6400 Side transmissions, Is this Normal?

Dan Trainor

Hello All,  On 6400... While tuning up today, I noticed something on the panadapter that I didn't notice in previous days. RF Energy transmitted about 55 KHz to each side of center VFO frequency. See attached picture. This happens on 40, 20 and 15 meter bands. Is this normal? Would this be something like 3rd harmonic IMD?  If that is it, are these levels too high?  Seems like it. I also see these spurs (if that is correct name) on my SDRPlay receiver when monitoring my transmissions on Flex. Thanks in advance - dan

Rob N4GA

IMD is typically in-band unless it's ridiculous bad. In-band would be inside your light colored vertical rectangle in the center.

3rd harmonic would be 21.280 x 3 away, so it's not that.

I too would be interested in what these are as I have seen them before too.

N4GA

Bill -VA3WTB

Dan, when you transmit or tune, the panadapter does not represent your actual transmit pattern.
So yes this is normal.
If you really want to see your transmit you can turn on FDX and open another slice on the same freq. Set that slice to receive XVTR, so transmit on slice A and receive XVTR on slice B. 100w should give you an S9 on the receive slice.

Ken has a great video on setting this up and demenstrating it.
https://youtu.be/CzT1qDKKySk

Dan Trainor

Hi Rob,  Thanks. I hope I did not confuse with term IMD or harmonic.  I am actually not sure what the appropriate term should be.  But, regardless I do see this RF energy on Flex panadapter and also on a separate SDR receiver.  dan

Bill -VA3WTB

Make sure the second SDR receiver is not receiving better than an S9.

Dan Trainor

Hi Bill,  Thanks for this information.  I watch the video and try this FDX method on monitoring.  I did monitor my signal on a completely separate SDR receiver which also has a panadapter and I saw the same thing.  This spurious energy on each side of center. Trying to understand what it is and why it is normal or not.  Thanks, dan

Bill -VA3WTB

On the seperate receiver what signal is it receiving, Aim for an S9 nothing more.
You radio should be really clean.

Dan Trainor

Hi Bill, OK I ran the test again with the SDRPlay/SDRUno SDR RX and it is receiving my Flex 6400 10 W transmission at S3 level as antenna input is grounded by a T/R switch.  I read on SDRUno panadapter the received carrier level at -86 dBm and these spurious side transmissions lower down at -128 dBm.  So 42 dBm down. dan

Dan Trainor

Hi Bill, it is receiving my Flex Radio 6400 10 W carrier signal and also these "spurious" side transmissions which are -42 dBm down from the carrier peak which is at S3 level. See post above.  Any thoughts?

Bill -VA3WTB

Our Flexes should get to -40db down, mine does.
What you should do is increase you output till your SDR play reads an S9. You should still look clean at S9, after you go over S9 things will start to show.

Dan Trainor

Hi Bill, Sorry what should get to -40 dBm down?  I don't understand.  What do you mean by "clean"?  OK, I boosted power up to 100W on Flex, but can only get an S6 level on separate receiver (as ant input grounded).  The received carrier is now increased to a measurement of -78 dBm and these spurious side transmissions increased to a measurement of  -118 dBm.  40 dBm down.  dan

Bill -VA3WTB

Ok that's fine, The radio can show an IMD of -40 DB down at full power. If you look at the horizontal lines on the screen on the receiver you count them from the very peak of the signal to the bottom to were the signal begines to spread out, that is your IMD.

So it could be set up at 5   so 5 10 15 20 25 30 35 40  or 10  10 20 30 40  

do you follow?

Dan Trainor

Hi Bill,  I understand what you are saying, BUT we may be talking about 2 different things.  The spurious energy I am referring to is 56 KCs away from carrier. See picture above.  What would you call this RF by-product?   thanks for help, dan

Bill -VA3WTB

I saw the picture Dan, you should not see that same thing on another receiver or with the FDX test feature we have. If your putting out 100w from your radio and the receiver is at S6, your signal should look clean as I think you said it does.

Remember, when you transmit, the Flex panadapter does not reflect your output signal. So you can't use that to determine if your clean.

If someone can hear you at an S9 signal and they are on a Flex, ask them how you look to them.

Ross Lambert

I see the same on my 6400

Bill -VA3WTB

You should see the same thing, or close. What we see on our panadapters is a bit of an education to understand what we are seeing. And this carries over to seeing other people's signals as well. One time I told a guy his radio was dirty on transmit, but I did not consider his signal was 20 over 9. Next day his signal was S9 and clean, lesson learned.

Dan Trainor

OK, thank you.  BTW, I am using a separate independent receiver to measure these artifacts.  I take a screen shot later. dan

Dan Trainor

My signal is "clean" if definition of clean is the RF modulation inside (or in vincity of) TX BW slice and is the focus.  But that is NOT what I am referring to at all.  I am taking about something entirely different. What I am noticing and measuring independent of Flex panadapter display is spurious RF energy transmission 56 KC to each side of carrier.  And, I still don't know what it is yet or if it is an issue. We may be taking Apples Oranges here, I suspect.  dan 

Dan Trainor

Hi Ross, what do you see?  And what do you call this?  Can you take a screen shot?  Thanks, dan

Bill -VA3WTB

Dan any time I talk about this, it is alway about outside the band pass, on 40M, any RF on the upper side band for example.

Unless you are over driving something or something is very wrong inside your radio, (brocken) your signal should look clean.

It sounds to me that SDR Play is not displaying your signal correctly. Do you see the same thing when using the FDX signal test? And try this on 40M.

AS I said, check with other staions if your signal is at least S9. What do they see?

Dan Trainor

Dan Trainor

Dan Trainor

Flex Radio Panadapter on TX 10 Watts.

Bill -VA3WTB

It looks ok.

Dan Trainor

Receiving same exact transmission (above) at same exact time using separate independent SDR receiver. We see the same artifacts on each side of center frequency.  What are they called technically?  And is it an issue? If it is an issue, to what degree?  Thanks for any insight or definition - dan

Jay Nation

Dan
It's just your radios TX being heard by the radios RX. Really just a display anomaly, more than anything else. Looks normal to me. 

     SDRgadgets

#FlexRadio IRC Chat

   73, Jay - NO5J

Dan Trainor

SDRPlay is OK and displaying signal with side artifacts as expected.   And I have also re-tested on other receivers including 7300 with same measurement results. Exactly. Next I will do the FDX signal test and I expect no change.  And a test with a Web SDR receiver close by.  But, I trust what I am seeing on the receivers here at my location.

Dan Trainor

Hi Jay, can explain further what a display anomaly is or how that works?  Are my receivers not truly receiving what is shown on their panadapters?  And this is display anomaly that just so happens to directly correspond to the transmitted signal in both freq and time?  I must be missing something....  Thanks, dan 

Bill -VA3WTB

Dan here is an example.

The top picture shows my audio signal as I talk,,you see it is way outside my pass band.
The as I said this does not represent my Tx signal.

Picture2 shows my top Panadapter on TX,,,the bottom is the 2nd panadapter on receive using FDX and XVTR port to see my transmit...it is clean looking transmitting 100w.

Bill -VA3WTB

I think the SDR Play is over loading.

Hear are some explanations From Flex on this subject.

 Steve - N5AC, VP Engineering / CTO

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Official Response





When the PA is on, the receiver can see the transmitter signal and can display it on the panadapter. The coupling between the transmitter and receiver varies by frequency and antenna selection. In some situations, the receiver will be slightly overloaded by the transmitter signal and so you may see the results of this in what would look like IMD in the pan adapter. Because of this, you should only use the display as a rough, relative idea for the on air signal, but should not be used to measure transmitter spectral purity. You can use two FLEX-6000s with a substantial pad to measure signal purity. 



During design of SmartSDR and the FLEX-6000, suppressing the panadapter or providing the exciter signal instead of the receiver were discussed, but each of these options had clear disadvantages we felt outweighed the minor overload artifacts that may appear.

Dan Trainor

Hello Bill,  thanks for taking the time out to run this test and show the results.  I understand what you are saying.  And it also confirms without a doubt that we are definitively talking about two completely different things.  I will attempt to explain the difference as I find the right words.  It goes something like this...The RF spurs I am seeing are NO WHERE NEAR the bandpass or have anything to do with the display in the passband or in the vicinity of the passband.  You are taking about an Apple and I and investigating an Orange.  I will try a another way of explaining my symptom which involves artifacts 50-100 KC away from and removed from the center frequencyy passband. Hope at least that is clear.  Thanks for you post again,  dan