External LPF filter board from K5BCQ under test

Kees K5BCQ has received his first set of boards. These boards will fit in the space currently occupied by the on-board LPFs.   The piece jutting out and marked “WOOF” is the space for the TX/RX relay (was K3).  The filter parts need to be transplanted from the main board onto small PCBS that are designed to plug in to the board as illustrated above (they are the same size as QRP-Labs filters).

Kees has already made some modifications for better wireability as follows:

1)   Eliminate R3 on the uBITX board and instead add it to the LPF Relay Board.  This frees up space on the µBITX main board and allows more efficient RF wiring for receive. Since the “old R3″ also switches M1 to M2, this requires modification of the board to short M1 and M2 and insertion of the audio pop mod on a v3 board (a v4 board already has the anti-pop mod included).

2) Replace 3 sets of dual 2N3904 Transistors in the PA driver with 3 sets of dual 2N2222A Transistors. Allison had suggested changing the emitter resistors from 22 ohms to 10 ohms (for dual 2N2222A’s).

3) Add a three 1N4148 diode-OR from TxA,TxB, and TxC driver inputs to a TxD driver to pick that relay, which removes the 10m/12m/(15m) LPF when inserting the proper (A/B/C) LPF during Tx. Yes, that means 4 relays are active during TxA,TxB, or TxC transmit. All four of the LPFs use the existing inductor/capacitor components off the uBITX board. They are just moved over to a small 1.5″ x 0.5″ bare LPF board (that footprint is also the one QRP labs has for their LPF/BPF filters, but they don’t sell blank boards.

4) uBITX Antenna wired to either one of two SMA connector pads.

5) T11 will be connected to the RF input on the LPF Relay Board with about 1″ of coax.

6) The smaller 12V 10 pin DPDT bifurcated contact relays can be found on ebay for about $1 each. They fit nicely.

7) Leave all the traces, just make a cut and remove 1/16” of the trace where needed.

[Photos of installation still to come]


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