QCX+ LOW POWER QUESTION #toroid #40m #alignment #calibration #power


kf7rcm@yahoo.com
 

The following post is a corrected message. I got some of the numbers wrong, I was in a rush.

Got it finished off and the only problem is I get an indicated 2.3w with 13v. If I turn my power supply all the way up (16.5v), I get an indicated 3.2w. I've done everything short of rewinding L1,2 and 3. I am willing to settle for the 2.3 at this point and hook up the amplifier once I am finished with that. Question is, has anyone rewound L1,2 and 3 in an act of desperation? And if so, did it do any good?
Bonus question: anyone know what the voltage should be at the BNC?


Curt wb8yyy
 

 If you built per instructions 2.3 watts is not shocking. Have you removed any turns?  Start with inductor on PA side. Remove 2 turns to see if power increases. Hans does have a tune up video. 

Curt


Evan Hand
 

Hans recorded a video on tuning the QCX+ for optimum performance. 
https://www.youtube.com/watch?v=eN7wER05T-c

Let us know if this helps.

73
Evan
AC9TU


kf7rcm@yahoo.com
 

Yes, saw the video, FB.
Removed two turns from L3, didn't do anything. I'd like almost four watts but honestly, I can live with 2+. I do get 3.3 on 16v, which isn't bad. I want to start getting out in the field to use it, so I will have to look into 16v power sources.


Ted <k3rta@...>
 

Four LiFePo cells in a row do make a nice 16v supply.  It would be good to see 4w at 12v, though.   

Ted
K3RTA


Charles Johnson
 

Got it finished off and the only problem is I get an indicated 2.3w with 13v. If I turn my power supply all the way up (16.5v), I get an indicated 3.2w. I've done everything short of rewinding L1,2 and 3. I am willing to settle for the 2.3 at this point and hook up the amplifier once I am finished with that. Question is, has anyone rewound L1,2 and 3 in an act of desperation? And if so, did it do any good? 
My QCX+ is also built for 40m. When I first powered it up, I was getting ~3W with 13.84V input. Adjusting the wire turn spacing on the toroids (L1-3 and the small red one) increased my output to ~4.25W (measured via QRP Labs 20W dummy load w/ 0.6V added to measured voltage to account for diode loss). All toroids were wound with the number of turns specified in the manual. Note: On all but one toroid (it may have been the small red one), evening out the turn spacing helped, but for one of them, when I evenly spaced out the turns, the output went DOWN, but when I pinched them together a bit, the power loss was made up and then, IIRC, there was a 0.4-0.5W output power increase on top of that.

Maybe I lucked out, but good solder joints for the toroids (and everything else, of course) and then some fiddling with the spacing on the toroids and I'd think that 4W or better is attainable.

Regards,

Charles Johnson
KF4AYT


R. Tyson
 

On Fri, Jun 24, 2022 at 03:05 PM, Charles Johnson wrote:
I've done everything short of rewinding L1,2 and 3. I am willing to settle for the 2.3 at this point
Might I suggest following the way Hans tunes up the QCX in the excellent video he produced.
I have built a couple of 40m QCX's and they do not need turns removing from the lpf toroids, assuming they have been wound correctly.
Spreading or compressing the turns, starting with L3 should allow you to bring the output power up.
I personally would not be happy supplying the QCX with 16v I prefer to run equipment at a level that shouldn't stress it. With 30 and 20m QCX's I have left two turns off L3 and that allows tuning for 4 to 5 w out but the 40m QCX tunes up nicely with the recommended number of turns on each toroid. For the difference you see between 12v or 16v supply it isn't going to be measurable by the other guy. I believe you are going to use an amp ? If it is the 50w amp then I find that does make a big difference.

Reg                              G4NFR


Colin Evans M1BUU
 

I recently (this week) built a QCX-mini 40. I used the number of turns on the LPF toroids as specified. I wound the toroids tight and with the turns close together to begin with.

I tweaked the LPF toroid turns with a sharpened wooden lolly stick, starting with the coils closed up, I spread the turns experimentally watching the change in transmitted power as I went - tweak a bit, transmit a bit, tweak a bit etc.

I got to 4.5w at 12v and decided that that was enough, it was possible to keep going higher. (I'm seeing 6w at 13.8v)

Following the video by Hans is good advice.


QCX mini 40 after tweaking turns for 4.5w RF output.

73, Colin, M1BUU 


kf7rcm@yahoo.com
 

Yes, their amp, and it's in the mail to me. I figured that even the amp at 12-13v will give something in the 25+/-w range. Since I will be taking it with me on a SxS (Cannot hike anymore due to being mangled in a car wreck), I don't really mind the little bulk and weight with the battery. 
I have to say that I am so happy with this radio that I have ordered the 20m version with the add-ons yesterday. I will probably be getting the mini version as well.


kf7rcm@yahoo.com
 

Just spent 20 mins messing with the torroid(s) and got another 0.01 of a watt more. I will be satisfied with that.


Gary Bernard
 

My 40-meter build had just under 5 when completed. A little adjusting and I now have 6. It pays.
Gary W0CKI


-----Original Message-----
From: kf7rcm via groups.io <kf7rcm@...>
To: QRPLabs@groups.io
Sent: Fri, Jun 24, 2022 4:18 pm
Subject: Re: [QRPLabs] QCX+ LOW POWER QUESTION #toroid #40m #alignment #calibration #power

Just spent 20 mins messing with the torroid(s) and got another 0.01 of a watt more. I will be satisfied with that.


kf7rcm@yahoo.com
 

Same thing, torriods? Or something else?


Curt wb8yyy
 

OM kf7rcm

Unless you have misplaced the caps in low pass filter, which I doubt, it's likely toroids. Thousands of builders know mostly because they have been there. I took 2 or 3 turns off my 20m mini. So when I suggested 2 turns it was just a thought. I see Colin has some nice details. So I think it needs more time. 

Operating at 15 or 16 volts invites damage if you ever experience a bad match. Such as using an antenna tuner. You can make contacts at 2 watts, enjoy, but I suggest getting up to 4 watts. The qcx PA also does better with added output from the rig.  

Be careful to only adjust one toroid at a time to sort out progress. 

Curt


R. Tyson
 

On Fri, Jun 24, 2022 at 10:14 PM, <kf7rcm@...> wrote:
I have to say that I am so happy with this radio that I have ordered the 20m version with the add-ons yesterday.
They are brilliant radios. I have been using them for some time now. I have had a 40m QCX+ for over two years now. I have the original version as well. With the 50w amp I can work them if I can hear them. I have several versions and they are a pleasure to use. I use a fan dipole at home so can change bands with no need to tune up.

Take your time when building the amp, Make absolutely sure that you have the leads from the toroids going into the right place on the board.
For the trifilar wound toroid I usually put a small piece of heat shrink on each lead so I know where it supposed to go. Make sure the enamel coating is cleaned off the leads well.

For home use I use older type Hewlett Packard laptop power supplies. The ones I use are 19v and around 9 amps. They are cheap and well screened. If you do get one then there is an outer sheath under the insulation on the connecting lead. Under that is a thick'ish white wire and in the centre of the white wire is a thin wire with blue insulation. You can ignore the blue wire, just cut it off, I think it is there to tell the laptop it has a genuine HP power supply attached.

Reg                                    G4NFR


kf7rcm@yahoo.com
 

I love my dbl bazooka inverted V, but I like your idea of a fan. Will certainly be looking into that.