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Q: I just bought a new car and installed my HF amateur transceiver in it. I followed the manufacturer's installation guidelines and everything is working out okay, except that when I turn on the engine, the noise level on every ham band goes up. The problem is very bad on 80 meters, about S7, but it is still S3 on 10 meters. The noise does not vary with engine speed and sounds the same across all bands. What causes this?
A: There are a lot of things that can generate noise in automobiles, but the symptoms you describe sound like they are being caused by a noisy electric motor. Other possible noise sources are ignition noise and computer noise (most cars now-a-days have computers controlling most engine and vehicle functions). Ignition noise is an "impulse" noise, and at low engine speeds it would exhibit a "tick-tick" sound. At higher speeds, this would change into a low-pitched whine. Alternators can exhibit a similar whine, but in both cases, the noise would vary significantly with motor speed. The computers used in modern cars can also generate noise, but much like home computers, the noise tends to consist of various birdies, bleeps and buzzes that definitely vary as the receiver is being tuned. The fact that the noise is constant across each amateur band and does not vary with engine speed points toward a small electric motor as the noise source.
Most motors in vehicles operate intermittently. If the noise occurred only when you ran your windshield wipers, for example, you would suspect the wiper motor instantly. In most modern vehicles, the fuel pump is electric and it runs virtually continuously as the motor is running. In most cases, this type of continuos noise is caused by the fuel-pump motor. It could be caused by other motors in the car, but the fuel pump is the most likely suspect. There is one test that you can perform that is diagnostic: Leave the car sitting overnight. With the vehicle off, turn on the HF receiver and adjust for normal reception. Then, turn the ignition switch on, without starting the car. If the noise appears for a second or two, then disappears as the fuel system pressurizes, the fuel pump is the source of the noise. The bad news is that the fuel pump is generally located inside the gas tank. This usually means that this is not a job for a backyard mechanic.
Some automobile manufacturers know about this problem. They have issued service bulletins that cover adding a filter inside the tank to cure fuel-pump RFI. Ford, for example, has published a Technical Service Bulletin (TSB), appended to the end of this message.
In the Ford TSB, the filter is installed inside the gas tank, with series inductors and parallel capacitors for each lead. Ford does not offer that this technique will work on any other vehicles.
If you have a fuel-pump noise problem, the place to start is with your dealer or automotive service person. They can determine if there are any service bulletins that apply to your car. This is especially true if your car is in warranty. In all cases, all work on vehicles should be done by people who are qualified to do the work and who are familiar with the vehicle. Gasoline tanks can explode if not serviced properly, so this is not a job for a backyard mechanic!
The ideal place to install the filter is right at the pump, which is inside the fuel tank. It is electrically possible to install the filter on the leads where they enter the tank, but if the tank is not well shielded, electrical noise could still be radiated by the leads between the filter and the motor. On lower HF, however, this radiation will be minimal and it may be possible for your dealer to install filters to the wires external to the gas tank.
Hams have reported various degrees of success using various filtering techniques. In some cases, ferrite inductors have been added to both wires feeding the fuel pump. It is usually more effective to use a separate choke for each wire. In general, at upper HF, one of the split bead types can be used, with a couple of turns of wire on each bead. At lower HF, it will be necessary to use a ferrite toroidal core, perhaps an FT-140-43, with at least 10 turns of wire. In addition, it may be necessary to try a 0.01 uF capacitor across the two wires, perhaps on each side of the chokes. Some have reported good results using just the capacitors. There are also mechanical considerations. Splicing wires can result in mechanical failure, or corrosion, with the result being a motor that will not run (these things seem to happen at the worst possible times!). In addition, heavy chokes or capacitors can vibrate as the vehicle goes over bumps, ultimately causing the wire to fail.
One last possible solution may involve replacing the fuel pump motor with an aftermarket electric fuel pump. The aftermarket pump may be less noisy and it may be easier to add the appropriate filtering to the external wires. These aftermarket pumps are usually installed external to the gas tank. It will still be necessary to have your service person remove the in-tank fuel pump, but once this is done, the external pump can be easily maintained. Your auto parts supplier should be consulted to determine which ones can be used in your car. Unfortunately, ARRL doesn't have any information about which ones are electrically quiet.
ARRL also wants to stress that any cure should be applied only by qualified repair personnel; gas tanks are not places for the backyard mechanic!
Article No. 99-12-9
FORD:
1990-93 TEMPO
1990-97 PROBE, THUNDERBIRD
1990-99 CROWN VICTORIA, ESCORT, MUSTANG, TAURUS
1997-99 CONTOUR
LINCOLN-MERCURY:
1990-92 MARK VII
1990-93 TOPAZ
1990-97 COUGAR
1990-99 CONTINENTAL, GRAND MARQUIS, SABLE, TOWN CAR
1991-99 TRACER
1997-98 MARK VIII
1997-99 MYSTIQUE
1999 COUGAR
LIGHT TRUCK:
1990 BRONCO II
1990-96 BRONCO
1990-97 AEROSTAR, F SUPER DUTY, F-250 HD, F-350
1990-99 ECONOLINE, F-150, F-250 LD, RANGER
1991-99 EXPLORER
1993-99 VILLAGER
1997-99 EXPEDITION, MOUNTAINEER, WINDSTAR
1998-99 NAVIGATOR
1999 SUPER DUTY F SERIES
This TSB article is being republished in its entirety to include 1997-1999 model year vehicles.
ISSUE:
A "whining"/"buzzing" noise in the speakers of the entertainment radio or two-way radio on vehicles with an in-tank electric fuel pump may be caused by electrical noise from the fuel pump.
ACTION:
Install an electronic noise Radio Frequency Interference (RFI) filter (F1PZ-18B925-A) on the fuel pump inside the fuel tank. Refer to the following Test Procedure to confirm that the concern exists, then refer to the Service Procedure for repair details.
NOTE:
SOME LIGHT TRUCKS REQUIRE ONE (1) RFI FILTER FOR EACH IN-TANK ELECTRIC FUEL PUMP ON MULTI TANK VEHICLES.
NOTE:
THIS TSB DOES NOT INCLUDE TAURUS FLEIBLE FUEL VEHICLES (FFVs) OR 1999 RANGER 3.0
TEST PROCEDURE
Fuel pump radio noise is relatively constant and changes only slightly with vehicle speed. If the frequency of the noise varies or the noise comes and goes with the vehicle speed, then it is not the fuel pump and this fix will not be effective. The following procedure will help determine if the fuel pump is the cause of the radio noise:
SERVICE PROCEDURE
a.Cut the wires to the fuel pump 76mm (3") from the flange of the fuel pump and discard the wires.
b.Connect the RFI filter connectors to the spade terminal on the fuel pump.
c.Cut and solder both the red and black wires of the RFI filter to the red and black wires of the flange. Use Heat shrink tubing (F5AZ-14A099-AA) over the solder connections.
NOTE:
HEAT SHRINK TUBING MUST BE USED OVER ALL SOLDERED CONNECTIONS MADE PRIOR TO THIS TSB. USE SUFFICIENT TUBING (ABOUT 50mm (2") OF THE SPECIFIELD TYPE TO ENTIRELY COVER EACH SOLDERED CONNECTION AND SHRINK APPROPRIATELY TO PREVENT EXPOSURE OF THE CONNECTIONS.
NOTE:
FOR SOME VEHICLES WITH EXTREMELY LONG FUEL PUMP GROUND WIRE CIRCUITS, IT MAY BE NECESSARY TO SHORTEN THE GROUND WIRE TO A POINT CLOSE TO THE FUEL TANK. IF THE GROUND IS MOVED, BE SURE IT IS SECURE AND PROTECTED FROM CORROSION SINCE IT IS THE OPERATING GROUND FOR THE PUMP. CHECK SERVICE LITERATURE (EVTM, etc.) FOR GROUND LOCATIONS.
WARNING;
ALL SOLDERING AND HEAT SHRINKING MUST BE COMPLETED AWAY FROM THE FUEL TANK AREA. USE A SOLDERING IRON ONLY FOR SOLDERING AND HEAT GUN ONLY FOR APPLYING SHRINK TUBING.
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