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!
Je to dobrá zpráva pro v?echny ?ekající. Není pot?eba kolektiv HF Signals nutit ke spěchu. Dělají, co mohou aby v?e bylo v po?ádku a osazení desek, kompletace a testování se nedají nijak uspěchat bez zhor?ení kvality. Proto na ně netla?me a ?ekejme, na v?echny se dostane. Snad by mezitím mohl b?t ke sta?ení nějak? manuál nebo instruktá?ní video, jak TRX správně nakonfigurovat nebo provozovat. Také se sice nemohu do?kat ur?itě v?borného TRXu, kter? je brzy na cestě k nám. Lev OK2PLL
Lev, ?Neváhejte pou?ít P?eklada? Google, proto?e jazyk pou?ívan? na fóru je angli?tina. U?ivatelé nebudou kv?li va?emu rozmaru hledat p?ekladatele, ale va?i zprávu budou ignorovat.
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Lev, feel free to use google translate because the language used by the forum is English. Users will not look for a translator because of your whim, but will ignore your message.
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.
Delighted that you found the problem. Interesting that both drains showed an AC voltage even though one device was effectively shorted. ?That is surprising to me.
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!
?Je to dobrá zpráva pro v?echny ?ekající. Není pot?eba kolektiv HF Signals nutit ke spěchu. Dělají, co mohou aby v?e bylo v po?ádku a osazení desek, kompletace a testování se nedají nijak uspěchat bez zhor?ení kvality. Proto na ně netla?me a ?ekejme, na v?echny se dostane. Snad by mezitím mohl b?t ke sta?ení nějak? manuál nebo instruktá?ní video, jak TRX správně nakonfigurovat nebo provozovat. Také se sice nemohu do?kat ur?itě v?borného TRXu, kter? je brzy na cestě k nám. Lev OK2PLL
Vypadá to, ?e se obrázky v první zprávě nevykreslily správně, tak?e zde je repost:
V?ichni jsme p?ipraveni za?ít dodávat jednotky zBitx v dávkách od p?í?tího t?dne a zákazníci by měli obdr?et va?e sledovací ?íslo, jakmile bude jejich jednotka p?ipravena k odeslání.
Mezitím jsme vám chtěli p?edstavit zBitx a nabídnout vám pohled na v?robu zBitx, abyste mohli ocenit práci a úsilí, které je do v?roby těchto rádií vlo?eno.
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Zde je krátké video zBitxu v akci:
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https://youtu.be/3NSLHjw3Egg Rádi bychom se s vámi podělili o některé novinky z montá?ní linky zBitx v na?em závodě v indickém Hyderabadu.
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Jakmile desky dorazily, t?m se pustil do montá?e. Spojují v?echny díly s pr?chozími otvory, jako jsou cívky, konektory, regulátory, headery atd.
Tyto desky byly poté p?edány dal?ímu t?mu, kter? p?ipájel IRF MOSFETy a namontoval je na zadní panel, kter? slou?í jako chladi?.
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Zatímco to probíhalo, jin? t?m za?al pracovat na desce displeje a p?ipájel displej, Raspberry Pico, kodér, konektory a reproduktor.
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Jakmile byly zobrazovací desky dokon?eny a integrovány s RF deskou, pro?ly kolem mechanické a elektrické kontroly. Jakmile to bylo hotovo, desky byly p?ipraveny k ohradě.
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After testing, the radios were packed along with the test report and kept ready for dispatch.
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The dimensions of the radio are 139x84x37mm and weighs about 385 grams without the 18650 batteries and about 485 grams with batteries.
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Since there was a lot of confusion about the 18650 batteries for the zBitx, here is a photo of the batteries we used during testing. They do not come with tabs and are flat topped. Please note, batteries aren't included in the package.
I have finally disassembled my sBitx fully and removed final MOSFETs.? I have to cut the away to not damage the PCB. One of the was still alive (so I'll probably use it for prototyping):
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But the second is broken (probably due to overheating):
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So it looks like a fan is the "must have" if one wants longer continuously work in digital modes.
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Now I have to decide if I should mount the new MOSFETs and reassemble the device as it is, or wait until the new aluminum-nitrid isolators arrive.
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I'm also afraid about the PCB state when replacement of finals may repeate multiple times. It seems that the pads of Q16 and Q17 are quite delicate. If they are gradually damage during replacements, at ID reaching 4 A (or even more in a pulse) the PCB may gradually deteriorate and finally fail.
On Fri, Feb 28, 2025 at 10:57 PM, JJ - W9JES wrote:
I think some folks misunderstood what I was asking for.?
The sBitx V2 has IRFZ24N MOSFETs. We want to continue to use them for the finals. What mods have to be performed to prevent oscillations and early MOSFET failures?
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Thanks.
No documentation was sent about any changes to the v2.
What happened was that the devices sent in April 2023 did not come with any information sheet, so on May 3rd, several messages came, which can be found on the sbitx.net page, how to set the performance and some similar information. The hardware modification was discussed on the forum and no information was released about the change.
So whoever modified it did it according to their own thoughts.
My own experience with the v2, which uses IRFZ24N FETs in the output stage:
1. I checked the electrical and mechanical connections of the device and repaired them as necessary. (FET clamper broke / D27 diode was faulty, so I replaced the power/swr diodes together / Bias adjustment was difficult, so I modified the circuit (see F5NPV website) / I replaced the mica insulator with Aluminum Nitride for better heat conduction / I cool the power stage heatsink with an external 92x92x25mm silent fan / I cool the RPi4 from the back with a 50x50x10mm fan fixed on an intermediate board / I use the PTT control of the power stage based on the designs of KX4Z Gordon Furthermore
2. I use the device with a current limit of 12.5V and 6.5 A, because it was not in use yet and I powered it from a battery, with a dummy load instead of an antenna, then one of the FETs of the power stage became shorted. The replaced and selected FETs have been working fine ever since! Currently more than 8800 QSOs and these FETs have 168/150 dxcc/lotw since November 16, 2023.
3. I use a single antenna on 3 bands. This is a vertical delta loop antenna installed obliquely. There are two ferrite rings at the feed point (about 10 meters high).
One is for 100/50 Ohm and the other is for symmetrical/asymmetrical impedance matching. I sized the 42.8 meter wire to 7 MHz, which can also be used at 14 and 21 MHz without an antenna tuner.
4. I consider myself a returning amateur radio operator because of sbitx, because I previously dismantled my antennas (2 el 5 band QQ, 20.8m high vertical) and I made this antenna only for sbitx, so that I could use it.
5. Most importantly, if it weren't for the amateurs who brought the development to the current level, I probably wouldn't be a device owner.
So a huge thank you to them for their continuous efforts to fix the bugs they find.
I suggest verifying that adjusting the PABias1 pot does change the voltage on the MOSFETs' gates.? As Gordon stated, you need to be careful when making this adjustment.? It is very easy to drive the MOSFETs to destruction, and the current will "jump" as you get close to the nominal setpoint.
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A safe way to test the bias control is to measure the resistance from the MOSFETs' gates to ground without power connected.? You should be able to vary from almost zero ohms (55 ohms) in the fully counterclockwise direction to nearly 10k ohms when fully clockwise.? Be sure to return the control to the fully counterclockwise position before restoring power.
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In addition to a faulty control, one of the bypass capacitors may be shorted.
I suggest verifying that adjusting the PABias1 pot does change the voltage on the MOSFETs' gates.? As Gordon stated, you need to be careful when making this adjustment.? It is very easy to drive the MOSFETs to destruction, and the current will "jump" as you get close to the nominal setpoint.
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A safe way to test the bias control is to measure the resistance from the MOSFETs' gates to ground without power connected.? You should be able to vary from almost zero ohms (55 ohms) in the fully counterclockwise direction to nearly 10k ohms when fully clockwise.? Be sure to return the control to the fully counterclockwise position before restoring power.
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In addition to a faulty control, one of the bypass capacitors may be shorted.
one of
the ports is for power, I don't think it provides data.
On Fri, Feb 28, 2025 at 5:06?PM Ken N2VIP via
<ken=[email protected]>
wrote:
The RPi Zero 2
W has two USB 2.0 ports, I guess you could use an
interposer board and include a USB-C connector, but
it would only work at USB-2.0 speeds and increase
the size of the radio.
Those two diets you were talking about are not normal diodes they are transient voltage suppressors. They won’t conduct until the voltage gets around 10 V.
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Be very careful with that PA bias. You can easily destroy the transistors with that. ?Turning it too far will cause the bias current to go to many amps!!
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The strange thing is that performing the bias regulation (as described on the website) I couldn't get the increase by 200 mA in the whole range of regulation.
Those two diets you were talking about are not normal diodes they are transient voltage suppressors. They won’t conduct until the voltage gets around 10 V.
Be very careful with that PA bias. You can easily destroy the transistors with that. ?Turning it too far will cause the bias current to go to many amps!!
There is some odd residue near the input of your output transformer. ?
On Feb 28, 2025, at 19:39, Gordon Gibby KX4Z via groups.io <docvacuumtubes@...> wrote:
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be certain that you have correctly identified the PA bias potentiometer. It would be very odd if turning that too far didn’t destroy the MOSFETs
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when you press push to talk the voltage on L 80 and L 81 should go up— because it is controlled by Q9. if Q9 is continuously on, then you have blown a different MOSFET, one or more in that complicated switching system around Q9. ?You might want to figure out for sure if you really can’t see switching action going on there.
HA3HZ
WK4DS
Lev