tune around looking for the peak of the noise (it may not be in the ham band, and note the frequency in case it turns out to be a harmonic and you decide to hunt down the fundamental), then start waving the antenna all over the car to see where that peak is the strongest.

 

[KMS]

Was it really noisy before you bonded everything with braid?

With the vehicle off I was perfect,with the truck on I would get 2-3 pounds of static with engine noise while in motion.I also went with thicker plug wires not that would really help on newer cars but it was driving me mad and tried it.

Newer cars and trucks blow,most of them are all plastic and carbon fiber....forget about really running any power out of it either...there is a chance of toasting your cars computer.

 

[jpm]

just out of curiosity, how old is the truck?

 

[cockpitbob]

just out of curiosity, how old is the truck?

2002 Isuzu trooper with V6 that has a coil on top of each plug.

 

[jpm]

any progress on this?

 

[uncle griz]

you can start by finding out how it is getting in. If you unplug the antenna and is still there, its coming in through power wires....if it stops, its coming in through antenna. Fuel pumps, injectors are a problem and comp hash also. I had to run power through 9913 coax one time. good luck, W1GRC

 

[cockpitbob]

It's coming in through the antenna and can be as high as S-7. If I unplug the antenna it's gone. If I run the radio off a seperate battery it is still there. I did have time to bond the 2 tail doors to the body but that didn't seem to do much.

I made the 8hr drive to PA on Wedesday. Here's where it gets weird. While driving sometimes the noise will drop as low as S-1. Other times it's up at S-7. It isn't affected by the A/C, headlights or anything else I could thing of playing with while driving. Go figure

I did have a first on this trip and actually got someone to come back to me on 146.52 simplex. I also learned something about how 20M behaves as you go over hills and through valleys.

 

[n1oty]

The exhaust system, being long, tends to re-radiate all sorts of vehicle emissions. I had the same issue in my truck years ago when I installed an Icom 7000. Clamping braid to multiple points along the exhaust system and connecting it to the vehicle frame solved this. Anything metal that is separated from the frame should be bonded.

 

[cockpitbob]

I think I have a lot of braid and sheet metal screws in my future. Thanks for all the tips.

 

[n1oty]

Large stainless steel clamps work well on the exhaust pipes or you can use muffler clamps.

 

[uncle griz]

Exhaust systems do just like John (n1oty) said. They tend to radiate other noise like an antenna. Most now days are suspended on hangers that have rubber insulators for vibration dampening, but that's not grounded very well. Do try what john said, and be patient, could take awhile to figure out....

 

[cockpitbob]

Thanks again for the tips. My schedule doens't have much play time in it, but when I do get around to adding straps I'll post my results.

 

[cockpitbob]

FOLLOW UP REPORT

As you recall, I reported getting S-3+ noise (up to S-6 in later drives) with the engine on. The only thing I had grounded was the SUV's tailgate doors where the lip mount antenna was.

While adding a ground strap to the exhuast system I noticed my Isuzu Trooper is a body-on-frame design with LOTS of rubber between the frame and body. I added a strap on each side from the body to the frame.

The noise is GONE. I can't hear any difference with the engine on or off and when the atmosphere is quiet the S-meter reads nothing.

It would be interesting to remove straps to determine if it was the exhaust or frame straps that fixed it, but I'm more lazy than curious.

BTW, this weekend is the IARU world championship and in a 2hr drive yesterday I made 14 DX contacts with 50W and a $14 MFJ Hamstick antenna. Having the noise gone really helped.