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#sbitx_v2 #modulation #sbitx_v2 #modulation

 

Hi.

I testet TX today for the first time on my #sbitx_v2 and I can't get a decent modulation on USB/LSB on any band. I tried all kinds of combination of mic / comp settings and the modulated signal is always very weak, distorted and crushed. It sounds like a bit crusher effect and is not usable. With mic settings above 50 I get some kind of digital background noise feedback.

Has anyone else experienced this kind of behaviour and has a solution for it??
 

try listening to the 2-tone and verify that it sounds correct.? ?That would allow you to diagnose it has having something to do with the microphone end alone.? ?Possible RF getting into the mic?? ?Above a certain value, there is distortion in the mic gain;? ?I run mine at 30 max, I think.? ??
I lost the original mic and had to make my own.? ? The audio on my DE version has been excellent, and I think it is the same on the V2.? ??
However, I had to use a mic cartridge with -24 dB SPL type response!

Let us know what? you find!

Gordon KX4Z


On Mon, Oct 16, 2023 at 8:25?AM Stefan Beck via <puncher_gallops0x=[email protected]> wrote:
Hi.

I testet TX today for the first time on my #sbitx_v2 and I can't get a decent modulation on USB/LSB on any band. I tried all kinds of combination of mic / comp settings and the modulated signal is always very weak, distorted and crushed. It sounds like a bit crusher effect and is not usable. With mic settings above 50 I get some kind of digital background noise feedback.

Has anyone else experienced this kind of behaviour and has a solution for it??

 

I had some distortion when I got mine.??I put a couple of torrids on the mic cable and it went away.??RF must have been getting in through the cable
On Oct 16, 2023, 9:01 AM -0400, Gordon Gibby <docvacuumtubes@...>, wrote:

try listening to the 2-tone and verify that it sounds correct.? ?That would allow you to diagnose it has having something to do with the microphone end alone.? ?Possible RF getting into the mic?? ?Above a certain value, there is distortion in the mic gain;? ?I run mine at 30 max, I think.? ??
I lost the original mic and had to make my own.? ? The audio on my DE version has been excellent, and I think it is the same on the V2.? ??
However, I had to use a mic cartridge with -24 dB SPL type response!

Let us know what? you find!

Gordon KX4Z


On Mon, Oct 16, 2023 at 8:25?AM Stefan Beck via <puncher_gallops0x=[email protected]> wrote:
Hi.

I testet TX today for the first time on my #sbitx_v2 and I can't get a decent modulation on USB/LSB on any band. I tried all kinds of combination of mic / comp settings and the modulated signal is always very weak, distorted and crushed. It sounds like a bit crusher effect and is not usable. With mic settings above 50 I get some kind of digital background noise feedback.

Has anyone else experienced this kind of behaviour and has a solution for it??

 

On Mon, Oct 16, 2023 at 03:01 PM, Gordon Gibby wrote:
try listening to the 2-tone and verify that it sounds correct.? ?That would allow you to diagnose it has having something to do with the microphone end alone.? ?Possible RF getting into the mic?? ?Above a certain value, there is distortion in the mic gain;? ?I run mine at 30 max, I think
Hi Gordon, what is a good spot to pick up the modulation signal on the board with a scope. Even the 2-tone modulation seems distorted at R56 / Q6
 

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RF may be getting into your scope probe

I would try to listen at low RF power, with another receiver or with a nearby web SDR?

I don’t have the schematic right in front of me but when I do I’ll try to get back to you.?
Gordon



On Oct 18, 2023, at 05:00, Stefan Beck via groups.io <puncher_gallops0x@...> wrote:

?On Mon, Oct 16, 2023 at 03:01 PM, Gordon Gibby wrote:
try listening to the 2-tone and verify that it sounds correct.? ?That would allow you to diagnose it has having something to do with the microphone end alone.? ?Possible RF getting into the mic?? ?Above a certain value, there is distortion in the mic gain;? ?I run mine at 30 max, I think
Hi Gordon, what is a good spot to pick up the modulation signal on the board with a scope. Even the 2-tone modulation seems distorted at R56 / Q6
 

Ok. So after a lot of reading it seems that the best way to check my modulation on a HF signal is to build a RF Tap / Sampler device first and use its output with a scope. Then I should see if my 2Tone signal is ok. It's a rabbit hole. :-)
 

Stefan,

I would use a spectrum analyzer like the TinySA Ultra with the appropriate attenuators.? You need a minimum RBW of 200Hz to see the distinctions in the tones.

An alternative would be to use a PC audio spectrum analyzer sourced from the R56/Q6 junction.? Here, you should see two clear tones around 12kHz.? Most PC-based audio analyzers should be able to go up to 24kHz.? You will need to build a probe to isolate the DC components.? A 1uF or greater capacitor should work.

73
Evan
AC9TU

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