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Author Topic: 2 meter mobile noise  (Read 3459 times)
N1DYX
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Posts: 35




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« on: January 25, 2012, 04:06:00 PM »

I've read a bunch of threads on noise but nothing seems to be the same as I'm experiencing; maybe someone has some ideas:

I have a 95 Buick Sylark, radio is a Kenwood TM221, antenna is a Diamond tribander, mount is a Comet trunk mount.  I installed power leads directly to the battery.
The noise I'm getting is identical to opening the squelch, it's a constant hash.  It stops immediately when turning off the engine.  No noise with the key on, only appears immediately with the engine running.  It does not change tone or frequency with engine rpm.  If I disconnect the antenna lead from the radio it disappears.
On most frequencies it's always about an S3 or 4 and can be eliminated by closing the squelch but when a repeater breaks the squelch it's in the backround especially if the repeater is on the weak side.  On 146.79 it's almost full scale.
I bought a brand new Yeasu mobile thinking the filters would be much better and they are, it's a real improvement but the same thing exists when I get away from the repeater a little, the noise overpowers the repeater.  146.79 is not nearly as bad but still very bad.
I've checked the continuity of the ground path from the trunk to the car body and even ran a temporary ground strap to bypass the trunk hinges but it's still the same.
Receiving stations tell me my signal is dead quiet.

I do have a handheld and also find that on 146.79 the squelch is opened periodically when I'm driving, in fact it's annoying as heck in the scan mode, I have to skip that frequency.

So it seems like there's some electronic gismo in my old care that's messing with the radio.  Any ideas??


Thanks
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K0BG
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« Reply #1 on: January 25, 2012, 06:08:14 PM »

If one believes the theory behind FM, then any AM noise shouldn't reduce, or interfere with reception. Unfortunately, that is not the truth.

Most modern transceivers are not really true FM. They are, instead, phase modulated. Most phase discriminator circuitry, which converts the phase modulation into a form we can understand (AM), are quite susceptible to to AM noise, if for no other reason than cost considerations. Aside from that, if the AM RFI from the on-board circuitry is high enough in amplitude, even the best of FM transceivers will be effected. This goes double for the TM-221, which is of modest design.

Adding a bit of injury to the scenario, is the trunk-lip mounted antenna, with its marginal (and typically intermittent) ground plane, ground straps notwithstanding.

The solution is obvious.

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K3WEC
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Posts: 260




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« Reply #2 on: January 25, 2012, 06:17:05 PM »

Fuel pump perhaps?
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N1DYX
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Posts: 35




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« Reply #3 on: January 25, 2012, 07:13:26 PM »

Fuel pump perhaps?

Yes good thought.  The pump runs for a bit just when the key is turned on but it doesn't seem to bother the radio then.
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N1DYX
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Posts: 35




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« Reply #4 on: January 25, 2012, 07:18:10 PM »

If one believes the theory behind FM, then any AM noise shouldn't reduce, or interfere with reception. Unfortunately, that is not the truth.

Most modern transceivers are not really true FM. They are, instead, phase modulated. Most phase discriminator circuitry, which converts the phase modulation into a form we can understand (AM), are quite susceptible to to AM noise, if for no other reason than cost considerations. Aside from that, if the AM RFI from the on-board circuitry is high enough in amplitude, even the best of FM transceivers will be effected. This goes double for the TM-221, which is of modest design.

Adding a bit of injury to the scenario, is the trunk-lip mounted antenna, with its marginal (and typically intermittent) ground plane, ground straps notwithstanding.

The solution is obvious.

I'll try some perminently mounted straps and report back, thanks for the suggestion
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N1DYX
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« Reply #5 on: January 28, 2012, 06:58:10 PM »

The straps had no effect whatsoever.  It's even heard on the FM broadcast radio in the car when I tune a frequency down low where there's no adjacent channels and it's quiet.  Maybe it is the fuel pump as was suggested, strange I don't hear it when the pump runs when the key is first turned on. I was tempted to remove the serpentine belt and run the engine without the alternator to see if it went away but it's a real job to get it loose in this car.
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K0BG
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« Reply #6 on: January 29, 2012, 08:01:51 AM »

After rereading this.....

I suspect the issue is a color burst CPU operating in the vehicle someplace. It is typical for CPU driven devices to use a color burst crystal in their oscillators. These crystals operate at 3.579545 MHz. The 41st harmonic is 146.76134 MHz, which causes problems with the 146.16/76 repeater pair. However, component tolerances can cause the harmonic to be anyplace between about 146.70 MHz, to as high as 146.80 MHz. The usual symptom is the squelch breaking when it shouldn't. If there are other harmonics mixed in, I suspect the RFI would sound like a high-level AM hash.
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N1DYX
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Posts: 35




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« Reply #7 on: January 29, 2012, 01:37:05 PM »

After rereading this.....

I suspect the issue is a color burst CPU operating in the vehicle someplace. It is typical for CPU driven devices to use a color burst crystal in their oscillators. These crystals operate at 3.579545 MHz. The 41st harmonic is 146.76134 MHz, which causes problems with the 146.16/76 repeater pair. However, component tolerances can cause the harmonic to be anyplace between about 146.70 MHz, to as high as 146.80 MHz. The usual symptom is the squelch breaking when it shouldn't. If there are other harmonics mixed in, I suspect the RFI would sound like a high-level AM hash.

That makes sense because 146.79 is just about full scale on the older radio. I guess I'll just put up with it, if it's too loud I'll listen to the XM radio!

Thanks for your comments.
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KI4SDY
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« Reply #8 on: February 01, 2012, 06:35:42 AM »

It could be time to get a new car ! No RF radio noise in my 1999 truck, so I am still driving it. If you do consider a different ride, temporarily install the radio equipment you intend to use with a cigarette lighter plug and a magnetic antenna as an acid test. If it works with without interference you are usually home free!  Grin

It is easier to find a clean ride than to try silencing a static screamer!  Shocked
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K0BG
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« Reply #9 on: February 01, 2012, 07:11:54 AM »

Not necessarily.

Taking an AM radio along, or using some gerry-rigged amateur transceiver, is not all encompassing as one would think. And, you can take two, otherwise identical vehicles, and one will have significantly more RFI than the other. If I knew why that was, I'd be rich!

My 2006 Honda Ridgeline is very quiet. Its computer busing system does cause birdies to appear throughout most of the HF bands, but they're almost inaudible unless the band is dead quiet. Part of the issue is the use of COPs which are much better RFI wise than any system that uses wires (like all GM V8s).

Hybrids are the worst of the lot, and none are anywhere near as quiet as any non-hybrid, no matter who made it. For example, a Prius is so RF noisy, it even limits the receive capabilities of most VHF transceivers.

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N1DYX
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Posts: 35




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« Reply #10 on: February 01, 2012, 10:51:10 AM »

It could be time to get a new car ! No RF radio noise in my 1999 truck, so I am still driving it. If you do consider a different ride, temporarily install the radio equipment you intend to use with a cigarette lighter plug and a magnetic antenna as an acid test. If it works with without interference you are usually home free!  Grin

It is easier to find a clean ride than to try silencing a static screamer!  Shocked

 Smiley Smiley You're not the first to suggest a new car!  But giving up my nice riding, 25 mpg, no monthly payment, low property tax, car in favor of the reverse of this is tough to take.  (See my reply to the next message)
Bill
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N1DYX
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Posts: 35




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« Reply #11 on: February 01, 2012, 11:01:34 AM »

Not necessarily.

Taking an AM radio along, or using some gerry-rigged amateur transceiver, is not all encompassing as one would think. And, you can take two, otherwise identical vehicles, and one will have significantly more RFI than the other. If I knew why that was, I'd be rich!

My 2006 Honda Ridgeline is very quiet. Its computer busing system does cause birdies to appear throughout most of the HF bands, but they're almost inaudible unless the band is dead quiet. Part of the issue is the use of COPs which are much better RFI wise than any system that uses wires (like all GM V8s).

Hybrids are the worst of the lot, and none are anywhere near as quiet as any non-hybrid, no matter who made it. For example, a Prius is so RF noisy, it even limits the receive capabilities of most VHF transceivers.

I love this........ well in addition to my nice old comfortably riding Buick I have a 2008 Ridgeline.  I've never tried the 2meter radio in it but I did have an HF radio for a while and that POS truck generates hash and ignition noise on every band.  The Kenwood HF radio had a pretty nice noise filter which did a good job of limiting the stuff but it was always present. I'll never install the 2 meter rig in it because I hate driving the uncomfortable, gas guzzling rough riding thing.   I sold the HF radio which solved the interference problem Grin Grin
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KI4SDY
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« Reply #12 on: February 01, 2012, 06:04:05 PM »

That is pretty funny!  Grin
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