Noise burst at beginning of transmission

K2CB Eric Dobrowansky

When transmitting using SSB, there is a loud nosie burst the beginning of every transmission.  It appears to be the transmit audio buffer filling with the ambient noise of the room (rx audio from the speakers) just prior to the beginning of the transmission.

If I use headphones, so there is no ambient noise in the room, then there is no noise burst at the beginning of my transmission. However, if I am using the speakers to listen to the receiver, then go and key the transmitter, the last 500ms or so of receive audio appears to be transmitted. 

If I increase the TX delay setting in the main setup TX window, to a value of 400-500ms, I can eliminate the noise burst on my transmissions, but then I have a corresponding 400-500ms delay in TX-to-RX transition, which is not good.

I did not have this issue with my prior SDR radio, nor does it exist with my other traditional transceivers. It appears the tx audio buffer is enabled prior to PTT being engaged.

Eric

K2CB

Les W6JKA

I have the same problem and put in a 250ms delay. This masks the issue.

Les W6JKA

Tim - W4TME

Eric,

Please describe how your mic and how you have it connected?  What are your SSDR phone settings?

K2CB Eric Dobrowansky

Shure SM7B fed into a Symetrix 628. The 628's xlr output is connected to the xlr input of the 6500. Using a foot switch for ptt. Smart SDR is set as follows: BAL input MIC to 40 COMP off or MIC 20 COMP on at 10 TX bandwidth set for 50-4050. Audio peaks at 0dbm. Average voice levels to the first L of LEVEL. Eric K2CB

Tim - W4TME

Thanks Eric.  Can you tell me if there is any appreciable difference between using the BAL input or the MIC input -AND- are you using the +20 dB boost on either of the inputs?  

K2CB Eric Dobrowansky

Same noise burst with both the front panel mic input and the rear xlr balanced input. I used the +20db boost with the front panel mic input, but no boost while using the rear xlr balanced input. Eric K2CB

Tim - W4TME

Thanks Eric. This looks like a software defect and I have written it up in or bug reacker for further investigation.  I appreciate the detailed information.  That helps us a lot figuring out what is going on.

Ken - NM9P

Tim, for additional information, if it helps:

I was listening to some ESSB guys on the low end of 80 the other day and one of them had the same noise on his 6000 whenever using his mike via the BAL port, but when He used his outboard processing/gating equipment, or used audio lines processed via computer and sent in via DAX then the noise went away.

Ken - NM9P

Tim - W4TME

Thanks for the additional information.

K2CB Eric Dobrowansky

Thank you, Tim.

Eric

K2CB

John Watson W4JCW

I have a friend that is having this issue and he is running a 6500 and v3.2.39...has there been a fix for this issue?

LA4XLA

Anyone still fighting with this ?

I think i might have a problem that can be related to the same issue. Flexradio 6400. When using SPE 1,3K-FA amplifier. The amp is sensitive to input power so i have limited RF power to not overide reccommended input power on the PA.

Mic gain medium and not higher than reccommended by the manual, but it seems i get some bursts sometimes that lead to exeeding the input power on the amp and PA goes into input protection.

If i reduce mic gain allot it works, but then i do not get the wanted mic gain and wanted output power from the PA beucase of to low input rf power.