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First Satellite Downlink Reception over sBitx (for me at least)

 

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Working on learning satellites for a few months now, building most of the gear, instead of buying stuff.
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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.? ?
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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)
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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)
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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.??
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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.? ?
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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.? ?
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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???)? ?
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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.
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Photos below
Gordon KX4Z
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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
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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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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:

?
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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Great advice, Dave! The loss through the coax is considerable and I should reduce that length and improve that problem.

As for power output I haven¡¯t measured it, supposed to be better than 30 W. Not sure I¡¯m getting that, used radio. ?I should measure that
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the 70 cm Yagi turned out to be quite well tuned, but the 2 m ?yagis have a few more problems¡ª a little more effort, there could have good outcome. This has been a prototype from the beginning all the way to now and it could certainly stand some improvement!
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thanks!
gordon kx4z?
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Unfortunately, SATPC32 does not appear to be able to do CAT control via Hamlib (otherwise it would be easy to control the sBitx)? -- but it can control ICOM type CIV on "Radio2"? ? Unfortunately, it also does not have capabilities to handle an sBitx with a TRANSVERTER.
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There are probably many solutions to this, but I have limited skills.
I already have an ICOM emulator system that can handle CI-V commands over serial port (see the WIKI for MODS)
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If I then intercept the CI-V commands coming from the SAT32PC program, and adjust for the transverter, and then forward them to my icom emulator -- that should work.? ?( A brighter person would go directly to the hamlib interface over tcp/ip....but I don't know quite how to do that....)
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I think I can do the interception with an Arduino, so maybe I'll work at that.... or alternatively I could just alter my ICOM emulator and produce versions that are based on this or that Local Oscillator frequency!? ? That is probably the easiest way!!? ?I may work on that.
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In that case, I could have the sBitx with its spectrum display, paralleling the receiver in the ic820H simultaneously.? ?That would be quite nice!
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Gordon KX4Z
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I'm away at our family vacation home in the western North Carolina mountains (where it is MUCH COOLER!!!) and without satellite gear.
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Now that I have proven that with a $100 preamp and $150 transverter, an sBitx can hear even the linear satellites without problems, I'm working on how to get it integrated into a satellite setup.? ?
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#1)? Using GPREDICT should be pretty straightfoward because it can output tcp/ip hamlib commands to control frequency of sBitx.? It also allows you to list the local oscillator frequency of a transverter.? You would need a second setup that could do the transmission, maybe more than the sbitx/transverter system normally produces.? ?FT991A or Icom7100 would work!? ?A problem is that I don't see a way to make little bitty offsets so you can hear your own signal immediately.? ?Not sure how to fix that....? ?Someone may know the solution, or else this would be a great thing for the 64-bit crew to create -- a way to set up an offset for the hamlib (rigctld) response.
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#2) Using SATPC32 (which Amsat encourages) makes it easier to adjust the offset and correctly handled my old ICOM820H (which Gpredict could not seem to be).? ?I updated my homebrew USB-connection software allowing Icom7300 emulation. so that I could work better at taking commands from SATPC32.? ?(I made it try USB0, USB1, USB2 before giving up, for example, a huge improvement).? ?I had it test the incoming frequency command and subtract the proper LO Oscillator for typical transverters for 144-146 146-148? 430-432? 432-434 MHz freuqencies and I got that to work properly!? ??
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The software continues to accept commands from WINLINK perfectly.
I also tested it with ION2G (the ALE software currently used by USA SHARES) -- and amazingly it works for that also!? ?I have the ION2G "scanning" using the sBitx!? ?(If you adjust the frequency limits of some of the configuration files, you should be able to get it to be able to sound and answer in the USA SHARES Federal Frequencies, if you have the proper licensure, outside of the ham bands).? ?I don't think there is much ALE usage INSIDE the ham bands, but with the proper QRG files, it should work fine.
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THE PROBLEM I'm having is that SATPC32 does not continue to update the frequency of the sBitx? ?It sends the initial frequency (and my software properly sets the sBitx in the 10 meter band) -- but then does not continue to send the Doppler-corrected updates.? ?Instead it is sending a zillion ICOM CIV commands 03hex (requesting reading the frequency)? ?I've tried to answer the requeist multiple ways, to no avail.? ?I'm not doing something right because I've watched this work with a 7300 I believe.? ?Oddly, if you tweak the offset in the CAT menu option (say, by 20 Hertz) the SATPC32 again sends the proper freuqency to the sBitx and it is synced up again!!!? ? ?If anyone know how to get it to keep doing that, and how I might be improperly answering their 0x03 frequency read reqeuest -- let me know!!!
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The spectrum display of the sBitx is a HUGE help on the receiver side of linear satellite operations.? ??
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Gordon KX4Z
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I'm away at a family retreat home and don't have all my satellite stuff with me, so difficult to test.??
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PROGRESS ON HARDWARE SOLUTION:
I tapped into a generic Icom CI-V cable.? ?These are open-collector bidirectional connections.? ?To transmit, the line is pulled "low" by collector.? ?Reading is done by simply watching the voltage on the line which is pulled "high" by a resistive source to about +4 or +5 (TTL levels).
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I took the signal from the open collector line and sent it to the RX and GND inputs of a UART that does USB <--> TTL levels.? ?
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The UART then got plugged into the raspberry pi of the sBitx SDR radio I'm trying to get set up as the "second receiver" to take advantage of its spectrum display (which my ICOM 820H lacks).? The CI-V line is controlled by SATPC32 on a Windows computer as if it were controlling an Icom 820H.
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Hooray!? ?Using my current software, I'm seeing frequency information flying past.? ?Since I don't have the IC-820H with me, read requests from SATPC32 for frequency still go unanswered.? ?I don't know how to do the response properly, but when I get back and connec the IC820H, I think that will be solved.
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Next I have to update my software so that it will pick the DOWNLINK frequency out of the two that are flying past, and I also have to build in a chance for the user to enter an offset to account for frequency errors.? ?I'm only a barely-able programmer, so this isn't going to be "pretty" but I may be able to get it "workable" and that will be good enough for me!!? ?There is always the chance that I can be slicker and read keyboard input to jiggle offset corrections on the fly!!
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Gordon KX4Z

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