Re: K5BCQ uBITX Relay Switched LPF/BPF board

Kees T
 

It looks like great progress is being made on spur reduction, so back to LPF switching and a few other things. Received the first set of boards and have already made some modifications for better wireability.

1) I decided to eliminate R3 off the uBITX board and instead add it to the LPF Relay Board because it frees up space on the uBITX and allows more efficient RF wiring for receive. Since the "old R3" also switches M1 to M2, I'm changing that to how it's wired on the V4 uBITX by adding a 2N7000, changing R70 to 1K, add a 1K R78, add a 1uF C79, add a D14, and driving the 2N7000 with a line over to T/R (a 2N7000 driven directly by T/R is faster than any speeding relay contact).

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 will be 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) Found some of the smaller 12V 10 pin DPDT bifurcated contact relays 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.

8) Will provide pictures later.

73 Kees K5BCQ 


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