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Author Topic: rf in stereo surround speakers with amp on  (Read 407 times)
VE7REN
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« on: November 08, 2009, 03:12:35 PM »

al 811 with pro3. barefoot works fine. turn power on amp with 55-60 watts drive is ok,then if i turn radio power up from 55 to 100 mark,the rf gets in my surround speakers in living room which is only 10 ft away in another room. the coax goes through a drake low pass filter also. any suggestions??
unsure of remedy.
brent
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N6PJB
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« Reply #1 on: November 08, 2009, 05:23:02 PM »

I had the same problem with my setup except mine would produce noise with the stereo amp off. The cure for mine was easy. I shortened the leads to the speakers to the minimum required. I had left the leads long in case I wanted to move them. All rfi was eliminated. I hope yours is as easy.
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VA7CPC
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« Reply #2 on: November 09, 2009, 12:57:54 AM »

Try putting a ferrite choke on each wire going to the loudspeakers.  Put the chokes at the _amplifier end_ of the wires.

            Charles
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NE5C
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« Reply #3 on: November 09, 2009, 02:09:01 AM »

I'm trying to remember, but you might try adding a .001 Uf ceramic disc capacitor added across the speaker wire connection Terminals. I recall this helping to solve some of those problems in the past.

Good Luck, God Bless, 73 8-)
DE N5JFJ Jerry
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VE7REN
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« Reply #4 on: November 09, 2009, 05:34:39 AM »

could my coax be poor shielded??

im using a rg 8x {smaller grey stuff}jumper from the radio to amp,then rg8u from amp to antenna.

i had read the rg8x is not good for much power over 600 watts,but its coming from a 100 watt rig toamp.


maybe i should change my jumpers to lmr400,or rg8u,rg213 or similar with better shielding?
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K0BG
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« Reply #5 on: November 09, 2009, 05:41:39 AM »

S T O P  R I G H T  T H E R E!

Do not put caps across the speaker terminals at either end! Doing this to some audio amp designs will cause the amp to oscillate, and go into thermal overload with predictable results!

The only safe method is split beads, and the best to use are Mix 31. The 3/4 ID units are ideal. DX Engineering (et. al.) sell 5 in a package for about $25.

If the problem is common mode current, then split beads will help that too.

Alan, KØBG
www.k0bg.com
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K5LXP
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« Reply #6 on: November 09, 2009, 05:59:10 AM »

No, it's not your coax shielding.

No mention of the antenna being used.  What/where is it in relation to the item being RFI'd?


Mark K5LXP
Albuquerque, NM
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N5LRZ
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« Reply #7 on: November 09, 2009, 08:16:39 AM »

Does this surprise me at all....Not at all.

You see electronics today are in general made so cheap that any kind of filtering adding a mere 4 0r 5 dollars is not going to be done.

Reason-->PROFITS.  Remember that these manufacturers sell vast/huge numbers of their product and even a savings on a mere way 1 million units will mean 5 MILLION more dollars in their pockets.  So they are not going to give a damn if a few people get RFI problems.

BUT THEN if I were going to make 5 million dollars MORE profits would I give a damn.  HHHHMMMMMM probably not.  5 million somehow has more value than a few ticked off customers.
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VE7REN
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« Reply #8 on: November 09, 2009, 04:14:15 PM »

my antenna runs parallel to my house. roughly 6 ft away from the eaves . ceneter fed dipole.rg8u coax from the amp out.
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WX7G
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« Reply #9 on: November 09, 2009, 07:58:10 PM »

With 55 watts drive being ok and 100 watts causing RFI you need only a 3 dB reduction to fix things.

The easy solution is to keep the exciter below 55 watts.

The suggestion of 0.001 uF caps is one to try. This will not irritate the audio amp. 0.1 uF might. You can also try 0.01 uF caps with 4.7 ohm series resistors. This provides a low impedance to RF while being perfectly ok for the amplifier. And as another suggests, ferrite cores on the speaker leads can be tried. Radio Shack stocks some that may help with several turns of speaker wire thru them.

Two other points of RF ingress to the audio amp are the AC line and the audio inputs. Ferrite cores can be tried on these lines.

Another thing to try are tuned radials. 1/4 wavelength at the frequency of RFI. Connect to the amplifier chassis. If there is no metal chassis accessable you might connect them to the shell of one of the audio input jacks.

Another thing to try is the 'laying on of hands.' Fire up the rig just short or the problem or at a power that just brings it on. Now touch various parts of the audio amp; speaker wires, chassis, input jacks and see what parts are sensitive.

Remember, you are after a 3 dB improvement and that should not be hard to obtain.
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VE7REN
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« Reply #10 on: November 10, 2009, 05:50:52 AM »

well
 i connested my verticle antenna which is 30 ft away from house. no problems with rf at high power. go back to dipole,and voila....rf. im almost sure it may be the orientation the dipole sits next to the house,and the poor coax i have going to it.dont have an ac issue. and i dont want to start adding chakoes,etc if i dont have to. i think im going to try a new coax first......then if that doesnt work,ill change the antenna configuration.
brent
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K5LXP
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« Reply #11 on: November 10, 2009, 06:07:44 AM »

Coax won't cause an RF overload.  The nearby antenna is radiating many magnitudes more signal than your coax is.

You need to reduce the incident signal into the AF system by either reducing power, improving isolation of the AF device (through chokes, shielding, etc), or moving the dipole further away.


Mark K5LXP
Albuquerque, NM
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K5END
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« Reply #12 on: November 10, 2009, 06:20:00 AM »

Alan, your comment about oscillations is interesting, especially pertaining to those above our range of hearing. I've seen a lot of audio amps in resonant, ultrasonic oscillations, usually from a fault in the negative feedback. "Amps gone wild." One owner only knew the thing had weak output and got hot.

I guess he could not hear 2 MHz?

...
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KI4SDY
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« Reply #13 on: November 10, 2009, 06:27:41 AM »

One thing you might want to check, before you try anything else or spend any money, is your coax connectors. If they are not mated correctly and screwed down completely they will leak RF into the surrounding electronics. This may account for the speaker noise at higher wattage levels, that is not noticeable at lower wattage levels.
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