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Re: Thoughts on Low Power and fewer turns on LP filter toroids
Arv Evans
In addition to Allison's comments, the filters are designed to work with 50 ohms input impedance and 50 ohms output impedance. If either of those impedances are not 50 ohms the filter cutoff frequency will be impacted. Arv _._
On Tue, Sep 8, 2020 at 11:29 AM ajparent1/KB1GMX <kb1gmx@...> wrote: Phil,
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QCX #smoked ?
#smoked
John Sharman
All working well on WSPR for weeks
This morning the display is acting weird and the buttons are sometimes not responsive This afternoon the display stats flashing on and off with smell of burins from transceiver!! Hope its just the 5Reg thats blown! The power supply i'm using is 12v from RS Components ad is giving out 13.8v Is the consensus that the item is Kaput!!!! Regards John
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Re: QRP-LABS Low Pass Filter upgrade
ajparent1/KB1GMX
Also PCB conductor size and spacing are a factor as well.
For example 100W is 1.4A into 50 ohms so heavier and larger relays become a factor. 20W is easy 50W takes care, more is significant revision. Allison ------------------------------- Please reply on list so we can share. No private email, it goes to a bit bucket due address harvesting
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Re: Thoughts on Low Power and fewer turns on LP filter toroids
ajparent1/KB1GMX
Phil,
THe AL used for winding of toroids has a variation of 10-15% so depending on how tightly wound plus individual batches you get variation. The Iron powder material is really like many high volume materials to get it as close as they tend to be takes a significant bit of effort. I strongly point to the spec. Add to that the caps used are 10% maybe 5% so when you plug in the variation it does get to be significant. That said I'se used those very same table and many over a 25 filters then tested them ( 5 bands * 5 per) and then tested them and they were remarkably consistent. Parts used were not the same batches but were drawn from my own stocks some quite old. Also did you adjust L4? All 4 of those inductors interact and due to reflected impedances and determine power and harmonic content. Allison ------------------------------ Please reply on list so we can share. No private email, it goes to a bit bucket due address harvesting
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Bob Ballard
Len,
Attached above is my input regarding an “antenna tuner” question asked last week.
73, Bob – KG5SQJ
From: QRPLabs@groups.io <QRPLabs@groups.io> On Behalf Of Len W1LEN
Sent: Tuesday, September 8, 2020 10:46 AM To: QRPLabs@groups.io Subject: Re: [QRPLabs] QCX+ T1 Toroid Wire Length? #20m #qcx+ #toroid
Hi, what is the gauge of the magnet wire supplied with the QCX+ kit for the toroids and transformer? Also, is there a particular antenna tuner or tuners that have been found to be most useful with the 50 watt linear amplifier?
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Thoughts on Low Power and fewer turns on LP filter toroids
I've completed a 20M QCX+ and have just fixed a friend's 30M QCX+. Both are working nicely, but at 13.1 volts I get about 3watts output on both, using the onboard RF tool to measure (and less on my Elecraft wattmeter).
To achieve that output, I had to take two turns off L1 and L3 and one turn off of L2 and fiddle around a little with the spacing of the windings. I did that with both radios. Any thoughts why the number of turns differs so greatly from that specified in the build instructions? Both kits were shipped about the same time. Could it be a quality control issue of the toroids? I measured the toroids on the 20M version before I installed them, and they were spot on before I took the turns off. I didn't measure them after the turns had been removed. I'm satisfied with the power output of the units. Just curious why they aren't meeting the specs as stated in the manual? Phil, K3UT
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Len W1LEN
Hi, what is the gauge of the magnet wire supplied with the QCX+ kit for the toroids and transformer? Also, is there a particular antenna tuner or tuners that have been found to be most useful with the 50 watt linear amplifier?
Thanks very much, Len W1LEN
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Re: Select Button on Alignment QCX+ 20m
Arv Evans
The left button (S2) completes a series circuit between R44 (3.3K) and R46(10K), with R44 going to +5V and R46 going to ground. If the right button (S3) works properly then R46 is probably not the problem. This leaves the value of R44 (3.3K) not being proper...or something miss-wired, shorted, or open someplace. It is just 2 resistors and a switch, so not a lot of parts involved. Current through S2, R44, and R46 (total resistance of 13300 ohms) should be 5V / 13300 = 0.376 ma. Voltage across R46 should be 13300 * 0.000376 = 3.759V Arv K7HKL _._ Arv _._
On Tue, Sep 8, 2020 at 4:07 AM Richard M0AUW <cotswoldgent@...> wrote:
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Re: QCX+ Display
#20m
Michael N6MST
On Tue, Sep 8, 2020 at 07:32 AM, Dave wrote:
Give it a bit of a tap. That might change things.That fixed 90% of the problems I ever had with my original Nintendo!
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Re: QCX+ Display
#20m
Just hit them all with a soldering iron. You'll know it when you find it. Mike WM4B
On Sep 8, 2020 10:53 AM, David Griffiths <davidmgriffiths42@...> wrote: Thanks Dave, a few taps on the back of the display and all was bright again. Finding the dodgy joint may take longer!
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Re: QCX+ Display
#20m
Dave
Great.
toggle quoted messageShow quoted text
Last week at our LARC Kit Building session I examined a members soldering, by looking closely at the component side of the board. When a joint has had the right amount of heat, flux and solder there is a tiny ring of solder around the component lead, filling the gap between lead and top pad. His were uniform and perfect. Dave
On Sep 8, 2020, at 10:53, David Griffiths <davidmgriffiths42@...> wrote:
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Re: QCX+ Display
#20m
David Griffiths
Thanks Dave, a few taps on the back of the display and all was bright again. Finding the dodgy joint may take longer!
David G4DMG
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Re: Help with strange audio fault
#qcx
Blimey Justin! Really pleased that it sorted your problem. My QCX has been powered up virtually every minute since and works like a charm.
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Re: QCX+ Display
#20m
Dave
Give it a bit of a tap. That might change things. Number one problem with kits is always poor soldering, cold joints, or even an overlooked joint with no solder at all.
toggle quoted messageShow quoted text
Dave
On Sep 8, 2020, at 10:28, David Griffiths <davidmgriffiths42@...> wrote:
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QCX+ Display
#20m
David Griffiths
Finished my 20m QCX+. Powered on and adjusted R47 to get a nice display, went through the alignment process, all OK, put top half of case on, all still OK
Powered off, went for lunch, came back, powered on and found a very dim display, barely readable, and adjusting R47 does not make it any better. Any suggestions gratefully received. David G4DMG
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Re: Select Button on Alignment QCX+ 20m
Alan G4ZFQ
The fact that the voltage changes at all says it is probably not a cold solder joint. I would check that R44 is the correct value (3.3K). It sounds like it may be too high.I seem to remember I suggested that 4 hours ago:-) 73 Alan G4ZFQ
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Re: Help with strange audio fault
#qcx
justin.munger@...
Ted (and others helped resolve this problem),
I have just built a QCX+ a few weeks ago and after it working for 2 weeks, i experienced the same exact problem you described. After a few days of troubleshooting on my own, I posted the problem in the QCX group and someone recommended I make the post in QRPLabs group. I'm glad I searched through all the posts and found yours. All my troubleshooting steps fell in line with yours--even all the voltage readings on IC10. I currently have a 1uF electrolytic capacitor in place of the ceramic one until i can get a replacement. Thanks for leading the way with solving this problem. Cheers! --Justin KN6IPA
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Al Holt
oops, make that LM317 or better yet, LM350....
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Al Holt
Hello again!
I'm taking baby steps towards building a matching speaker/power supply for my QCX+ I've got an enclosure on order through eBay listed as: "150x105x55mm Aluminum Enclosure PCB Shell Cooling Box Case Split Type" I'm planning on using a LM318 type variable power supply and I think the current demand of the QCX+ and a small audio amp shouldn't exceed 1.5 Amps. At the moment, the use of a toroidal power supply transformer has caught my interest. I think a 30VA unit is about all that can fit into the case and still leave room for PS and amp modules. At this VA rating, the transformer's diameter is around 3 inches (Hammond). So much for all that room inside the case :-) The most common approach I've seen is to have split primary and secondary windings. This gives you the 120/240V option on the primary side. There's at least one transformer available that offers two 9V secondary windings @ 1.7A. That gives us 18V which should be plenty to regulate down to 13.6V, I would think. For the audio amp, it seems like a 5W module should do the job and not require too much current from the power supply. Not the best RFP, it's a 'seat-of-the-pants' approach to design. What do you think? Cheers! --Al
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Re: Select Button on Alignment QCX+ 20m
Richard M0AUW
Hi Steven,
Looks like you're right, R44 looks to be the 33k orange orange black red brown, instead of the 3.3k orange orange black brown brown! ( i did measure but obviously got the decimal point wrong...Doh!). I swap them out and see how it goes....Many thanks for your help. Richard M0AUW
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