RX A and bypass of ATU

Chuck - KJ6HT

I received a Pixel Antenna for Christmas and so far it is performing very well. I live in an suburban environment and I am able to null out some very nasty noise. It is attached to my 6500 on RX-A. I am very new to using the RX-A input so this may be normal operation. I have noticed that there are times, it seems to depend on frequency, when I bypass the ATU the noise level on my RX-A drops dramatically. I have observed drops of over -10 dBm in the noise floor according to the mouse-over of the signal strength meter. Why would the ATU have any affect on RX-A? I could understand if I was using ANT1 or ANT2 for receive but RX-A should never be in the circuit for the ATU. This is not a 1.6.17 issue, I observed it on 1.5.1 before I upgraded. Any thoughts?

Ken - NM9P

1) Watch your preamp indicator when you do it and check if there is any change. There may be something glitchy happening there. 2). How close is your pixel loop to you other antenna? Could the tuning of the transmit antenna be detuning your loop or interacting with it in some way. Just a couple stabs in the dark. Ken - NM9P

Chuck - KJ6HT

Hi Ken,

Thanks for the reply. I just double checked, the indicated state of the preamp does not change. I can observe the noise floor drop just by bypassing the ATU, no tuning needs to take place.

Again, thanks for the suggestions.

Chuck - KJ6HT

https://www.youtube.com/watch?v=llfK7yAcMLg
Made a video of the issue. I mouse over the signal level so you can see that it is at -86.9 or so. I then select the ATU button to bypass the ATU. You can see the change in the noise level, I mouse back over the signal level and it indicates -96. That is almost a 10 dB change. This indicates to me that the RX-A input is in circuit with the ATU.

Ken - NM9P

I notice that when you turn the atu off, that the noise level drops, but that three or four signals stay the same and now come up out of the noise. This looks more like there is a noise source being generated when the atu is turned on. It would be easier to tell if there was sound with the video. Do you get this on other bands? If so, is the noise shift the same? It could be a hardware issue either inside or outside the rig. I would recommend opening a help desk ticket and see if they can help you sort it out. Ken - NM9P

Ken - NM9P

Another question.... If you have your safety switches installed on the pixel, Is there any change on the switching voltage going to it as you turn atu off and on? Do you have ferrite beads on the power and safety relay leads?

WA2SQQ

Just a thought, could the antenna tuner be acting as some sort of preselector, similar to the "antenna trimmer" control on legacy receivers? I have a Pixel loop and I'm going to try this tonight.

Chuck - KJ6HT

Hi Ken,

Those signals you see come up out of the noise floor are valid JT-65 / JT-9 signals, that is what troubles me about this issue. It truly affects what stations can be heard or copied. I checked the switching voltage, no change. I do not have any ferrites on the power lead or the switching signal. On the video I am bypassing the ATU not activating it, so I doubt if it is RF getting into something. Thanks again for your reply

Hi Robert,

I would appreciate your findings from your pixel. it appears to me that the ATU is in the RF path for RX-A, I'm not sure why that would be from a design stand point. I am going to test with another antenna on the RX-A port. I think it will occur regardless of antenna type on the RX-A port.

Tim - W4TME

It does act as a preselector.  It is in both the RX and TX signal path.

Tim - W4TME

The ATU does act as a preselector.  It is in both the RX and TX signal path.

Chuck - KJ6HT

Hi Tim,

Thanks for the reply. As you can see the affect of the ATU (preselector) on RX-A is pretty dramatic. Any possibilities of removing it from the RX-A path on future loads? Seems like it would be possible since you can affectively remove it by going into bypass. Maybe a future option setting - "Automatic Bypass on Receive"

Bob N7ZO

According to the signal flow diagrams in section 12 (page 40) of the current hardware manual, the ATU cannot be in the RX-A path.  Is the manual wrong?

I know this discussion was for the 6500, but certainly with the 6700, a single ATU cannot be in both RX-A and RX-B paths.  I would not expect the 6500 signal path to be that different.

73, Bob, N7ZO

Chuck - KJ6HT

Bob,

You make an excellent point. According to the signal flow diagram, the ATU should be out of the picture when RX-A is selected for receive. This is how I thought it worked.

WA2SQQ

I just got home and tried it. I am unable to duplicate this problem. I'm running a 6500, Pixel Loop and 1.6.17
Perhaps a factory reset is in order. Something else to consider. Like all of us, you imported your profiles. Have you tweaked and resaved at least one default set of profiles under the new version? I would think that at least the GLOBAL profile might handle some features slightly different.

Chuck - KJ6HT

Thanks Robert, I have tried a factory reset, no change. I think at this point I will open a help desk ticket.

W9OY

I have a Wellbrook loop on RX-A in my 6500 and notice no difference in S meter reading whether tuned or bypass

73  W9OY

Tim - W4TME

It is in the signal path if the RX antenna is the same as the TX.  For RX-A/RX-B is is not.

Tim - W4TME

A 10 dB drop is way more than the insertion loss for the ATU, but since you are using RX-A, the ATU is not in the signal path on RX.  It is only in the signal path when the RX antenna is one of the ANT-x antennas.  I misread your statement above.  Sorry about that.  

Opening a HD ticket is the right course of action at this point so we can figure out what is happening.

W9OY

Try a different ant on RX-A to confirm if its the radio or the antenna

73  W9OY

Chuck - KJ6HT

Lee,

Thanks for your reply. Just tried a different antenna and I still see the issue. It does not appear to be as pronounced but the substitute antenna is not as quiet as the Pixel. I have opened a help desk ticket and received a reply from Dudley, I am confident He will get it sorted out. I will report back the findings.