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6600 noise levels +10dB higher on my new 6600 vs. my older 6500

K9SO Member ✭✭
During testing of my brand new 6600, I see a higher noise floor than I had on my 6500. With no antenna connected (unterminated), a 400Hz CW BW and 0dB gain on the preamps, I have a -110dBm noise floor on the 6600 as compared to -123dBm on the 6500 ( measured on the S meters).

The displayed noise line is lower of course but is consistently almost 10dB higher on the 6600 than the 6500 with no antenna. 

There may be SW issues as I'm running the 6600 on the latest V2 software and the 6500 on V1 for this comparison (I had not upgraded the 6500). 

I'm in a very quiet rural location and my 40m noise level is about -108dBm  with the antenna connected. In other words, I see very nearly the same noise levels with and without the external antennas connected. Nothing wrong with the antenna in TX. 

So I'm concerned that the 6600's internal noise is close to my atmospheric noise levels which would not be very good.

Does my 6600 have a problem or am I being overly critical?


  • Joe N3HEE
    Joe N3HEE Member ✭✭
    edited February 2019

    Fred. I agree that would not be good.  I am noticing issues on 160 meters with RXA input being 10 db worse when radio is using bandpass filters.  In WIDE mode the noise floor drops 10 db and siganal levels and signal to noise ratios dramatically improve.  This does not happen with ANT 1 input.  I have not checked noise floor levels with and without antenna connected.  I will check that tonight and report back.  I am about to open a ticket with my findings.  I will also produce a video of the issue.  -Joe N3HEE
  • Joe N3HEE
    Joe N3HEE Member ✭✭
    edited February 2019
    Gerald.  Thanks for the detailed response and information.  I totally agree with this.  However it did not answer what we are seeing when the receiver is in WIDE with RXA antenna input connected.    Does RXA go through the bandpass filters ?  Why are we seeing better receiver performance in WIDE mode on 160 meters ?  Can you please shed some light on how signals routed from various antenna inputs. Thanks -Joe N3HEE
  • Gerald-K5SDR
    Gerald-K5SDR FlexRadio Employee ✭✭
    edited April 2019

    When you go into WIDE mode it bypasses the band pass filter and only has a high pass filter to remove the AM broadcast band.  This is true no matter which antenna connector you use.  The receiver signal chain is the same for ANT1, ANT2, RXA, RXB, XVTA, and XVTB.  There is no harm in going to WIDE mode on 160m or any other band unless there is a strong co-located (e.g Field Day) signal on another ham band, which won't normally be the case.  Lots of strong signals actually add and subtract randomly to look like Gaussian (white) noise in the ADC.

  • Joe N3HEE
    Joe N3HEE Member ✭✭
    edited May 2019
    Thanks Gerald.  That's good info to know.  So what we are seeing is normal ?  If so this would be good info for the user manual.  I found this by accident.  Going into WIDE with RX antennas on 160 meters makes a big improvement when working weaker DX ! 

    It would be nice to be able to switch into WIDE mode without needing to zoom out on the panadapter.  In other words a switch that would turn it on or off and maintain the current resolution of the panadapter. 

  • K9SO
    K9SO Member ✭✭
    edited January 2019
    Thanks Gerald. I just got back in town and tried your suggestion. I was not taking into account the added loss of the new filters in the 6600 and was not introducing enough preamp gain, especially on 20m.

    Surprisingly, I need between 16 and 24 dB of preamp gain to reach the "8-10dB drop" in noise floor with/without the antenna on 20m. Much more gain than what was needed with the 6500. As I said, I am in a quiet rural location. I see 20m daytime noise levels of about -120dBm (antenna) vs. -128dBm (no antenna) with the 16dB preamp setting. 

    The old processor between the ears has been reprogrammed to understand this now. I appreciate your explanation. 


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