QCX+ RF Power #qcx


David Griffiths
 

My 20m QCX+ is working quite happily albeit only on receive so far.
I have been measuring the output with a scope across the QRP Labs Dummy load and with a 12 V supply I am seeing 23.2V peak-to-peak, which I calculate at 1.3W.
At 16V supply this rises to 31.2V or 2.4W.  I don't know if it is relevant but the supply current  goes from 450mA at 12V to 580mA at 16V.

This is somewhat lower than expected, any suggestions gratefully received.

David
G4DMG


Evan Hand
 

David,
Where are you measuring on the dummy load?  If across the resistors and not the power tap, then your power measurement is correct.  If you are using the Power Connection on the dummy load, that is rectified voltage, so you would use the Vp*Vp/100 to get the approximate power out.  That would then be more like 5 watts.

The most accurate would be across the resistors.

73
Evan
A


David Griffiths
 

Across the resistors Evan, before the diode.

David
G4DMG


Ronald Taylor
 

Hi  David. On the 20 Meter version, some folks find that removing a couple of turns from L1, L2 and L3 will increase power output, if the issue is a lower than expected power output due to lower than expected cutoff frequency of the lowpass filter. You can also spread or squeeze turns on these toroids to get some improvement. I wouldn't remove more than 2 turns unless you have a spectrum analyzer to verify you are still meeting the spurious output requirements.

This turns removal is mentioned in the last sentence before the conclusion in Hans' troubleshooting procedure. https://qrp-labs.com/qcx/qcxtrouble.html
which is a very interesting and informative read..... 73 ... Ron


On Fri, Sep 11, 2020 at 10:46 AM David Griffiths <davidmgriffiths42@...> wrote:
Across the resistors Evan, before the diode.

David
G4DMG


David Griffiths
 

Thanks Ronald, Actually after winding L1, 2 and 3 they measured about 10% high on my Peak LCR45 so I took a turn off, they were still over the nominal inductance.

I will read Hans' troubleshooting guide again.

David
G4DMG


David Griffiths
 

I took one turn off L1, 2 and 3 but it made absolutely no difference to the RF output.
I don't think I want to take another turn off as I don't like too much rework on the pcb.

David
G4DMG


Ronald Taylor
 

You can still squeeze or spread turns spacing to vary the inductance a bit. You indicated you had removed 1 turn each after checking with the LCR meter, then you removed one more from each. So, if you have now already removed 2 turns total from each one, then you should be fairly close on inductance. So you should be at 14, 15 and 14 turns for L1, L2 and L3 respectively at this point. Turns are counted as times the wire passes through the center of the core, so you might want to verify that is correct. It's very easy to have one more turn than you thought. 

Also, L4 and C30 form the Class E resonant circuit. You should verify the turns count on L4 and make sure the right value of capacitor is in place for C30. You might want to pull C30 and measure it's value. This is a broadly resonant circuit but some have found it can be tweaked a bit. 

In one case out of many, I found a bad C29 causing a low power output issue, but this is only a very remote possibility.

If you have an oscilloscope, do some checking around the driver and PA sections according to the troubleshooting procedure.

Good luck ... Ron

On Sat, Sep 12, 2020 at 4:51 AM David Griffiths <davidmgriffiths42@...> wrote:
I took one turn off L1, 2 and 3 but it made absolutely no difference to the RF output.
I don't think I want to take another turn off as I don't like too much rework on the pcb.

David
G4DMG


ajparent1/KB1GMX
 

Try one turn from L4 and spreading the turns for best output.

Allison
--------------------------------
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Arv Evans
 

Might be interesting and informative if some ambitious person 
would do some tests and make chart or on-line calculator that 
shows the effect (tuning range) of spreading and compressing 
turns on a toroid.  This could possibly show ends of tuning ranges 
and indicate at which point one would need to add or subtract 
a turn versus where compressing or expanding turns could be 
effective.

Arv
_._


On Sat, Sep 12, 2020 at 11:09 AM ajparent1/KB1GMX <kb1gmx@...> wrote:
Try one turn from L4 and spreading the turns for best output.

Allison
--------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Phil/K3UT
 

Squeeze the turns on L1 and L2 together so that there is no space between turns. 

Worked for me on 20m and 30m versions after taking two turns off L1&L3 and one turn off L2. 

Don’t worry. Rework on the LP filter is quite simple to do. 

Phil K3UT 


Al Sines
 

Arv,

Not sure if this is exactly what you are thinking but so far with my new QCX PLUS 20 meter these are the RF output results:

Input voltage 14.5 
Reverse polarity diode is installed

After winding coils L1, L2 & L3 as specified in the manual:

1 watt out measured on bird wattmeter 

After spreading the windings on all three coils as much as possible:

3 watts out on the bird wattmeter 

After removing one turn each from L1, L2 & L3:

4.5 watts out on the bird wattmeter. 

I wound my coils very tight and close together at the start. 

I am thinking about removing one more turn each from L1, L2 & L3 to see the effect on the RF output.

In a way I am hesitant to do so cause it all works so well but sometimes my OCD makes me want to get the whole 5 watts out at about 13.2 volts (13.2 is the voltage of my bioenno when charged)


What say you?  Thanks

Alan, W3AL




On Sep 12, 2020, at 13:14, Arv Evans <arvid.evans@...> wrote:


Might be interesting and informative if some ambitious person 
would do some tests and make chart or on-line calculator that 
shows the effect (tuning range) of spreading and compressing 
turns on a toroid.  This could possibly show ends of tuning ranges 
and indicate at which point one would need to add or subtract 
a turn versus where compressing or expanding turns could be 
effective.

Arv
_._


On Sat, Sep 12, 2020 at 11:09 AM ajparent1/KB1GMX <kb1gmx@...> wrote:
Try one turn from L4 and spreading the turns for best output.

Allison
--------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Arv Evans
 

Al

My idea was to determine the tuning range of compressing versus expanding windings.  Once known this could predict whether you need to add or remove turns or just adjust turn spacing.

Adjustment of turn spacing is more about distributed capacitance than about changing the inductance, so making a predication formula or software tool may be a bit difficult.

Arv
_-_

On Sat, Sep 12, 2020, 4:05 PM Al Sines <sasines@...> wrote:
Arv,

Not sure if this is exactly what you are thinking but so far with my new QCX PLUS 20 meter these are the RF output results:

Input voltage 14.5 
Reverse polarity diode is installed

After winding coils L1, L2 & L3 as specified in the manual:

1 watt out measured on bird wattmeter 

After spreading the windings on all three coils as much as possible:

3 watts out on the bird wattmeter 

After removing one turn each from L1, L2 & L3:

4.5 watts out on the bird wattmeter. 

I wound my coils very tight and close together at the start. 

I am thinking about removing one more turn each from L1, L2 & L3 to see the effect on the RF output.

In a way I am hesitant to do so cause it all works so well but sometimes my OCD makes me want to get the whole 5 watts out at about 13.2 volts (13.2 is the voltage of my bioenno when charged)


What say you?  Thanks

Alan, W3AL




On Sep 12, 2020, at 13:14, Arv Evans <arvid.evans@...> wrote:


Might be interesting and informative if some ambitious person 
would do some tests and make chart or on-line calculator that 
shows the effect (tuning range) of spreading and compressing 
turns on a toroid.  This could possibly show ends of tuning ranges 
and indicate at which point one would need to add or subtract 
a turn versus where compressing or expanding turns could be 
effective.

Arv
_._


On Sat, Sep 12, 2020 at 11:09 AM ajparent1/KB1GMX <kb1gmx@...> wrote:
Try one turn from L4 and spreading the turns for best output.

Allison
--------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Dave VE3GSO
 

I am reminded of a time a friend retuned a 25W 2m transmitter and eventually got almost 60W output, as measured on a Bird Wattmeter. Unfortunately the fundamental was still only 25W, with the remaining power contained in spurs and harmonics that earned the wrath of the regulators.

So all I am saying is have a way to check for second and particularly third harmonic levels when you start raising the cut off frequency of the low pass filter.

Yes, it is entirely possible that the inductors are higher value than the design goal. And reducing turns to achieve the design value is a very good thing. Just be careful out there!

Dave


On Sep 12, 2020, at 18:53, Arv Evans <arvid.evans@...> wrote:


Al

My idea was to determine the tuning range of compressing versus expanding windings.  Once known this could predict whether you need to add or remove turns or just adjust turn spacing.

Adjustment of turn spacing is more about distributed capacitance than about changing the inductance, so making a predication formula or software tool may be a bit difficult.

Arv
_-_

On Sat, Sep 12, 2020, 4:05 PM Al Sines <sasines@...> wrote:
Arv,

Not sure if this is exactly what you are thinking but so far with my new QCX PLUS 20 meter these are the RF output results:

Input voltage 14.5 
Reverse polarity diode is installed

After winding coils L1, L2 & L3 as specified in the manual:

1 watt out measured on bird wattmeter 

After spreading the windings on all three coils as much as possible:

3 watts out on the bird wattmeter 

After removing one turn each from L1, L2 & L3:

4.5 watts out on the bird wattmeter. 

I wound my coils very tight and close together at the start. 

I am thinking about removing one more turn each from L1, L2 & L3 to see the effect on the RF output.

In a way I am hesitant to do so cause it all works so well but sometimes my OCD makes me want to get the whole 5 watts out at about 13.2 volts (13.2 is the voltage of my bioenno when charged)


What say you?  Thanks

Alan, W3AL




On Sep 12, 2020, at 13:14, Arv Evans <arvid.evans@...> wrote:


Might be interesting and informative if some ambitious person 
would do some tests and make chart or on-line calculator that 
shows the effect (tuning range) of spreading and compressing 
turns on a toroid.  This could possibly show ends of tuning ranges 
and indicate at which point one would need to add or subtract 
a turn versus where compressing or expanding turns could be 
effective.

Arv
_._


On Sat, Sep 12, 2020 at 11:09 AM ajparent1/KB1GMX <kb1gmx@...> wrote:
Try one turn from L4 and spreading the turns for best output.

Allison
--------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


R. Tyson
 

Hi,

You are getting 4.5 watts output.... good.
You want to fiddle about to get another 0.5 watts so you have 5 watts.....  hmmmm.

Why ?  You would have to increase your 4.5 watts to 4 times that level i.e. to 18 watts in order to gain 1 S point on the other guys reception of you. Why be OCD about 0.5 watts ?

Reg           G4NFR


Al Sines
 

Hi Reg

Yeah I know that’s why it’s called obsessive compulsive DISORDER!🤣

73,  Alan W3AL. 


On Sep 13, 2020, at 14:24, R. Tyson via groups.io <tysons2@...> wrote:

Hi,

You are getting 4.5 watts output.... good.
You want to fiddle about to get another 0.5 watts so you have 5 watts.....  hmmmm.

Why ?  You would have to increase your 4.5 watts to 4 times that level i.e. to 18 watts in order to gain 1 S point on the other guys reception of you. Why be OCD about 0.5 watts ?

Reg           G4NFR