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Author Topic: "Popping" on 20m and 30m  (Read 1800 times)
KC9IMT
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Posts: 48




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« on: June 15, 2007, 11:19:17 PM »

Hey all,

I know this has probably been discussed before, but I can't find any real solutions on here...

I own a 2005 Saturn Ion and I just installed an FT-857D.  I have a Comet UHV-6 using a Diamond truck lip mount to a duplexer with the radio mounted in the trunk.

On 15m, 17m, 20m and 30m, I get a really bad "popping" noise, almost like a machine gun, while the car is idling.  The "popping" speeds up (and eventually goes away) as the car runs at higher RPM.  When the car is off, the noise goes away.

I've read that my car might be a COP - whatever that means.  I'm wondering if it's this, alternator, or if I need something in between my battery connection and the radio to eliminate AC...  I'm really not sure.

Suggestions?

Thanks and 73,
--
-Chris
W9BKO
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KC9IMT
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Posts: 48




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« Reply #1 on: June 16, 2007, 12:06:18 AM »

On a side note, I tested the rig tonight *without* an antenna on the mount and the noise was gone.  I'm not exactly sure what that means...  Perhaps because my antenna isn't grounded well?  I have no idea...

Thanks in advance for suggestions!
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K5LXP
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« Reply #2 on: June 16, 2007, 06:01:25 AM »

Popping means you're picking up either spark plug or injector energy.  COP means "coil over plug", which is a system that has no spark plug wires- the coil is integrated onto the top of the spark plugs.  It could be aggravated by insufficient bonding, have you gone through the door/trunk/hood/chassis/driveline bonding process with this vehicle?  Being a Saturn I know a lot of the body panels may be plastic, but there's still chassis and driveline to consider.  Before going through any corrective measures, bond everything first.

Mark K5LXP
Albuquerque, NM
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K0BG
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« Reply #3 on: June 16, 2007, 07:37:39 AM »

This is no doubt ignition noise. If you go to my web site, and look under Noise ID, you'll find some samples. There are also articles on curing the noise, and other important mobile requirements.

Alan, KØBG
www.k0bg.com
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KC9IMT
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Posts: 48




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« Reply #4 on: June 16, 2007, 09:21:44 AM »

Okay, I've verified that everything is grounded to the chassis...  My multimeter says so.  ;-)

Now, I still have the popping, but it's only significant on 30m, 20m and 17m...  Everything else is fine.

The interesting part is, I put another antenna on the mount (a Diamond VHF/UHF) 1/2w on 2m...  No noise.  I'm no antenna expert (probably not even a real beginner when it comes to antennas), but I would at least expect to hear something given how loud it is with the Comet UHV-6...  Or am I completely wrong?

Thanks again!  Alan, I'll order some of that 3M 1181 Copper tape and see what I can do with that - it seems like the logical next step...

--
-Chris
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KE3WD
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Posts: 5689




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« Reply #5 on: June 16, 2007, 11:41:06 AM »

I'll bet its the electric fuel pump.  

Those electric pumps that use a simple solenoid that breaks its own connection at rise via points at the top are veritable spark gap transmitters.  

They are mounted internally to the fuel tank, too, for cooling and don't worry about the contact arc and spark, with no air and all gasoline it cannot ignite.  

I've had success with this one by placing clampon ferrite choke with both positive and negative power wires to fuel pump wrapped around the choke as close to the fuel tank as you can get.  

If you contact the dealer, parts dept, there may be a supression kit available, too.  These typically combine coil and capacitors to suppress the wideband rf those fuel pump points radiate on their power lines.  

To isolate whether it is the fuel pump or not can be easy to problematic, depending on the engine control scheme of the vehicle in quesion.  Some simply power up the fuel pump with ignition on and that is easy to spot, simply have the radio running first and then turn the key to on but not to start.  If you hear the offending noise, even for a bit and then it stops, suspect that fuel pump.  This is not always the case, though, for some vehicles computer controllers now operate the fuel pump and it may not simply come on with the ignition.  

Ford trucks seem to be the worst at this BTW -- but it is a solvable problem.  

My Ford truck owning DX crazy 10 and 12 meter friend, I finally installed a ROTARY aftermarket fuel pump just outside his gas tank and disconnected the stock internal fuel pump for complete pulse noise removal.  Extreme, but Rusty is an extreme kinda guy.  


.
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K0BG
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« Reply #6 on: June 16, 2007, 01:56:48 PM »

It isn't a fuel pump! With just a couple of exceptions, GM products all use rotary pumps. Some do have brushes, but most are piezo driven brush-less DC motors.

Remember, FM isn't sensitive to AM impulse noise until it gets REALLY bad. On the other hand, SSB is, and even a sub-microvolt signal can be exasperatingly loud.

If the vehicle has plug wires, 90% of the time the impulse RFI is ignition related. Occasionally, it's just one or two wires causing most of the racket. If the plugs and/or wires are over a couple of years old, replace them with factory parts, be darned the mileage or factory recommendations.

Fuel injectors cause some RFI too, albeit low in most cases. The worse ones I know of are the new direct injectors used on some gasoline engines. Most of these operate at about 1,500 BAR! Thankfully, the coils are usually deep inside the valve heads.

Lastly, minimal antenna installations will ALWAYS have more perceived ignition RFI. It's all related to S+N/N. Which incidentally, has nothing to do with capture area!

Alan, KØBG
www.k0bg.com
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KE3WD
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« Reply #7 on: June 16, 2007, 06:50:10 PM »

You caught that and you are right, Alan.  

GM.


oops.



TNX


.
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K5LXP
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« Reply #8 on: June 16, 2007, 06:51:03 PM »

A multimeter won't tell you the merit of your grounds, just that there's continuity.  Just as in a gamma match for an antenna, you can have a DC short that appears as an open circuit at some frequencies.  Since the injectors and COP circuits all run on high power square waves with lots of harmonics, that energy goes well into HF and beyond.  Go through the bonding exercises, even if they seem superfluous to you.  It is way faster and easier to shotgun the problem in this way than to surgically attempt to find the point source(s) of interference, which likely will require the same bonding effort to fix anyway.

K5LXP
Albuquerque, NM
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AD5X
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Posts: 1437




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« Reply #9 on: June 18, 2007, 05:13:40 AM »

ESPECIALLY ground the exhaust end of your tail pipe - and preferable a point in the center as well.  As stated above, an ohmmeter check doesn't help in many cases.  The tail pipe is DC grounded, but it is also close to a 1/4 wavelength on 20 meters and does a nice job of radiating ignition noise.  Alan's website has great info on all of this.

Phil - AD5X
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