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Author Topic: Alternator whine.  (Read 18404 times)
KW4M
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Posts: 11




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« Reply #15 on: September 22, 2013, 11:38:55 PM »

I've had good results using Jim Perkins' filter.
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KD8GEH
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Posts: 466




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« Reply #16 on: September 23, 2013, 06:27:45 AM »

Way cool , the filter look interesting!  Im going to Lowes Smiley

Thanks David. 

Dave KD8GEH

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KG6YSF
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Posts: 91




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« Reply #17 on: September 24, 2013, 01:02:10 PM »

Okay the only progress I was able to make is to tell you that there is only alternator whine when under load. At idle and while sitting with it out of gear there is no whine when the engine is reved.
Will have the wife go with me to do the other tests this afternoon.
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
W8JX
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« Reply #18 on: September 24, 2013, 01:10:32 PM »

Okay the only progress I was able to make is to tell you that there is only alternator whine when under load. At idle and while sitting with it out of gear there is no whine when the engine is reved.
Will have the wife go with me to do the other tests this afternoon.

That kinda points to a bad diode. It would be worse under load.
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KG6YSF
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Posts: 91




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« Reply #19 on: September 24, 2013, 07:21:42 PM »

Okay a stupid mistake compounded the problem. I disconnected the coax from both ham and cb, the coax on the ham was loose Shocked, oops, the cb was tight. When disconnected the ham was absolutely quiet. The cb had a very, very faint wine still when turned all the way up; so not too bad. The Ham after being tightened up was a bit better. The rfi did nit break the squelch any way. Though rfi is still present when squelch is opened by rx. It can no longer be heard by others though.
I am ordering a ball mount, heavy duty spring and Fiberglass 2m Firestik antenna. w/tune-able tip. I have heard good and bad about the antenna but, it is rugged for off road abuse. As well I will contact Powermaster about the posability of a bad diode.
Now what else should I do?
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
VA7CPC
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Posts: 2392




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« Reply #20 on: September 26, 2013, 10:38:28 PM »


Ferrites work at RF, not AF frequencies.  "Whine" falls in the AF frequency range.
. . .

"Whine" falls in the AF frequency range _after it's been processed by the receiver_ !

When the polarity of a single coil in the alternator changes, the attached diode goes from reversed-biased (no current) to forward-biased (current flows).  And current from that coil starts to flow through the diode.

The _start_ of that flow is sudden -- it's a transient, and its spectrum extends into the RF region.  That's true even if the diode is perfectly good.

If that transient gets repeated (as it will, as the alternator field coil rotates), it generates a series of pulses at the RF frequency the receiver is tuned to.   Those pulses are _radiated_ from the alternator "+" wire, and picked up by the antenna.

And the receiver demodulates those pulses --

. . . and out comes "alternator whine".

The ferrite(s), on the alternator output, "chokes" the high-frequency (RF) components of the transient's spectrum.  The "whine" is still present (in the receiver output), but its amplitude is reduced.

That kind of whine will (usually) _disappear_ if you disconnect the rig's antenna.

.             Charles
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K5LXP
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« Reply #21 on: September 27, 2013, 07:56:31 AM »

When the polarity of a single coil in the alternator changes, the attached diode goes from reversed-biased (no current) to forward-biased (current flows).  And current from that coil starts to flow through the diode.

The _start_ of that flow is sudden --

Well, sudden in the sense of current to the load but it's not a "transient".  The transition from reverse bias into conduction is comparatively gradual due to the AC sine input and forward conduction curve of the diode.  Very little harmonic content there, especially at VHF and UHF.


Quote
That's true even if the diode is perfectly good.

But the problem isn't present when the diodes are perfectly good.  The noise we're discussing here is when there's a bad diode.  They usually fail shorted.  Where is the "transient" when the diode is shorted or open?  The noise observed is conducted, not radiated.  The waveform out of the alternator is very much at audio frequencies and at significant amplitudes.  


Quote
the receiver demodulates those pulses --. . . and out comes "alternator whine".

An FM demodulator won't.  The noise heard is usually from the final AF PA.  They're usually sourced direct from the 12V power input so the AC ripple gets coupled right to the speaker.


Mark K5LXP
Albuquerque, NM
« Last Edit: September 27, 2013, 08:38:43 AM by K5LXP » Logged
KD0REQ
Member

Posts: 971




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« Reply #22 on: September 27, 2013, 10:31:50 AM »

there is probably light corrosion at the light bar and other accessories.  if you're radioing, they need to be bonded with straps to frame.  if there is any green on the antenna, hood, etc. straps they need to be replaced, corrosion forms its own diodes.

it definitely sounds like you have a marginal diode in the alternator(s).  it happens, but in normal automotive use, with the radio amp frequently decoupled with a LC network, you don't know until the BAT light comes on and your car computer gives it up.  the marginal diode eventually gives up and you have lost 1/3 of your alternator power, possibly also "wobbly" lights.
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AA4PB
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Posts: 12891




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« Reply #23 on: September 27, 2013, 10:47:14 AM »

In many cases the alternator whine can be heard even with the volume control turned all the way down. This confirms LXP's assertion that the alternator whine is conducted into the audio PA stage and/or drivers.

If you put a .01 ufd capacitor in series with a high impedance headset you can sometimes hear alternator whine when connecting the headset between two different ground points on the chassis.

You can verify if you have a multiple ground issue by isolating the radio from all ground connections except for the negative power lead. Use a rubber duck antenna (insulated from the vehicle) for the test.
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KG6YSF
Member

Posts: 91




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« Reply #24 on: September 27, 2013, 07:48:36 PM »

You can verify if you have a multiple ground issue by isolating the radio from all ground connections except for the negative power lead. Use a rubber duck antenna (insulated from the vehicle) for the test.


Since the antenna at this point is still a mag mount could I not just place the antenna on the steel work table I have outside and then remove the radio form the mounts?

Secondly The coax at the ball mount for the cb has bear ends. Could that be a point of RFI leak /penetration? I.E. should I cover the ends with heat shrink to insulate them, with obvious exception of the ring terminals themselves.
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
AA4PB
Member

Posts: 12891




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« Reply #25 on: September 27, 2013, 08:36:02 PM »

You can put the mag mount on the bench, pie pan, etc so long as it is not connected to the vehicle chassis.

Heat shrink isn't going to do anything to stop RF. Again, alternator whine is not normally RF. It is an audio frequency that is usually conducted by wires into the audio circuitry in the radio.
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WB6DGN
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Posts: 619




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« Reply #26 on: September 28, 2013, 12:19:16 AM »

Quote
...the receiver demodulates those pulses --. . . and out comes "alternator whine".
An FM demodulator won't.

Depends on the type of FM demodulator used.  For example, a discriminator will hear considerable AM when the limiters are not saturated.  So will a ratio detector despite theory insisting it won't.  This is from practical experience with radios employing such circuitry.  Even with the myriad detectors found in modern commercial equipment, the "all-in-one" chip usually includes a couple of limiter stages anyway.  Problem is that, at low signal levels, they still act as amplifiers with varying degrees of AM "noise" still present, such as the alternator noise discussed.
Tom
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KG6YSF
Member

Posts: 91




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« Reply #27 on: September 28, 2013, 08:46:26 PM »

Okay disconnected from the mount (radio supported by hand) and the mag mount antenna on a cleared off 3'X4' steel work table, outside, there is still noise on the open carrier; though it is quieter.
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
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