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Help with rfi

Discussion in 'General CB Services Discussion' started by Rcr619, Sep 10, 2017.

  1. Rcr619

    Rcr619
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    I dug out my old galaxy saturn turbo tonight. I wanted to see if it still works and possibly use it as my dedicated shack radio but have a bit of an issue! When i key up, my family can hear me through the surround sound in the house about 40-50ft away. I asked my neighbors if they had any interference, and they didn't hear anything.



    I had the internal amp turned almost all the way down when it first started. It continued even after the amp was switched off. Im using a sirio gain master antenna about 20ft off the ground and 30 ft of coax.
     

  2. loosecannon

    loosecannon
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    well the first step would be to put back any of the modulation limiters that have probably been cut in that radio, and return it to 100% modulation. IE: back to a stock radio.

    If you insist on running it modded, then all i can say is good luck to you in your RFI abatement.

    pretty much all consumer grade electronics these days skip the RF shielding, and bypass capacitors that help mitigate this type of interference in order to save money.

    most likely, all the wires going to the speakers are acting like little antennas and picking up your transmissions.

    get a bunch of snap on ferrite beads, and wrap three or four turns of speaker wire through them.
    do this at both ends of the speaker wires.

    If this cuts down on the interference but doesn't completely cure it, start adding more ferrite until it gets down to an acceptable level.

    if it doesn't seem to make any difference, you are probably overloading something with your RF and might need to consider moving the antenna to the opposite side of the house.

    here are some good articles on RFI:
    http://www.arrl.org/radio-frequency-interference-rfi

    https://www.acma.gov.au/Citizen/TV-...dio-interference-in-stereo-or-audio-equipment

    http://palomar-engineers.com/rfi-kits

    hope this helps,
    LC
     
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  3. Rcr619

    Rcr619
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    I pulled the cover off and i cant find anything thats been clipped inside the radio. The internal amp doesn't have the little metal cover on it though.

    Ill have to find some of those snap on ferrite beads and give that a try.
     
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  4. loosecannon

    loosecannon
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    well you should have that cover on the amp, as it is a shield, but seeing as how it's probably a hard part to come by, you might have to make something.

    even a cardboard box covered in tin foil will be better than nothing.

    if it was removed with the intention of reducing heat, then just put it back, as that is not where the heat is coming from.

    look for Q32 to be cut or removed (right front area of PC board) and look for VR14 to be maxed out.

    also look at the big transistor on the right rear of the heatsink around the PC board and look on the solder side of the PC board under this transistor.
    if you see a diode and resistor there, or some other non factory parts.
    remove them.
    LC
     
  5. Rcr619

    Rcr619
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    I have no idea why the heat sheild on the amp is gone. The radio is the way I bought it second hand and it was probably removed by the previous owner.

    Q32 is still there and none of the legs are cut. I tried twisting it but it wont budge.
    VR14 still has plenty of room to be turned up also.
     

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  6. Rcr619

    Rcr619
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    I turned VR 14 both ways and put it back where it was set to be safe.
     

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  7. Rcr619

    Rcr619
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    The only extra looking part on the solder side i can find is this diode circled in the picture. Im not sure if it should be there or not.
     

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  8. loosecannon

    loosecannon
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    that diode is factory, and you can leave it there.

    Just so we are on the same page, that metal cover is not a heat shield, it is an RF shield AKA a "faraday cage" and it keeps all the RF that the amp creates from interfering with the radio, among other things.

    have a look at this page: https://www.deepsouthradios.com/forum/showthread.php?t=21835

    here you will find two different parts of the board to look at for modifications.
    if you find anything on your board that seems like what they are talking about on that page, then you should remove those parts and put the stock parts back in.

    one dead giveaway that your modulation circuits have been messed with is that adjusting VR14 will seem to do nothing. IE: you will have the same swing regardless of where VR14 is set.

    if your radio is stock in this regard; turning VR14 all the way in one direction should bring the modulation way down if not all the way down.

    remember that RFI cures rarely work on the first try, and that you will usually have to combine two or more methods to get a satisfactory result. This is why it pays to do research online before you go buying ground rods and low pass filters etc.

    the more reading you are willing to do, the less money you will spend in your endeavors.
    LC
     
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  9. unit_399

    unit_399
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    If you're running your antenna 20' above the ground and close to the house, this may be part of the problem. I would raise the antenna to at least 36'.

    - 399
     
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  10. Jay Mojave

    Jay Mojave
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    Hello All: Yeah what U399 said, get the antenna higher.

    More then likely the near RF Energy Field is getting into the speaker wires and being amplified. This is a common problem with consumer home electronics. As the electronics has little or no RFI Filtering.

    Installing snap on chokes on the speaker wiring has worked for me many times. Working with the local TVI Committee and some Ham guys who couldn't pour water out of a boot with the instructions on the heel, the snap on chokes have worked very well.
    See: https://www.dxengineering.com/search/part-type/rf-suppression-snap-on-ferrite-beads

    http://palomar-engineers.com/ferrite-products/snap-on-split-beads

    http://www.radioworks.com/crfi.html

    Good luck

    Jay in the Great Mojave Desert
     
  11. Riverman71

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    Guys, I have never experienced any interference of any kind that I could find any indication of nor have my neighbors.

    None of my outside antennas have been more than 15' high, all were attached directly to house and none were grounded. Have also had several attic antennas.

    I only run barefoot these days and all of my antennas have been homemade (except for a ProComm Patriot 12 that I tried once before eventually hack-sawing into several pieces). :D

    Am I just lucky or do I have the inefficiency of my antennas to thank? o_O
     
  12. nomadradio

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    Here's what I did.

    The AM modulation limiter will prevent the vast majority of interference to nearby devices. Odd, but overmodulation with low power will tend to cause more trouble than high power with the audio properly limited.

    To prove this, I put the modulation-limiter pot "AMC" on the front panel of my Turbo. Didn't need the echo knobs. Took out that board and had a spare spot on the front panel for it.

    At the time, we still had analog cable TV and a 19-inch mid-1980s color TV across the room hooked to cable. This was my RFI monitor.

    Found that if I simply turned down the AMC control on the front panel until the TV behaved itself I could talk all I wanted without problems from the neighbors. Full-bore modulation with the AMC disabled would tear up the picture something fierce.

    I didn't have a 'scope hookup that worked on the beam antenna, only on the dummy load. But switching to the dummy after the AMC set to make the TV happy, I would see just under 100% AM modulation.

    The kicker was when I turned on the MLA-2500 amplifier. Not stock, has two 3CX800 tubes. With FULL audio, it would peak 2200 Watts. With the modulation limited to the "TV" threshold, I would only see about 1600.

    But the TV didn't know I was there. Blew me away.

    Used to baffle the folks I talked to. I would hear them argue about whether or not I was barefoot. The only reply I gave to that question was "Who are you kidding?" Wouldn't reply "yes" or "no", only that.

    Got amused listening the other folks on the channel after I signed out with them.

    One guy across town would swear I had to be amplified, since I covered up some guy a couple of blocks from him.

    The next one would swear I had to be barefoot because he dropped down one channel and couldn't hear any "splash" from my audio peaks.

    Go figure.

    73
     
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  13. Riverman71

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    That's probably why I've escaped it.
    Three and a half watts with a stock mic and no mods to my radio.
     
  14. Jay Mojave

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    HelloR71 and All: Good for not having any RFI (Radio Frequency Interference) its a pleasure not having to deal with it.

    But Every RFI Problem is different as the operators radio, amp, and antenna is different as is the consumer home electronics. I moved into a new house years ago and put a Interceptor 10K Antenna with it connected to nothing on purpose. The coax coming thru the window in true red neck style and NOT connected to anything, I showed a few neighbors to satisfy their concern of some type of RFI. It wasn't me.

    Even stock radios can case RFI into neighbors consumer electronics and such. Again these home electronics have little or no RFI Filtering. Being a good neighbor is a good call, but also should things escalate into the courts and get blown out of any logical reasoning, and they have, being a good neighbor is again a good call.

    I have been asked on occasion to write a letter explaining why some homes experienced some RFI while others did NOT have any RFI in a housing track back on the east coast. Not being there to take any measurements or see any thing I had to state this and give a option of the RFI problems in the neighbor hood. Telling about all RFI are different, little or no consumer electronics RFI Filtering, near and far location of neighbors, TV's receiving off the air signals that are out of the service areas of the TV Transmitters, Old consumer electronics, improper consumer electronic installations and antennas, and of course problems with the local CB/Ham transmitter that a local TVI committee could check out. There are books on the RFI/TVI issues and such, out there on the net. So if you don't have any RFI count your blessings.

    Jay in the Great Mojave Desert
     
  15. Riverman71

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    Thanks, Jay.
    I understand now that with so many variables it really is a crapshoot and I've been very lucky.

    619, I hope you get your problem resolved. There are a lot of kind and knowledgeable people here willing to help. I know because they've aided me on numerous occasions.
     

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