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How to ruggedize the sBitx V3
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Hi there, I've been seeing posts about burnt finals, melted transformers, etc.
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Is there a way to "invest" into parts for the sBitx V3 to make it more resilient. I would not mind to?
buy beefier elements for the radio and swapping them out to make the radio more resistant to failure,?
especially a cascading failure.
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What steps would you recommend to take such action?
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Thanks.
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Couple of questions: Is it because people are experimenting more with sBITX that we are seeing more failures? Does it have automatic output reduction in case of High SWR as in case of regular commercial SDR? Disclaimer: I am not a BITX user. Joined the group to learn more about them as many in this region use it. In fact it was not available for purchase when I had no radio and was looking for it! 73 Jon, VU2JO On Sat, Mar 1, 2025 at 3:57?PM Bravo Delta via <sbitxv3=[email protected]> wrote:
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Bravo Delta,
I've read almost every message since the summer of 2022, but I don't remember a melted transformer. Could you give me a link to what I missed. If you read my post today about v2, then I don't need to write more. Use a current-limiting power supply and an antenna that is tuned to the frequency and you will have few problems. Another important thing is the quality of the mechanical and electrical connections. The components go through a lot of checks during production, but despite this, failures can occur. The last time I opened the device was to replace the CR2032, because the date display went crazy.
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Gyula HA3HZ |
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This radio is ground-breaking in that it is NOT a $1200 Icom and Yaesu and yet it has many of their features, and sometimes does things far more expensive radios cannot.? ? Instead of using $15 final amplifier MOSFETS (which would be much easier to design for!) it uses $1 MOSFETS. The ICOM 718 went through at least THREE different designs for it output power stage over its course of years (and possibly more).? ?I have worked on one with bipolar transitors and another with mosfets!? ?Wonder if their owners even knew? The VHF parasitic oscillation caused a lot of problems, and required redesign of the T/R system as part of the eradication.? ?That resulted in an elegant diode-switching system (where Hans is said to have helped out greatly) and that made this an even better radio.? ?? I think there are still a few "gotchas" in the diodes connected to?+12 without series limiting resistors -- but if you never venture in there with a probe, they will do just fine.? ? Many of us prefer to change out the mica insulators to Aluminum nitride and at the same time, polish the matching surface of the heatsink.? ?? I remember when some of the most expensive radios on the market were found to have huge linearity issues -- very embarrasing?-- and the company came up with fixes eventually and solved it.? ? The use of a LINUX COMPUTER as the controlling microcomputer is new and different for many of us, and that has both advantages and disadvantages.? ? I can't remember if the software includes "foldback" on the power but if it doesn't, that could easily be added.? ?What I think we've generally realized is that on a 12V supply, going to 100V MOSFETS gives a great level of protection against poor SWR.? ? The GATE was another weak spot and in recent designs, Ashhar has chosen to adjust the gain around to reduce that risk, and he has also in some cases added TVS protection diodes.? ? ?? There is a little 3-mosfet power switcher that we think has a "gotcha" built into it that can be fixed by adding one resistor and for the adept, that is a good idea.? ? Past that, it is an incredibly fun radio!? ?And cheap enough that I can own TWO of them!? ? It got me onto 2-meter SSB for the very first time (with the addition of a transverter) and the ability of the microcontroller to run other software at the same time is helping me begin to forage into satellite communications, something I've never done before.? ?? It is NOT the radio for "appliance operators"? who are better off teething on ICOM or YAESU (I prefer Icom).? ?There are all kinds of people in ham radio and not every radio fits every person, at every stage of their growth! What a fun radio! 73 Gordon KX4Z On Sat, Mar 1, 2025 at 7:05?AM Evan Hand via <elhandjr=[email protected]> wrote:
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On my SECOND sBitx (which I bought used, once again) here are the items I plan to do (I prefer the V2 model, just because it offers me a bit more "headroom" for digital etc on the lower bands -- I think Ashhar made the right choice for the mass production with the changes he made fir the V3) 1.? A few added resistors:? ?/g/BITX20/wiki/36110? ? That will eliminat?a couple of known traps 2.? Change the insulators to Aluminum Nitride and slightly polish the heatsink 3.? I'm debating with myself whether to change the output MOSFETS to IRF520.? ? It is slightly tricky mechanically, but the V2 I purchased has the better securement for the bar, which makes it less tricky (and is probably on all of the current V3s)? ? So I may go ahead and switch out. 4.? I like the TVS diode protection, so I'll add those back in.? ?On the V2 this requires scraping a few leads of their protective coverage and then carefully soldering these incredibly tiny devices.? ?? Either use my own modified software or the recent 64-bit software from JJ that greatly improves the sampling of the CW system and also the T/R delays.? ?I have just installed the 64-bit software and operating system on that particular unit, and was very happy to see it work fine with the upgraded software.? ? Haven't learned how to compile yet, but that will come.? ?This is a radio for tinkerers like me!? Additions:? (These aren't protections, they are just things that I happen?to like) A.? ?I will probably put in the output optocoupler SEND output that I came up with, because I still have parts and this is helpful to me in controlling a linear amp or a transverter. B.? Since I do a bunch of digital that works better with a Windows PC, I'll probably add back in the secparate?audio output independent of the one for headphones etc.? ?? I do SSB, digital and a good bit of CW.? ?You just can't get this same level of FUN on CWwith my Icom 7300. I like having everything assembled into a "go box"? ? I don't go hiking, I just drive up to places and pull out the simple plywood "go box" -- it has everything I need, including antenna tuner, power supply, and sometimes even a built-in CW paddle!? ? That's just my preference; others do their own thing! Part of the joy of ham radio (as opposed to FRS/GMRS / CB / cell phones ) is our ability to tinker and improve? Gordon On Sat, Mar 1, 2025 at 7:18?AM Gordon Gibby KX4Z via <docvacuumtubes=[email protected]> wrote:
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I am a programmer, and the fact that the radio has a built in RPi was the point that sold it to me (together with the bands covered, features, power level, and portability). I do have an antenna tuner and analyzer, so SWR is under control.
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Thank you for all the suggestions. I guess I should start on the thermal control side first. Replacing the mica insulator, and adding a temperature sensor, seem like easy and useful firsts. |
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More power to you. Remember in the "thermal cascade" the JUNCTION of the device is what counts.? ?Needs to stay well below 175 C at all times.? Mosfets have a problem with a localized heating effect as well that I don't well understand, has to do with local variations in sensitivity to bias.?? To get heat away from the junction there are several thermal resistors in series, and at every one, temperature is lost, keeping the junction HOT and reducing the efficiciency of moving heat OUT Junction to tab -- this is pretty high in the TO-220 case, esp for MOSFETS that really were not built for this RF stuff.? ?Maybe 2 deg C/watt?? ? This means you CANNOT know the actual temp of the JUNCTION. CAse to heatsink -- this is made worse by the mica (or other insulator).? ?So the heatsink is even further COOLER than the junction heatsink to ambient room -- this is made worse by lack of air movement Ambient room -- if the room is HOT things are even worse. Measuring closer and closer to the junction is problematic, too!? The Drain is RF-HOT!? ?Lots of RF voltage/power there.? ?Potential for FEEDBACK if you couple something that carries RF away (wires, etc).? ?So could be a problem where the measurement....causes damage to the radio!? ? Not certain I would be so quick to put measurment devices there that go back toward the raspberry pi.... Putting a little thermistor to an external consumer temp measurement (think, the "external" probe of a consumer thermometer) next to the tab, separated by some insulating but thermally somewhat conductive glue or caulk.... then maybe making a common-mode choke ofthe sensing wire system by putting 5 or 6 turns of a coil of it over a pencil shape.... or putting some snap-on ferrites?? ?Might make this work and not CAUSE TROUBLE.? ?Dunno.? ? Easier to measure the temp of the heat sink NEAR the mosfets, but that is considerably removed from the JUNCTION, too.? ?? It isn't a slam dunk simple project, I think. Let usknow what works! Gordon KX4Z On Mon, Mar 3, 2025 at 5:42?AM Bravo Delta via <sbitxv3=[email protected]> wrote:
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HA3HZ
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