Internal noise on mic input Flex 6500

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I have been operating my 6500 for about two weeks. I am new to the radio. The following is with no mics connected to the transceiver. I have noticed if you key the transmitter using the bal input in the rear of the transceiver with no modulation the system is totally clean and noise free. I have noticed if you switch to the mic input and key the transmitter without modulation you can hear a small amount of internal noise. I believe I have selectively shut down all items in the shack to eliminate external sources. Has anyone experienced this phenomenon?
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Bill K8WLK

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Posted 4 years ago

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Tim - W4TME, Customer Experience Manager

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Bill - This behavior has been previously reported.  It is due impart to the front panel mic input being an unbalanced microphone input.  The rear XLR/TRS input is a balanced audio input and is less susceptible to inducted noise due to differential signaling.  Therefore if possible, it is always a best practice to use a balanced input in RF "rich" environments if possible.
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Bill K8WLK

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Thanks much Tim....Great Radio!
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Kevin Wallace

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I experience this same behavior with my 6300. I've never heard this much noise on the MIC connector from any radio I've ever owned. I am currently using the ACC connector to transmit audio and it doesn't appear to exhibit this behavior, but I would assume the noise I'm hearing on the MIC connector is NOT normal. Hopefully it can be cured with a software update!
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Tom

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Same here, noise on MIC connector is not normal, even without microphone being connected to it.
All my rigs except FT9000 dont have balanced input but still free of noise.
I have balanced microphone but sometimes I want to use Heil pro unbalanced set but noise is surprisingly high.
For me it is anomaly or malfunction to be addressed.
Answer from FRS (Tim) about best practice was not serious,
Tom, 9A6TKS
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Jon - KF2E

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I think that the issue here is that the Flex is somewhat more susceptible to RF than traditional radios. When I first got my 6500 I experienced a lot of distortion using the front unbalanced mic input. This problem is exacerbated if you use the front input with a balanced mic. I went to a PR781(balanced) plugged into the balanced input and my issues went away. Later, I added about a dozen mix 31 ferrites to the feed point of my antenna. Since doing so I don't have any issues regardless of the input I use.

Jon...kf2e
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Jay

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Has this issue been solved in anyway? I have this problem on 6300. Sent it in and tech did not find a problem, but it is still there. Image below shows noise during xmit. If i lower mic gain it goes down but just  a bit. Downward expander hides it.
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Jay / NO5J

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Ticket has been opened! Take a look at it.
Request #14029  

73, Jay - NO5J
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Jay / NO5J

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Or, I suppose I should have used the community search function to see what information has already been provided about this issue, "first".

This rather old thread, if still accurate information, seems to hint at what the reality is.

https://community.flexradio.com/flexradio/topics/panadapter_signal_during_transmit

I'm comfortable just ignoring the panadapter noise seen when the Downward Expander is off, or misadjusted.

DEXP seems capable of removing noise both "seen" and heard. I almost always have to enable it anyway, due to PC fan and hard drive noise, The business ends of my mics are all within 3 feet of 3 PC's. So in my case a portion of what's seen on the panadapter is confirmed to be external  to the 6500. 

Kind of nice knowing that my PR781 is sensitive enough to hear noises I can't really hear. Kind of nice that the DEXP removes anything I'm ignoring or can't really hear also.

That's my current opinion, but I'm interested in other opinions too.

73, Jay - NO5J
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Ken - NM9P, Elmer

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Jay. Two things that can help you get a picture of this.

1) Try the full duplex method I posted to YouTube.
Set your transmitter to xvtr so you are not really transmitting over the air.
Mute slice A.
Set slice B to the same frequency and mode with RX filter the same, or wider, than your transmitter.
Activate FDX, and use headphones to monitor your slice A transmitter on slice B.
Make sure your RX EQ is off, and agc-t is set so that the background noise just starts to drop a little. Agc speed at medium.

Now key the Mic and just listen to your own signal in slice B..... If DEXP is off, you will hear a lot of stuff your mike is picking up. Now activate DEXP and slowly bring the level up and you can hear and see on the display exactly when it takes effect. Cool!

2). A second technique, though not as dramatic, is to use the monitor function with headphones.

BTW... The old post you linked is informative, especially the discussion of what the pan on txt actually displays. I have found that for SSB and digi signals, what is within the RX passband strip is VERY accurate to what I used to monitor on my 1500 as I transmitted with the 6500. What is outside the RX passband...not always accurate.

My interpretation is that most of the garbage seen in the RX panadapter is internally generated phantom signals, and that the noise seen in the TX passband when there is no mic connected is the minuscule internal noise generated by solid state devices. We just have the "luxury" of Boeing able to see if I!

Also....Did you notice Steve's statement that in the initial design the -80 dB tap from the transmitter was originally made in order to allow adaptive predistortion? Contrary to the nay-sayers, APD has been in the plan all along. It is just a matter of timing and priorities, (and perfecting the software.) I thought that was interesting. I had not caught that two years ago.
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Jay / NO5J

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Ken

I really think the in the TX passband garbage seen on the panadapter with DEXP disabled is just inaccuracy. My mic audio thru the monitor, using the Full Duplex trick, or Recorded and then played back, is always dead silent unless the DEXP is disabled. It sounds like what's described as full quieting, I've always thought that even full quieting is probably visible on a spectrum analyzer, as almost but not quite a 0 dB level. It may just be that the panadapter which is useful when observing received signals is not the best display to use observe transmit audio.

What I'm really interested in is confirmation that that noise on the panadapter, (that the DEXP removes) is likely a display anomaly.

The thread I linked makes me think it is.

Possibly being misinterpreted as something it's not. I don't expect to ever see the noise floor flat line no matter how high I set the averaging. So why worry about random digital noise on the input of the panadapter input tap. The difference between 0dB audio and 0.001 dB audio should still register as a 0.001 dB peak on the display, even if it's a meaningless peak because it never registers as anything but 0 dB at the input of the PA. 

How loud, or quiet, is quiet?
Is my zero less than your zero?
How perfect, is perfection?
I think it is, what it is.
Good enough for Amateur Radio!
Might even be better than that.
We could just be satisfied.

Even with on air playbacks of my mic audio recorded on another 6XXX my mic audio sounds full quieted or at least as full quieted as the mic audio from the other 6XXX.

Which is better, worrying about nothing, or being happy, that it's nothing?
Worth thinking about, when you think about it.

73, Jay - NO5J

And yes, the two Jays posting in this thread, are really two different people, even I get confused.
 
(Edited)
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Ken - NM9P, Elmer

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That is why I like the DEXP. It keeps things quiet. If I set it right, it even quiets my breathing sounds from the mic!
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N3NER

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I see this as well on my 6300 however, if you look at the power output when this noise is introduced there is no output on the meter (dummy load or connected to an antenna).  So it's not transmitting anything on the output so there must be something going on where the noise is getting picked up someplace in the audio chain but it being transmitted at all.  I see this in the MIC and PC position but not in the ACC position. 
(Edited)
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Tim - W4TME, Customer Experience Manager

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My advice is the same as what I gave to Steven - open a HelpDesk support ticket so we can investigate this issue.
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Jay

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Try with your normal mic level afterward and let us know if there is any change in level.
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Jay

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Question for Ken do you have to impedance match your behringer mixer to the radio?
Jay n2gq
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Ken - NM9P, Elmer

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The BAL input is at a commercial audio impedance and line level, so impedance is correct going from the balanced mixer output to the BAL input on the 6500/6700. I just used an balanced to balanced patch cable. You can use an XLR to XLR or a TRS to TRS. I used a TRS because I had one. (Actually, I had a dual TRS male to male cable and used one to the 6500 and the other went from and AUX send/output to an AUX line in adapter I made for the 1500 I used to have. That allowed me to sent my mic audio to both rigs simultaneously and adjust the level independently for each rig. ).

If I remember correctly, I used a mixer mic level at mid-range, mixer line output at about mid-range, and the 6500 BAL input without +20 boost and level at about 35 got me close. I did initial level setting with the mixer MAINS output control. Then fine tuned it a bit by bumping the control on the 6500, since each profile needed a little different mic level setting, depending upon TX EQ levels.
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Jay

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I also tried this on my kenwood Ts2000 into dummy load and and listened on flex radio and wow noise there too.
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Mark - K9MQ

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I have the same issue with the Flex-6300.  Last November, I made a video similar to Steven's and submitted it to the helpdesk.  Tim replied right away that something is up and immediately issued me a UPS return label.  The service department could not find anything wrong with the rig and verified that the rig had all of the latest ECO's on it.  It was returned and I was still having the same issues.

I did some diagnosing and did find, there was a little bit of fan noise mixed in, but the noise was still present even with the fan temporarily disconnected (the fan noise problem went away).  I opened up a second help desk ticket with a link to the same video and Dudley replied that it shouldn't be doing that and issued a UPS return label.  When, I returned the radio, I included documentation that had a link to the Youtube video and a screenshots from SmartSDR showing the waveform for the tech to review.  The tech could not duplicate the issue, but they went ahead and shipped me a new radio anyway.  

The new radio did sound somewhat better, and the fan noise was not present anymore, but still had the internal noise present.  It is critical for me to run the downward expander to mask the noise.  I'm an convinced that this is how the product is designed and not a hardware failure.  I can hear this noise in full duplex mode and on my Kenwood TS-2000.        
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John Bailey

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I have the MIC input noise issue here as well.  200Hz and its harmonics only on the mic input.  Noise goes up and down with mic gain or the +20dB in setup.  The dexp helps, but is only masking the problem.  ACC input looks clean as well as PC audio.  It's NOT an RF issue, unless it's internal to the flex.

John KB1YFD