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QCX+ 3.98 Watts to 7.9 Watts...Here is what I did...


Brian N7BKV
 

I have been running my QCX+ for a couple of weeks now.  Initially the onboard power meter (Menu 9.2 RF Power) indicated 3.98 watts when I first got the radio powered up on 13.8 volts supply.

So I went back into the radio today and did another alignment procedure several times.  Cleaned up a few things and remeasured  into a dummy load.  This time the onboard watt meter pegged at 5.2 watts (that is all it goes).  I put the MFJ 868 Wattmeter inline and it measured about the same.

So I reviewed Han's video on Tuning Up Your QCX.  It is on the QRP Labs YouTube channel.  Messed with toroids just like he said   Measured performance at each messing.

The net of what I did was this: I spread out L4 windings, L3 stayed the same in the end,  Spread L1 a bit.  And REALLY compressed L2.   There were some not so good tries along the way that proved no good. So I just reversed the effort and tried the next thing.  Your experience will be different.  Measure watts at each step you take.

End result:  6.5 watts !!!!!!  Yippie!!!!  It seems mostly  in the toroids--Twist and Shout!!!!

Watch the vid and document your steps and results.

Once I had that all put to bed I switched from the Samlex 13.8 volt power supply to the Toshiba 15 volt supply.  That is the one I powered my original QCX with, which ran reliably at 7 watts.  This new QCX+ is delivering 7.9 watts into the antenna!!  I am happy.

Hope this helps someone.

Next step is to put the 50W PA on the new 20 volt PS that arrived today.  On 13.8 volts  and all tuned up it was delivering 47 watts. 
More to come!

73
Brian N
N7BKV


Shane Justice
 

Brian,

Great work! Congratulations! Now if I can do the same, I'll join you on the bands!

Cheers,
Shane
KE7TR


On Oct 17, 2020 at 20:32, Brian N7BKV <cl@...> wrote:

I have been running my QCX+ for a couple of weeks now.  Initially the onboard power meter (Menu 9.2 RF Power) indicated 3.98 watts when I first got the radio powered up on 13.8 volts supply.

So I went back into the radio today and did another alignment procedure several times.  Cleaned up a few things and remeasured  into a dummy load.  This time the onboard watt meter pegged at 5.2 watts (that is all it goes).  I put the MFJ 868 Wattmeter inline and it measured about the same.

So I reviewed Han's video on Tuning Up Your QCX.  It is on the QRP Labs YouTube channel.  Messed with toroids just like he said   Measured performance at each messing.

The net of what I did was this: I spread out L4 windings, L3 stayed the same in the end,  Spread L1 a bit.  And REALLY compressed L2.   There were some not so good tries along the way that proved no good. So I just reversed the effort and tried the next thing.  Your experience will be different.  Measure watts at each step you take.

End result:  6.5 watts !!!!!!  Yippie!!!!  It seems mostly  in the toroids--Twist and Shout!!!!

Watch the vid and document your steps and results.

Once I had that all put to bed I switched from the Samlex 13.8 volt power supply to the Toshiba 15 volt supply.  That is the one I powered my original QCX with, which ran reliably at 7 watts.  This new QCX+ is delivering 7.9 watts into the antenna!!  I am happy.

Hope this helps someone.

Next step is to put the 50W PA on the new 20 volt PS that arrived today.  On 13.8 volts  and all tuned up it was delivering 47 watts. 
More to come!

73
Brian N
N7BKV


Ian VA7ITM
 

Great job Brian. What band is your QCX+?

73 Ian


m0bmn
 

Thats a lot of power from 3 x 170 fets!
I see your running it with the 50watt amp, the manual suggests keeping the drive to below 5 watts so it maybe a good idea to drop the voltage on the QCX a little to prevent problems with the amplifier. 
But good job on getting that much power out, mine runs 5 watts on 13.8v and i am feeding that into the amp , mind you i only have 13.8v powering the amp too, i get about 25watts set like this.
is amazing how much power you can get out of the QCX really and if it did give up you can swap out all three fets for less than a quid  (or Dollar to friends across the pond).
great job, now waiting for the QCX mini and then the QSX !


@CurtisM
 

if we think in dB, its not a vast delta between 4.5 and 7 watts -- and the strain on the QCX may not be worth it.  add the strain to driving the QCX PA (and potentially compromising its emission purity some.  good to experiment, but sometimes the answer is moderation.  and remember our wattmeters don't necessarily read the same levels, and they can be impacted to the actual load impedance of the antenna (or dummy load).  

enjoy you radiations.

curt


g4edg
 

Brian

I think you need to verify the accuracy of your power meter. Everyone seems to struggle to get just 5w out of their QCX. You quote the output of your 50w amp as 47w at just 13.8v....a full 22w above the best case (40m) situation according to the 50w amp documentation.

Perhaps you can check the input current taken at these power output levels and see if you have an appropriate level of efficiency?

If you have a scope measure the voltage developed across your dummy load and calculate the power from those figures.

Regards

Steve G4EDG



Brian N7BKV
 

All of this was quite a bit of experimentation. When I am done with one more test, the 20 V supply to the amp, I will probably back off and run both from the Samlex 13.8v supply through the RigRunner fused distribution box.  Keeps things simpler.  And also spread the L2 windings back out a bit.  Compressing them resulted in the greatest increase. Hopefully this will dial it down and still leave plenty of performance. And not over-task the input attenuator.

The "20V" PS I will try out is a genuine Hewlett Packard new old stock laptop PS from back when they still built good consumer electronics.  It is rated at 19.5v and 7.7 amps.  Hope it is as quiet at the 15v  Toshiba running now.

And as a side note, the 50 W blew it's 5 amp supply line fuse.  It really does draw the 5 to 6 amps per the book!   I put in a 7.5 amp fuse.  So far so good. Will see how long that lasts.

Pushing the QCX output was mainly to see just what all the fiddling per the video can do.  Point is there are some people a bit disappointed with their QCX output but don't need to be.  Yet pushing it like I did is not necessary either. 

Thanks for the feedback.  I have been enjoying the ride.  Reports from ops on air are great.  And no smoke yet!

73
Brian N
N7BKV


On Sun, Oct 18, 2020 at 06:49 AM, @CurtisM wrote:
if we think in dB, its not a vast delta between 4.5 and 7 watts -- and the strain on the QCX may not be worth it.  add the strain to driving the QCX PA (and potentially compromising its emission purity some.  good to experiment, but sometimes the answer is moderation.  and remember our wattmeters don't necessarily read the same levels, and they can be impacted to the actual load impedance of the antenna (or dummy load).  


Brian N7BKV
 

40 Meter


On Sun, Oct 18, 2020 at 01:14 AM, Ian VA7ITM wrote:
Great job Brian. What band is your QCX+?


Brian N7BKV
 

I was jamming 15v into the QCX and the 7.9w out was probably rolling right over the 50w input attenuator.  I kept measuring components with the IR thermometer and only operating a few seconds at a time.  But, yes, the MFJ Wattmeter is only giving me relative differences from one condition to another as I fiddle around.  It is certainly "indicated" and not necessarily "true" power.

The chart in 8.1 was using a QCX putting out 3.2 watts.  So I am in no-mans-land with my experiment.  My outputs will be different than the chart, but how different and how accurate I cannot say without some better test equipment.  I just hope I don't bust something up before I am done!


On Sun, Oct 18, 2020 at 08:52 AM, g4edg wrote:
You quote the output of your 50w amp as 47w at just 13.8v....a full 22w above the best case (40m) situation according to the 50w amp documentation.


Hans Summers
 

Hi Steve

I think you need to verify the accuracy of your power meter. Everyone seems to struggle to get just 5w out of their QCX.

I've quite frequently seen 40m QCXs giving in the 7W ballpark at 13.8V supply after adjustment. 

I've received a lot of compliments on my video on QCX tune-up, see https://youtu.be/eN7wER05T-c

With the procedure demonstrated in the video, it should not be a struggle for anyone to get 5W out of their QCX on any band version. 

73 Hans G0UPL 


R. Tyson
 

Pushing the QCX and the 50w amp will not ensure a long life for them.
It's a sad fact of life but... if a QCX (or any other radio) is putting out a 4 watts signal then in order to increase that signal by 1 S point it would require 4 times the power. To bump up the other guys S meter by 1 point means your RF power would have to increase from 4 watts to 16 watts.

Increasing the voltage on the QCX is only going to stress the components and at the end of all the fiddling to get an extra watt or two is barely going to register on the other guys S meter. If you want more power than the QCX provides when set up normally then you need a different rig.

Reg          G4NFR


R. Tyson
 


I've received a lot of compliments on my video on QCX tune-up, see https://youtu.be/eN7wER05T-c
 
With the procedure demonstrated in the video, it should not be a struggle for anyone to get 5W out of their QCX on any band version. 
 
73 Hans G0UPL 

I will take the opportunity to compliment you as well Hans. It was fascinating to watch so thank you for that video.

Reg                             G4NFR


Brian N7BKV
 

So here is the final result of my experimentation which shot the power WAY up for a QCX and 50W:
After trying different combinations of power supply voltages to the QCX+ and the 50W PA in the end I settled on this:

13.8 volts to the radio.  Dialed down from 15 volts
13.8 volts to the amp.  Dialed down from 20 volts.
I spread the L2 back out to reduce the watts to 5.6 on the 13.8 volts supply
Indicated under those conditions on the MFJ SWR/Wattmeter are 42 watts out to an antenna.
Before closing everything up I did an final 9.2 RF Power check of the radio TX into a dummy load/no amp.
Result was 5.2 watts.  That's the peg on that onboard meter.  So the 5.6 watts on the MFJ for radio/no amp is probably pretty close

Following all that exercise I squared away the rig and operating desk and spent several hours on the air
Good results and QSO's. 
And I also checked the temp over the heat sinks with an IR gun and read nothing higher than about 85F.  About 10 degrees above ambient.

Good results.  Leaned a lot.  No smoke.  Works great!
Thanks to all who contributed thoughts on the exercise.

PS  For those who are curious, supplying 15v to the radio (with the compressed L2 windings) and 20 v to the amp the MFJ 868 Wattmeter indicated over 65!!!!   (Don't cringe Hans)
Can't say how accurate that meter is under those conditions, but also the SWR went from 1.1 to 1.6.
I only keyed down for a couple of seconds at a time and give it a lot of rest in between. And held my breath that nothing blew up.


Hans Summers
 

Hi Brian 

No cringing here... I think if i recall correctly my record was 86W! Into QRP Labw 20W dummy load.   :-O

But I would recommend much more than 50W ordinarily. 50W is safe and durable and I've not counted recently but at the last count, I've had over 500 QSOs with a bit over 50W on 40m. 

73 Hans G0UPL 



On Mon, Oct 19, 2020, 07:12 Brian N7BKV <cl@...> wrote:
So here is the final result of my experimentation which shot the power WAY up for a QCX and 50W:
After trying different combinations of power supply voltages to the QCX+ and the 50W PA in the end I settled on this:

13.8 volts to the radio.  Dialed down from 15 volts
13.8 volts to the amp.  Dialed down from 20 volts.
I spread the L2 back out to reduce the watts to 5.6 on the 13.8 volts supply
Indicated under those conditions on the MFJ SWR/Wattmeter are 42 watts out to an antenna.
Before closing everything up I did an final 9.2 RF Power check of the radio TX into a dummy load/no amp.
Result was 5.2 watts.  That's the peg on that onboard meter.  So the 5.6 watts on the MFJ for radio/no amp is probably pretty close

Following all that exercise I squared away the rig and operating desk and spent several hours on the air
Good results and QSO's. 
And I also checked the temp over the heat sinks with an IR gun and read nothing higher than about 85F.  About 10 degrees above ambient.

Good results.  Leaned a lot.  No smoke.  Works great!
Thanks to all who contributed thoughts on the exercise.

PS  For those who are curious, supplying 15v to the radio (with the compressed L2 windings) and 20 v to the amp the MFJ 868 Wattmeter indicated over 65!!!!   (Don't cringe Hans)
Can't say how accurate that meter is under those conditions, but also the SWR went from 1.1 to 1.6.
I only keyed down for a couple of seconds at a time and give it a lot of rest in between. And held my breath that nothing blew up.