Farhan,
I'd suggest that people that havn't blwon up stuff to hold for a few days
to get this to some? working solution so they can continue without damaging
hardware to much.
Why Q10 would remain powered up if the Rpi has commanded a zero
suggests RF in the wrong places and maybe a need to buffer that signal.
I've not seen that other than during power up due to the Rpi be a sleep
and the IO not yet initialized.? The RC delay seemed to help that some.
if only keeping RF off the affected gates.
The bus that Q9 drives (TX_switched_12V) is really low current over
all in the 200ma range.
I need to buffer R-TX(digital board) (TX on main board) so that any fault?
on the main board cannot cook the Rpi port.? Generally people do that but
its high risk in some cases.? Also a suitable gate there with a RC can add
a power up inhibit on that signal to the main board.? 74act08 would do
that fine.
Additionally PTT from the main board to R pi is both unbuffered and?
totally unprotected so RF or static can potentially kill the port or drive it.
I pan a RC snubber on the digital board Pin23 to the Rpi.
I'm also working on a comprehensive set of changes.
its based on some earlier work for diode switching and?
the breadboard as tested shows enough isolation.
Over all its switching the port that is the end of the 30Mhz LPF
exclusively between the between the TX input? and the RX path
from the Switched LPF.? ?Right now that is a shared common
point and TX can feed though the RX path under some
conditions (failure or relay stick).? To do that a 60db of isolation
(minimally) is needed in the switch and also controlling leakage
around it.? Additionally insuring the rf power amp? is off during RX.
The core of it is removing K9... its gone.?
U3 as well.
Removing some PCB traces.
Creating a board with the diode switching matrix.
located t the left side of the main board away from the output switched LPF.
This is the low level end of the radio RX or TX.
?
Also the Switched DC to drive the diodes off the
TX control signal.
Then testing.
Other changes is to protect asm1117 regulators added a
pre-regulator lm78l05 for the main board and a 7805 to220?
for the digital board.? The idea is 12V to 5V then 5 to 3.3.
5V is enough headroom for the as1117 to do its job.
LM78l05s and 7805 are pretty durable.? I have a bag of them
so why not.? The thought being the radio must be safe to run
on nominal 12V (13.8-14.2V) supplies used for commercial
radios.
I've added chokes for the DC lines around the finals
3 total.? Goal is to keep final RF and driver RF from
propagating out to the 12V bus and other parts of the board.
Added two more posts in the middle half of the board rear section
to mechanically support the board and add local ground to bottom
of case.? Only for the rear section of the ground plane.
Right now stability is the thing I'm working toward.??
from there looking at more things.
However if it works it would be handful to implement for many.
Lots of cuts and routing....
So far I've not blown any finals.? I plan to keep it that way.
Likely I'm taking a different path but I have drawings if interested.
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
