QDX TX current in spec/slightly above on one band only.


Mike Easterbrook
 

Hi All
Completed my build after replacing short circuit C38 (see separate thread)
Now in set-up phase, still with minimal resources after house relocation (have only laptop, 50 ohm dummy load, DMM, soldering iron and QCX 20 &17 - no HF antenna, no SWR/Power meter)
Fortunately challenges are always welcome.

Original version, T1 wound for 9V, 9V supply, only mod is 3.3 v regulator fed from 5v line. I think I updated firmware to 1.03 but not sure as it all happened very quickly.  Is there a way to determine installed firmware version?

Current Measurements (FT8 Mode): 
                Stand-by/RX 120 mA on 20,30,40 
                Stand-by/RX 110 mA on 80

               TX 20 metre 260 mA
               TX 30 metre 1030 mA
               TX 40 metre 240 mA
               TX 80 metre 340 mA
I have reflowed solder joints to all hand-wound inductors - no significant change in any current measurement.

PA FETs very hot to touch after running FT8 for 3-4 cycles.

Anything I could be usefully looking at now before I get more of my tools together.

Thanks
Mike 9V1LX


Alan G4ZFQ
 

Is there a way to determine installed firmware version?
Mike,

The terminal (Putty)
Also I think you will see it if you go to upgrade mode, the filename shows the installed firmware version.

Make sure it is the latest.

Stand-by/RX 120 mA on 20,30,40
               TX 20 metre 260 mA
               TX 30 metre 1030 mA
               TX 40 metre 240 mA
               TX 80 metre 340 mA

PA FETs very hot to touch after running FT8 for 3-4 cycles.
I guess that is on 30m only?

The currents are strange, why around normal on 30m I reckon. I run mine well under voltage so do not know how hot the BS170s get at full power.
I wonder if the LPF switching is working?
Try the filter traces with a dummy load and the terminal.
Check the voltages on the LPF diodes on each band.

73 Alan G4ZFQ


Evan Hand
 

On Sun, Mar 6, 2022, at 04:57 AM, Mike Easterbrook wrote:
Is there a way to determine installed firmware version?
Hi Mike,

The current firmware version is displayed in the terminal program of the QDX on the home/start-up screen.

My rev 1 QDX is built for 12 volts.  The 4 bands are close to the same power(4.5watts) and current (0.7amps).  When the transmitter power/current varies beyond expected values, the first suspect is the low pass filter.  The QDX uses the same LPF for both 20 and 30 meters, so I would first verify the turns on the toroids and the capacitor values.  Here is a picture of the LPF section of my QDX. 



Note that I have "tweaked" the 20/30meter toroids near the top of the picture.  I used an LC meter that I trust to adjust the inductance values to be the same as the schematic before installing them.  I did this for all 6 LPF toroids (that is why the turns are not evenly spaced around the toroids).

Making some quick approximations, The problem that you seem to have is that 30meters is the only band close to the correct power level, yet that is the one you stated causes the finals to over-heat.  With my QDX, I can use the terminal program to put the QDX in transmit and hold down the T key for a minute without causing the finals to overheat.

First, I would check that the correct filter is being selected by measuring the voltage drop across the 6 selected diodes.  Only the two for the band selected should show forward voltage.

I would also check the drain and gate voltages of the final BS170 FETs when transmitting.  You should have 2.5volts on the gates and the supplied voltage on the drains.  The gate signal is a 5volt square wave, so it should read 2.5volts on a DMM.

Above are suggestions.  You may need to get out your test equipment to diagnose more.
73
Evan
AC9TU


Mike Easterbrook
 

Hi Evan
Thanks for the feedback.  I had already checked the BC170 voltages and all showed 0/2.5v as expected.  What I omitted was to repeat the measurement across all four frequency ranges (and didn't note the selected band at the time!.)  Getting late here now so will do this tomorrow.  I also checked the inductances of all the coils during the build and adjusted spacings accordingly. Would be good to compare with your build but unfortunately the image file won't open from e-mail. Are you able to resend in a different format?
Mike 9V1LX

Virus-free. www.avg.com


Evan Hand
 

Here is the raw file


Mike Easterbrook
 

Hi Alan, Evan

Apologies for having taken up your time with this enquiry.  I have now downgraded myself to "Newbie" having committed one of the basic kit building sins (I believe the photo says it all).  Remaining three LPFs now have their diodes in place!

Current draw versus band now much closer to specification:

Supply = 9v
Standby/RX:   120mA
TX 20m 970 mA
TX 30m 1110 mA
TX 40m 940 mA
TX 80m 910 mA

PA FETs 30m bearably hot, other bands warm.

Planning to run with 8v which I think will be close to Hans' suggested 6W max output.

Need to get some connectors for patch leads and I'll be able to measure power and hopefully connect to my multiband dipole.

Still haven't figured out PuTTY.   The instructions seem to be in a language I'm unfamiliar with!

Mike 9V1LX

Virus-free. www.avg.com

On Sun, Mar 6, 2022 at 7:55 PM Alan G4ZFQ <alan4alan@...> wrote:
>Is there a way to determine
> installed firmware version?

Mike,

The terminal (Putty)
Also I think you will see it if you go to upgrade mode, the filename
shows the installed firmware version.

Make sure it is the latest.

 >Stand-by/RX 120 mA on 20,30,40
>                 TX 20 metre 260 mA
>                 TX 30 metre 1030 mA
>                 TX 40 metre 240 mA
>                 TX 80 metre 340 mA


> PA FETs very hot to touch after running FT8 for 3-4 cycles.

I guess that is on 30m only?

The currents are strange, why around normal on 30m I reckon. I run mine
well under voltage so do not know how hot the BS170s get at full power.
I wonder if the LPF switching is working?
Try the filter traces with a dummy load and the terminal.
Check the voltages on the LPF diodes on each band.

73 Alan G4ZFQ






Virus-free. www.avg.com


Alan G4ZFQ
 

Still haven't figured out PuTTY.   The instructions seem to be in a language I'm unfamiliar with!
Mike, OK about the diodes, now I'm wondering how you got the strange results you did:-)

Putty just needs installing on whatever system you use. Windows for me.
Start it, set it as in the firmware manual. Windows, set the COM port number not that funny Linux identifier.
"Open" then you should see the QDX menu.

73 Alan G4ZFQ