SDG1032X modded to 62X sine wave sounds "watery"

[wdbarker3]

I have a recent (1.01.01.33R1B6) SDG1032X. I applied the SDG1000X_30R1_eevblog and removed my bandwidth_update_license. I then reapplied 1.01.01.33R1B6 successfully.

The device now thinks it is an SDB1062X. I'm wondering if there are also hardware differences in addition to the firmware that make it work. The reason is that a 50MHz sine wave sounds watery (whatever that means) on my radio.

Has anyone else noticed this?
Does anyone have a factory 62X to try it on?
I'd love to see if it is just a limitation of the base device. If so, I'm glad I didn't spend the extra bucks to go for the 62X!

If you, like me, are wondering what "watery" sounds like, I imagine I could post some audio clips, but that would be very subjective (and I don't know how to do it anyhow).

Reference 14MHz signal, Elecraft K3S, P3 Panadapter (spectrum analyzer for the non-radio-amateurs): .

"Watery" sounding 50MHz signal: .

PS: The modifications still work, but I do not know if the result is as good as the "real thing".

[Grandchuck]

Perhaps some frequency instability?  Just guessing about watery sound!  Sidebands indicate modulation.

[Hexley]

Here is a modified SDG 1032X sourcing 50 MHz at 5 Vpp into 50 ohms. This FFT has a 50 MHz center and a +/- 1 MHz span, so it matches your Elecraft setup.

Looks OK at large span like this.

But when I listened to the signal with an FT-857 tuned to 50 MHz, I also heard a bit of a quaver.

[Update]
And some more data. I took FFT spectra of the audio output from the FT-857, comparing the signal from the Siglent to that of an HP8647A signal generator. The latter appears cleaner.

[wdbarker3]

Interesting results. Thanks for looking.

I guess I'd better look at my FFT too. Never thought of it. The Tek 465 I've used until a few months ago didn't do that<g>. My 1104X-E is modded to 1204X-E specs, so it should do that effortlessly.

But, the real question, is does the factory 62X have these same outputs?

[wdbarker3]

Well, this is embarrassing. I had ordered some 50 ohm terminations, but they hadn't arrived when the above photos were taken. Instead, I'd used a BNC-cliplead connection to a 51 ohm resistor.

I'm guessing there might have been a few impedance discontinuities (you think?) causing a lot of ringing that showed up as those sidebands. Can't really blame the Siglent for me being stuck in HF while playing in the VHF world!



Yesterdays image came from the set-up on the right. Today's from the one on the left.



We can ignore the two artifacts down over 30db, but the "watery" sound is still there. It's like the frequency is hunting over 5 or 10 Hz instead of staying on 50,006.000 kilocycles. I moved up 6k to get off of a spur from somewhere in the neighborhood. It was present with the SDG powered off.

Of course, we don't usually listen to these sorts of signals, and 10 Hz out of 50 Million is 0.2 ppm. Maybe that's expected.

Anyhow, my ugly and misleading plots aside, does the factory 62X do this too? This is not an issue with my setup, though. Hexley heard it too (assuming the equivalence of quaver and watery).

[DaJMasta]

I don't know what you mean by watery, but since it's in the audio band, can you make that waterfall plot of the demodulated audio?  If you can find out what's happening in the frequency domain of the  demodulated signal, you may be able to determine what's happening before it's demodulated.  Since it's something you can year, it's probably some low frequency mixing product that's coming through, so capturing specifically the low frequency of the output tone could be useful too (if it's some audio band noise bleeding through), otherwise it could be an interaction with the harmonics with the demodulation or even some kind of desynchronization between timebases depending on your configuration.

[Hexley]

Here is a more detailed FFT of the audio output from the 50 MHz receiver. The phase noise from the Siglent AWG is quite apparent. Not unusual for a DDS signal source, I suppose.

The signal from the HP8647A Signal Generator looks better, even though this generator is not known for low phase noise.

[tubularnut]

 It's like the frequency is hunting over 5 or 10 Hz instead of staying on 50,006.000 kilocycles.

Is this the 10Hz you are looking for? Though it is 56dB down on carrier.

Factory original SDG 1062X



Excuse me if I have any measurements incorrect, as I am still getting use to spectrum analyser. Please correct my mistakes if needed.

[wdbarker3]

Well, the link below includes audio, so you can hear for yourself what I hear. I have no idea if this is normal behavior - I've had signal generators before, but never "listened" to anything over 10KHz.

At 00:04, in the recording, I go to a "clean" signal. You hear a different tone and see the FFT (only 50Hz wide around 500 Hz audio output) be quite stable. At 00:11, I go back to the Siglent.

This is most likely completely normal, but it just sounded funny (har har har).



Those horizontal divisions are 5 Hz wide, and it's jumping several of them. Far less than a ppm, but a surprise none-the-less.

Alass, I don't have a spectrum analyzer, so what my P3 and 1104X-E (with 200MHz key) and my ears say is all I know.