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Re: Interesting thing happened on my 20-10 meter QMX after loading the latest FW 1.01.003
I'm one of those people posting about 20.? I re-ran all three calibrations for 20 one at a time and have been able to make QSOs
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I'm also having issues with sensitivity on 12 m and 10 m.? I didn't know if it was band conditions or something else. I noticed dB levels being significantly low in between cycles.?
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Evan,
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My guess is that this thread is looking at RF amps in general, and how to evaluate the voltages and currents that might blow the finals.
Curious, on revisiting that uBitx amp, it looks like a current mode topology, which would expect the LPF to short harmonics to ground.
I don't think the LPF's on the uBitx do that.
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The post you pointed to has a bad link to the LTSpice schematic pdf, that was corrected a few posts later in the thead:
The schematic for the uBitx is here:
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Jerry
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On Mon, Mar 24, 2025 at 10:56 AM, Evan Hand wrote:
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Re: Software Development and Requirements Creep
I rather like the Musk approach to innovating.? The big, establishment space company, United Launce Alliance, tries to get it right the first time, spends twice as much as SpaceX, but takes forever and then ... blows it.? Multiple times, actually.? Musk's approach is let's build it, launch it, and see what breaks.? Fix that, launch again, it goes further before something breaks, fix it, launch again, rinse and repeat until you're successful.? ?He's made space affordable, brought internet and texting to places that would never have it, etc, etc, etc.? I'm sure the engineers and programmers who work at Elon Musk's companies have a whole lot more fun than those working at Boeing.
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No offense to my friends across the pond, but if you want lots and lots of innovation, you know where to find it...? ? :-)
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Best,
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Jim
K8DDV |
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Re: Interesting thing happened on my 20-10 meter QMX after loading the latest FW 1.01.003
Hi Adam,?
Im not sure. I’d have to check and see. I’m done with it for now. I tried to use it today and for some reason 10 meter sensitivity is not as good as it was previously. Not sure why. I could hear a station 30 miles north of me on a 705 connected to discone. On The QMX connected to the long wire I could barely hear that same station.?
I’ve ordered the mic kit from QRP GUYS and will try it when that arrives. I’m getting a lot of noise on the audio and it doesn’t sound right. I’m running the mic gain at 50 and compression at 5.? It actually sounded decent when it was on 40 meters. Not so much now. It’s just a cheap Baofeng mic. I noticed that if I turn on the mic equalizer it’s completely unintelligible. Also noticed during testing at 20 meters the readings are not even close to what they should look like. I don’t remember the setting at the moment but it was bad. I’ve seen others that have the same issue on 20 posting on here.
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Don. |
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Re: QDX: Adding a 1N4148 across L14
It should not matter. The reverse voltage is less than either value, and the forward current is very short in duration. The 1n4148 is the best choice because of the junction's switching speed. I would go with the least expensive, most available device.
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73
Evan
AC9TU |
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As others have reported, I have lost half of the previous output power on my QMX+ after running the calibration.?
I am beginning to suspect that I lost one or more of the transistors in the final power amplifier.? I will do some more testing to verify.? I ordered some replacement BS170s just in case. ?
The calibration routine appears to stress the finals and sort out the weak from the strong MOSFETs.
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Steve KA0SM |
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QDX: Adding a 1N4148 across L14
I have four QDX's and I've decided to add a 1N4148 across L14 as many other have done here to add some protection against accidental high SWR.??
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Digikey lists several versions, including a 100V 200ma version and a 75V 300ma version.? Is one better than the other for this application?
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Best,
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Jim
K8DDV |
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Allison and others.... To be clear, I brought up this old thread to understand the discussion about the RD16HHF1 being a "16v max" device. I have no interest in the original question from another poster in 2021 in trying to put different finals in the QCX 50w amp, or get 50w out of the RD16HHF1.
? I'm exploring a small amplifiers for POTA/SOTA etc, and trying to learn along the way. That research is causing me to want to understand the datasheet limits, so I can understand max DC voltage for transistors used in the 10-30 watt amplifier range.?
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Jerry's comments are also of interest to my exploration of reducing QDX output power and finals.?
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Just wanted to be clear that I'm not trying to do anything magical! ?
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-Nate?
N8BTR |
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Question for Hans,
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Have you seen anything like the spectrum I (and Jim) posted?? During my regular weekly QSO with a friend about 170 miles away, while he was able to copy me and it did not sound bad (still trying to get the sound bite he recorded of my transmission), he was able to corroborate that I was producing RF up and down from my Fc that he could see on his SDR SW (he runs PowerSDR).
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I am going to try a couple of different mic's (QRP Guys and Adam Kimmerly's which are on the way to me) and redo calibration but wondering if the issue will persist.? I tried using both a (connector modified) Icom HM-12 and a Behringer XM-8500 with poor results (as spectrum pic I posted previously shows).
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Also, no one replied regarding calibration with or without a mic plugged in.? From the beta page one might infer that with a mic plugged in would be correct as the calibration section follows the mic drive setup section.? It is not explicitly stated and wanted to ask to be sure.? So, mic or no mic during calibration (or does it even matter)?
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Thanks and 73,
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Robert, WA2T |
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Re: Software Development and Requirements Creep
On Mon, Mar 24, 2025 at 01:03 AM, G8JCF wrote:
The current UK population is around 69,438,564 humans, source Well if you want a more conservative estimate, then 25% of the working age population have a criminal
record too -
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Hint - thats still a lot of millions.
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Best laugh I've had all day.
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And with that, thanks for the show, no need for me to provide further input on this one.
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Do not do calibration in one set. Do it one by one with 5 minutes break in between to let the finals have some time to cool down.
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20:38, 24 March 2025, "Azgael via groups.io" <azgael@...>:
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Donald S Brant Jr
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