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Author Topic: mobile TX on 2m and CB wipes out car radio (2001 Subaru Forester)  (Read 3025 times)
KB1TXK
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« on: November 24, 2012, 07:14:37 PM »

Just mounted a 2m center-loaded mobile antenna, as well as a Firestick Firefly ( 4' ) antenna for CB (and hopefully 10m). 2m is permanent NMO mount, firestick is mounted to roof rack w/wire running from shield to bolt on roof.  SWR on 2m is 1.1:1 @ 146.52 and firestick is 1.4:1 on 27.200 (tested using MFJ analyzer). R ~ 50ohm on both mounts.

If I have the car radio on in the forester and I TX on either the ic-2100 or radio shack CB, the car radio signal is completely wiped out.  This wasn't an issue when the 2m was mag-mounted to a Toyota.  On the forester, the car stereo antenna is integrated into one of the pieces of side-glass on the back of the vehicle.

I assume this is a fault w/ the car stereo, but wanted to make sure there isnt something else I could be looking at.  I'm also having a problem w/ noise, but after visiting k0bg's site its obvious the noise is from the alternator. The alternator noise is present on both RX and TX.  Could a bonding problem cause this sort of behavior (enhanced alternator noise, wipes out car stereo signal completely)?
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KC2BUN
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« Reply #1 on: November 25, 2012, 03:03:24 PM »

There could have been a filter on the Toyota?
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KB4QAA
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« Reply #2 on: November 25, 2012, 10:12:25 PM »

Your question(s) are less than clear...

-Don't judge one car by another.
-Your Firestick mounting on the luggage rail with dangling ground wire is less than ideal.
-It wouldn't surprise me for either of the radios to affect your car BCB radio. But, so what?  You shouldn't have it audible anyway when transmitting.

You could have a couple issues; pure power overload of the car stereo or some sort of common mode.

-Does the problem lessen or go away with lower power transmissions?
-What are the distances from the ham antennas to the car antenna (thinking overload)

From the common mode perspective, take a look at Alan's website http://www.k0bg.com/
things to consider are bonding doors, hood, trunk for beginning, and chokes on antenna coax, control head wires, speaker wires.

Bill
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KE3WD
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« Reply #3 on: November 26, 2012, 07:19:54 AM »

Are your transmitter power leads hooked directly to the battery terminals?  Both of them?


73
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VA7CPC
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« Reply #4 on: November 26, 2012, 08:42:27 AM »

Quote
From the common mode perspective, take a look at Alan's website http://www.k0bg.com/
things to consider are bonding doors, hood, trunk for beginning, and chokes on antenna coax, control head wires, speaker wires.

And a large clip-on ferrite on the alternator "hot" wire, close to the alternator.

.        Charles
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KB1TXK
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« Reply #5 on: December 05, 2012, 06:15:05 AM »

Okay so you have me on the "i should have the stereo down when I TX" thing Tongue

Right now I don't give two shakes about the CB/10m because its not really being used at the moment.  The alternator whine on 2m is my primary target, heres what Ive done so far:

5 snap-on chokes around the alternator control wires.

sanded/brushed all OEM ground-points (removing paint from metal *sigh*) and reconnected securely.

I had a thick -gauge grounding system (bunch of pre-made wires w/ eyelets) that i had put in my impreza a while ago. dont drive the impreza, so used those wires to connect engine block and one of the alternator mounts to negative battery terminal. The OEM set up also grounds transmission, front-left strut tower and sub frame (above left headlight).

The DC cables from 2m radio have always been directly on the battery terminals, however the negative is fused and I keep seeing that pop up as a bad thing in the course of my research.

I have 2 large square/cube shaped snap-on chokes, so i have one on each DC lead (from radio), wrapping the wires 2 or 3 times around them.

The 2m coax may not be routed very well under the dash. The antenna is mounted towards the rear of the forester, the coax entering through the trunk hatch. Inside the plastic molding along the top, down the A-pillar and straight over all the wires that come in through the firewall, including the ECU wiring.  I'm thinking that may be an issue as well.
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WX7G
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« Reply #6 on: December 05, 2012, 08:35:34 AM »

Why would you transmit with the car radio on? If music is playing you cannot have that go out over the ham bands.
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KB1GTX
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« Reply #7 on: December 05, 2012, 12:28:44 PM »



  The alternator whine on 2m is my primary target, heres what Ive done so far:

5 snap-on chokes around the alternator control wires.




I have 2 large square/cube shaped snap-on chokes, so i have one on each DC lead (from radio), wrapping the wires 2 or 3 times around them.



How about a capacitor of a few mf right on the alternator?   those snap on chokes wont do any thing at about 1000hz and that's where that ripple frequency is at.

You may need one on the stator winding wire too "if you have one"

« Last Edit: December 05, 2012, 12:35:11 PM by KB1GTX » Logged
N4CR
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« Reply #8 on: December 06, 2012, 08:02:50 AM »

For the whine, you need a low pass filter in your DC lead.

First, ground both radios to the frame right next to the radio and stop running a wire all the way back to the battery. The frame provides a lower resistance ground and eliminates second ground paths. Yes, you have it fused. Totally unnecessary. Ground at the rig.

Second, build yourself a whine filter (or buy one) to eliminate the whine.

http://www.worldwidedx.com/home-brew/31492-building-simple-alternator-whine-ignition-filter.html
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
M6GOM
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« Reply #9 on: December 06, 2012, 08:24:21 AM »

My VHF/UHF transceiver - a TM-D710 is installed about as good as it is possible to do. Antenna mounted by hole drilled in the middle of the roof, wiring to battery with 50A rated cable, all panels bonded. No problem hitting a repeater 60 miles away over a range of hills.

It will desense the FM radio in the car when I transmit. It is more to do with the poor filtering of the FM radio than the 710 installation.

Manufacturer car radios are built down to a price. You would probably find a decent one such as a Clarion would not suffer as much.

At the end of the day though if you've got an antenna with a radio transmitting 10W, 25W, 50W on VHF a few feet away from another one for the FM radio you are going to get desense unless you start using bandpass filters or using a stub to notch the 2m frequencies.
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AA4PB
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« Reply #10 on: December 06, 2012, 09:14:01 AM »

Sometimes the alternator whine can be the result of multiple ground connections on the radio. This is especially true if the radio is one that has the negative power lead terminated on a PC board run inside the radio. Alternator currents can find a path through the antenna or mount grounds, back through the negative ground lead to the battery terminal.

In my case I could hear the whine even with the volume control turned all the way down, indicating that it was getting into the audio amplifier stage in the radio. Filters on the power lead didn't help because the noise was being transferred on the negative lead. Next, I isolated the radio by disconnecting the antenna and setting it on the seat so that it had only one ground connection via the negative power lead. No whine while operating that way. If I connected the antenna shield or touched the radio to the grounded mount the whine came back.

My solution was to connect the negative power lead to the mount before it went back to the battery. That provided a path for the alternator currents on the negative lead to get back to the vehicle ground without passing through the PC board inside the radio. This solved the whine on both receive and transmit audio.
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K7KBN
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« Reply #11 on: December 06, 2012, 10:33:33 AM »

This has been an effective alternator filter for lots of mobile installations:

http://www.worldwidedx.com/home-brew/31492-building-simple-alternator-whine-ignition-filter.html
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73
Pat K7KBN
CWO4 USNR Ret.
KB1TXK
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« Reply #12 on: December 06, 2012, 12:27:35 PM »

Ok I'll ground the radio at the same post the car stereo is grounded at since the 2m is installed directly above the stereo

Also noticing static bursts when I roll the windows up/down too.  This car DID sit for a year and I'm wondering if there is an OEM ground that compromised (that may not be helping).

I read that those in-line filters can drop the amount of power going to the radio so I didn't check into those (yet).

I honestly thought I was doing something correctly by going straight to the battery. Guess not heh.

Thanks for the tips. I'll let you know how it all turns out this weekend.
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KB1TXK
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« Reply #13 on: December 06, 2012, 12:30:19 PM »

This has been an effective alternator filter for lots of mobile installations:

http://www.worldwidedx.com/home-brew/31492-building-simple-alternator-whine-ignition-filter.html

Totally trying that!
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K0CBA
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« Reply #14 on: December 08, 2012, 08:01:08 AM »

I didn't see if you were talking about a new car, newer car, used, really used car or possibly a piece of 'tow-truck bait'  but before you try a few or all of these ideas, some of which could void any possible warranty you may have left, use your favorite search engine and check for 'Sabaru Service Bulletins'.....read and become informed.

You may just find that they have a no cost (to you) fix.
If not, you may find all sorts of other free dealer 'fixes' for problems you didn't know you had.       
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