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RFI 6400

6400 RFI issue-

I looked thru the previous posts & it looks like I may have a unique RFI issue with my 6400, but many of us have struggled with this perennial.

When I run the amp at 400-600W, I get reports of RF on the audio on LSB 80M.  I have 3 other rigs that do not have the issue.  I have a Balun Designs RF isolator in line.  I have 31 mix donuts on the mic cord, LAN cable, power cable, etc.  All radios use the same coax cables & power supply.  The RF is there with the supplied mic & a Heil HM12 and home made XLR cable. 

I have not tried a full reset of the 6400.

Pretty much at my wits end.  Any suggestions?



  • Ray SylvesterRay Sylvester Member
    edited March 2019
    what is your antenna
  • Ora SmithOra Smith Member
    edited March 2019

    All I can think of are grounding and feed line radiation. You might  experiment with changing the length of the ground wire to the Flex and changing the length of the transmission line from the amp to the antenna.  Also, regarding grounding, I don't know your situation, but improving the grounding lay out to the extent possible could be helpful. 


    Ora W9DJ
  • Homer1952Homer1952 Member
    edited March 2019
    I have an 80M loop & a End fed random wire/9:1 balun, with the same result.
    My fear of messing with the ground system is I have 3 radios that work well with what I have.  But it is on the list of things to investigate.

    Bob W8RMV
  • Ray SylvesterRay Sylvester Member
    edited March 2019
    hI bOB. YOUR 2 ANTENNAS HOW ARE YOU SWITCHING BETWEEN THEM?  By chance if you are using a antenna tuner to do it there is none available than shorts the unused antenna to ground .
    I would use only one antenna at a time to see if your rfi issue goes away. if it does the repair is simple a alpha delta coax switch on the output of your atu  and let the a/d do the switching if you would like to talk on the phone my number is 781 944 7543   73   Ray  NR1R
  • Homer1952Homer1952 Member
    edited December 2019
    Good thoughts, Ray.
    I completely disconnect the unused coax/antenna.  I then insert the unused PL259 into a shorted SO239 to ensure no induced RF gets back into the shack.  Also, I have 2 sets of active speakers in the shack.  A pair of Fostex 6301B's for the 6400 & just above them I have a pair of wood cabinet M-Audios connected to my computer.  No RF comes out of them.  I have an old Field Strength meter near the window & that barely shows any movement at the 600W level.  The Balun Designs 1116di is one of the best isolators on the market.  ????  I have 2 Icoms, a Kenwood and a Yaesu (I recently sold) that did not have the issue.  I used the HM12 on the Kenwood & Yaesu with appropriate Heil cables & a SM30 on the 2 Icoms.

    Bob W8RMV
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited March 2019
    How are the Fostex speakers connected? Make sure any cables from the radio and the speakers are well sheilded cables. Even if you can't hear RFI in a speaker does not mean it is not an antenna.

    Also RFI may be getting into the DC power cable to the radio.

    So eliminate things one by one.
  • Roy - W5TKZRoy - W5TKZ Member
    edited March 2019
    Bob, Quote: "I completely disconnect the unused coax/antenna.  I then insert the unused PL259 into a shorted SO239 to ensure no induced RF gets back into the shack."

    I had the same type of RF problem several years ago and it turned out to be an unused feed line from an old 2 meter antenna that had lost it's ground. I also placed an isolator between my rig (Flex 6500) and amp. (Ameritron ALS-600) to break up ground loops.  So check all the lines into your shack for grounds.

    Good luck

     Roy - W5TKZ
  • WX7YWX7Y Member ✭✭
    edited June 6
    How far away are your Antenna's from the shack? Do they go right over the top of the shack if so how high above? 
    if your radio is grounded to a common ground then temporarily remove the ground for a test.

    If you have a friend HAM close by can you take it to there QTH and test it?

  • Jim  KJ3PJim KJ3P Member ✭✭
    edited April 23
    I had a big RF problem in the shack on 80M.  Someone suggested that the transmission line might be a critical length, so I added 40 or 50 feet of  line...problem solved.  This may not be your problem, but at least it's an easy thing to try.

       --jim KJ3P

  • Homer1952Homer1952 Member
    edited March 2019
    How does one know how well shielded a cable is?  Does Flex have a recommendation?

    It is an OFC Y cable.  Has gold contacts on the 3.5mm stereo jack & has a silicone sheath.  I know those details may not speak to the shielding, but it feels/looks like a quality product.  It does split to 2 RCA jacks so the "balanced" connection is lost at the Fostex 1/4" psuedoXLR jack.  Because of your comment, I added 3- 31 mix donuts to the cable and I'll give that a try tonite or tomorrow.

    I previously added ferrites on the power cable also, to no avail.  My other radios do not have ferrites on the power cable & they haven't been an issue.

    The only unique things to the Flex is the LAN cable & mandatory active speakers & psuedoXLR mic connector.

    Bob W8RMV
  • Bob- W5TXBob- W5TX Member ✭✭
    edited March 2019
    How long is the Ethernet cable? At this point in your search process I would suspect it as a potential cause. I have had various RFI issues when rig used Ethernet connections. I installed fiber converters at each end of Ethernet cable and since no issues when running legal power. Pair of converters on eBay was <$30.
  • Homer1952Homer1952 Member
    edited March 2019
    The router is downstairs, so the cable is routed under the 1st floor in the basement, to a router about 30' away, which is in a direction & location away from the antennas.  There is only about 4' of cable upstairs.

    I am not familiar with fiber converters.  I will take a look.

    I should have mentioned earlier, that there was a time a few months ago, that I did not have any RF complaints.  Also, I have not made any changes to the shack, antenna systems, router, cables, etc. 

    Bob W8RMV
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited March 2019
    I'm starting to wonder if you even have RF trouble. It could be possible that you may have a setting problem, EQ problem, mic gain problem, mic connect problem that some may think is RF but isn't.
    Can someone who hears you strong record you and send it to you? then you can post the recording hear?
  • Homer1952Homer1952 Member
    edited March 2019
    Was that a dyslexic RF? ;-) 
    I am open to other suggestions. 
    Everyone who hears me says it sounds like RF.  At 100W or less, the 6400 by itself seems to be clean. 
    I put the amp on (Acom 1500 running 4-600W), I get the roughness. 
    I use that amp & everything else the same (minus the LAN,Speakers, mic cable) with another rig, no problem.
  • edited March 2019
    Bob Get the DX Engineering Ethernet RFI filters Solved my Problem with RF getting into Flex with HF Linear on ! 73 Mike
  • edited March 2019
    80meters is usually the Band where RFI is noticed End Fed Antenna’s on 80 meters have a lot of RF Currents traveling down Ground Shields, Ethernet Lines, etc 50ohm RF Line Isolators will help but Top bands like 160meter & 80meters Play havoc for RF getting into everything Suggest Ethernet RFI Filters, RF 50ohm Line isolators, Balun’s On Dipoles, FT-240-31 Cores, RFI AC line Filters,etc 73 Mike
  • Jay NationJay Nation Member
    edited May 2019
    Just throwing this in, I didn't see it being discussed. 
    Could it be Ground Loop Hum, instead of RFI?


    #FlexRadio IRC Chat

       73, Jay - NO5J

  • edited March 2019
    Well Only happen when he uses 400watts to 600watts Output so that more than just a Hum Ground Loop
  • K9SOK9SO Member ✭✭
    edited March 2019
    Hi Bob,

    The problem with random wire antennas is that they are, well, random. You may have unluckily selected a length of wire that causes a very high RF voltage at the feedpoint. That might be very hard to filter out.  Adding some length (1/2 wavelength) to the wire might shift the feedpoint to a current node and help with your problem. 

    Alternatively, you can experiment with adding a clip-on ferrites to the wire that would electrically change its length. Or a couple of turns of wire through a toroid core. That may seem counter-intuitive (adding a RF "filter" to your antenna wire), but all you're doing is adding some inductance and changing the resonant length. Your tuner should be able to handle the impedance change. 

  • Homer1952Homer1952 Member
    edited March 2019
    I know it is hard to read & digest all comments, but the RF issue is on both the 80M loop & end fed.  I use the loop 99% of the time.  Use the endfed mostly on 160M.

    I am liking the LAN cable as the culprit and maybe the speaker cables.  I have not had a chance to get on the air to check out the effect of the additional ferrites & relocation of the LAN cable.

    I am surprised at the number of users who have commented on the LAN cable as being a problem.
    Also, I am not entirely sure I don't have a problem using the 6400 barefoot.  I need to have good band conditions to connect with the local hams I talk to to see if I sound good at 100W.

    I'll report back then & thanx for all the replies.

    Bob W8RMV

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