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Re: QDX Build Videos Thread
Ryan Flowers
Very nice, John! And don't you hate it when that happens? I can never seem to get the inductors to line up either, and that drives me crazy. Short drive, mind you ;-)
More videos published: QDX Build Part 11: Little Red LED: https://youtu.be/u2EZdIcA8nMQDX Build Part 12: USB, Power, BNC Connectors!: https://youtu.be/AZ8emza9dOEQDX Build Part 13: Electrolytic Capacitor: https://youtu.be/ZDBLlC2kE3AI've also made a playlist that is exclusively build videos from start to finish, although I haven't got the video series finished just yet. I'm hoping to have all the editing done and the videos published tomorrow. Here's the QDX Build Playlist: https://www.youtube.com/playlist?list=PLDP9oGiu60jJdiQOQx6-5DRn3l5GrfQQM -- Ryan Flowers - W7RLF MiscDotGeek - QRP and More (Website) QDX News, Tips, Build Series (YouTube) |
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Re: Classic QCX C1 fully meshed
But....
if you're getting two peaks, that means it is peaking with capacitance to spare, right? So if that is so, what exactly is the issue? Or am I misinterpreting what you're saying? -- Julian, N4JO. |
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Re: Classic QCX C1 fully meshed
Hi Dave,
Yes, adding capacitance should, within limits, have the same effect as adding turns (inductance). The resonant frequency is 1/ (2* PI ( sqrt(LxC))). In simple terms, the resonant frequency goes down if the product of L and C goes up, so that making either one bigger makes the product bigger. Now here's the problem: you just said that you started with 2.2pFd, and ended up adding 39pFd in parallel with the 30pFd trimmer, and got no change. That should be doubling the capacitance, so it sounds like there's a problem. My suspicion is that the capacitors you are adding might be bad: if they are leaky, they will pull down the Q factor of the tuned circuit, possibly to the point that it won't peak noticeably, Are they from the early kit? Also, to pick at your words here - just to be clear - you said "yes, there were two peaks, but at opposite ends of the plates". I presume you mean at opposite sides of the fully meshed position, right?? Theoretically, if you added just the right value - say 22pFd, you would move the resonant points down to either side of the full unmeshed position. You didn't achieve that inadvertently, did you? -- Julian, N4JO. |
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Re: QDX next batch
richlim11
Hans, just got home…long day. Yes you are correct, that is what I read early this am. Maybe I need to have my morning coffee before answering emails! Thank you and sorry about any confusion/stress I caused.
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Rich KQ9L
On Monday, November 1, 2021, 12:00 PM, Hans Summers <hans.summers@...> wrote:
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Re: Classic QCX C1 fully meshed
Curt wb8yyy
If the receiver works to your satisfaction I am so tempted to say don't change anything. If you got a great calibration with good nulls, and your qcx is receiving lots of signals, time to enjoy it.
Curt |
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Classic QCX C1 fully meshed
Hans, Julian, I just built a Classic QCX I bought from Hans at Dayton years ago. C1 only peaks at fully meshed position (or close, maybe 95% full mesh). Another advisor suggested adding some capacitance to C1 ( In the 30 meter version you don't use both caps at positions C5 and C8 so there was a spot to add capacitance). So I started with 2.2 pf, and went up 10 pf, 15 pf, 33 pf and finally 39 pf but it didn't change the meshing of the plates. They stayed 95% meshed no matter what cap I put in place. Yes, there were two peaks but at the opposite ends of the plates. The rest of the alignment went as the manual describes. I know the instructions say to add 5 turns to T1 and I can do that but adding a cap sounded so much easier. Or maybe go smaller. Take the 22 pf cap out of C5 and go smaller??? I am old and am getting confused which way to go (other than follow the directions and add 5 turns.....ha!) Can you two gentleman shine light on this idea...... Thanks. Dave K8WPE |
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Re: QDX - how to best check the filter performance
There are two possible concerns with the filter alignment on transmit; maximizing transmitter output and checking for harmonics and spurs. You should be able to get plenty of output with no adjustment at all, and the filter design is not identical to the QCX (where adjustment of the filters has been beneficial), but you still might be able to squeeze out a bit more output by adjusting the wire spacing on the toroids. Hans has posted on adjusting the QCX for maximum output. As for checking spectral purity, you don't need to. If you build your QDX properly you will be just fine. Again, YOU DO NOT NEED TO DO THIS. (Emphasis added to keep Hans from getting lots of unnecessary requests.) If you don't have the gear to test it, just build and operate the thing and be happy; Hans has you covered in the design. But you asked. If you DO want to have a look you will need two or three tools: a spectrum analyzer, a wide range SDR, and an attenuator or RF tap. The last of those is used to reduce the output of the QDX to a safe level for the other two. The full output of the QDX will range between +33 dBm and +36 dBm (in other words, 3 to 6 watts), depending on operating voltage and how you wound the binocular transformer. Depending on your test gear, you probably need to get that down to somewhere between 0 dBm and -20 dBm (in other words, one milliwatt to 0.01 milliwatts), so you'll need anywhere from 33 to 56 dB of attenuation. A good test setup for testing QRP rigs that isn't too costly is a good fixed attenuator or RF tap in the 30-40 dB range, plus a step attenuator to switch in the exact amount you want. (The fixed attenuator goes FIRST; the step attenuator can't handle the full output of your rig.) For these tests you are connecting the test gear directly to the output of the QDX through the attenuators; no antenna is involved. If you use an RF tap rather than an attenuator you also need a dummy load that can handle the full output of the QDX. The spectrum analyzer is the tool for checking for harmonics and out of band spurs. Use the attenuator to get the signal down to a level your analyzer can measure and then have a look. The inexpensive TinySA is sufficiently capable for this test; something fancier like a Rigol, a Siglent, or a surplus Hewlett-Packard is nice to have but more than you need. If you are patient, there is also software that will turn some SDRs into a rather slow spectrum analyzer; that is adequate for looking for major problems, but the SDR's gain over a wide bandwidth may not be flat enough for accurate measurements. (The software does hundreds or thousands of tune-measure steps, captures the data on your PC, and plots it as a spectrum.) If you have a spectrum analyzer with a nice narrow minimum setting for analyzer bandwidth (RBW), which means the minimum width of signal it can display, you can do all the tests with it. If you are using one with a wider RBW such as the TinySA, an SDR is a useful tool for checking for near-in spurs and the width of your transmitted signal. Once again, use the attenuator to reduce the output to a safe level for your SDR, tune the receiver to your output frequency, and have a look at the spectrum display. You can use a dedicated SDR that tunes the appropriate range such as an Airspy or SDRPlay, an inexpensive Softrock, or the spectrum display offered by some fancy transceivers. An RTL-SDR dongle paired with a transverter will also work though its dynamic range is more limited. In addition to looking at the output frequency, you can also tune near the harmonics and spurs to see if anything unusual is going on there. You can use the same procedure to look at the spectral purity of any rig, not just the QDX. You'll need an attenuator that can handle more power (and more attenuation in front of the step attenuator) if you want to test non-QRP radios. If you want to start building your own transmitter designs, this kind of test setup is important to make sure that your transmitters are compliant with the rules where you live. You can duplicate most of the tests that the ARRL Lab does with a couple of hundred dollars worth of gear, something that was not true a decade ago; that is a huge step forward for homebrewers. On Mon, Nov 1, 2021 at 8:06 PM Bob Benedict, KD8CGH <rkayakr@...> wrote: Please see the QDX manual section on terminal apps starting on page 82. Section 6.6 on page 89 describes the built in Rx RF filter sweep. |
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Re: QDX on 60 meters?
In an earlier post that is, where I noted that the US and Canadian rules allow only one CW or digital signal on each channel, which must be at the center frequency of the channel. Therefore, transmitting FT8 at any offset other than 1500 Hz is not allowed.
On Mon, Nov 1, 2021 at 8:15 PM Shirley Márquez Dúlcey <mark@...> wrote:
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Re: QDX on 60 meters?
I'm aware that there is plenty of US activity on 60 meters. By my reading nearly all of it is a violation of the rules, as I explained in my post, and therefore I can't recommend that US hams (nor Canadians, because they have rules identical to the ones in the US) buy a QDX to transmit FT8 on that band. There are still plenty of other reasons to buy one, which is why I am eagerly awaiting mine.
On Mon, Nov 1, 2021 at 8:06 PM August Treubig <atreubig@...> wrote: Shirley, |
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Re: QDX on 60 meters?
Shirley,
FT8 on 60m in the US is very busy and allowed. Aug AG5AT |
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Re: QDX - how to best check the filter performance
Please see the QDX manual section on terminal apps starting on page 82. Section 6.6 on page 89 describes the built in Rx RF filter sweep.
-- 73 KD8CGH |
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Re: QDX on 60 meters?
Not everybody lives in the US. There are many parts of the world where FT8 activity is fully legal on 60m.
On Mon, Nov 1, 2021 at 7:34 PM Lee <Lee@...> wrote:
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Re: QDX on 60 meters?
Lee
Why? What would you use it for?
-Lee- WA3FIY
------ Original Message ------
From: "John AE5X" <ae5x@...>
Sent: 11/1/2021 7:25:00 PM
Subject: [QRPLabs] QDX on 60 meters?
With a firmware change & using the 40m LPF? Es posible? |
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QDX on 60 meters?
John AE5X <ae5x@...>
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Re: QDX Build Videos Thread
John AE5X <ae5x@...>
I didn't notice that out-of-alignment cap until I posted the photo - now it's bugging me big time. Now I gotta make like an orthodontist and snap that little baby into place.
-- John AE5X https://ae5x.blogspot.com |
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Re: QDX Surface Mount inductors
Curt wb8yyy
It would be interesting to know the context of how and where part is used to determine if it's a problem. Presumably the qdx works already is what I am thinking. In a few apps designers I observed in the past wanted to operate near self resonance, but that may not be intended here. Don't readily jump to conclusion there is a problem yet, in particular if part isn't a sole bias choke.
Curt |
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Re: QDX Build Videos Thread
John AE5X <ae5x@...>
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Re: QDX BPF/LPF Switching Frequencies and tuning range.
Lee
So ... it appears the QDX is not useful on 60 meters. It will not do pactor or PSK31 which are the only modes allowed on 60 meters. That ARRL posting is quite enlightening. Oh, the QDX does not even cover 60 meters so that settles that question! :-)
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Been thinking about getting an QDX for my traffic work here when they become available but have not yet learned enough about it to know if it would serve. Now that they are coming on line, I hope to learn a lot more about the finer points of that thing as new users comment on various features. BTW my 40M QCX is useful for traffic. Enough selectivity, power and frequency stability. Nice break-in keying and, with an audio clipper, nice smooth operation. But, since I often need to switch between 80, 40 and 30m in a given session, I currently use an Argonaut VI. Now there is a wonderful traffic radio! :-) I suspect the QSX will be likewise! Maybe I will just wait for that one! :-) 73 de WA3FIY Lee
------ Original Message ------
From: "Mike Perry, WA4MP" <editor@...> To: QRPLabs@groups.io Sent: 11/1/2021 12:18:23 PM Subject: Re: [QRPLabs] QDX BPF/LPF Switching Frequencies and tuning range. The ARRL has a lengthy statement about amateur operation in the U.S. on 60 meters that includes this:Digital OperationRead the entire posting for other details. Keep in mind that we share this band with services that have a higher priority, so we need to play well. |
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Re: QDX BPF/LPF Switching Frequencies and tuning range.
The US rules for operation on 60 meters require that CW and digital signals be at the center of the channel. That would appear to allow only one FT8 signal in each channel at an offset of 1500 Hz. That is almost totally incompatible with how FT8 is used, and devoting an entire channel to a single low bandwidth FT8 signal would be a waste of a channel. Therefore it is not practical for US hams to transmit on the band at this time. Receiving FT8 on 60m can still be a useful way of gauging whether the band is open to non-US locations. Allowing only one CW signal on a channel that is nearly 3 kHz wide is bad enough. I hope that the US regulations on 60m are eased in the future, but for now we have to live with what we have. On Mon, Nov 1, 2021 at 12:51 PM Evan Hand <elhandjr@...> wrote: Allison, |
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Re: QDX Surface Mount inductors
I was thinking that it might be more trouble than it is worth when you mentioned digging for new inductors. If you are worried about the leaded ones physical security to the board, once you get it working, simply epoxy them down. That's an industry fix on prototypes and for many "white wire" changes. Fred W0FMS On Mon, Nov 1, 2021, 10:12 AM Gregg Myers <gregg.w7grm@...> wrote:
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