80m harmonic fix by changing the capacitance of the LPF

Howard WB2VXW previously mentioned that he would try to reduce the harmonics by changing the output to 25 ohms and adding a step up transformer to go back to 50 ohms for the output. This would allow tripling the values of the capacitors at the input and output of the filters, reducing the effect of the stray relay and layout capacitance.

In the end after more simulation, Howard decided just to change the filter characteristics and retain the 50 ohms termination impedance.

Howard was able to come up with a filter that doubles the capacitance.  At least on 80 meters, with this new filter design, the harmonics don’t exceed -45 dB in his tests. Not as much margin as he would like, but legal.

Howard changed the 3 inductors to 1.6 uH by adding 2 turns on each.  He added an extra 1000 pF cap in parallel with the input and output caps, bringing the total to 2000 pF.  He also added a 620 pF cap in parallel with the one of the two paralleled 1000 pF caps in the middle two sections for a total of 2620 pF. (750 pF would have been better, but he didn’t have one).

Howard is asking others to give this ago.   After validation of the 80m LPF redesign he plans to try a similar solution for the 40 meter band.


Some mods to improve RX sensitivity

George UR4CRG/RX3ARG  suggests some mods to improve RX sensitivity:

  1. Add a parallel capacitor to R12.  Try C=470 pF.  George found in his signal analyser that this gave a 3 dB rise in gain at 30 MHz.  He placed an 0805 SMD (or your could use a 1208 SMD part) over R12.
  2. Add two 100 Ohm resistors to  the collectors of Q11 and Q12.  You will need to cut the PCB tracks to add in the resistors.   The emitter-followers do not like HF signals and a small collector resistor gives light feed back

After these modifications, reception was noticeably more sensitive/



W0EB TSW release forthcoming for 5″ touch screen

W0EB’s uBITX is built with a 5″ RA8875 type Color TFT display connected to a BITeensio Card.  This gives an “uncluttered” display.

This version of the BITeensio TSW firmware is almost ready for release.  It is just awaiting completion of the accompanying instruction manuals  and the arrival of a small  adapter board for connection to the display.  The adapter boards will be supplied in the BITeensio kits upon request.

This display, like the previous 2.8″ Colour touch panel display and the 4 Line I2C display (2004) are capable of utilising an optional external USB Keyboard for rig control and CW. The W2CTX RCP (Remote Control Program) works with this as well.

For information and updates see the TSW website.

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.


SSM2167 install details

John VK2ETA some time ago provided information about his experiments with the SSM2167 module available on eBay.com and Aliexpress.com for a few dollars.   The following shows the wire up diagram:

Picture of 4 pin molex connector added to the V3 Raduino for pickup of T/R (D7), +5V, I2C SDA, I2C SLD.

Note that the Arduino was replaced and put on headers as John uses a remote LCD display.


Single-ended relay board for existing LPFs 

Gordon has been testing out his mult-relay single ended board.  The concept here is that the existing LPFs and relays are reconfigured on the µBITx main board and the ends of the LPFs are connected to a new daughter board attached behind the LPFs and relays to provide for greater RF separation between LPFs.

And this photo shows the cuts made to the top of the board:

And showing the connections to the add-in board

And a different view showing the wiring to the main board:

And the relay power on connections:

The results seem promising.

A separate board with all LPFs mounted on the external board  (e.g. this one) would not be much larger overall and would require fewer connections to the main board.

A document with all the explanations of how to create this modification, including photos of traces to cut can be found here.


Long distance contacts on the uBITx

EI Frank asks: “So what’s your personal best distance on SSB?”

  • EI Frank – 380 km’s (236 miles) on SSB, with an End Fed half wave wire on 40m with a uBitx
  • iz oos – New Zealand, ssb 3w qrp with the Spanish ILER20. I logged that as an ordinary qso. I was not in the States of course… But in Italy. New Zealand is exactly on the other side of planet earth from my qth. Just let me say that if you hear anything around s9 or more if you use a qrp you can have a qso, of course it will be more difficult during a pile up. So give up FT8 and come back to cw-ssb!
  • Don ND6T – First SSB contact with new uBITX was with JE6EHP on 20m with an end-fed random wire. Nice long chat. Well over 8,000 Km.
  • Joel N6ALT – worked a station in Antartica from his QTH in Oregon USA, a distance of 10,455 miles, on a Bitx17A running 8 watts into a EFHW antenna. He has the QSL card to prove it!
  • Pete VK3YE  –  About 2600km on 80m – with a half-collapsed wire antennahttps://www.youtube.com/watch?v=pZcXBVX-tJk
  • Don KM4UDX – so many of you have gone really far. I am but a grasshopper. But it might be fun to get other distance records? I was pleasantly surprised to see this.
  • Doug Wilner – The K1JT modes sure do give you a high action to watt ratio.  I have FT8 QSO’s between USA and ZL on just over 4w which is 13,176.51km (8,235.318 miles). On my raspberry pi WSPR rig I have reports from ZL as well and that is on .1w.
  • Brent Seres – I managed southern Ontario to northern Brazil with my bitx40 on 40cw and end fed wire

LPF board from Nick VK4PP

Nick VK4PP (earlier he was VK4PLN) has come up with a small circuit board for mounting replacement LPFs (or the existing LPFs removed of scraped off your µBITx).

A topside view:

And a bottom side view:

Posting of the boards has resulted in lots of comments on layout and we can look forward to further enhancements of the design.