eHam

eHam Forums => Mobile Ham => Topic started by: KD0PBO on August 13, 2012, 07:21:44 PM



Title: 10m mobile RFI issues
Post by: KD0PBO on August 13, 2012, 07:21:44 PM
Okay, so I wasn't sure if I should post this here or in the actual RFI forum but since it retains to mobile RFI I decided to post here. Anyways, I've been having issues with RFI in my 04 Nissan Frontier on the 10m and 11m CB bands (Before you shoot me, the CB is for the farm to communicate with other trucks, balers, combines, and such). My problem isn't so much trying to figure out how to get rid of the RFI but more so identifying the source. The signal is an S5 whine on both radios (Realistic HTX-100 and Cobra 29) with RF gain maxed and about an S3 with RF gain dialed back to 3/4. What has me perplexed is that it doesn't follow the engine speed like alternator whine or create a pulsed signal like ignition noise. The noise however, does DECREASE in pitch slightly when I hit the gas pedal leaving me to believe it is something that comes under a load when I gas the engine. The only "motor" or noise source I can think of that would do this would be the fuel pump.  ???

I do not get this noise on 2m so it seems it is only isolated to the 27mhz-29mhz range, though I have no other HF bands available to test this. Or it could just be that FM is not effected by it. It also only occurs when the engine is running.

Any thoughts or experience to prove or disprove my theory of the whiny fuel pump? Want to rattle some other brains before I go hacking up my fuel pump power lines to put RF chokes on them.

It's not a absolute need to get this fixed but it is rather annoying...

KD0PBO 73


Title: RE: 10m mobile RFI issues
Post by: W9MMS on August 13, 2012, 07:57:59 PM
Based on the limited amount of info you gave concerning your setup, one can only try to guess at what can be some of the causes.
Try some of the suggestions in this article .....

http://www.k0bg.com/loops.html

Also ....

http://www.k0bg.com/ground.html

Hope this helps.

(((73))) Milverton.


Title: RE: 10m mobile RFI issues
Post by: KD0PBO on August 13, 2012, 08:55:34 PM
Based on the limited amount of questions you ASKED about my setup, I can only guess as to what I need to tell you. I have looked at k0bg's website many times to try to pinpoint what and where this issue could be coming from with no avail. I have tried a few of the tricks he talks about such as wiring straight to the battery and bonding the exhaust, bed, cab, and frame to provide a better RF ground. Hasn't really help to reduce the noise.

Also have relocated the antenna coax, added RF chokes, power filters, and the like. Whatever it is, is being pickup through the antenna and put into my receive. I need to kill it at the source, which is why I'm asking what could be creating the RFI.

73


Title: RE: 10m mobile RFI issues
Post by: W9MMS on August 14, 2012, 09:34:24 AM
>>> Based on the limited amount of questions you ASKED about my setup, I can only guess as to what I need to tell you. <<<

 Questions that I asked? What am I missing here!? ?????
You are having issues with your setup which is right there in your presence.
Nobody on this forum can see or know what your setup consist of, or how you mount the antenna among other things.
It is not incumbent upon us to QUIZ you about the way you setup your vehicle or the type of Equipment in the setup.
Should you take the time to further acquaint us about how you have things setup, then someone will be able to give you some insight on their experiences.
I would strongly suggest you go back and read again Alan's article on "GROUND LOOP"

(((73))) Milverton.

 


Title: RE: 10m mobile RFI issues
Post by: K0BG on August 16, 2012, 10:44:07 AM
Based on only the information given, and assuming it is not a ground loop, here's where to look: Engine cooling fan(s) and/or HVAC fan.


Title: RE: 10m mobile RFI issues
Post by: VIPER21700 on August 17, 2012, 09:04:43 PM
It is most likely the electric engine cooling fan. TEMPORARILY, for a very short time, disconnect the electric fan. As you accelerate, the fan pulls less amperage and voltage due to the outside airflow free-spinning the electric fan, at idle speeds, and at slow speeds the fan pulls more juice. That would be my first guess. Had the same issue with a CB radio on my old XJ. As soon as the electric fan kicked on I would get a whine on the CB. It was annoying, but the only solution I found was to re-locate the antenna, which helped somewhat, and I went over the chassis grounds for vehicle electrical with a fine tooth comb cleaning and tightening every one. It never went away totally, but it did quiet it down greatly. JMTC
good luck
kk4lak


Title: RE: 10m mobile RFI issues
Post by: KE5PPH on August 18, 2012, 09:49:58 AM
If his noise is coming from engine fan, does anyone have expirence with the variable speed models being any worse than the single speed type?


Title: RE: 10m mobile RFI issues
Post by: K0BG on August 18, 2012, 10:22:05 AM
Yes. There are two types.

The brushless ones have a two speed controller, and it is built into the fan. They're easy to spot because they have three wires running to them. I've never known one to generate RFI.

The brushed ones use a PWM controller. The width is control by the engine CPU (or the HVAC controller as the case may be). The RFI they produce sounds like a saw tooth wave because of the integration of the wave form by the fan motor itself. Usually, the RFI isn't too noticeable, yet the audio noise (especially on HVAC fans) is very noticeable. In fact, there is an article in the August issue of Motor magazine about the latter issue.


Title: RE: 10m mobile RFI issues
Post by: VIPER21700 on August 18, 2012, 03:10:55 PM
The brushless ones usually dont generate RFI, UNLESS a chassis ground in the engine bay is corroded or loose. Also, the fuel pump on some vehicles will create a bit of noise, dont ask me why.


Title: RE: 10m mobile RFI issues
Post by: KE5PPH on August 19, 2012, 07:16:46 AM
Oh yeah, I can verifiy the fuel pump noise. It's not just the RFI either!!!!   Good ole' Jeep ;D


Title: RE: 10m mobile RFI issues
Post by: KB9IGG on August 19, 2012, 07:25:43 AM
I HOPE YOU HAVE YOUR RADIO GROUNDED TOO THE BATTERY NEGIVE AND POSTIVE.ALWAYS GO 1 SIZE THICKER THAN THE RADIO.ON THE RADIO WIRE.RUN YOUR WIRES OPPOSITE OF THE COMPUTER UNDER THE HOOD.WHAT TYPE OF CAR IS THIS FOR.