RF Gain and diminished receiver sensitivity when on 6 meters

  • 1
  • Question
  • Updated 2 years ago
  • Answered
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 screwed up.

Anyone else experiencing this?

Norm - W7CK



Photo of Norm - W7CK

Norm - W7CK

  • 745 Posts
  • 151 Reply Likes

Posted 2 years ago

  • 1
Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

  • 8498 Posts
  • 3181 Reply Likes
Official Response
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.