The AM Forum

When my SWL Retro 75 was hooked up mobile, powered off the DC vehicle voltage, the RFI completely overpowers the receiver -- almost  blocking out signals.  With the ignition off, the receiver receives well, but as soon as the engine starts there is a mixture of loud ignition, and various switching or timing (oscillator) sounds.  The vehicle is a 2002 Ford Ranger 6 cyl.  Noise is definately entering through the DC power line as no antenna is connected to the rig.

I have seen many types of filters with RF choke in-line and filter cap to ground. Some also use a .5 mf cap to ground in a PI net arrangement.  I have even thought of isolating the v+ lines to the receiver and supplying the receiver from a 9 volt battery.  I have read much of the K0BG site on mobiles. He recommends much bonding of panels, exhaust etc.

So any ideas or experience with simple receivers powered off the vehicle 12 Volt supply???
Tnx, Mike K8WEU

Mike,

   I wonder if you plan to run QRP AM mobile, or if you have some sort of brick to put in the feedline? Your battery idea might be a good test. If that works, then you might be able to pre-regulate the rcvr V+ to 9 or 10v with a regulator, or a resistor-zener combination. Since the Retro pull less than an amp, filtering the power might be easy. Some ideas come to mind:

* Tap the power off the car battery directly (no cigerette lighter plug), and have a 1 or 2 amp inline fuse at the battery side.

* Take the incoming 12v to the pwr plug, and wrap the wires bifiliar around an emi clamp on ferrite bead. Use as many turns as possible.

* Take the 12v return inside the chassis jack, and ground to the back panel.

* Take the + 12v inside the chassis jack, and bypass with a combination of capacitors, like 1000 uf 16v, 1 uf (105) ceramic, and .05 uf.

* Pre-regulate the rcvr V+ with something like a 39 ohm 1 watt resistor, and a 5w 10v zener diode. Bypass the zener good too.

I wonder if the transmit audio is also being modulated?

Jim
WD5JKO

Works fine in my 1998 S-10 ! Maybe a trade in is in order ?
Lots of computer trash in the new cars . The CAN bus is a twisted pair running thru the entire harness . Plenty of noise from the BEC and ECM lines. The injectors are actually solenoid coils that can also generate noise.
 As already mentioned, good grounding, bypassing all power feeds and speaker leads etc can pay off.

  I wound up using a separate battery to supply the power for my motorcycle mobile . Totally cleaned up the noise issues.

I used to have a 2000 Crown Vic and the COP...that is coil-over-plug ignition and it was a RFI mess.  You no doubt have the same system.  The ground returns run all around the engine and that is just the start of it.  There are some websites that do address this problem including shielding the COP units.  Also the fuel pump is a known problem.  So you have some work to do to fix it....if you can.

Of course I solved it by replacing the Ford with a German diesel...nice and quite on HF ;D

Peter

Hi


If You are sure ,that the RFI came,from the "power supply"(car baterie )
 .
Than like any power supply  .it must be filtered,and smoothed it till the Ripple (caused by the ignition coil,and statik noise that comes into your "power supply") is brought down to the lowest level.

Using a biffiliar wound coil on a ferrite rod ,and filtered it with A 4700 uf and parralled it with a 100 nf  C may help.

Hey guys, thanks for the second opinions.  Your ideas to lessen the RFI from my Ranger truck are mostly things I thought might be helpful.  Looks like I have some experimenting to do...but that's what hams do.  So far I have been using the accessory 12V jack on the dash to get power.  I will try using a direct line from the battery (installed already), and then add some filter and bypass caps, along with the chokes recommended.  If I can get an indication of the RFI on a scope, that would help a lot for comparison as I make changes. 

I will post any findings of interest here. ... BTW, bonding of panels and exhaust may be necessary even if I get the DC cleaned up, because holding a AM broadcast transistor radio anywhere near the body picks up the same noises -- ignition, fuel pump and more.

If I ever get this problem settled, I might use a Heath mobile supply and experiment with either a linear (6146?) or a class C amplifier with its own modulator and drive it with the Retro 75. But, one step at a time.

Thanks Jim, Gary, Peter and Gito  de Mike K8WEU.

I'm not sure any amount of filtering will take out the hash.  I have the same problem when driving around with a portable radio trying to sniff out line noise.  The portable radio has its own self contained batteries. 

A mag-mount exterior antenna, mounted smack in the middle on top of the car roof, helps but doesn't completely eliminate the problem. I have been known to get up a little speed and then turn off the ignition and coast in neutral while line noise hunting.

My  best and cleanest RFI is the 50 GMC PU! No noise at all. Well some vibrator hash. Damn technology

  Had a ton of voltage regulator noise in my 1940 Chevrolet. Needed resistor wires to minimize the ignition noise , shielding would have probably helped.
A bit later , Essex Wire and Cable Co introduced "Magwire" A magnetically suppressed Monel Metal wire core cunductor wound in a spring like manner. Far more robust and effective than the carbonized threads known as "resistance wire. The resistor type plugs are another method towards relieving ignition impulse emissions.
A lot of the noise in computer equipped late models is from the CAN bus , riding in on the power feed.The 1998 S-10 is clean, from a noise standpoint.

Hi

I agree,there are many type of high voltage cable (spark plug cable)

A cable with copper inside as the conductor

a resistance cable,as I know  there are two kinds of cable,

A cable with resistance wire as the conductor

A cable with carbon inside wire as the conductor.

these two types of cable is especially made for Spark plug cables.

I preferred A cable with resistance wire,since a cable with carbon wire,with time can broke,
 using resistance cable is a must,in a gasoline Car that uses spark plug.
And using  the "RFI" filter.


I used to monitor Broadcast station ,with  a car radio or a portable radio.
And found no problem in receiving it.


Gito.N

I found that the electric fuel pump on my old Ford Ranger was by far the noisiest culprit. A choke and a couple of .5 caps solved the problem.

Does your vehicle noise directly follow engine RPM or is it more or less constant in pitch? If it's the latter, then it's likely the fuel pump.

Ford, Chevy and Chrysler often have service bulletins concerning RF hash in their vehicles for use by public safety agencies.

Maxima - fuel pump.

Mike,

Hate to mention it because of the way the service is looked down upon, BUT, I do believe it would help here.

The Ford vehicles are KNOWN for hash.  ESPECIALLY the fuel pump.  Back in the CB shop days, we found only ONE surefire way to cure it.

YES, it comes in via the DC cables, moreso than the antenna.  This was verified by running the truck next to another mobile which had it's key in the off position.  What was S6-S8 in the Ford was about S1 in a vehicle NEXT TO IT.  Put jumper cables on, and it jumped up about an S-Unit, if memory serves me well.

The fix?  Install a high end Cobra (148 style).  Once I figured that out, I copied their dc input circuit and would install that in Fords.  I'd estimate, that circuit alone fixed or made the problem bearable, at least 80 percent of the time.

Simple circuit, DC pos and neg bypassed to (chassis) ground, and choke input on both DC leads.  Then LARGE amount of filter C.  The schematics are available online for the 148. 

I'd ONLY trust the SSB chassis values, I found the AM only radios where garbage in comparison....  When it came to reducing or eliminating the noise on the DC leads.


I don't normally even mention this because the L used is usually hard to come by when wanting LARGE amounts of current, but since your retro is basically the same output, I'd say give it a try.

As others have said, run straight to the battery.  A solenoid off the ign switch to cut DC if you want it switched.  I've also used old braid to shield DC leads when I had to go near ignition and other sources of noise...  With todays smallish cars, that's a usual, rather than the exception.


--Shane
KD6VXI

Injectors took the words right out of my mouth. I had a Tacoma truck and injector noise wiped out 17M.......... NEVER anyone on the air, until one day I turned off the ignition.  Injectors made a nice S-8 noise. They were grounded!!!!!
I moved the ground connection to the chassis instead of the engine and the noise went away. Fortunately all of the grounds for all of the injectors arrived at one central location so, it was easy to move to another location.

Fred