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The calculation is simple, but the concept of impedance is not always easy.
Few radio amateurs without an engineering background ever figure this stuff out completely.

Impedance is like resistance, but adds the complication of phase.
To keep the formulas simple we use "complex numbers".


Normal "real" numbers only have one dimension, along the number line.
Complex numbers have a second dimension perpendicular to the real axis.
Weirdly enough, the math all works out beautifully if we assume the perpendicular axis
has units of the square root of -1, often expressed with the symbol j.

Once we express impedances as complex numbers, we can use the same formulas
to combine impedances as we do for resistors.

Ohm's law still works too, divide an AC RMS Voltage by and impedance and?
you get a current in Amps, where all three values are complex numbers.
The phase of the complex number for the current will be shifted with respect to
the phase of the voltage, exactly as?you would see with an oscilloscope.



Lets assume the 45mhz filter does have an input impedance of 650 ohms?
in parallel with 3pF as Gerard shows in his diagram.
The 3pF is in parallel with the 22pF of C212, resulting in 25pF of capacitance.
The formula for the impedance of an inductor is zL = j * 2*pi*f * l)
where f is the frequency in Hz and l is the inductance in Henries.
The formula for the impedance of a capacitor is zC = 1/(j * 2*pi*f * c)
where f is the frequency in Hz, c the capacitance in Farads, and zC the impedance in ohms.

That capacitive impedance is in parallel with the 650 ohms resistance,
which can be calculated as:? ?zP = zC*650/(zC+650)
And that impedance in series with the 720nH inductor L7 is zIN = zL + zP

Python is a simple programming language that knows about complex numbers,
We use exponential notation for the big and small numbers, so 720e-9 is 0.000000720
We can write this up as a python script:
On Mon, Mar 25, 2024 at 01:02 PM, ajparent1/kb1gmx wrote:

The IF amps and associated DBMs were 50 ohm not 500 ohms.?
The TIA amp is 50 ohms and the DBM is also 50 ohms.

The actual network is L network and the calculation is simple.

Note C250 and 216 are not there (zero value means not installed.).

Also c211 and C251 are large enough to be near zero reactance at 45mhz
and serve as DC blocking.

So the active network is L7 and C212 and the mirror components on the other side.


--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.

Re,

I sent the files to a friend of mine what has a 3D printer and he said that it was warping and wasn't printing for him. Would someone out there be willing to print me a case or is there a company that could print one for me??
I really like the sun shade, it is a great idea

--
'72

AE9J,

The hw_settings.ini file is in the data folder in the sbitx folder
/home/pi/sbitx/data

I suggest copying the entire folder as your customization settings and the log file are also stored there.

73
Evan
AC9TU

So where is this "hw_settings.ini" file?

Does this file get changed by the "txcal" command?

I guess I should copy that file off somewhere before I even think about changing it.

Thanks.

On Sun, Mar 24, 2024 at 08:51 PM, Mark Hatch wrote:

But it is great benefit to others!

Agreed!

Also, I found the following on the sbitx group on Facebook that I think will be of interest to POTA operators:




?

Thanks to Jared for sharing!
?
--
Regards,
Dave, N1AI

And complementing this solution, I also remove the fake-hwclock ugly workaroung, that is installed by default:

|apt-get remove fake-hwclock|

Cheers,
Rafael

It is just a matter of loading the appropriate overlay to make Linux use the installed RTC as system RTC.

I use:

|dtoverlay=i2c-rtc-gpio,ds1307,bus=2,i2c_gpio_sda=13,i2c_gpio_scl=6
|

Then wipe the userland I2C BB code (and use kernel I2C interface). If you need a reference:


Cheers,
Rafael

JJ,

If the address of the RTC? is 68 without the sBitx program running, you should be able to sync the RTC to the Pi. That doesn't look like the RTC address.
--
Jerry Ponko, AC9NM

I wish that the sBitx had used the standard I2C overlays instead of bit-banging. Back when the sBitx first appeared, I was not convinced that the WM8731 codec and the Si5351A could not work together on a Pi-4 connected to the same I2C bus, So I built my own WM8731 module board according to the manufacturer's datasheet and connected it to the Raspberry Pi 4 along with a Si5351 module and had them both working on the same bus. The date sheet also says it can be controlled by the SPI bus or I2C. I used the standard 12.288MHz crystal? on the codec as well and not the 12MHz as used in the sBitx. If I remember correctly, I used a rotary encoder and some python library code to control the Si5351A to change frequency while listening to some internet music coming from the WM8731 headphone output. I didn't detect any problems with either device. I've been tempted to build my own version of the sBitx hardware without bit-banging or other workarounds but I don't want to deal with all the code changes plus I'd get rid of WiringPi as well. IMHO, the correct way to implement the RTC would have been to make it a system device and then have the sBitx software just read the system time. I'm more familiar with programming MCUs then the Raspberry Pi SBC but when I program a MCU, I try to use standard methods and libraries and if a device doesn't work properly, try a different library or device and not reinvent the wheel.?

So now we have a RTC that's not really a system RTC unless you run the sBitx software.

--
Jerry Ponko, AC9NM

On Sun, Mar 24, 2024 at 08:52 PM, Jon / W2JON wrote:

Does this adafruit article bring any useful?information?

Seems that this is the same / similar implimentation.

Thanks for the link, Jon. This is really good info. I started to play around with some of the commands and may go further to see if I can use it in the 64bit build.

This is a good way to test the RTC and see if it is known on the I2C bus. UU means the driver is loaded and working.




-JJ

On Sat, Mar 23, 2024 at 07:37 PM, HA3HZ wrote:

Now I'm only interested in the fact that there is a built-in RTC and it is not visible with the timedatectl command.

Hi Gyula, according to the info at "sbitx.net", the RTC is only accessible via the sbitx program.? Have a read here :?

So, it seems that the Raspberry Pi cannot access the RTC.? Sad really, as the RTC should be keeping the RaspPi clock working while it is off.
?
--
Pete VK3PYE

On Sat, Mar 23, 2024 at 03:21 PM, JJ - W9JES wrote:

You are a genius! This was the fix or Band-Aid for the time dilemma.

Good job JJ and Jerry, many thanks for your ongoing work with this amazing little rig.

I have applied the update to your 64bit beta2 version JJ, and can confirm that it works, and to quote you: "This was the fix or Band-Aid for the time dilemma."

I dual boot my sbitx_v3, and so I tried the 32bit "Buster" version 3.02 (as supplied by HF Signals) and interestingly, it still has that bit of code [ return ?(millis()/1000l) + time_delta; ]?in there, and yet the sbitx UTC clock is correct.? Hmmmm .... [scratching my head]

Anyway, it's working and that is what matters.
--
Pete VK3PYE

I am with Evan here and would just buy a sBitx.

I am having a lot of fun enhancing and extending KD8CEC for picos and teensy, ?but after buying my own sBitx, I don’t see my work ever catching up with a sBitx. It is a great radio! So I don’t see my work ever being a reasonable upgrade path for ubitx owners. ?

I am going to continue working on kd8cec, and will make available Raduinos designs ?for pico and teensy. ?But doing so for my own fun and on my timeline.?

73
Mark
--
AJ6CU/7
KD8CEC 2.0, Nextion Screens,? and open source uBITX Raduino boards for Arduino IOT, BLE, RP2040, Teensy 4.0, and Raspberry Pi Pico
https://github.com/aj6cu

Excellent! ?Will update both Thingiverse and GitHub. Might be a few days as I don’t have access to my development system. But it is great benefit to others!

73
Mark
--
AJ6CU/7
KD8CEC 2.0, Nextion Screens,? and open source uBITX Raduino boards for Arduino IOT, BLE, RP2040, Teensy 4.0, and Raspberry Pi Pico
https://github.com/aj6cu

The uBitx V6, with Nextion display and KD8CEC software, does have a screen saver mode. This is accessed via the Control Menu, LCD button. The LCD Setup screen allows setting display brightness, and also provides the option to have the screen Always On, or blanked after 3, 10 or 20 minutes. It seems like that should satisfy your friend's screen blanking requirement.

I think the KD8CEC software utilizes some computing power inside the Nextion display for some additional functions (not only display related). Therefore, you might unexpectedly lose some important functions by disconnecting the +5V power to the display.