Re: Plug-in modules for uBITx
Thank you to all those who responded with kind words of encouragement.
I am attaching the draft design for initial review and comments.
1. There are two connectors, one that sits on the board and the other
that is attached to the PCB. I haven't got a nomenclature for these
2. The RF Preamp is being kept as a provision for future expansion
3. The RF Preamp and the CW filter will be switched via separate SMD 12V relays
Apols if the circuit diagram seems all over the place, I put it in an
order that I thought was correct. The reader may have to flip between
pages to check connectivity.
LEDs are placed on each daughter-board to show if the board is active
or not. One side of the board will have the RX section and the other
will have the TX section.
I am planning to make the base board on a 100mm x 100mm board but this
seems like a tall order at the moment.
What are people's thoughts on using a double line right angle pin
I understand that rigidity might be at stake here, but other
connectors that can be used to fix the board, might cost more?
For the adventurous reader - A brief writeup of the design follows:
Stage 1: A J310 RF Preamp has been introduced. This design is
available here: https://www.sv1afn.com/j310preamp.html. The RF Preamp
will be switched in only on receive mode and will be in the RX RF
Chain. Care will need to be taken to ensure that the break-before-make
is established with microcontroller (uC) control to ensure that stray
TX RF does not leak into the switching circuitry. It may also be
possible to bring the switching control to the front panel instead of
using a uC.
Stage 2: The first TIA stage has been broken down into a single
section and has been terminated using pinouts. This will allow for a
small SMD board to be utilised to host the RX chain and the TX chain.
This board is meant to be a plugin version and allows for any
prototype TIA circuitry to be implemented in this section. The actual
board size is estimated to be 1.5" square and has the RX chain on one
side and the TX chain on the other side. A Red/Green LED is provided
on each side to indicate if VRX or VTX is powered on. Additionally
each board also has a ferrite bead/choke/inductor on the VTX, VRX and
the GND lines to prevent spurious RF/uC hash from passing through.
Stage B - Baseboard: The Baseboard contains all components that are
not on the daughtercards, this includes all coils, mixer (ADE-1+),
Xtal filter, and the Audio Amplifier. These base components are not
expected to change frequently.
Stage 3: This is the second TIA stage and and follows exactly the same
concept of Stage 2. See note above.
Stage 4: I decided to try a new AGC RF+AF and the schematic for this
stage has been taken from the JackAL AGC addon that has been presented
on the forum.
Note: All components are SMD (1206) with the exception of the large
transistors and the XTAL filter.
Stage 5: The CW filter is taken from here:
https://www.youtube.com/watch?v=SEUSYfw4coA Which was earlier taken
from QRP Notebook by the late Doug DEMaw W1FB. This is also in SMD and
will be either switched by a relay or a front panel switch. I may be
able to get some more info on the theory of operation later
Stage 6: The AF Amplifier chosen is a discrete design and has been
proven in use earlier. This replaces the LM386 and/or the TDA2822
Stage 7: The QEX ladder filter design has been kept the same, but is
now based on a modular board. At the time, it was thought that varicap
diodes could be added to the filter, but this was later removed as it
was thought that there could be impedance mismatched. Instead of
varying the bandwidth of the filter, it was also thought that an
Active CW filter would be a better approach. Passband filtering may
also be achieved by changing the LO2 frequency and this is left to the
Stage 8: A post filter amplifier has been added to compensate for the
low signal level in the RF chain. The gain of this stage may have to
be adjusted and this is left to the experimenter. This stage will also
be built on a daughtercard.
Stage 9: A Mic speech processor and Preamp has been added. This has
been designed by KPS Kang
On Tue, 10 Mar 2020 at 10:13, Ravi Miranda via Groups.Io
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