Re: #ubitx-help advice needed-display issue #ubitx-help

Jerry Gaffke
 

We've had some really long threads here about switches and fuses and diodes and such.
Here's a few of them:
    https://groups.io/g/BITX20/topic/7489182
    https://groups.io/g/BITX20/topic/19250730
    https://groups.io/g/BITX20/topic/21608328

It's one of those things were everybody has an opinion.
Most of them would work enough.

If you don't have a 3 Amp fuse in line with the power supply, the shunt diode scheme shown on the 
wireup page of hfsignals.com won't necessarily work.
You are describing a variation of this, with a fuse in the black wire between the shunt diode and the power jack, 
this would mostly work except that antenna ground is often somehow connected to power supply ground
which can give a path around a blown negative side fuse.
I'd say you want to fuse the positive side first.
Allison has suggested also fusing the negative side, but that is not often seen.


This is what I have implemented:


                                  +------0.5Afuse----Diode----------RedToMainUbitx12v
               jack               |                      bar
PowerSupply=====O-------Switch----|
                |                 +------3.0Afuse--------------------BrownToIrf510s 
                |
                +----------------------------------------------------BlackToGround


I am using polyswitches instead of fast-blow fuses, no need to replace them when a short occurs.
    https://www.taydaelectronics.com/circuit-protection/polyswitch-devices.html
Just power down to let the polyswitch cool and reset itself, fix the fault, then power back up.

Having a separate 0.5A fuse for most of the uBitx means less damage will occur on a fault
than the damage we would have if it was a 3.0A fuse to everything.

The power switch could be the one on the volume control provided.
Instead I put in a toggle switch right next to the power jack on the back of the chassis to avoid long wires.

I prefer a series diode as shown (not shunt) for polarity protection of the main uBitx board, we lose 
some fraction of a volt across that diode but it does not affect radio performance.
The provided Schottky diode could be used, or use anything from the 1n400x series such as the 1n4007.

The PA-PWR to the IRF510's is only protected by the 3.0Amp fuse, if polarity is reversed then the IRF510's
will conduct and blow the fuse, so this is a shunt protection scheme that avoids any diode voltage drop
A small drop in voltage here will reduce available power out when transmitting.
 
Jerry, KE7ER



On Sun, Jun 24, 2018 at 06:33 pm, <entilleser@...> wrote:
So, then, regarding the wire-up of the jack/switch/fuse/et cetera:  Positive pole of jack to one pole of fuse: other pole of fuse to one pole of switch: other pole of switch to red and brown wires of radio power connector.  That it???  Also, negative pole of jack to one pole of second fuse: other pole of second fuse to black wire of radio power connector, and to black end of diode: ring end of diode to positive pole of power jack.  Yes???

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