开云体育

I just finished building a QDX board version 3 with the latest 1.10 firmware installed and have been testing it. I built it for 9v operation and am using a variable bench power supply to test it. I have made a few FT8 QSOs on both 40m and 20m, I am noticing the power starts out at about 4w and slowly drops to about 2w by the end of the FT8 transmission cycle. The voltage from the power supply is a rock solid 9v. The current draw on transmit starts at about 1.02 amps and drops to about .4 - .5 amps by the end of the transmission cycle. Is this normal and if not, what should I be looking at?

?

73 Doug WB5WRC

Doug, that's not normal, no.? I'm not sure what to point to, though. Something impacted by current...... so could be T1, L14, or BS170 soldering faults? I suppose if something in the LPF was heating too, but I assume this is happening on 20 and 40m, so probably not that.??

?

-Nate

N8BTR?

Hi Doug,

?

I agree with Nate that the symptom you describe is not normal.? My guess is that the BS170s are getting warm.? The resistance of a MOSFET increases as the temperature rises, reducing the power output.? The best way to verify this is to open the lid of the QDX and use canned air to cool the BS170s.? If the power increases, then heat is the cause.

?

73

Evan

AC9TU

Thank you for your responses and yes that makes sense. I wasn't thinking about how mosfets behave when overheated. I checked all the solder joints and ohmed out Q8 - Q11, T1 and L14 to see they had continuity where they were supposed to have it on the circuit board. I suspect I have either wound T1 incorrectly or I have scraped some enamel off the wire and it's shorting to an adjacent wire or the core. I am considering rewinding it with fresh wire if I can get it off the board without damaging it. I'm open to alternate suggestions. ?

?

73 Doug WB5WRC

Hi Doug, May I suggest to remove T1, cut the leads with a flush cutter and then remove the individual pieces left. Use a solder sucker and maybe some solder braid to clean things up. Also if you need to, use a dental pick to open the holes while heating with your soldering iron to make enough room to put the new wires in.

Dean - KC9REN

?

On Sat, Mar 29, 2025 at 05:23 PM, Doug wrote:

Thank you, that is the plan. Just waiting on the wire to arrive.?

?

73 Doug WB5WRC