Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
What interesting to me...? is I've been following this.
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This is a rerun of the same issue for uBitx V3 series, Sbitx, and
appears here now.
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General issue is pushing transistors for more gain (not power)
than reasonable. and the basic lack of band pass filtering.? ?
that results in as long as everything is linear,? the world is good,
run out of gain and start pushing to get power and it turns
sour with spurs.
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Most of the "fixes" need to be checked? for spurs on all bands
especially those above 20M.
?
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
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Re: First Satellite Downlink Reception over sBitx (for me at least)
Gordon, Sounds like great progress. Sadly I got rid of my transverters a couple years back when I bought a IC-9700, so I haven¡¯t tried using my SbitX for satellite work. I did experiment with using the SbitX just as a Raspberry Pi ¡°laptop¡±, running GPredict and Hamlib for Doppler control of the 9700, which works ok, but would benefit from a larger screen.
I did find that it worked quite well to access it via VNC from my iPad to see the whole screen. So I moved to a stand-alone headless RPi 4 for that project. I¡¯m trying to keep everything small and light so I can go portable.
Yep, having a spectrum display on the downlink makes things so much easier! That¡¯s the only way to go.
Regarding your signal through the satellite - how well is your uplink antenna matched? At 435 MHz you¡¯re already giving up nearly 3dB with 100 feet of LMR-400 even if it¡¯s perfectly matched. It really doesn¡¯t take much TX power to get a good signal through the bird. You didn¡¯t mention how much power you are using.
Hope to work you ¡°live, via satellite¡± someday!
73 de W0ZF?
On Sat, May 24, 2025 at 10:23?AM Gordon Gibby KX4Z via <docvacuumtubes= [email protected]> wrote:
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Working on learning satellites for a few months now, building most of the gear, instead of buying stuff.
?
TODAY for the first time, I heard my own CW by way of the satellite, monitoring an sBitx (V2) using a Ukranian transverter (neither of which seems to be terribly sensitive).? JO-97, in its pass over the eastern USA around 11AM Eastern time.? ?
?
Main rig was older ICOM820H transmitting on 70cm through a homebrew yagi/homebrew dual axis rotator system controlled by homebrew PCB using K3NG controller, controlled by SAT32PC.? ?With some effort I found my signal on THAT setup with a CAT correction of 5kHz? (I don't know why that is so far off yet)
?
SBITX
SECOND RIG was a sBitx crudely "tee'd" in with simple PL259-Tee, so it got the same signal as the Icom820H.? ?I was unable to provide suitable doppler correction to the sBitx, because Sat32PC doesn't seem to know how to use hamlib; however, I could have done so using Gpredict directly to the radio (which was on 192.168.1.10 in this experiment; the antenna rotator is controlled over wifi using a raspberry pi)
?
The spectrum display on the sBitx was a HUGE help.? ?I could easily see my own CW on the waterfall and therefore tune to my frequency!? ?I would say as a first cut that the sBitx and the 820H were running reasonably about the same as far as receiving.? ?These passes are ONLY 10 minutes long, but on he Sbitx I could SEE other SSB conversations going on (and they seemed to have more power than my signal.....) -- so I could QUICKLY tune to them on the Sbitx and receive them just fine!? ?On the Icom820H (without a spectral display) you have to tune up and down the band.??
?
Signal Levels:? ?I have the antenna system 50 feet out into the driveway.? ?The 70cm transmitter is going through 100 feet of LMR400 to a crossed Yagi homebrew.? ?The 2meter downlink goes first into a diplexer to protect it from 70cm pickup? () and then into an inexpensive GaAs FET preamp Moonraker M-100 Professional ()? turned all the way up, theoretically 20dB gain.? ?At that level, both the 820H and the sBitx/transverter hear considerably more SIGNAL as evidenced by increased background noise.? ?
?
Without the preamp I'm pretty sure the Ukranian transverter and sBitx would hear nothing, and I'm not sure about the 820H -- haven't gotten good records on that.? ?My experience with the used Icom 820H is that I generally do best by keeping that preamp at +20dB.? ?
?
?
WITH the preamp I have heard amazingly good SSB signals -- like full quieting FM quality!? ?The sBitx was showing MY cw maybe 10-15 dB above the noise baseline (IF was set to 84 on the 10 meter band)? ?but my recollection is that the SSB signals were 20-30 dB above noise -- stronger than my CW signal.? ?(So maybe I need more oomph on transmit???)? ?
?
?
This proves that you can use an sBitx as a satellite downlink receiver with transverter and preamp.? ?In fact, it would be a very nice one because of the spectral display!!
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I think it would be easiest to use a second sBitx or other transmitter to do the transmit side, with a second transverter, and possibly an amplifier to get some more power.....I was surprised that my signals looked weak compared to what I heard from SSB stations on the satellite.
?
Photos below
Gordon KX4Z
?
?
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Re: First Satellite Downlink Reception over sBitx (for me at least)
RS-44
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First CW contact on a satellite.
Transmitting via Icom 820H on 2m
Receiving via transverter --> sBitx and simulatneously the Icom 820H
?
Conclusions/Data
1.? For SSB able to hear myself (on the Icom820) seemed to be a fudge of -4100 Hz.? ?Not sure why and not sure if this adds to previous or not.
2.? Ran the cheap Moonraker preamp at +20dB.? ? At that setting, the sBitx/transverter and the Icom820H appeared to have SIMILAR OUTCOMES on their receiver.? ? The baseline on the sBitx (64 bit code) with IF = 90'ish was about S9.? ?On the ICOM it was not discernible.
STRONG signals CW on the sBitx appeared to have a signal to noise ratio of 10-15 dB.? ?Similar for the peaks of SSB signals.? ?On the ICOM820H I saw S3 and maybe S4 or 5 once.? ?Most signals below those
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3.? The sBitx is WAY easier to "find myself" but is not yet connected to doppler corrections.? ??
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4.? I was able to make a CW contact!!!? ?N4AKV (I didn't have a pen so this may be poor memory) -- he appeared to hear me fine and I heard him fine also.? ?
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5.? With a huge amount of effort, I barely managed to hear my SSB signal.? ?I could SEE myself at times on the sBitx and HEAR myself somewhat on the 820H at a fudge cat (SAT32PC software) of -4100 -- but not a good enough signal to be sure.? ?My SSB signal (from the icom820H) just didn't seem to be powerful enough to be heard.? ?The CW signal appears similar to others, maybe 2-3 dB lower but similar on the sBitx.? ? The SSB seems a lot weaker.? ? Will have to work on that!!!? ? ?Spectrum analyzer work will allow me to compare the two and work on them....
?
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The sBitx when added to a cheap dual band transverter (I was on the 70 cm band, with F+ activated, receiving around 29.6 MHz on the sBitx) DOES WORK as a satellite receiver system when used with the Moonraker preamp and a homebrew crossed yagi system!? So it can be used as a receiver on BOTH VU and UV satellites.
?
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Gordon KX4Z
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Re: Accessing zBitX on RealVNC
#zbitx
default login is? pi / hf12345
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It is a RasPi, so use standard RasPi tools to change password
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Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
How accessible is C22? ?Is there a photo showing its location? ?I would like to try to reproduce N3SB's experiment, and replace C22 with a 1000 pF capacitor. ?If that experiment works, the low 2 MHz spur can be attenuated by using an external bandpass or high-pass filter, which might allow one to transmit at FCC compliant levels with the zBitx. ?Thanks. ?73, Ron, N6YUW
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Re: Sbitx high swr on a 1 to 1 antenna
Tim
hHere is a residual remnants?of the Resident Ghost o]f the Original Ghost On the Air in all units of the SBIITX and ZBITX..... The remnants of the ghost does some strange things, normally resolved by replacing the SD Card with another copy of the same -just ensure that you?have multiple copies of the sd cARD AVAILABLE. If you change the boot order and get it to boot from the USB Drive, it gives you some additional options!!!!!!...... PUT THE GHOST ON THE AIR TO REST!!!!!!
Frank
Have you made any progress?
Scotty
On Thu, May 15, 2025, 12:40 PM W1WCI via <timothy.macdonald= [email protected]> wrote: Sbitx - antenna switch - swr/power coupler - antenna
?
Previously radio showed power and 1.0 swr on 15, 20, and 40 meters with similar readings on the off board meter.
As of this morning swr on the radio and the off board meter show high SFR 2 to 3:1.
Removed the radio from the antenna line and replaced it with an antenna analyzer, it shows a perfect 1:1.?
Another radio shows 1:1 on the radio and the off board meter.
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Previously, maybe a month ago I had the same problem, spent time chasing down the antenna to no avail. Then one day all was well with no intervention at or in the radio.
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All bands that were workable for the antenna show the same behavior today.
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Trouble shooting help welcomed.
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Tim
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-- 73,
FRANK - VU2FR
241 Naveen Niketan C-7 Safdarjung Development Area Hauz Khas Village Road NEW DELHI - 110 016 INDIA
Phone: +91 99108 44088
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First Satellite Downlink Reception over sBitx (for me at least)
?
Working on learning satellites for a few months now, building most of the gear, instead of buying stuff.
?
TODAY for the first time, I heard my own CW by way of the satellite, monitoring an sBitx (V2) using a Ukranian transverter (neither of which seems to be terribly sensitive).? JO-97, in its pass over the eastern USA around 11AM Eastern time.? ?
?
Main rig was older ICOM820H transmitting on 70cm through a homebrew yagi/homebrew dual axis rotator system controlled by homebrew PCB using K3NG controller, controlled by SAT32PC.? ?With some effort I found my signal on THAT setup with a CAT correction of 5kHz? (I don't know why that is so far off yet)
?
SBITX
SECOND RIG was a sBitx crudely "tee'd" in with simple PL259-Tee, so it got the same signal as the Icom820H.? ?I was unable to provide suitable doppler correction to the sBitx, because Sat32PC doesn't seem to know how to use hamlib; however, I could have done so using Gpredict directly to the radio (which was on 192.168.1.10 in this experiment; the antenna rotator is controlled over wifi using a raspberry pi)
?
The spectrum display on the sBitx was a HUGE help.? ?I could easily see my own CW on the waterfall and therefore tune to my frequency!? ?I would say as a first cut that the sBitx and the 820H were running reasonably about the same as far as receiving.? ?These passes are ONLY 10 minutes long, but on he Sbitx I could SEE other SSB conversations going on (and they seemed to have more power than my signal.....) -- so I could QUICKLY tune to them on the Sbitx and receive them just fine!? ?On the Icom820H (without a spectral display) you have to tune up and down the band.??
?
Signal Levels:? ?I have the antenna system 50 feet out into the driveway.? ?The 70cm transmitter is going through 100 feet of LMR400 to a crossed Yagi homebrew.? ?The 2meter downlink goes first into a diplexer to protect it from 70cm pickup? () and then into an inexpensive GaAs FET preamp Moonraker M-100 Professional ()? turned all the way up, theoretically 20dB gain.? ?At that level, both the 820H and the sBitx/transverter hear considerably more SIGNAL as evidenced by increased background noise.? ?
?
Without the preamp I'm pretty sure the Ukranian transverter and sBitx would hear nothing, and I'm not sure about the 820H -- haven't gotten good records on that.? ?My experience with the used Icom 820H is that I generally do best by keeping that preamp at +20dB.? ?
?
?
WITH the preamp I have heard amazingly good SSB signals -- like full quieting FM quality!? ?The sBitx was showing MY cw maybe 10-15 dB above the noise baseline (IF was set to 84 on the 10 meter band)? ?but my recollection is that the SSB signals were 20-30 dB above noise -- stronger than my CW signal.? ?(So maybe I need more oomph on transmit???)? ?
?
?
This proves that you can use an sBitx as a satellite downlink receiver with transverter and preamp.? ?In fact, it would be a very nice one because of the spectral display!!
?
I think it would be easiest to use a second sBitx or other transmitter to do the transmit side, with a second transverter, and possibly an amplifier to get some more power.....I was surprised that my signals looked weak compared to what I heard from SSB stations on the satellite.
?
Photos below
Gordon KX4Z
?
?
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Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
You guys are AMAZING. Gordon KX4Z
On Sat, May 24, 2025 at 11:06?AM Steve Beckman via <ssteven3sb= [email protected]> wrote: Hi Gordon;
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Yes - a tuned circuit at the emitter bypass of Q3. LTSpice simulation suggested replacing C22 with 150 pF and R33 with a 100 nH chip inductor. This combination does appear to work, with a further reduction in spurs, along with slightly more drive as a bonus.
?
I also started using ChatGPT to examine various inductor & capacitor combinations. It's so much simpler and quicker to ask ChatGPT to find the resonant frequency of an LC circuit, or to determine the capacitor value required to make a given inductor value resonate at a specific frequency. It will even offer to generate Spice simulation files, or Python code to simulate the result.?
?
Farhan was probably the first to use AI for SBitx work - he created some of the user interface code with the help of AI.
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73; Steve, N3SB
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Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
Hi Gordon;
?
Yes - a tuned circuit at the emitter bypass of Q3. LTSpice simulation suggested replacing C22 with 150 pF and R33 with a 100 nH chip inductor. This combination does appear to work, with a further reduction in spurs, along with slightly more drive as a bonus.
?
I also started using ChatGPT to examine various inductor & capacitor combinations. It's so much simpler and quicker to ask ChatGPT to find the resonant frequency of an LC circuit, or to determine the capacitor value required to make a given inductor value resonate at a specific frequency. It will even offer to generate Spice simulation files, or Python code to simulate the result.?
?
Farhan was probably the first to use AI for SBitx work - he created some of the user interface code with the help of AI.
?
73; Steve, N3SB
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Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
Hi Gyula;
?
Thanks for your suggestions. I do need to look closer at the power filtering to this part of the circuit. Keeping the stray RF out of the buffer stage could possibly be more effective than trying to filter it out after the stage has picked it up.
?
73; Steve, N3SB
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Accessing zBitX on RealVNC
#zbitx
I am almost certain that there has been some discussion about what username and password to use when remoting onto a zBitx using RealVNC, but I cannot find it.? So sorry for the repeat, but please advise me:
1. What is the default username/pwd for connecting to a zBitX via RealVNC?
2. How do I change the password?
Thanks in advance!
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Generally speaking, you can enable usb booting with no sd card on a Raspberry Pi Zero 2.
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https://forums.raspberrypi.com/viewtopic.php?t=322604
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I finally managed to boot from an external USB on my zbitx.
I had to modify /boot/cmdline.txt? on the internal sdcard to point rootfs to the external device UUID.
Of course if I remove the external device the zbitx doesn't boot because it is waiting for the root file system which is not there .
Not sure how the zbitx boot process works but it appears that the internal sdcard is needed to actually boot from the external sdcard. Not sure why that is?
Once the zbitx is up and running on the external device I am able to unmount the internal sdcard and everything runs ok.
/dev/sda1 is mounted as /boot and
/dev/sda2 is mounted as /rootfs
It looks like what is needed is a? check to see if the internal card is present and the external card is not then boot from the internal card and its file systems otherwise boot from the external sdcard?
Ideas?
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Leo, AI5II
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Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
"This is as far as I have gotten. The Q3 stage may need to have an LC band-pass filter added to it's input or its output to better filter out the RF being picked up from the transmitter stages. I'm hopeful that a simple solution is going to be found soon, that results in a clean transmitter with plenty of margin for spectral compliance. ? 73; Steve, N3SB"
Steve, what about a series LC tuned to 40 MHz instead of the C22 capacitor?? ?That might give much faster rolloff of gain at HF?? ? If that isnt?enough, then a series LC in the output or a parallel LC shorting the output at HF?? ? ?
Your assessment of RF coupling back to the power regulator seems perfect because then the RF appears on the?+V line having been injected into the ground connection (the same way a fixed regulator can be turned into a variable regulator by raising its "ground" pin.? ? You're already working to improve "ground" throughout the circuit.? ?Would adding additional bypass capacitors to reduce the injected RF into the power system help?? ?In my case, I found it often did, but once it caused a real problem because of some inductance I added with a wire to add the bypass.? ?
You are doing fantastic work! Gordon KX4Z
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Re: Failure on first use?
Russell,
Check your power supply (or batteries if using). ?Two of us from our club bought the zBitX at FDIM and bought batteries in the flea market. ?After about 15 minutes of just listening the screen flickered, went gray, and the radio shut down. ?We thought we had bought duds. ?But on getting home I used a stable power supply (and later with new 18650 batteries) it works well. ?Later we heard that the flea market seller was selling 8 year old batteries he had bought cheep as one of our group went back to exchange a defective charger.
Just hoping that is your problem.
toggle quoted message
Show quoted text
On May 23, 2025, at 9:57?PM, Russell Brown via groups.io <russterus@...> wrote:
? I received my new ZBitx last week and pulled it out for an initial operation today. Mostly checking out FT8, recriving signals and had answered a couple when suddenly the receiver started putting out noise and could not hear anything but the noise. ?Verified the antenna was good by hooking up another transceiver, checked and messed with the various options to no avail. ?Any thoughts on possible causes? ?I took some pics and videos and will reach out to HF Signals after the weekend unless anyone does have some suggestions. Definitely disappointed.
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Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
I remembered wrong because it was in the 3v3 circuit and the values ??were 47uH and 22uF.
--
Gyula HA3HZ
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Re: zBitx +-2 MHz transmit spurs? --> SHOWSTOPPER for transmitting
Steve,
I remember that it is possible to isolate individual circuits from the power supply with a series inductor and an electrolytic capacitor.
It would be worth trying if you are already so deep into measurements and I certainly wouldn't miss it as an option.
I remember when the Tiny spectrum analyzer was still in its early stages, some of us built and designed modifications and serial 22uH and 10uF isolation on the pcb for the 5 Volt supply.
I may not remember the numerical values ??well, because I have since changed PCs and store the data elsewhere. The series resistor placed in the signal path also has a noise reduction role.
--
Gyula HA3HZ
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Re: Failure on first use?
On its predecessor, the sBitx, the?codec would occasionally go out to lunch (usually on startup) and then you get zilch nada nothing.? ?There have been various improvements in the I2C connections, but the chip has been difficult.? ? I don't know if that is what is happening to you, but if it is, there is a decent chance it will work within a bit again.
And of course, there could always be a bad connection, too......the world of just-built radios is just like the world of "new cars" and "new houses" -- not everything is always perfect!
Gordon KX4Z
On Fri, May 23, 2025 at 9:57?PM Russell Brown via <russterus= [email protected]> wrote: I received my new ZBitx last week and pulled it out for an initial operation today. Mostly checking out FT8, recriving signals and had answered a couple when suddenly the receiver started putting out noise and could not hear anything but the noise.? Verified the antenna was good by hooking up another transceiver, checked and messed with the various options to no avail.? Any thoughts on possible causes?? I took some pics and videos and will reach out to HF Signals after the weekend unless anyone does have some suggestions. Definitely disappointed.
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I received my new ZBitx last week and pulled it out for an initial operation today. Mostly checking out FT8, recriving signals and had answered a couple when suddenly the receiver started putting out noise and could not hear anything but the noise. ?Verified the antenna was good by hooking up another transceiver, checked and messed with the various options to no avail. ?Any thoughts on possible causes? ?I took some pics and videos and will reach out to HF Signals after the weekend unless anyone does have some suggestions. Definitely disappointed.
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KD2HBV
David Wilcox K8WPE
HA3HZ