Title: PA calibration problem
Post by: f5ugq on 04. April 2019, 18:26:45
Hi all,
I'm trying to do the "PA calibration" step following the procedure https://github.com/df8oe/UHSDR/wiki/Adjustment-and-Configuration-Manual#pa-power-calibration. PTT pressed, I've got a current of 460mA, so I must ajuste the PA Bias to 960 (460 + 500) but I can only go to 115. Any suggestion ?
73's, Stéphane, F5UGQ. |
Title: Re:PA calibration problem
Post by: SP3OSJ on 04. April 2019, 18:43:53
Hi
Do you have good RD16HHF1 transistors?
http://sp3osj.kooikerhondje.com.pl/zdjecia/49.jpg (http://sp3osj.kooikerhondje.com.pl/zdjecia/49.jpg)
73
Artur |
Title: Re:PA calibration problem
Post by: f5ugq on 04. April 2019, 18:57:18
Hi Artur,
Thank's for your reply and after verification I've got the .... bad ones :(. I didn't known that there were somes. I will order the good ones.
73's, Stéphane, F5UGQ |
Title: Re:PA calibration problem
Post by: peter_77 on 05. April 2019, 16:02:44
If you want to be sure Box 73 in Berlin has them:
https://www.box73.de/product_info.php?products_id=1260 (https://www.box73.de/product_info.php?products_id=1260) |
Title: Re:PA calibration problem
Post by: f5ugq on 06. April 2019, 09:36:19
H Peter,
I ordered them yesterday at Box 73 :).
73's, Stéphane, F5UGQ. |
Title: Re:PA calibration problem
Post by: f5ugq on 20. May 2019, 18:13:35
Hi all,
I received the new transistors, from Box 73, and solded them on the RF board but I have still a problem in the PA calibration. I've got 560mA with a 13.8V supply and when I proceed to the calibration phase, I'm using the CW paddle for TX, the current don't move, it's still 560mA. I added 3k3 resistor between pin 1 and 4 of the U18, like mentionned in section FAQ PA Bias of the link https://github.com/df8oe/UHSDR/wiki/Adjustment-and-Configuration-Manual#pa-power-calibration, but same result, I don't try the 2k2 resistor yet.
Is somebody have an idea ??
73's, Stéphane, F5UGQ. |
Title: Re:PA calibration problem
Post by: DF8OE on 21. May 2019, 05:56:21
You can neither use CW paddle than TUNE for calibratiing the PA BIAS. Why? In both cases RF is produced and you need TX without RF!!!
Please switch to SSB, reduce Mic gain to "0" and press PTT on MIC. Now turn PA BIAS to lowest number and read the current which is consumpted by the whole TRX. Your task is now increasing PA BIAS so that it is ~0.5A higher than the level you got before.
Physics behind PA calibration are quite simple:
MOSFETS are becoming lower inner resistant if voltage at gate pin increases > ~2.9V. So you can check if gate voltage increases when you crank up PA BIAS. At the other hand you can check if 13.8V goes by nearly 0R to drain pin of MOSFETS - that is all which you need to test.
vy 73
Andreas |
Title: Re:PA calibration problem
Post by: f5ugq on 26. May 2019, 09:32:46
Hi Andreas,
Thank you for yours explanations. I changed the CW paddle by the microphone, I had to find one because I din't have one. The gate voltage increase well when I increase the PA Bias value but not the current, and there is no output power. I think there is again a problem with the transistors.
I continue the investigations.
73's, Stéphane, F5UGQ. |
Title: Re:PA calibration problem
Post by: DF8OE on 26. May 2019, 09:36:10
Hi Stéphane,
gate voltage must increase up to 3.2V. Please take a measure if you press PTT and crank up BIAS adjustment so that gate voltages are ~ 3.2V at the drains of PA transistors to GND. If you see complete Vcc of 12V you do have problems with transistors. If voltage is much lower than 12V your supply chain via inductors and transformers to drains is cut somewhere.
vy 73
Andreas |
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