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]


Kees LPF and Relay external board

This is Kees K5BCQ 6x LPF/BPF board showing one LPF plug-in. The LPF parts were removed from the uBITX and moved to the plug-in board. This is easy with a hot air rework station like the ones all over eBay for about US$50. The relay removal is also “relatively ” easy with no pulled pads (using the large square tip which heats 4 pins at a time).

The plug-in footprint is the same as QRP Labs uses on their LPFs/BPFs.  Kees mounted the pins on the other side of the board because it reduces the overall height. You can solder the coax to the SMA connector footprint or use SMA connectors. Many options.

The photo below shows the four transplanted filters from the main µBITx board and the main board LPF corner that is now stripped bare.


Kees has been busy sending out boards!

Kees K5BCQs has 403 paid orders for AGC and/or Anti-pop Mini-Kits and 399 of these have been shipped.  He has additional boards and parts and will continue to supply these Mini-Kits as long as there is demand. Details are in the “Files” section of the BITX20 webpage under his call K5BCQ.

Kees was somewhat surprised to be able to process such a quantity over a short period of time. That indicates there are opportunities for others to join in with their ideas. As Kees notes, the uBITX is a great vehicle for modifying and improving.


K5BCQ boards very popular

The list of potential orders for Keys K5BCQ on 3 May is surprisingly high (250+).   Email Keys  K5BCQ(at)ARRL.net (to keep from overloading this “topic”) and he’ll update the spreadsheet to include or amend your order.


VA7AT Audio Pop and ND6T AGC Fixes: PCBs


Would you would like to have fixes in your µBITx for the audio pop and the missing AGC issues?

There are now two proven designs to the audio pop and AGC issues from:

  • VA7AT for the audio pop problem
  • ND6T for an effective AGC

Kees K5BCQ is taking orders now for two small PCBs to make it easier for constructors to complete these fixes.  The PCBs require the use of surface mount components.    They are tiny (about 1″ square) and can easily be mounted in any case.  They will be very cheap and available both in the US and DX.