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Re: Low output on 20 meter QCX

Hans Summers
 

Hi all

To confirm, all QRP Labs kits capacitors are always NP0 (also known as C0G, CC4, Class 1 dielectric types), both in the LPFs, BPFs, and any other places in the circuit where capacitors below 10nF are used. 10nF and above, including the ones used in the 630m and 2200m LPF kits, are NOT NP0 because the capacitors were not available in NP0 at high values. But on 630m and 2200m it is not so critical anyway.

If the Low Pass Filter has an incorrect shape, such as a cut-off below the operating frequency, then the filter will attenuate at the operating frequency, which will reduce power output. This attenuated power must go somewhere! For example, in a 14MHz filter, with a 5W transmitter, if the 3dB point is actually at 14MHz, then you will only get 2.5W output. What happened to the other 2.5W? It is dissipated as heat in the LPF components! The capacitors are small, and any heat dissipation in them naturally results in a temperature rise. These inescapable laws of physics apply regardless of the capacitor type. And naturally, if you replace the tiny NP0 capacitors supplied, with larger silver-mica types... then all other things being equal, the larger types will exhibit a lower temperature rise, even if they dissipate the same heat energy - just because they are able to radiate it away faster due to their larger size. 

This is why the 3dB cut-off is supposed to be a bit higher than the operating frequency, so that hopefully at the operating frequency the attenuation is near zero. If this is not the case, then it is possible that the component values are wrong - either due to component tolerances, or winding style; I have found that the easiest way to fix this is just to remove a couple of turns from each of L1, L2, L3. After removing turns I generally do NOT try to put the wire back in the hole... I just solder the wire to the pad on the top side of the PCB with a small blob of solder. Check that in removing the wire, the through-hole plating or traces were not damaged. The DVM DC continuity check is well worth repeating, after re-installing the toroids. 

73 Hans G0UPL

On Wed, Feb 14, 2018 at 12:22 AM, Jim <ei8igjim@...> wrote:

Hi Randy,

 I had the same problem here !! I just took 2 turns off L1 L2 & L3 now Ive got 3.5 watts out on keyup ( I did have 3.5watts after holding down the key for about 15 to 20 seconds but was back to 1 wat straight after un keying again) Now 3.5 watts straight away !! Happy Happy

On 13/02/2018 14:27, Randy Ott wrote:
Just finished building a QCX for 20 meters.  I am only getting about 1.5 watts output with 12V input. After holding the key down for 10 or 15 seconds, the power output will slowly climb to about 2 watts.



Re: Low output on 20 meter QCX

Jim
 

Hi Randy,

 I had the same problem here !! I just took 2 turns off L1 L2 & L3 now Ive got 3.5 watts out on keyup ( I did have 3.5watts after holding down the key for about 15 to 20 seconds but was back to 1 wat straight after un keying again) Now 3.5 watts straight away !! Happy Happy

On 13/02/2018 14:27, Randy Ott wrote:
Just finished building a QCX for 20 meters.  I am only getting about 1.5 watts output with 12V input. After holding the key down for 10 or 15 seconds, the power output will slowly climb to about 2 watts.

_._,_._,_


It’s home and first QSO!

Jess Gypin <ontarget1911@...>
 

My QCX 40 finally found its way home from Hans. Working perfectly. First QSO was KH7XS Hawaii. 559 given. My antenna is. 100 foot end fed with a 9:1 balun.
Could not be happier. One small glitch. I tried editing the memory for a CW message. Got it loaded and really don’t know how to play the messages yet (I know RTFM) and some where in the process I pressed the built in key I think. Now when I press the left select button to edit the message, the display fills with asterisks and I cannot edit the message via the key or the rotary. I really don’t want to reset the radio, I just got it back! Any clues out there?
Full 5 watts out, great receiver, awesome radio. Thanks Hans for the radio and support. Glad I was one of your Guinea Pigs!

Jess AE0CW


Re: Low output on 20 meter QCX

Randy Ott
 

I am preparing some toroids with fewer turns and larger gauge wire in order to attempt improvement of the LPF. As I look around at discussions on the internet on this issue, it appears that low power and capacitor heating on 20m QCX has been a known problem for several months. I am surprised there has not been a solution for this problem yet. I'm certainly not the only one having this issue.
K5HJ 


QCX 20 #1935

Glen Sr
 

I relocated L5,  connecting it to pins 7 and 20, and unit turns on immediately. My next problem is when I turn power on the calibration signal comes on immediately. It is adjustable by volume control. What should I look for since I have yet to ask for it? I tried factory reset numerous times with no change? Thanks! Glen n8we


Receiver module FST3253

Martin Wilens
 

Just curious,

I was looking at the scematic of the Receiver module in receiver.pdf
Why is pin1 of FST3253 called VEE while de datasheet says OE Output Enable?
Is it not more logical to draw it on de upperside of the IC1 blok instead of drawing it near de powersupply in the leftcorner?

Thanks for answering,
Martin 


Re: Low output on 20 meter QCX

Randy Ott
 

Thanks to Richard and Alan for your responses.
I would be very happy with 4.4W output and cool running capacitors.

I do suspect that the supplied capacitors and too high of a DF for this application.
I had some cheap ceramic disc capacitors from a Chinese eBay assortment but they aren't so great either.

I measured the inductance of all of the toroids before installing them but I'll take a look at lowering the inductance as well.
I will also model the circuit and see what it looks like after I catch up on my sleep. ;-)

Thanks,
Randy K5HJ


Re: QCX 40m - BPF 9 with Tone but C1 Unresponsive

Steve Z
 

Turn down the volume pot so that the indicator is 04 to 06. Once you do this you should be able to optimize the C1 trimmer cap.

Steve N9SZ


Re: Low output on 20 meter QCX

Richard Harris <g3otk@...>
 

Randy,

I changed (with some difficulty) the C25 and C26 390pF capacitors and replaced them with a pair made up of 330pF + 56pF 100V NPO ceramic caps.  In the end I cut out the original 390pF and soldering the replacements to the back of the PCB.

With the original 390pF caps I was getting about 2.5W earlier this afternoon, which slowly increased as the key was held down.  With the new caps I am getting 4.4W (measured using my digital scope across a 5W 50 Ohm resistor) and the voltage remains constant..  Both measurements were at 13.8V input.  I speculate that the capacitors provided might not be NPO/COG but perhaps X7R or similar.  

Richard G3OTK




On Tuesday, 13 February 2018, 15:49, Richard Harris via Groups.Io <g3otk@...> wrote:


Hi Randy,

Your email prompted me to check out the filter area of my 20m QCX.  I have an IR thermometer and although it is difficult to be sure exactly what it is looking at, there is a fairly rapid temperature rise in the immediate vicinity of those two capacitors.  I have a useful stock of 100V NPO ceramic capacitors and I may try changing C25 and C26 with a combination to make up about 390pF.  

Richard G3OTK


On Tuesday, 13 February 2018, 14:29, Randy Ott <k5hj@...> wrote:


Just finished building a QCX for 20 meters.  I am only getting about 1.5 watts output with 12V input. After holding the key down for 10 or 15 seconds, the power output will slowly climb to about 2 watts.
If I raise the input voltage closer to 15V, I can get about 2.5 watts.  Again, this is after several seconds of key down.
It turns out that the two 390pF capacitors, C25 and C26, in the lowpass filter get very hot. I tried replacing them with some small ceramic disks of questionable heritage that I had on hand but they get hot as well.
I am thinking that these need to be silver mica capacitors rated for at least 100V.  Unfortunately, I don't have anything suitable that I can get my hands on easily.

Any thoughts on my findings?

Randy, K5HJ





Re: Low output on 20 meter QCX

Richard Harris <g3otk@...>
 

Hi Randy,

Your email prompted me to check out the filter area of my 20m QCX.  I have an IR thermometer and although it is difficult to be sure exactly what it is looking at, there is a fairly rapid temperature rise in the immediate vicinity of those two capacitors.  I have a useful stock of 100V NPO ceramic capacitors and I may try changing C25 and C26 with a combination to make up about 390pF.  

Richard G3OTK


On Tuesday, 13 February 2018, 14:29, Randy Ott <k5hj@...> wrote:


Just finished building a QCX for 20 meters.  I am only getting about 1.5 watts output with 12V input. After holding the key down for 10 or 15 seconds, the power output will slowly climb to about 2 watts.
If I raise the input voltage closer to 15V, I can get about 2.5 watts.  Again, this is after several seconds of key down.
It turns out that the two 390pF capacitors, C25 and C26, in the lowpass filter get very hot. I tried replacing them with some small ceramic disks of questionable heritage that I had on hand but they get hot as well.
I am thinking that these need to be silver mica capacitors rated for at least 100V.  Unfortunately, I don't have anything suitable that I can get my hands on easily.

Any thoughts on my findings?

Randy, K5HJ



Re: Low output on 20 meter QCX

Alan G4ZFQ
 

After holding the key down for 10 or 15
seconds, the power output will slowly climb to about 2 watts.
If I raise the input voltage closer to 15V, I can get about 2.5 watts. Again, this is after several seconds of key down.
It turns out that the two 390pF capacitors, C25 and C26, in the lowpass filter get very hot. I tried replacing them with some small ceramic disks of questionable heritage that I had on hand but they get hot as well.
I am thinking that these need to be silver mica capacitors rated for at least 100V.  Unfortunately, I don't have anything suitable that I can get my hands on easily.
Randy,

I suggest you try removing a turn or two from the LPF inductors as described.
There is probably nothing wrong with the capacitors, just getting hot because of mismatch. Hans did suggest this.
I know some have reported that SMs "cure" the problem but not many report the capacitors getting hot under normal operation.

73 Alan G4ZFQ


Re: QCX 40m - BPF 9 with Tone but C1 Unresponsive

Charles Jessee
 

Any harm in just pushing on with alignment?
Bret/N4SRN


GB3SEV

Richard
 

Tristan if you still require a bandpass filter for the beacon please contact me .
I have a cavity bandpass spare
richard@...

73 Richard G8JVM


Low output on 20 meter QCX

Randy Ott
 

Just finished building a QCX for 20 meters.  I am only getting about 1.5 watts output with 12V input. After holding the key down for 10 or 15 seconds, the power output will slowly climb to about 2 watts.
If I raise the input voltage closer to 15V, I can get about 2.5 watts.  Again, this is after several seconds of key down.
It turns out that the two 390pF capacitors, C25 and C26, in the lowpass filter get very hot. I tried replacing them with some small ceramic disks of questionable heritage that I had on hand but they get hot as well.
I am thinking that these need to be silver mica capacitors rated for at least 100V.  Unfortunately, I don't have anything suitable that I can get my hands on easily.

Any thoughts on my findings?

Randy, K5HJ


QCX 20m with Optical Encoder

Richard Harris <g3otk@...>
 

QCX s/n 2908 (20m) - PCB assembled, power applied and the receiver burst into life.  A few minutes aligning, a quick check of transmitter power (3W with a 13.8V supply) and good to go. 

I've now fitted a 64 pulse/rev optical encoder (Bourns EM14 series) but kept the supplied encoder for menu changes, with a toggle switch to select the appropriate encoder.  The optical encoder gives a much better "feel" for tuning.  I use 100 Hz/step for tuning around and selecting 10 Hz/step gives a traditional VFO-like tuning, albeit with less than 1kHz per rev. 

The encoder that I have used costs about half that of the complete QCX kit (and there is a version available with a push switch) but it is a significant improvement in my opinion.  There are less expensive (but very nicely made) optical encoders available from China on Ebay.

Richard G3OTK


Re: 20 metre QCX has died?? #qcx

Sven Ladegast
 

Am 13.02.2018 07:53, schrieb Rick W via Groups.Io:

Sven DJ2AT - I agree that one of the fuses is likely messed up or
worse and it may require a new controller chip.
Hello Rick,

I don't think this requires a new controller chip! - All you need to do is setting the fuses correctly for the controller to work.

I think you might have messed up the oscillator fuses...?

How did you flash the new software (which flash program, hardware)? - We could alter your setup that you will not need any new controller and you are able to flash any new firmware that comes out.

So Ricik, it is your task!

73!

Sven, DJ2AT


Re: Use of Buck/Boost circuit with a QCX Xcvr

MartienPA4H
 

I use an LM2577 boost circuit to get 13,8V from a LiPo pack. Just to be sure I put a ferrite ring on both the input and the output leads (as a common mode filter). I also decoupled the power to the QCX with an inductor of about 3uH and a 22nF capacitor. The convertor is mounted outside the (metal) QCX housing.
I found no issues like RF feedback or noise. Works really well.

73's Martien PA4H


Re: Use of Buck/Boost circuit with a QCX Xcvr

Dave MM0HVW
 

I have a QCX 20m running off a buck DC to DC converter , to reduce battery pack from 14 to 10v,  with no issues in both CW and WSPR modes

73 Dave mmohvw


On 13 Feb 2018, at 07:27, M0RON <eustace.andy@...> wrote:

Hi,
Not QCX But in my U3s I have two DC-DC boards inside the official case alongside my U3s and relay board. 
One runs at 5.5v and feeds the main board, which in turn feeds the gps, the other runs at 9v to feed the 3 pa transistors. 
No problems whatsoever, u3s performs well with no drift on Wspr and QRSS is sent well. Obviously there is no receiver in the u3s so I can't comment on whether that would be affected. There is no filtering, I also run my FT817 from a DC-DC board but that is well filtered and double screened. Again, no problems.
Andy


Re: Use of Buck/Boost circuit with a QCX Xcvr

M0RON
 

Hi,
Not QCX But in my U3s I have two DC-DC boards inside the official case alongside my U3s and relay board. 
One runs at 5.5v and feeds the main board, which in turn feeds the gps, the other runs at 9v to feed the 3 pa transistors. 
No problems whatsoever, u3s performs well with no drift on Wspr and QRSS is sent well. Obviously there is no receiver in the u3s so I can't comment on whether that would be affected. There is no filtering, I also run my FT817 from a DC-DC board but that is well filtered and double screened. Again, no problems.
Andy


Re: 20 metre QCX has died?? #qcx

Rick Williams - VE7TK
 

Thanks to all who have responded.

I have found that I do indeed have a 20 MHz signal on pin 9/10 of the controller (apologies to all I must have miscounted).

However, the symptoms have not changed.

Alan G1FXB - I have 5 VDC on pins 7 and 20 of the controller (IC2).

Sven DJ2AT - I agree that one of the fuses is likely messed up or worse and it may require a new controller chip.
--
73, Rick
VE7TK