On Fri, Oct 27, 2023 at 10:58 AM, Ken N2VIP wrote:

A) the firmware in the RPi 4 has always supported USB booting, the RPi 3 had the ability to modify the firmware to boot off USB directly, otherwise a bootloader on a MicroSD could do the same thing. (Boot off MicroSD, then transfer to USB)

All true. I used the 'rpi-clone' script from which cloned the sdcard's contents onto the NVMe and set up the bootloader to use it as the favored boot device. I think there were a few things the script didn't cover with regard to sbitx setup (some permission issues) so it wasn't perfect, but overall the end result is the system booted off NVMe and the sdcard was still discovered at boot time and made available so I could write updated software from the NVMe to the sdcard. Now I will go through /home/pi/sbitx/install.txt to see if there are any things I need to fix up.

-- Regards, Dave, N1AI

My solution to the problem: industrial velcro! It's a thing, search for it on Amazon. It comes in three inch wide strips. Now I can hang external USB-to-NVMe sticks on the back of the sbitx unit. Can also hang batteries, etc. See attachment.

-- Regards, Dave, N1AI

I have the same big problem with the FT8 transmit-receive-time-slot management from the FT8 software .
Anybody knows a solutions how the FT8 program-code must be edited / new programmed that FT8 will work correct ???

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Great work! ?I note that the uBitx v6 has

I just finished measuring the transmit spectra from my uBITX v6. Test setup: uBITX running CW at 12 volts into MFJ dummy load, to which I added a -50 dB tap. Tap is -51 dB at 1 MHz, -41 dB at 50 MHz, -36 dB at 100 MHz as measured on a NanoVNA. The tap goes to a TinySA spectrum analyzer, and I used tinySA-app to capture the spectrum to a file. I wrote a short Python program to read the spectrum, correct the spectrum for the dummy load tap variation over frequency, and then converted the spectrum from dBm to relative to the carrier peak at the fundamental in dBc.

I measured it from 80 meters to 10 meters. The worst band is 30 meters, with the third harmonic just a little better than -40 dBc.

Gordon,

I think the first path to eliminate is the voltage doubler/HV link used to reverse bias the unused filters.? There is only the RFC to keep the signal path isolated.? If, when connecting that link, the second harmonic increases, then I would look to increase the RF suppression on that line.

If you still have the HV connected, then the solution is to use relays instead of the PIN diodes.

73
Evan
AC9TU

OK, so I had some time tonight and very carefully I dissected out? soldering until I was able to take the output from the final transformer and send it DIRECTLY to the highest low pass filter, and DIRECTLY from there to the SWR bridge/antenna output.? ?There are NO switching diodes involved this way.? ? ?I haven't thougth through exactly what happened to the T R switch (hope I didn't do anyting stupid!)




Using commercial pads and attenuators here is the spectral output:



The main fundamental is almost -18 dBm.? ?Subtract 43dB from that and you get -61dBm

There are a few IMD products that are just a tiny bit over the line, but for me the key measurements are:

2nd Harmonic:? ?-64 dB which is -46dBc -- clearly legal
3rd Harmonic:? -77 dBm which is -59dBc -- very legal.

This is the WORST CASE for that filter -- this is the same filter used for the upper 3 bands, and I am testing it at 21.010 MHz -- a WORST CASE test.? ??

Compare? this to measurements I made on 10/8/2023 (using the same attenuator system, but with the filter within the switching system), and the 2nd harmonic from my written notes was -26dBc and the 3rd Harmonic was -30 dBc!!!!? ?Tonight, by going DIRECTLY through the filter, the 2nd harmonic is 20dB more suppressed, and the 3rd harmonic is 30dB more suppressed.

So even with low-cost MOSFET parts, this is basically a legal amplifier WHEN DIRECTLY INTO THE FILTER.? ?And the associated circuitry is in some way making it a lot worse.? ? ?

I'm still not seeing any spectra from anyone other than me and one other user.? ? Anyone else able to confirm or refute these findings?? ?In medicine we call this "an N of 1" and ONE is not a very large sample.? ??

But it shows that we can have a clean signal if we can solve where the problems are.? ?That should be the next effort.? ? Steps in that direction are to first connect the "input" switching diode and see what happens, and then maybe the "output" switching diode, possibly witth a couple or three in parallel??

Gordon KX4Z

This project was never stated as a fully polished device but a work in progress that had unbeleivavble potential to be something very uniques and powerful. Also something that still needed polish and was highly customizable andcould be improved on by the user over time.? That is how it has been discussed and marketed.? In My Opinion, If that is not what you wanted you probably bought the wrong radio because you didn't do the proper research.? YMMV

Jens, I'm sorry you had this experience. It was clear to me that it was an in--process, somewhat-experimental transceiver. Those of us in my club who bought them expected to be involved with at least making updates and maybe lighting up the soldering iron. Mine has served me well as my on holiday transceiver.

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...what if you bought a kit car, that you had to assemble yourself?

YT here:

Petr, OK1RP

Hi all,

I have the Sbitx V2 #005 for sale. Unit is new, almost untouched, original plastic foil on LCD, complete with all accessories from factory in original sealing and boxing.
On arrival the radio has been unboxed, tested shortly for RX/TX > presented hot receiver and full 40W output during few QSOs
and boxed back then it stays untouched until now on shelf.
Unit has no MODs, no updates, no any changes in hw or fw. So, you can modding it according to your preference's own self.

This unit has been dedicated as donation for our local kids radioclub but due to personal changes in the radio-club leadership?
no one is able to be unboxing it and start to play, modding and enjoy it in the club.

Additionally, it comes with BNC adapter, BNC-BNC 1m jumper, additional blue power banana cable, 3D printed sloped stands and the HDMI plate?that allows easy access to the HDMI port > all unused and sealed. Includes original working SD card installed in factory. I am asking $529 shipped worldwide double boxed. Its orig. factory box + additional box to enhance protection of the unit.

73 - Petr, OK1RP

I just wanted to give an update to the group of everything that went wrong i.e. a perfect storm. First of all the original motherboard was defective. Which intern tossed obviously a power spike or something to the RPI which also corrupted the SD card. In initially I had no reason to believe that the last two were defective ?so I was very frustrated upon putting a new motherboard in but it’s still didn’t work ?I knew logically that there were only certain things that would cause this not to work I was confident that the new motherboard was working correctly as I took power measurements. Therefore I eliminated the main board and focused on the RPI. I end up having to purchase a new RPI. Once I plug that in is when the SD card problem came about eventually I got the right image loaded on the SD card and everything worked finally.?

my sincere thanks to all those that responded whether positive or negative.?

--
Jack, W8TEE

I find that amazing you could do that with an iron.... I had a tough time doing it with a hot air station.

To hold the IC in place I took a metal strip from a windshield wiper blade and bent it like a hair pin
to clamp the IC down.?I tinned the leads on the IC... clamped it down and lined it up just right. Then I
could hit it with the hotair gun without it blowing away.
You could clip a ground on to it if your worried about static. I didn't take a picture when I did the raduino
but this is the basic idea.




73's Dave K0DLP

Steve -- surprise, surprise, surprise!
Now we may be getting somewhere.
I reconnected D30 and L201 to bring the switching systems back to where they are supposed tobe.

Then using two 9V batteries in series, I applied +18V to the point marked "HV" on C201.
That should back-bias the low pass filter diodes by 4-6 volts or so....

And surprise!? ?The isolation only improved by a small single digits dB.? ?Like maybe 2 or 3 dB; the entire curve with all of its series resonances (I'm looking from 2MHz all the way to 82 MHz now, with tracking generator and spectrum analyzer).

I was hoping it would have become FLAT at -60db or -70dB.? ?It did not.

(A) So I think we do have some evidence that signals can LEAK? ?*around* the excellent low pass filters.

(B) But if you look at the photos that I shot of the filter performance WITH all the switching diodes in place (see:? ?/g/BITX20/message/105633?) you don't see much evidence of signals getting "around" the low pass filters.

I don't understand how both (a) and (b) can be true.? ? ?I'm still missing something.

Copied from that previous message, here are the measured (IN CIRCUIT) rejections of the various filters:


BAND? ? ? -1db point? ? ? ?2nd H. Freq? ? -24 dB point? ? ?3rd H. freq
80 M? ? ? ? ? 5.4 MHz? ? ? ? ? -22dB? ? ? ? ? ? ~ 7.06MHz? ? ?~-60 dB
40M? ? ? ? ? 11.4 MHz? ? ? ? ? -21 dB? ? ? ? ? ~ 14.6 MHz? ? ?-51 dB
20M? ? ? ? ? ?16.4 MHz? ? ? ? -44dB? ? ? ? ? ? ?21.6 MHz? ? ? ? -57 dB
15M? ? ? ? ? ~3dB@...? ? ?-21 dB? ? ? ? ? ? ?43 MHz? ? ? ? ? -57 dB? ?(I had to change the Siglent to go to much higher frequencies to get this one measured)

How can the 20meter 2nd harmonic rejection be -44dB and my measruements of the 20 meter 2nd harmonic be -30dBc??? ?That suggests the output diode is mixing to creating more of the 2nd harmonic on the spot.? ?

In post?/g/BITX20/message/105656? ?I showed that a modest attempt at shorting out the "output" diode on the filter used for 15 meters resulted in a 6dB reduction in the 3rd harmonic (to almost legal levels) while the 2nd harmonic was not much changed.? ? ?I did NOT test shorting out the "input" diode -- indeed it could be making harmonics and on some bands the filter has only 20dB reduction on 2nd harmonic, so if the switching diodes are making harmonics....that could be again the source of the problem.

I have not yet done the drastic step of disconnecting all of this switching circuitry and just going directly into a filter and out to the antenna, which I discussed in post?/g/BITX20/message/105666? ? ?

Since I still can't really explain what is going on, I may? have to go ahead with THAT experiment....If that succeeds (who knows, it might!)? then the solution would likely be to go back to the DE circuity with relays to switch the LPF's and diodes to do the T/R switching.? ? But there is no proof at this point that this is the solution.?


Gordon KX4Z



But it looks like?

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Steve, thanks very much for the ideas. ?Inhad not thought of what you just pointed out!! ?I could get an 18 V source and connect it via resistor to the HV point and solve that…. ? ?maybe I can try that tomorrow. ? Thanks!!

Gordon - sorry, I don't have a V2. Maybe some day...

Your tests appear to demonstrate that a reverse bias needs to be applied to the switching diodes to turn them off (or reduce their junction capacitance.)

Note that because of D20 and D21, the reverse "HV" bias will be LESS than the forward bias if one of the low pass filter sections is NOT turned on. Only by turning ON (selecting) one of the filters will there be a voltage drop across R201/R202 and R203/R204, which will allow the reverse bias voltage to be higher than the forward voltage.

Do that, then try bypassing L22 at R203/R204.

73; Steve, N3SB