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RF Gain and diminished receiver sensitivity when on 6 meters

Norm - W7CK
Norm - W7CK Member ✭✭
edited June 2020 in SmartSDR for Windows
I have a problem on my 6700 and would like to know if anyone else is experiencing anything similar.  I'm following up with a trouble ticket, but I thought I'd post here just to see if this problem is unique to my 6700.

RF Gain and diminished receiver sensitivity when on 6 meters

To eliminate any configuration issues, I first did a factory reset by first backing up all profiles then shutting down the 6700.  I then held in the OK button while turning on the 6700 until it completed it reset countdown.

Next, I opened 2 panadapters

1st one defaults to 20m cw ANT1             

2nd one defaults to 20m cw ANT1

Change 2nd panadapter to 6 meters, set it to ANT2 on TX and RC and set the RF Gain to 20db.

Panadapter 1 which is still on 20m was selected for TX.  I then switched TX from 20m to 6m panadapter then back to 20m panadapter.

I immediately noticed that the RF Gain on 6m panadapter may or may not change on its own, but the signal strength and noise floor drops dramatically.  If you go to the 6m panadapter and change the RF Gain from 20 to 10, the noise floor comes back to normal.

Change the RF Gain on the 6m panadapter back to 20db and the TX between the 2 panadapters and the RF Gain / noise floor will drop on the 6 meter panadpter nearly every time.  You have to go to RF Gain and select 10 then 20 again in order to get it to come back to normal.

This has been happening on my 6700 since new.  I just assumed it was an anomaly like when I use 2 meters and all of the other HF panadapters get all **** up.

Anyone else experiencing this?

Norm - W7CK




  • Roger Rockwell/na4rr
    Roger Rockwell/na4rr Member ✭✭
    edited February 2017
    Hi Norm,

    This reply is going to be like the ones I hate to see.  No real information:  That being said, I think I have seen the same thing on my 6700.  I have always been in the middle of doing something else and never taking the time to document the work flow as you have nicely done.  I am in the process of getting the rv set up for a three month trip so don't have access to radio to make sure I can dup what you are seeing but I think I can.

  • Bill W2PKY
    Bill W2PKY Member ✭✭
    edited March 2017
    My radio was built last month and it does the same thing. Think the issue is when the HF has no preamp selected and 6M has a boosted setting. On my radio if the HF has some boost then I do not have the issue.
  • Ken - NM9P
    Ken - NM9P Member ✭✭
    edited June 2020
    Since I have a 6500 I may not be totally versed in some of the 6700's idiosyncrasies. Do you get any indication of whether your 6 Meter slice is on the same or a differenc SCU as the other HF frequencies?

    If it is on the same SCU, then the last preamp command given might affect all slices on the SCU, like it does on the 6500. I would assume that if it is on a separate SCU from your other HF slices, that it has its own preamp and should operate independently from the others. It this not happening?
  • Bill W2PKY
    Bill W2PKY Member ✭✭
    edited March 2017
    My suspicion is each antenna is connected to a separate SCU. So when an antenna is selected the signal comes from a specific SCU. So ANT 1 is probably SCU1 etc. There is no indication to select a specific SCU. Tried to find a block diagram of the 6700 with no luck. Each SCU obviously has a Preamp and associated circuitry to the antenna connector. The problem is the software can not remember the Preamp setting for each SCU when one SUC has no preamp boost and the other has boost selected.
  • Norm - W7CK
    Norm - W7CK Member ✭✭
    edited December 2016
    I'm assuming since the slices are on different antennas that they are also on separate SCUs.  

    It looks to me like when switching between panadapters using different antennas, the preamp reverts back to zero on the radio but the indicator in SmartSDR still indicates 20.

    I am a bit concerned that no one else is chiming in and reporting the same issues though.  This makes me feel that it might not be a software issue but rather a hardware one.  I'm going to wait a little while longer and see if anyone at all reports having the same issue.
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited June 2020
    Bill W2PKY is on target.  Technically the radio is working as designed.  The behavior you are seeing is a result of the dynamic SCU allocation logic based on antenna selection.  The RF preamp is associated component of an SCU (along with the ADC and the preslectors). 

    There is one way to force an SCU to a particular antenna and have it retained.  That is by using the RX port.  RX-A is always connected to SCU0 and RX-B is always connected to SCU1 via a fixed RF signal path in the 6700.  So, using this information, you can use the RX loop feature to "force" and SCU to a particular antenna.

    6m is my favorite band and I dedicate an SCU to ANT-2 which is connected to my 6m beam.  Consequently, ANT-1 is connected to my all band delta loop.  I want the 6m pandapter and associated settings to be persistent, so I installed a small BNC jumper on the RX-B in/out.  On the 6m panadapter, the RX and TX antennas are set for ANT-2 and then  I enable the LOOP-B.  Once you do this, switching the TX slice does not initiate the SCU dynamic allocation logic and the SCU (including the RF preamp settings and preselector settings) will not change.

    Once you have this set up, create a global profile so you can easily and conveniently re-enable this particular radio state.
  • Ken - NM9P
    Ken - NM9P Member ✭✭
    edited December 2016
    Tim, I knew there had to be some way to do that, but not familiar enough with the 6700 to come up with it.

    I remember in the early days of "pre-release" SSDR there was a lot of chatter about the complexity of the antenna switching logic and all the different possible permutations that had to be allowed.

    Is there a way that this SCU-fixing logic could be programmed as a feature without requiring a loop jumper?  Perhaps a "Lock slice to SCU" button in a future release?

    Just thinking out loud here....

    Ken - NM9P
  • [Deleted User]
    edited May 2016
    Tim wrote -

    Bill W2PKY is on target.  Technically the radio is working as designed.  The behavior you are seeing is a result of the dynamic SCU allocation logic based on antenna selection.  The RF preamp is associated component of an SCU (along with the ADC and the preslectors). 

    The ANT1-ANT2 craziness isn’t limited to this. There are problems with it during startup.

    For several months I have been trying to describe lack of functionality in the SCU-ANT1-ANT2, and if it is designed to work as follows, then the design is questionable:

    Three panadapters, as follows:

    1 HF Split Operation, Slice A-Rx, Slice A-Tx; Slice B-Rx, Slice B-Tx 

    2 6m Operation, Slice C-Rx, Slice C-Tx
         BOTH ASSIGNED to ANT2

    3 6m Operation, Slice D-Rx, Slice D-Tx
         BOTH ASSIGNED to ANT2

    When this setting is made, saved as a Profile, and the 6700 is shut down, the rig WILL NOT come back up this way. Instead, Panadapter #3 comes up this way -

    3 6m Operation, Slice D-Rx, Slice D-Tx
         Slice D-Rx --> ANT1
         Slice D-Tx --->ANT2

    I presented this problem to Dudley before Christmas, and even made a movie of this glitch. 

    Re-visit the dynamic logic allocation of the SCU and look for timing issues related to startup.

    Please make some progress on this. 

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