Merci à tous pour vos réponses très technique.

but...

Hello Jens,

Gordon is correct.? The original DE and V2 bias were to be set at 250ma.? Here is the link to the archive of that directive:


There is other information on that site.? It is worth a read-through.

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I think the original suggestion was 0.250 for the current through the MOSFETs. ?I think I said some of mine at 0.360 amps.?

Ford said::? "The calculated solution for 650 to 500 is 969 nH and 3 pF."
As Allison pointed out, we are targeting an input impedance for the network of 50 ohms, not 500 ohms.

He also said:
"It seems to me that the only way to actually find the correct solution is to lift the filter out of the circuit.? Terminate it using a 500 ohm resistor, and put a NanoVNA on it to measure the R +/-j.? Even then, the NanoVNA is itself a 50 ohm device so an approximation may be to use a 9:1 transformer on the VNA to filter to at least match it to 450 ohms.? Even better would be to use the 9:1 and a series 50 ohm resistor."

A nanoVNA is indeed most accurate around 50 ohms, but a few hundred ohms should be well within its range to give good results.
Adding a transformer introduces a bunch more sources of error, and I'd guess would make the result less accurate than a direct measurement.
When measuring the input impedance with a nanoVNA, terminate the far end of the filter module with exactly what the datasheet claims it should be, including any reactance.

However, Allison suggests that you will not measure the datasheet value, as the datasheet specs the
source and load impedance that you should give the filter module, not what the filter gives you.
I defer to Allison on this matter, as she is most often right.

Here's a selection of 45mhz crystal filters:??
I'm guessing Gerard is looking at something like the 45R15A1 at 7 lines down,
which presents an impedance of 650 ohms in parallel with 3pf.
The one immediately below that has an extra spec of Cc = 9pf,
which I assume is capacitance to a metal shell, I'll ignore those parts.

Farhan says the ones he buys are 500 ohms, but I'd guess they are more like the 45R12A1,
which is 500 ohms in parallel with 5pf.
The 5pf is not insignificant at 45mhz, having a reactance of 1/(2*pi*f * c) = 1/(j * 2* 3.1416 * 45e6 * 5e-12) = j707 ohms.
Clearly, we can't use the formulas Gerard found that assume the impedance of the filter module is purely resistive.

Let's go with the one filter module similar to Farhan's.
The impedance of 500 || 5pf is the parallel combiniation of 500 ohms and -707j ohms.
Using the python interpreter, we find that:? ? (500 * -707j) / (500 - 707j)? =??333.3 - 235.7j ohms
We perform that calculation the same as we would for two parallel resistors.
(Python insists that the j follows the number, most other sources have j preceeding the number.)

Plug it all into the calculator on the webpage that Ford found at? https://leleivre.com/rf_lcmatch.html
Our inputs to the calculator:? Freq=45 mhz,? Zs=50+j0, Zl= 333.3-j235.7 ohms,
The top network agrees with the topology Farhan chose, and gives values of L7=530.5nH and C212=16.22pf

Now plug all that into my python script as a double check:

Gerard.?

I believe that statement refers to the crystal filter module, without L7 and C212.
There are such modules that are 500 ohms resistive, though they also have
a significant capacitive reactance in the impedance they present.

As Allison says, it is the input to the complete network (including L7 and C212) that should be 50 ohms resistive.

Jerry, KE7ER

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What I find interesting is uBitx V3 though 6 the terminations for the filter that is
the crystal filter plus matching network is between a Mixer (DBM) and TIA amp.
Both of which are NOT 500 ohms and are optimized for 50 ohms.? So the matching
network has that as its?input and output? terminations.

The filter is characterized as 1500ohms 2pf That is not what it presents,
its what it expects as a load to produce the desired and expected filter shape.
However... I have parts tha texpect 470ohms to as high as 2000ohms resistive
for the termination. So you do need the data sheet for the filter in use.

The above is critical to the filter used as when done tight the loss though the
filter will match the data sheet and also the passband frequency and shape will
be as specified on the datasheet.? Crystal filters are not an exact match to LCR
filters, most LCR fitlers are designed for restive termination where most crystal
filters are designed to expect some reactance as part of the termination.? Altering
that alters the filters behavior (pass band and shape).

Also I have the experience with V3 and a lot of testing.? I found with the supplied
filter and the matching network it performed only marginally well.? Testing using VNA
(Agilent) the matching network values used both skewed the filter response and
created a large amount of ripple in the pass band. causing RX degradation and
also degrading RX and TX audio (for mine).? The values I used were close to
calculated once I had filter data.? I did have to adjust for the trace to ground
capacitance.? The results when properly matched improved.? The filter
pass band was properly centered at 45.000mhz and the loss was lower.?
FYI the filter used wanted a termination of 1500ohms and parallel of 3pf
as a match.

And like Gerry said its not a pure resistive match.

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

Hello,

Thank you, Farhan, for pointing me in the right place.
I compiled all info to the single document, corrected typo errors and saved as .pdf into Files/SBITX_V3 folder.
Maybe it will help to someone...

73 - Petr

The calculated solution for 650 to 500 is 969 nH and 3 pF.

It seems to me that the only way to actually find the correct solution is to lift the filter out of the circuit.? Terminate it using a 500 ohm resistor, and put a NanoVNA on it to measure the R +/-j.? Even then, the NanoVNA is itself a 50 ohm device so an approximation may be to use a 9:1 transformer on the VNA to filter to at least match it to 450 ohms.? Even better would be to use the 9:1 and a series 50 ohm resistor.??

Y1 is known to be extremely reactive over frequency.? The model of Y1 is a complex collection of L/C/R configuration that is highly reactive.? The 650 to 500 solution is an over-simplified description of the actual problem to be solved, which is to match at 45 MHz.

Ford-N0FP

I use on-line calculators to figure out matching.? One of my favorites is here:



Using 45 MHz

In the configuration on the schematic, 50 j0 ohms into a series C211 of 0.1uF (X= 0.04 ohms @ 45 MHz) into series L7 of 720 nH (X = 204) into shunt C212 of 22 pF (X = -161) does not appear to work at 45 MHz.? At 38.3 MHz the solutioin comes out almost exactly a series 720 nH to shunt 22 pF.

At 45 MHz, the solve for 50 j0 to 650 j0 is a series 613 nH to shunt 19 pF.

The practical issue of knowing the characteristic impedance of Y1 is clearly a factor.??

Ford N0FP

I have downloaded both prints and can spend the time to figure out which components need changing to goto the 510 finals but was hoping there was a .txt file on github. I looked and didnt see anything, where do I find those notes?

Hi folks,

is somewhere the manual for latest sBITX V3 please? I found just an old V2 document...
Looking for user manual as same as latest schematics and mods done on V3.

Thanks,
Petr

A common problem, especially with petg filament and perhaps a glass bed. Base level is not sticking fully. Happened to me once but I forgot how fixed it. Maybe more squish on first layer? Or more hairspray…

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

Great idea that shade should be pretty easy to add to the 3d model. Let me think about it when I get back to my desk.?

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

Gordon,

many thanks for detailed info.
I asked for it as few owners reported cutting first CW element because of long T/R switching time in V3.
I did not find any video where someone would be able to show standard CW keying at normal speed of 25-30wpm.
If the CW delay is possible to set, then it would be interesting to know how low it could be set...?
Anyway, many thanks for help Gordon.

Petr