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Re: ArduinoShrink - reduced size Arduino AVR Core
As someone who started in I.T.? on a Mainframe with 16 k Magnetic core memory no disc drives and only ran a single program at a time there was always a bottleneck. Whenever a routine had to run with minimal memory and as fast as possible it was a good candidate for optimising, rewriting or if that didn't achieve it it was rewritten in machine code. It's funny in some ways not much has changed. There are still bottlenecks. On Thu, 8 Apr 2021, 3:02 pm Tom, wb6b, <wb6b@...> wrote: On Wed, Apr 7, 2021 at 09:33 AM, <quad@...> wrote: |
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Re: Many uBitx's have reduced power on 40m CW
I put my v4 back together with the stock L1-4 toroids.? The only change I made was to C81.? I put a 2.2nF in parallel with the 470pF that was there.? Here are the CW results with 12 volts to the rig:
80meters? ? ?3.510MHz? ? ? 13.4watts 40meters? ? ?7.010MHz? ? ? 14.5watts 30meters? ? ?10.110MHz? ? ? ?7.8watts 20meters? ? ?14.010MHz? ? ?12.6watts 17meters? ? ?18.078MHz? ? ? ?9.9watts 15meters? ? ?21.010MHz? ? ? ?7.0watts 10meters? ? ?20.010MHz? ? ? ?3.6watts The only abnormality with that mod is the dip for 30meters.? I am not going to pursue that issue as I consider it a good tradeoff for the 40meter increase. So here is what I think that I have learned: 1 - The production filter is not optimal, but does work 2 - The modification that Curt used works, though through playing with LTspice the optimum value that I found is 2500pF for C81.? The closest I could come was 26700pF which worked. 3 - Probably the biggest impact with changing the C81 value is the impedance impact on the LPF, not really the gain.? The mismatch on the impedance was causing signal distortion that reduced the CW output to 40meters. 4 - Going too high a value for C81 will produce a larger difference in the 80meter vs 10meter output.? Increasing the capacitance does impact the gain of Q90 as well as the impedance. I still need to do the purity tests for both CW and SSB.? I will do this by modifying my v6 with the above change to C81, test to see that I get the same results, and then do the spectral analysis.? I did change the relays on the v4 and tests with my TinySA confirmed that the harmonic issue was resolved, however, I have not done the spur fix yet.? The v6 should be clean before the mod, so that will be the test to indicate if there is an impact on the signal purity. This is Fun!? Thank you, Jerry, Curt, and Farhan for the feedback!? Jerry especially thank you for the LTspice link and information. 73 Evan |
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Re: uSDX
Justin,
FYI, There is a Groups.io for that work.? It is here: /g/ucx The original project was called ?CX, which the group felt was too close to the QCX/QSX names that are used by QRP-Labs.? The official name is now ?SDX or uSDX though the Groups.io page (like this page) has a different net ID. Have fun! 73 Evan AC9TU |
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Re: ArduinoShrink - reduced size Arduino AVR Core
On Wed, Apr 7, 2021 at 09:33 AM, <quad@...> wrote:
ArduinoShrink?replaces Arduino AVR Core functions with smaller and faster versions.Looks really cool.? Upon reading his explanation of his code, I need to revisit my assumption that writing assembly is almost never worth the effort now days.? Although it looks like he put an additional restriction on specifying pin numbers (probably not a bad thing) to do some shrinking in the wiring library. Tom, wb6b |
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uSDX
After getting my feet wet with the UBITX I ran across this interesting sounding project:
I sent off the Gerber files and I'm waiting for the boards to arrive by slow-boat as I am in no hurry.? If anybody else might want to play around with this I will have extra boards.? Minimum order was 10 PCB and with shipping was a whole $24! Hope I'm not breaking any rules. 73, Justin B. KI5GKD |
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Re: Many uBitx's have reduced power on 40m CW
The AL of a T30-6 core can vary +/-5% of the nominal value, and inductance is proportional to AL.
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? ?? Yet another handy factor to blame bad results on. Inductance is proportional to the square of the turns count. Having 8 turns instead of 9 is a 100*(9*9-8*8)/(9*9) = 21% reduction in inductance. Different spacing around the core and loose vs tight windings can make a sgnificant difference. As you have noticed. Jerry, KE7ER On Wed, Apr 7, 2021 at 04:27 PM, Evan Hand wrote: The most recent observation is that there is a HUGE variation in the inductance of the toroids depending on the turns AND the spacing.? |
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Re: Many uBitx's have reduced power on 40m CW
The plot thickens.
The most recent observation is that there is a HUGE variation in the inductance of the toroids depending on the turns AND the spacing.? I tested this because my first attempt at winding the "better" filter toroids produced unexpected measurements with my LC meter.? I then remembered the QCX LPF tuning that Hans Summers has documented for the QCX.? I now have another test to perform.? Now I need to see if adjusting the spacing on L1 to L4 can optimize the LPF. Based on my LC meter, the inductance of 9 turns on a T30-6 can vary from 290nH to 310nH.? It could mean that "tuning" the inductors could balance out the power levels.? That could also explain the production variations, coupled with the gain differences in Q90. Oh well, more tests to document. 73 Evan AC9TU |
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Re: Many uBitx's have reduced power on 40m CW
Farhan,
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Perhaps driving harder will help, worth trying. However, the middle picture of this post shows TP1 when operating 40m CW: ? ? ?/g/BITX20/message/87328 The first image here shows TP1 when attempting to operate 40m CW, except Evan has removed L4,C204, and replaced them with a?47 ohm termination to ground: ? ? ?/g/BITX20/message/87415 As you can see, the mixer behaves much better when properly terminated. In this post: ? ??/g/BITX20/message/87369 he finds that rotating RV1 fully clockwise to shut down the power amp has no effect on what he sees at TP1. So the dirt at TP1 is not getting coupled in from the high power stages of the final. This is why I'm simulating the input impedance of the filter at L1,2,3,4 while driving the Q90 stage. Going back to the v3 values for C81 and R83 brings it much closer to 50 ohms. Not stated, but I believe those screen shots are taken from a v5. Evan also has a v4 and a brand new v6. Jerry, KE7ER On Tue, Apr 6, 2021 at 11:40 PM, Ashhar Farhan wrote:
The CW signal is generated by injecting a DC current into the diode mixer, upsetting the balance.? |
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Re: Many uBitx's have reduced power on 40m CW
As Curt found, increasing C81 seems to be key here.
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The filter and mixer see much closer to 50 ohm loads with the v3 values of C81=0.1uF, R83=10ohms. But v3 had too little power on the high bands. I wonder if we could go back to the v3 values on C81,R83 to give the filter and mixer closer to 50 ohm loads, then whack at the Q911,912 stage to increase power on the high bands.?? Jerry, KE7ER On Wed, Apr 7, 2021 at 01:07 PM, Evan Hand wrote: All comments are welcome.? I will post the actual values after I have done construction and measurements. |
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Re: Many uBitx's have reduced power on 40m CW
I think I am done playing with LTspice.? Here is the circuit I plan to change my v4 to:
The LTspice file is attached. I wanted to balance out the input impedance issues with the gain issues at higher frequencies.? P{er the model, this seems to be the best compromise. I did change the Chebyshev filter for a 32MHz cutoff to give at least the lower part of 10meters a chance at power (thinking of the new Techs and increasing sun spots). All comments are welcome.? I will post the actual values after I have done construction and measurements. 73 Evan AC9TU |
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ArduinoShrink - reduced size Arduino AVR Core
An interesting new contribution by "NerdRalph" - this may help the uBitx Raduino code size -
ArduinoShrink?replaces Arduino AVR Core functions with smaller and faster versions. The Arduino Blink example sketch built for the Uno takes 924 bytes of flash, but only needs 196 bytes with ArduinoShrink. |
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Re: A simple question, I hope...
Testing on-air? There's a tuning device that was very popular a few decades back, and schematics are still available online.? It uses a 555 to generate approx. a 30% duty cycle CW key-down, and you can add a second 555 (or use a 556) to superimpose an audio signal on the CW.? It replaces your mic and just uses your keying line, unless you mix in audio.? Either way it sounds like crap but it's a quick and easy way to get something to test CW and/or SSB out.? Use of a dummy load is recommended.? This link shows some possible options. <> Because it's basically an unfiltered square wave, you'll have enough key clicks to get a signal on SSB.? When I built mine back around 1990 I labeled the box "N6OTQ Death Ray" because of the horrid noise it made on air.? Thankfully, nowadays it's fallen out of favor among the QRO folks. 73 ?Jim N6OTQ |
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Re: Many uBitx's have reduced power on 40m CW
Jerry,
I am still playing with LTspice and have not yet gotten to building the circuits.? In my playing around I did come to the realization that if I did the transformer impedance match I would solve the problem of the 40meter CW drop off.? That would seem to me to then create a receiver sensitivity issue as even with Q90 off, there is still around 320ohms on the C80 side of the transformer that would be transferred to 80ohms on the other side that would be across the antenna input.? Unless switching is added I do not believe that the transformer is viable.? Would you agree with the impedance values??? Attached is the circuit with the transformer.? Here is a screenshot of the transformer analysis in transmit mode. 73 Evan AC9TU |
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Re: Many uBitx's have reduced power on 40m CW
The CW signal is generated by injecting a DC current into the diode mixer, upsetting the balance.? At present, the R104 and R105 inject approximately (4.4V/ 3.2K =) 1.5 mA of current into the mixer. The diodes have an on resistance of approximately?(26mV/1.5mA) = 39 ohms. To increase the RF carrier leakage, we can increase this. If we replace the 2.2K of R105 with a lower value (for instance by strapping a 470 ohms across it) we should be able to get the carrier level up back. - f On Tue, Apr 6, 2021 at 11:38 PM Jerry Gaffke via <jgaffke=[email protected]> wrote: Given the variation in impedance as seen in the simulations of ideal components, |
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Re: Dead Or Just Sick? (P.S. - It was just sick!)
Curious, that's two bad 0.1uF 1206 caps found shorted recently.
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Both of them on the 3.3v supply rail from Nano to the Si5351. The Raduino has two such caps on the 3.3v rail, and three identical caps for DC isolation from the three clocks going from the Raduino out to the uBitx main board. Makes me wonder how many shorted DC isolation caps we have out there, and what the symptoms would be. I doubt these caps failed because of abuse, they are operating at a tenth of their rated voltage. I'd guess poor quality control on the part of whoever manufactured those caps. Possible that the auto-insertion equipment was handling them roughly or the boards are getting flexed somewhere, but those both seem doubtful. I personally found a shorted 0.1uF cap on a Bitx40 main board built at the end of 2016. The uBitx main board has about three dozen of the same cap, and the rig won't work if pretty much any of them decide to be shorted.? Some of those would be hard to find. If we suspect there might be a shorted cap, a good start would be to compare ohmmeter readings across each cap for a good board compared to the bad board (with power off). That may not identify exactly which cap if it's on a power rail with 10 such bypass caps plus bunches of other parts, but could help point the direction to go. The old thread for this particular story can be found here: ? ??/g/BITX20/topic/81064470 Jerry, KE7ER On Tue, Apr 6, 2021 at 03:37 PM, secondchancesailor wrote:
I finally got back into the shack after almost a month.? And I am glad to say, the uBitx lives!? ?I want to thank everyone for the excellent advice!? ?I started by removing C1 and replacing it with a small discrete capacitor.? ?My plan was to work my way through the capacitors until I found the problem.? ? After replacing C1, the radio was fixed!? ?Other than re-reading all the posts here and taking a few minutes looking at the schematic, the whole repair took about 10 minutes!? ?Thanks again for all the help from so many knowledgeable individuals!? ? This is truly an amazing group! |
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Re: Dead Or Just Sick? (P.S. - It was just sick!)
I finally got back into the shack after almost a month.? And I am glad to say, the uBitx lives!? ?I want to thank everyone for the excellent advice!? ?I started by removing C1 and replacing it with a small discrete capacitor.? ?My plan was to work my way through the capacitors until I found the problem.? ? After replacing C1, the radio was fixed!? ?Other than re-reading all the posts here and taking a few minutes looking at the schematic, the whole repair took about 10 minutes!? ?Thanks again for all the help from so many knowledgeable individuals!? ? This is truly an amazing group!
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Re: A simple question, I hope...
Bob
I am agreeing with the others. If you don't have a power meter, well you could try a cq in cw and see what RBN spots you get. If you get a few spots on a band with signals, likely the transmit chain beyond the mixer is intact. Testing ssb even with a power meter is harder. Injecting a steady audio oscillator or if you can do a steady loud whistle would work. As there isn't ALC in this rig, some microphones may not have enough audio drive. We can't blindly determine your microphone is adequate. Component failures out of the box are believed to be very rare.?? Because the cw and digital paths are different on transmit in the ubitx, best to test both of them. Requires a power meter, key or piece of wire, and an audio oscillator. A pc can produce an audio signal, in fact Ashhar discovered something like 1khz.com? Curt |
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Re: Many uBitx's have reduced power on 40m CW
Given the variation in impedance as seen in the simulations of ideal components,
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it's amazing to me that the output power manages to be as flat as it is. Fun to figure out what all is going on here, more than it might seem at first. From a practical standpoint, Curt's bigger C81 strikes me as the best fix, for those that care about the slightly reduced power when operating 40m CW. But with C81 too big, the difference in output power between 3.5mhz and 30mhz may become too extreme. For the v3 configuration with C81=0.1uF and R83=2.2ohms, my simulation shows that the Q90 stage has an input impedance of 51 ohms to 45 ohms, at 173 to 165 degrees Voltage gain ranges from 4.5 to 3.65. These values are for a range of 3.5mhz to 30mhz, in that order, Q90 stage has a load of 50 ohms. On v4, R83 was moved to 2.2 ohms for more gain.? ? Input impedance dropped to a range of 18 to 19 ohms, 170 to 183 degrees. Voltage gain ranges from 5.5 to 6.7.? On v5,v6 the cap at C81 was moved to 470pF so high frequencies have more gain than low frequencies, this compensates for losses at high frequencies in the various power amp stages. Input impedance now ranges from 200 ohms to 45 ohms at 150 to 100 degrees. Voltage gain for the Q90 stage runs from 1.0 at 3.5mhz to 5.5 at 30mhz. The v3 configuration is likely the best as far as giving the filter and mixer a proper 50 ohm load. But we needed more gain at higher frequencies to get sufficient power out, without too much drive on 3.5mhz. I haven't analyzed the effect of the Q90 impedance phase angle on how the filter or mixer might behave. Jerry, KE7ER On Tue, Apr 6, 2021 at 03:25 AM, Evan Hand wrote: I also looked at changing C81 to .1uf and find that the impedance is better across the spectrum of interest.? I do not know how to see if there is an impact on the rest of the amp without building it. |
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Re: A simple question, I hope...
The problem of low SSB output where CW output level is good, might be something as simple as a defective microphone.? Some of the microphone cases have the sound hole covered or miss-aligned with the electret mike element.? Other SSB transmit level problems arise when trying to use the wrong style microphone (dynamic or crystal) in place of an electret element. You can use other style microphones or mike amplifiers but you will have to alter the microphone input circuit to provide proper voltage levels and to isolate power from the audio path. _._ On Tue, Apr 6, 2021 at 5:01 AM Evan Hand <elhandjr@...> wrote:
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Re: A simple question, I hope...
Bob,
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