SB II build project


As I eagerly await the delivery of a shiny new Slop Bucket kit I've been imagining the specifics of how I'd like to box it up.  I'll be using it almost exclusively portable for SOTA, which helps to clarify some of my design goals, and on that note I have a few thoughts/questions I'd like to run by the group.

Power Supply
I plan on using 4x 18650 lithium cells as the power source, if I swap out the 16v electrolytic capacitors for 25v versions would it be appropriate to use an input voltage of 16.8v?  I'm also planning to change the protection diode for a P-channel mosfet (see fig 5 in order to avoid any voltage drop.  The extra RF output would probably be quite small, but it would extend operating time slightly which would be beneficial while trying to activate in cooler weather. 

In regards to the batteries, is it worth picking up one of the many inexpensive BMS boards I see on various Chinese marketplace sites?  Also, would I need a separate balanced charger module if I wanted to charge the batteries internally?  I'm hoping to wind up with a transceiver that could be used for a while without opening it up.

I found a neat 44x100x100mm enclosure that should reduce volume a bit compared to the 50x100x100mm cases and also have enough space for the SB II and four 18650 lithium batteries.  I had looked at using a 30x100x100mm case with some flat lithium cells I found on battery space, but it would have been a tight squeeze and frankly I'm more comfortable with cylindrical cells that are already inside a metal case.  Here's the link to the enclosure:

While we're at it, any advice on how to weatherproof something like this would be greatly appreciated.  I don't expect it to be water tight, but I'd like it to withstand a bit of rain and damp weather.

Voice compression
I have a few small voice compression modules kicking around based on the SSM2167 and thought I might try to integrate one into this kit for a bit of extra punch.  These are the next generation of the same chips used in some popular compression modules made for the FT-817, though those ones follow up the compressor with a basic amplifier.  At this point I'm not sure if I'd have to do the same with the slop bucket, though I imagine I'll find out while determining the correct compression ratio (not too much!)

SWR meter/Antenna tuner
If there's any space left over it would be nice to include something like the TinySWR board designed by DK3IT (  It would also be nice to have some sort of tuner for high impedance antennas, though I strongly doubt there would be any room with all the other stuff that's crammed in there.  This will definitely have to be a 'wait and see' addition once everything else is in there.


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