What many people fail to realise when using a diode bridge for
reverse polarity protection is it means neither of the power wires
are at ground potential. If used in vehicle with battery having
one terminal grounded the grounds are not at same potential. So
your metal case and vehicle body have a diode drop difference.
On 31/01/18 06:05, Jerry Gaffke via
Reverse DC is not a problem for the IRF510. It has an intrinsic
reverse diode from source to drain,
will blow the traces or coils between it and the power supply.
Or, with some foresight, the fuse
you put into that power supply lead. Where you need reverse
protection is going into the remainder
of the board, be it Bitx40 or uBitx. A 1n4148 diode would
suffice, a 1n400x would not get quite so hot,
but there is no problem with running all that stuff at 0.7 volts
Having a full wave rectifier in line with the power supply to the
IRF510's would reduce the voltage
there by 1.4 volts. And have a significant hit on output power
On Tue, Jan 30,
2018 at 04:54 am, John Brock wrote:
I have not
received my uBitx yet. I’ve been reading this forum for about
two weeks. Looks like PA failures is a huge problem.
Are the two
main causes reverse DC power and high SWR?
For the DC
polarity problem how about a full wave rectifier at the DC
input? Two diode voltage drop a problem with this approach?
What would be
the best way to limit PA power out to a very small value to
allow a manual tuner to be used for the SWR issue?