2V2 on Q1 collector seems to be too low. I have had similar problem in this situation, the oscillator does not start.
You should try a 100k trimpot, if you have one, or a 68-75K and check again the operating point.
I don't believe that the problem was related to the MMBT hfe, I have tried several parts without any problem.
I havent 100K smd trimer, so I soldered out the trimer and I soldered in a fix 100K resistor. I have fortune, it gives about 3V on C3. But nothing changed, not start the oscillator...
If it does not start anyway the problem is the gain of the active device that does not overcome the crystal losses.
It's very strange because my 45/49 MHz crystals start with all MMBT I have tried.
You could try moving back to the BFR182, or increasing the value of the capacitor C2 to 2.7/3.3 pF, or better with a trimmer capacitor 1-10 pF if you have one.
I 'll try to get parts. I found just 3-10pF trimmer first. My question: Is it enough the NP0 smd capacitors tolerance 5%? Usually I found it instead of 1%.
Are there any passive components to try changing on board, other R, C? Or just the C2 would be the problem?
For total tuning flexibility you also could temporary replace C1 and C3 with trimmer capacitor.
My feeling was right
I ve changed back the BFR transistor and it work on the suitable frequency stabile! Maybe my MMBT seria was a lower hFE by the factory.
My feeling was right
Maybe my MMBT seria was a lower hFE by the factory.
Glad to know the issue is solved. Enjoy! and let us know your impressions.
I m looking the Driscoll manual, but it dont include the 5/6 MHz SC cut crystal parts in BOM. Is the Driscoll board can use without modification of the circuit what we using now? Where will be the list of the parts what need for it? Or you are testing and designing it just in near future?
Have you got bare Driscoll PCB at home yet?
I maybe join GB with a 5MHz SC, I hope it will work.
How many are the MOQ, 10 pcs? I saw there is low interesting this time...
Update the GB. It will be long long time to reach MOQ I think, no serious interesting
andrea_mori: 3 x SC-Cut 5.6448 MHz + 3 x SC-Cut 6.144 MHz + 3 x SC-Cut 11.2896 MHz + 3 x SC-Cut 12.288 MHz + 3 x AT-Cut 5.6448 MHz + 3 x AT-Cut 6.144 MHz
rickmcinnis: 1 x TWTMC-D finished with AT-Cut 22.___ MHz
gabor80: 1 x SC-Cut 6.144 MHz + 1 x Driscoll board
andrea_mori: 3 x SC-Cut 5.6448 MHz + 3 x SC-Cut 6.144 MHz + 3 x SC-Cut 11.2896 MHz + 3 x SC-Cut 12.288 MHz + 3 x AT-Cut 5.6448 MHz + 3 x AT-Cut 6.144 MHz
rickmcinnis: 1 x TWTMC-D finished with AT-Cut 22.___ MHz
gabor80: 1 x SC-Cut 6.144 MHz + 1 x Driscoll board
Hi Andrea,
Formerly you wrote that you have spare 45.1584 and 49.1520 SC crytalls.
Is these SC crystals are functional with Driscoll board?
45.1584 MHz 3rd overtone MOQ
49.1520 MHz 3rd overtone MOQ
Yes, they work correctly with the Driscoll oscillator board with component values indicated in the last BOM.
Theoretically they should work with the MMBT5179 bjt, in practice seems that this depending on the manufacturer batch, so you can use the NE85633-R25 or the BFR182 as the active device.
Are these 2 crystals available? I want to buy both.
1 x SC 45.1584 MHz 3rd overtone
1 x SC 49.152 MHz 3rd overtone
Stock update
Sorry, I forgot to update the list, the above crystals are no longer in stock.
Follows the updated list:
Crystals:
3 x AT 12.288 MHz fundamental
1 x AT 24.576 MHz fundamental
2 x AT 33.8688 MHz 3rd overtone
1 x AT 98.304 MHz 5th overtone
4 x SC 90.3168 MHz 3rd overtone
6 x SC 98.304 MHz 3rd overtone
Finished boards:
1 x TWTMC-D finished with AT-Cut 98.304 MHz
1 x TWTMC-P finished without crystal
Sorry, I forgot to update the list, the above crystals are no longer in stock.
Follows the updated list:
Crystals:
3 x AT 12.288 MHz fundamental
1 x AT 24.576 MHz fundamental
2 x AT 33.8688 MHz 3rd overtone
1 x AT 98.304 MHz 5th overtone
4 x SC 90.3168 MHz 3rd overtone
6 x SC 98.304 MHz 3rd overtone
Finished boards:
1 x TWTMC-D finished with AT-Cut 98.304 MHz
1 x TWTMC-P finished without crystal
