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6400 Side transmissions, Is this Normal?
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


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Answers
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
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
You radio should be really clean.
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.
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?
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.
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?
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
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.
Hear are some explanations From Flex on this subject.
Steve - N5AC, VP Engineering / CTO
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.