Transmit audio has fast echo

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  • Problem
  • Updated 6 years ago
  • Acknowledged
Flex 6700 SmartSDR 0.16.4 On SSB there is a very fast echo on the transmission almost like the reflection or echo from a sound travelling down a long drainpipe. This is heard at a low level 'on air' and also more clearly via the front panel phone monitor socket.
It is not RF getting into the radio as it is the same into screened dummy load. It gets progressively worse as the RF power level is increased towards 100w. Any ideas?? G4BIM
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G4BIM

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Posted 6 years ago

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G4BIM

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I understand that I am not alone experiencing this issue and whilst this is to a degree comforting, it is no less a worrying issue. I have carried out further dummy load tests this morning and find that it is an issue on AM transmission also.Its intensity is directly proportional to the PA power or drive level. I am now no longer using the 6700 and have gone back to the 5000A to avoid embarrasing on air comments. Come on FlexRadio, don't let me down...
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Gerald - K5SDR, Employee

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There was an issue on v0.16.4 when first upgrading where the audio CODEC DSP code did not get updated until you do a manual reboot. I personally saw this cause an echo on the receiver but not on transmission. We have fixed the CODEC load problem in the latest software, which will be included in the v1.0 release. Try rebooting the radio and see if you still have the problem. You should also try it next week after we release v1.0.

By the way, if you hear the echo in monitor mode in the headphones with the power turned to zero, the problem is almost certainly the CODEC software load. In this mode the transmitter is not in the loop at all. Everything you are hearing is inside the CODEC itself. I would be very interested to know if that is the case. Until v1.0, rebooting is the best solution.
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G4BIM

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Thank you for your prompt response Gerald.
On the monitor Phones socket with power zero there is a tiny trace of the echo and it might not be noticed if you were not listening for it, but it is there.
It progressively gets louder as you increase the power setting, at 100 its quite bad and very noticeable. The radio has been re booted several times since the installation of v0.16.4. I believe this problem persisted on earlier software versions, I did not previously mention it before because I thought it may just be a characteristic of the monitor circuits and that it could not be noticed by the listener; I was wrong.
The monitor phones are Sony MDR CD 3000.
I am a 'dyed in the wool' Flexer Gerald, This is the biggest performance leap in a radio I have ever experienced in over 40 years, your team have done a brilliant job...if I can help any more with this issue just mail me.
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Bruce

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With v0.15 my CW signals received outstanding comments on keying and the radio sidetone sounded just right; however with v0.16.4 I heard a "raspy" click after each character was sent. The noise coming from the sidetone was confusing to say the least. I went back and installed ver.0.15 and all worked as it should. I have stayed with this version and hope ver.0.17 will not pick up this error.
N5FD
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Gerald - K5SDR, Employee

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That sounds a lot like RFI into the microphone since it increases with power.

Please tell me what microphone you are using and how it is wired to the connector. I am interested in how the microphone ground return lead and the shield are wired. Make sure Mic- goes to pin-7 and NOT to the shield. The shield should go to the connector housing and not be connected to Mic-.

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Joe WD5Y

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Gerald,

I have this same issue and I believe it is RF. It appears just as it is stated, the volume increases into the speakers when increasing the radio power out. What is confusing for me is that I can put the external power amplifier in line and the audio into the speakers does not increase, actually I can lower the radio output to around 10 watts and with the external amplifier inline there is very very little audio feedback with an output of 600 watts. I am running a microphone into the balanced XLR input. I still believe it is RF but not sure of a remedy. I did install line isolators and ferrites in the audio cabling, it seems the feedback volume is lower but still there.

Thanks and 73's,
Joe
WD5Y
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G4BIM

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Gerald

This issue occurs irrespective of the microphone, it happens even with the fist mike supplied with the 6700.

If it is an RF feedback problem, then it must be within the radio itself, since it occurs with a screened dummy load or an Expert 2k linear at 2.4KW peak into a 4 ele Steppir. It is the same with either setup... The more I listen to it the more it sounds like a DSP artifact. Is there anything else you would like me to try???
You must be able to replicate this issue at the factory, do you agree it is a known issue that you like others have experienced?
Kind regards

Peter Bentley G4BIM
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Joe WD5Y

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Peter,

I have to mention this, I have a close friend (ham) that ordered a 6000 when I did. Actually, his radio is one serial number produced from mine. I have checked with him very closely on this and he does not have this as an issue at all, believe me we tested to the extreme. I do believe it is RF but the remedy not sure of. I plan on changing some cabling along with equipment locations as my station is very tight. If you come up with something specific please post it.

Thanks and 73's
Joe
WD5Y
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G4BIM

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Thank you for your input Joe.

Please explain to me how it can be RF at power setting 1 (1 watt) and antenna 1 connected to a screened resistive dummy load via half a meter length of RG8U???
I never had any issues at all with RF affecting the 5000A, same setup same cabling same earth paths and at power levels up to 2.4kW peak on 160m thru to 6m.
No its not RF, it is not even frequency dependant. it sounds like a digital artifact, but how do we cure it?
Kind regards
Peter G4BIM
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Joe WD5Y

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Peter,

We may have different issues, I'm not sure? I do know that what I hear sounds like audio feedback and I can reduce it greatly by turning the volume of the powered speakers all the way up while lowering the volume control on the radio to set overall volume, this seems to diminish the feedback greatly. I just took it that when the other 6000 was tested did not show this that it was on my end as possible RFI. One thing I just thought of is that I do have the GPSDO option installed and the other tested radio does not, that is the only difference.

73's
Joe
WD5Y
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G4BIM

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Thanks Joe, we will wait for Geralds response.
Kind regards
Peter
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Sergey, R5AU

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Peter, I have tested supplied with my F6700 mic first couple of minute and after immediately kick out this toy. Right set up for me now is: balanced heil781 with 2k-fa amp - no any issue at all. My RST now is - studio quality
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G4BIM

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Dear Gerald

I have now installed SmartSDR Ver 1, thank you for that.

This has made no difference to the echo on the transmit audio issue.

I cannot see how it can be RF related in terms of RF outside the box/cables/earthing getting back into the internal of the radio for the following reason:

The echo becomes noticeable at levels of RF power setting 20 and is not transmit frequency dependant. Above that level it increases in a near linear fashion as you approach 100. So at setting 20 the radio is generating up to 20watts. However, if you connect the linear amplifier to the radio with a gain of some 15dB, the RF in the vicinity rises from 20 watts to over 500 watts. However, this increase in RF field has no effect on the level or intensity of the echo.

It points to me to be a problem within the radio box, which may be RF related internally. Although it is a fast echo it is also distorted. Could it be a digital circuit 'ringing'. its a long time since I worked on this stuff and it was a lot slower then.

Are you saying you are not able to replicate this issue?
If so , thats good because it means it must be related to this particular radio number

1713-3011-6700-4266 alone...

kind regards

Peter G4BIM
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Gerald - K5SDR, Employee

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This is a new issue to me so I am fishing in the dark. Note that RFI is very shack and configuration specific.

Peter, does the echo occur at a power setting of zero?

Am I correct that you are listening in Monitor mode when you hear the echo?
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G4BIM

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Gerald
It does not occur at power setting zero.
I am listening in monitor mode with headphones
It has been reported back to me on air in QSO from as far away as Capetown, in fact the guy recorded it and played it back to me.
If you keep the power level at 15 or less it is not normally noticeable by the guy at the other end in QSO. It is excessive at power level 65 to 100. It occurs at the moment of normally silence at end end of a spoken word. It decays to nothing after half a second or so.
Are you able to reproduce this... Or is it an isolated condition with my radio.
I thought their were two other users reporting this.
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Tim - W4TME, Customer Experience Manager

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This sounds like RF getting into the radio. I'll let Gerald have the final say.
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G4BIM

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Thank you Tim, but how do you explain this written earlier today..

The echo becomes noticeable at levels of RF power setting 20 and is not transmit frequency dependant. Above that level it increases in a near linear fashion as you approach 100. So at setting 20 the radio is generating up to 20watts. However, if you connect the linear amplifier to the radio with a gain of some 15dB, the RF in the vicinity rises from 20 watts to over 500 watts. However, this increase in RF field has no effect on the level or intensity of the echo.

I ask again for the third time... Have you or have you not been able to reproduce this effect on a radio in the U.S.
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Gerald - K5SDR, Employee

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Official Response
I have not been able to reproduce this here at any power level. I am listening to the monitor while transmitting. Monitor audio is a closed loop that exists within the audio CODEC itself and the power control has no effect on its internals. There is virtually no delay within the monitor path so any delayed echo would point to RF ingress. Very hard to tell from here since I can't reproduce it. You should probably open a help desk ticket if you need additional support assistance. You can do so through the Zendesk link on the community home page.
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Rick KN3C

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I have the echo problem with version 1.0 using the balanced input or the microphone supplied with the radio. There is no difference in the problem running the radio directly into a DL, or driving an amplifier with 1 KW output into an antenna. The problem does seem to be affected by microphone level and compression level. I can mitigate it somewhat by manipulating those controls. You can clearly see the echo on the spectrum monitor in transmit mode.

I can hear the problem clearly in my headphones when the transmit monitor is engaged. The stations I am talking with can clearly hear the echo. I believe the problem is worse with the +20 dB boost turned on.

What is the nominal input level for the balanced input? I assume it is mic level, somewhere around - 60 dBm?

I stopped using my 6700 and went back to my 5000A because of the echo problem.
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G4BIM

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Hello Rick,
I had a very similar problem to the one you have described, but I seem to have solved it by careful adjustment of the maximum audio input level to the balanced input. I run an Orban Optimod 9300 into the 6700 balanced input, which I now limit to a maximum input of -6dBu. If you exceed this there is a tendency to make something 'ring' in the Flex audio stages. At first I thought it might be RF feedback but into a dummy load? I don't think so, unless it is within the 6700 Hardware....
So with a BAL level of 45 maximum (no 20dB boost) it works just fine, no trace of echo or ringing. Software version is current 1.05.
E-Mail me direct if you want to chat. I am on QRZ.com. PS don't go back to the 5000A, it is a great radio, but I recon the 6700 is 3 to 6dB better on RX and much cleaner TX audio.
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Rick KN3C

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I'm driving the 6700 with a Shure M67 using the mic level output. If I do not engage the +20 dB boost, I have to run the microphone gain nearly wide open to get a reasonable level on the mic meter. I do believe the echo problem got worse with the +20 dB boost engaged. The echo does exist using the factory supplied hand mic.

I tried taking the line level output of the M67 (+4 dBm) and padding it down thinking I could avoid using the +20 dB boost, but the results were disappointing. I was well below the - 6 dBu you mentioned, with the +20dB boost turned off, but had a great deal of distortion, so I abandoned that idea.

I will go back and try driving the 6700 with the 20 dB boost turned off, and see what it looks like. Appreciate the suggestions.

Oh, and I tried 1.05 but felt that the problem was considerably worse so I went back to 1.0.
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Fred, AB1OC

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I have the exact same problem with my Flex-6700 that is described here. The symptoms that I am experiencing are pretty much identical to those indicated by others here -

1) Delayed transmit audio on the line and headphone outputs with Tx power at or above about 10W. I am transmitting into a 50 ohm dummy load and the problem is easy to reproduce that way.
2) Tx Audio on output lines is delayed and somewhat distorted
3) I have tried all manner of shielded speakers, cables, chokes on the Ethernet and audio cables out of the radio and nothing helps.
4) Using the line-in microphone jack does not help either
5) The problem is just as bad with the supplied microphone as it is with the various Heil and high quality Yaesu mics in the shack
6) My shack has a very well built RF ground and the radio is properly grounded.
7) I had a Flex-3000 in the same position in my shack with the exact same grounds, speakers, cables, etc. and I never had a problem with hearing my Tx on the audio outputs. I seriously doubt that this problem has anything to do with the environment that the Flex-6700 is operating in here in my shack.
8) I have tried both the 1.0 and latest versions of SmartSDR and the problem is the same with both versions.
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ai6re

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I notice that this is only reported on Flex 6700 and I don't find this problem on my 6500. I wonder if having two scu's might be related to the problem.
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Rick Markey

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My problem has gotten a lot better, and is most likely solved with the latest beta, 1.0.24 and some suggestions from G4BIM. Fred I'm the same as you - same audio chain feeding the 6700 as feeds my 5000A and never an issue with the 5000A. It's a Shure M67, EV RE16, no external EQ, no external compression, and a 40 dB pad between the line output of the M67 (+4 dBm) and the input to the 6700 balanced input. I am also not using the +20 dB boost in the 6700.

I followed the audio setup instructions that came with 1.0.24 and noticed a huge improvement in the overall audio quality. The TX EQ also works much better in my opinion. The guys I talk with on a regular basis, some of whom are audio fanatics, have commented that the 6700 now sounds as good or better than the 5000A.

Sometimes I think I can hear just a touch of the echo, but no one has commented on it, and I don't hear any trace of it in the recordings that I make.

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