Transmission outside transmission bandwidth into the other sideband

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WM4CH
Posts: 59
Joined: Wed Nov 09, 2022 1:20 pm
Location: Cape Cod, MA

Transmission outside transmission bandwidth into the other sideband

Postby WM4CH » Thu Jun 08, 2023 4:53 pm

Has anybody seen this or know what the issue could be?

My radio 7000DLE MKII is transmitting outside the SSB transmission bandwidth ABOVE the selected frequency.

You will see on the pics that the selected freq is 3.940 LSB and I am transmitting out to 3.942 into the USB spectrum.

It shows up on my display and it shows up on the receiving transceiver on another radio far away, so it isn't an artifact of he display, it is amplified by the amplifier even when using pure signal.

This happens all bands. Even with 0 watts power output.

It happens LSB and USB. All transmit profiles. Noise gate on or off.

Is this a software issue / setting or is this a hardware issue?

Is this normal?

My son's 100D does not do this.

Any help is appreciated.

While talking. 50 hz low cutoff transmit profile. Notice how the signal above 3.940 in the USB looks to be an exact mirror image of the first 200 hz below the transmit freq in the LSB

2AF2523E-6685-4178-9320-CD4B03519863.jpeg
2AF2523E-6685-4178-9320-CD4B03519863.jpeg (4.81 MiB) Viewed 2268 times


The white area is the transmit filter

While not talking with downward expander being used as a noise gate. Notice how the spike on either side of the transmit freq is exactly the same offset from the transmit freq.

39980248-246B-42FF-8ECF-25C4B8A2773B.jpeg
39980248-246B-42FF-8ECF-25C4B8A2773B.jpeg (5.28 MiB) Viewed 2268 times




This is the transmit filter low cutoff at 300 hz and you can see it is still signal 300 hz outside the filter cutoff

E9C5BF0C-EC97-4BD8-A888-765C22EA6F68.jpeg
E9C5BF0C-EC97-4BD8-A888-765C22EA6F68.jpeg (5.05 MiB) Viewed 2268 times
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K1LSB
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Joined: Wed Feb 05, 2020 5:25 pm

Re: Transmission outside transmission bandwidth

Postby K1LSB » Thu Jun 08, 2023 5:27 pm

I have seen that condition on a few transmissions by Anans in the past, I just always assumed (possibly incorrectly) that it was a result of the operator not knowing how to properly tailor his transmit audio, such that he's overdriving some feature of Thetis' audio processing chain (maybe AGC, or something in the CFC settings, I don't use any of that stuff so I don't know how to adjust it).

I've also observed that if I set a very low value in DSP>Options>TX Filter Size, my transmitted SSB audio will spill over a bit into the opposite side of the TX zero-beat frequency, similar to what your screenshot shows. So I set my TX Filter Size to a rather large value to make sure that doesn't happen:

DSP Options.jpg
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Mark
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WM4CH
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Location: Cape Cod, MA

Re: Transmission outside transmission bandwidth into the other sideband

Postby WM4CH » Thu Jun 08, 2023 5:36 pm

That did it Mark. That made a big difference. It is the SSB Filter size. Mine was 1024. I made it 4096 and it looks much better with a steep rolloff below the low transmit filter hertz

I have been looking for some type of setting to change the transmit filter db roll off and could not find anything. Changing the filter size made a huge difference.


Thank you, so glad it isn't a hardware issue.

I guess this should be moved to the Thetis section.

The hardest part of this radio is guessing which section a post belongs in :)

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