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Re: How to ruggedize the sBitx V3

 

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=gmail.com@groups.io> wrote:

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=gmail.com@groups.io> wrote:
Hi Gyula,
?
I remember reading about a failed DE output transformer. The stacked toroids cracked due to heat, leading to the V2 and V3 redesign.
?
?
73
Evan
AC9TU
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