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Re: #sBitx Sample Rate #sBitx

 

great work, gang and great explanations, thanks!
Gordon KX4Z



On Wed, Oct 25, 2023 at 8:30?AM Mark Erbaugh <mark.election@...> wrote:
My solution was to put the change to the LO in both places where the mode was set. On my todo list is a re-write consolidating the radio commands into a single place where changes like this could be made.

I have a public GitHub repository at?. It was originally forked from Ashar's original code, but I've made lots of changes and I'm not intending to merge them back into the code.? I've removed the web interface as I prefer to operate the classic display. It's not well commented. I haven't commented most of my changes and I've left some of Ashar's comments in where I've changed the code to where they no longer apply. IOW, beware - use at your own risk. The latest code I pushed to it does run, but the spectrum and waterfall haven't been updated for my change to the LO.

I basically use the GH repository as an online backup of my local code, but anyone is welcome to look at it and use it if they find it useful.

--
73,
Mark, N8ME

Re: #sBitx Sample Rate #sBitx

 

My solution was to put the change to the LO in both places where the mode was set. On my todo list is a re-write consolidating the radio commands into a single place where changes like this could be made.

I have a public GitHub repository at?. It was originally forked from Ashar's original code, but I've made lots of changes and I'm not intending to merge them back into the code.? I've removed the web interface as I prefer to operate the classic display. It's not well commented. I haven't commented most of my changes and I've left some of Ashar's comments in where I've changed the code to where they no longer apply. IOW, beware - use at your own risk. The latest code I pushed to it does run, but the spectrum and waterfall haven't been updated for my change to the LO.

I basically use the GH repository as an online backup of my local code, but anyone is welcome to look at it and use it if they find it useful.

--
73,
Mark, N8ME
Re: #sbitx #speaker #sBitx #speaker

 

Ok. Never mind. I just brought a few plugs and the one that fits is a PSK 254. Just in case somebody else is searching for this.
Re: #sBitx Sample Rate #sBitx

 

On Wed, Oct 25, 2023 at 02:52 AM, Mark Erbaugh wrote:
One thing: I was looking for a single place in the code to detect mode change, but could not find one. The mode appears to be changed in both set_mode (sbitx_gtx.c) and sdr_request (sbitx.c), so currently I'm changing the LO in both places.
That's what I am looking for too. Did you come up with a solution for this? And are your code changes public somewhere? Thx
Re: #sBitx Sample Rate #sBitx

 

That explains something I noticed with my code. The audio sounded fuller. That’s due to the filter skirt difference.
--
73,
Mark, N8ME
Re: #sBitx Sample Rate #sBitx

 

Mark,
I just remembered. The 40 mhz crystal filter is sharp on the upper sideband and shallow on the lower sideband.
Using it as an upper sudeband filter will make the opposite sideband kuch shallower. This is the way of all ladde filters, they are also called LSB filters (imagine the filter with inductors in place of the crystals, it becomes a ln LPF).
- f

On Wed, Oct 25, 2023, 6:22 AM Mark Erbaugh <mark.election@...> wrote:
Well, I hacked in the code to change the Local Oscillator (clock 1) between 40,035,000 (current default) for USB modes and 39,987,000 for LSB modes.

Seems to work.? I still need to adjust the spectrum and waterfall.

One thing: I was looking for a single place in the code to detect mode change, but could not find one. The mode appears to be changed in both set_mode (sbitx_gtx.c) and sdr_request (sbitx.c), so currently I'm changing the LO in both places.

--
73,
Mark, N8ME

Re: #sBitx Sample Rate #sBitx

 

Well, I hacked in the code to change the Local Oscillator (clock 1) between 40,035,000 (current default) for USB modes and 39,987,000 for LSB modes.

Seems to work.? I still need to adjust the spectrum and waterfall.

One thing: I was looking for a single place in the code to detect mode change, but could not find one. The mode appears to be changed in both set_mode (sbitx_gtx.c) and sdr_request (sbitx.c), so currently I'm changing the LO in both places.

--
73,
Mark, N8ME
Re: #sBitx Sample Rate #sBitx

 

Ah, Harry Nyquist ... I remember as an engineering student at North Dakota State University learning that Nyquist was a graduate of the University of North Dakota just up the road in Grand Forks. Made me proud!

I just discovered this on his wiki page ... "Bell Labs patent lawyers wanted to know why some people were so much more productive (in terms of patents) than others. After crunching a lot of data, they found that the only thing the productive employees had in common (other than having made it through the Bell Labs hiring process) was that "Workers with the most patents often shared lunch or breakfast with a Bell Labs electrical engineer named Harry Nyquist. It wasn't the case that Nyquist gave them specific ideas. Rather, as one scientist recalled, 'he drew people out, got them thinking'"

--
Mike - kb2ml
Re: #sBitx Sample Rate #sBitx

 

I am thinking of doing it. I hadn't seen the comment in the code. I just thought I'd ask if there was some compelling reason not to try. Why spend a lot of time on something that you had already figured out wouldn't work.

I've replaced the initial DFT on the receive signal from the original complex to complex one with the real to complex one in FFTW3. That one doesn't generate the bins above half way (Nyquist frequency) so I've had to adjust the code. I've already fixed the agc calculation and the spectrum / waterfall display to use only the lower bins, but I still had to write code to invert the sideband.

--
73,
Mark, N8ME
Re: #sBitx Sample Rate #sBitx

 

I commented about this in the source code too, it can be done. I didn't do it. You want to give it a shot?
- f

On Tue, Oct 24, 2023, 5:55 PM Mark Erbaugh <mark.election@...> wrote:
Ashar,

Thanks for the reply. I think I'm finally starting to understand this.

Related to this, I see that the sideband inversion for LSB is done in the DSP software. Was any consideration given to doing sideband inversion moving the 2nd mixer above the first IF like was done in the uBitx? That would invert the spectrum, but the sBitx is already inverting the spectrum twice by using the top half of the DFT output then plotting from high to low.
--
73,
Mark, N8ME

Re: #sBitx Sample Rate #sBitx

 

Ashar,

Thanks for the reply. I think I'm finally starting to understand this.

Related to this, I see that the sideband inversion for LSB is done in the DSP software. Was any consideration given to doing sideband inversion moving the 2nd mixer above the first IF like was done in the uBitx? That would invert the spectrum, but the sBitx is already inverting the spectrum twice by using the top half of the DFT output then plotting from high to low.
--
73,
Mark, N8ME
Sbitx V2 #108 for sale

Hank Beisheim
 

I have the Sbitx V2 #108 for sale. Purchased at Hamvention. $325 w/o a Pi, $375 with the Pi installed. Plus split shipping. Also comes with 3D printed legs/stand and the HDMI plate?
that allows easy access to the HDMI port. Includes original SD card that may or not be corrupted (Sbitx files are intact) and a 2nd working SD card.

Hank W6IR
Re: New board is dead!

Hank Beisheim
 

Carl,
That's because it boots into the RasPi OS. It has the sbitx info in the 2nd partition which is not readable by Windows.
Put it in the Pi and boot up the radio.

Hank W6IR
Re: New board is dead!

 

I finally got a new RPI installed and installed the RPI iOS. The link that HF signals gave me for the sbitx_iimage.rar extracts to be identical to the rpi iOS
can you provide me a link to a valid SBITX image file
tools I am using Belina etcher on a Mac air book running the latest version of Sonoma.?
Re: #sBitx Sample Rate #sBitx

 

Mark,
The bandwidth is limited by our crystal filter. I couldn't make it wider than 25 KHz. If, instead, we had used phasing method, we could have achieved a full 96 KHz spectrum display. I discarded the phasing method for two reasons:
1. Performance: The phasing method critically depends upon keeping both channels flat with their phase and amplitude response throughout the 96 KHz pass-band. It becomes impossble to achieve more than 55 dB of suppression (the Elecraft KX3 promises just that). This means if you have a 599+20 dB CW signal 1 KHz away on CW, it will drown out the 559 signal you are trying to copy as the image will overlap.
2. Ease of Homebrewing: Many of us already ar comfortable with superhets. The sbitx architexture adds SDR backend to those radios.
If scan the commercial offerings, phasing radios are no longer being offered by anyone with the exception of KX2 and KX3.?
This said, apart from a few lines of code in rx_process and tx_process, there is very little to prevent the code from being adapted to a phasing radio.?
- f

On Tue, Oct 24, 2023, 3:35 AM Mark Erbaugh <mark.election@...> wrote:
The sample rate appears to be 96 kHz, but the bandwidth is only 24 kHz. Shouldn't it be 48 kHz, half the sampling rate? Is this due to the overlap-discard processing?
--
73,
Mark, N8ME

#sBitx Sample Rate #sBitx

 

The sample rate appears to be 96 kHz, but the bandwidth is only 24 kHz. Shouldn't it be 48 kHz, half the sampling rate? Is this due to the overlap-discard processing?
--
73,
Mark, N8ME
Re: sBitx V2 SN #141 Spurious/Harmonic Measurements

 

Impressive that the harmonics are NOT a problem.? ?I don't remember ever being much worried by them on my DE, either.
I've seen those low low frequency spurious signals a lot.? ? I think changing the si5351 drive to 2mA thoughout and adding in a tiny bit more bypassing capacitors got rid of most of them.? ?Also increasing the idling current.? ?See article beginning page 9:? ?? ? Increasing the magnification of the page allows the screen shots to be read more easily.? ?I think there may be products in those photos that actually come from mixing in the Heathkit cantenna diode.... but I still got them way way lower...and you can see basically zero 2nd harmonic of the 14MHz signal in the last photo.? ?That was the DE, using RELAYS.? ? If I re-measure it, it may be even cleaner than I knew.? ?

I need to go back and re-measure my DE now that I've removed the unnecessary diode from the Heathkit Cantenna; or else use a "flat" high power pad.? ? My "allowance" (I'm retired, hooray!) will allow me this week to order a higher power version.? ?That makes it a lot easier to do these measurements, because no corrections needed.? ?The one I have already is only good to about 15 watts and I was pushing it pretty hard.? ??

I think this is a ground breaking radio and I'm hoping we can cure any difficulties so that it achieves what it desrves.? ??
You might try increasing your idling current if nothing else fixes those low frequency spurs.

Thanks for publishing those, it helps.
Gordon KX4Z
Re: sBitx V2 SN #141 Spurious/Harmonic Measurements

 

Gordon,

Here are two spectra for 80 and 10 meters.? 10 seems to be the worst, with both lower-than-set frequency spurs and a higher 3rd harmonic:


Based on the latest measurement, I may have a possible issue with some mixing products unrelated to the LPF.??

73
Evan
AC9TU
Improving Dial Scale Linearity on a 15-10 meter BITX rig

 

Kind of old-school.? No rotary encoders or si5351s here.? Just L and C for the VFO.?



73? Bill N2CQR
Re: Baofeng Microphone for uBITX #microphone

 

I would like to get a project enclosure and have a cable out the back for the microphone cable on the radio. Have 2 jacks, one for the electrict microphone and the other for PTT. It would be nice to have a amplifier and such but I don't know anything about making something like that.??
--
'72
Aaron?
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