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Re: #qmx QMX and waste heat from the finals
#qmx
Thanks, Cliff. You've been a tremendous help on this. Where did you find the heat sink you have on top of the finals? Wayne KB4DSF On Wed, Aug 30, 2023 at 11:41?AM Cliff <ae5zaham@...> wrote:
-- Wayne Greene |
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Re: 2nd QMX Build and it wont power on and an update on my old unit...
Hans,?
The sweeps were terrible. And I have no audio out of the 1st QMX. I worked with John Zbrozek a good bit with the 1st unit and we got it that far and we decided that the PCM1804 was likely bad. I went looking for a replacement and found several models on digikey or Newark (one of the two) but was unsure which to purchase. No you hadn’t missed replying before… I did however try to send you a private message on here a while back and I’m not sure if it ever even went…? Cliff, I did try swapping power boards from the old unit one at a time to the new. My old 5v board and my new 3v board allowed me to get the unit powered up to apply firmware, but now it will not power up again. Swapping the power boards every which way gives me no change now. And putting the old boards back into the old QMX sends it back to the way it was this morning when started…. I’m pretty confused haha. Thanks, Devan KD8MST |
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Re: 2nd QMX Build and it wont power on and an update on my old unit...
开云体育Have you tried the power boards one at a time from the old unit that does power up in the new QMX?73, Cliff, AE5ZA
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Re: #qmx QMX and waste heat from the finals
#qmx
开云体育Wayne,There is just a hole through the plate to hold it in place and a foot that you can't see almost at the left hand edge under the plate the same as the one that is visible on the right hand side. It was made from a piece of aluminum molding that happened to have those two feet in the right place. I may try to put a piece of it under the finals on the QMX, but without the feet, as I'm sure there isn't enough room for the extra height of the feet. I also added the diode across L14 so hopefully it will be as bullet proof as I can make it and baring operator "destructive" testing should last a long time. Here's the reference from John Z to the diode "fix" in case you are interested. The diode simply is in parallel with the 47uH inductor L14, with the orientation shown in the photo provided by Paul W9AC. Cathode towards the power supply connection, anode to the transformer center tap. Any of the diodes he mentioned ?(1N4448, 1N4148, 1N914) will do a fine job of absorbing the end-of-transmission voltage spike it produces. I have used a 1N914. /g/QRPLabs/message/105256 73, Cliff, AE5ZA
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Re: #qmx QMX and waste heat from the finals
#qmx
The BS170 (finals) are low power devices with a thermal impedance of 150C/W.? Trying to reduce the internal chip temperature by lowering the already low external thermal impedance is pretty futile.?
(thermal impedances add together just like electrical impedance). So imagine a bad SWR causing the dissipation in the four finals to dissipate 2W, 0.5W each, then the rise within the transistor will be 75C.? If you find the mounting surface feels painfully hot to touch (cannot keep a finger on it) then it is 44C only a rise of 15C to 20C over the case temperature - a fraction of the transistors internal temperature rise.? Someone can take the time to do the thermal modeling, its quite simple. |
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Re: 2nd QMX Build and it wont power on and an update on my old unit...
Hello Devan There's only one ADC on the main board which is the PCM1804. But I'd suggest first checking what you see on the RF sweeps (apologies if you've already posted that here, too many topics to follow).? 73 Hans G0UPL On Wed, Aug 30, 2023 at 5:46?PM Devan Phillis <devan@...> wrote: Good morning, |
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Re: QMX - sockets for BS170s
开云体育So I think the discussion about pin headers for the PA transistors is adventurous. The most important point with all devices QCX, QDX and now QMX is absolutely the use of a tuner. The antenna needs to be adjusted. This has now been cleverly solved with the QDX with the SWR bridge. The QMX will not work without an adapted antenna. Of course, if you do WSPR with 12V or even 13.8V with the QCX or QDX, you damage the device and yourself. ? Yesterday I did FT8 with the QMX for about an hour, with 12V. You could no longer touch the device because it was too hot. It didn't do him any harm. So use thermal paste. Then the PA transistors have a low thermal resistance and everything is chic. ? 73 Reinhard DL3AS ? Von: [email protected] [mailto:[email protected]] Im Auftrag von Cliff ? The sockets work out great on the QDX. I'm about to try them on a QMX so can't say how that works. Space may be tight. ? 73, Cliff, AE5ZA ?
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2nd QMX Build and it wont power on and an update on my old unit...
Good morning,
I have received and built my second QMX according to the current build guide, and cannot get it to power on. I built it for 12v operation and I tried starting at 7v and then up to 10v (painful past experience). I know the screen will be blank and off until the FW is loaded. The unit does not even power on enough to be recognized as a USB device. I tried reflowing all of my connections on the main board as well as the connections on the buck converter boards and I even reflowed the USB port.? My first QMX had a bad day from the word go (fed with almost 14v by accident), and it will power on now after many repairs and much troubleshooting, but has no RX, I believe I may have fried one or more of the of the a/d converters on the main board but I do not know what part to replace them with, there are too many options. Maybe Hans can speak to that? Thanks, Devan KD8MST |
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Re: QMX: Kit Build complete - My observations
Hi Bojan ? Everything went well. Then I assembled the rest. Nice beast. Awesome ? And yes Hans, if you don't know already, there is really really no place left on that board. What were you thinking? Haha. Well it was all about romance. Marriage. Of QDX and QCX-mini. For whatever reason, I was determined to make it all fit in the same enclosure as QCX-mini. And use through-hole capacitors in the filters so we can have different band-coverage versions, like QDX, just by choice of supplied components. The mechanical design was going to be more like QCX-mini and the electronic design more like QDX (plus extras). Ask my XYL, she says I'm the most obstinate thing she's ever known (and as often as not, wishes she didn't). Of course, I disagree. But then again I did absolutely refuse to back down from my fixed PCB size, to fit in the QCX-mini enclosure. And when there still wasn't space in the building... well I just put in another floor (the SMPS floor!).? 73 Hans G0UPL |
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Re: #qmx QMX and waste heat from the finals
#qmx
Hey, Cliff. How did you mount the plate under your finals?
Wayne KB4DSF |
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Re: QMX - smoke - another C107/Q108 failure
Hi Kees ? What a complete detailed response and education for everyone. I am impressed with your bandwidth and expertise relative to this wonderful QMX product. Hi hi, bandwidth and expertise? You should ask my family, how often I showered, shaved, even SPOKE to them in the last few months! It's by far the biggest project I've ever done. So yeah I know every resistor and every line of code! I could probably write it all out from my head with very few errors! 73 Hans G0UPL |
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Re: #qmx QMX and waste heat from the finals
#qmx
Hey, Cliff. How did you mount that plate under the finals?
Wayne KB4DSF |
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Re: QMX - smoke - another C107/Q108 failure
Thank you, Hans, for your detailed reply.
For my own part, I've been reassured as I measured my 9V QMX build. ?I posted the scope screenshots in the hope of sharing that reassurance with others and to deepen my understanding of the QMX's design. ?I've definitely been successful in the latter. Jonathan KN6LFB |
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Re: QDX-M on 6 meters?
TNX Ross!? That would be really helpful.? ?I have an unbuilt QDX R2 that I can build up as an M.? Just leave out the multiband stuff and go for 6M I'm trying to get on 6M now with a TenTec 1208 transverter and 20M Phaser ( or QDX ).? I'd like?a stand alone 6M rig though. BTW, do you use any RF gain (preamp) on the 8 or 6M versions?? I'd think sensitivity is lacking at 50MHz and above. Bob WA1EDJ EM83du On Wed, Aug 30, 2023 at 1:02?AM Afghan Kabulldust via <kabulldust=[email protected]> wrote:
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Re: QMX thoughts
Hello Bojan Operation of the volume?control is a known firmware issue I need to address.? Yes one could have designed it with a single SMPS regulator, at the expense of higher supply current. Though this is a "trade-off" not a win-win (higher supply current being a bad thing!). It would simplify the circuit but it would not achieve much else; the two SMPS are synchronous anyway so on the same interference?schedule.? 73 Hans G0UPL On Wed, Aug 30, 2023 at 4:02?PM Bojan Naglic <bojan.naglic@...> wrote: Hi Hans, |
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Re: QMX - sockets for BS170s
开云体育?I use two rows of 6 machine pin sockets on all my QDX and QMX and 4 pairs for the BPF caps.? See attached HB QMX prototype.? 73 Ross On 30 Aug 2023, at 11:51, Cliff <ae5zaham@...> wrote:
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Reinhard Gr?nz
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