S-Meter on BITx40

Vic WA4THR has now added an S-Meter to his BITx40.  This uses the code supplied with the µBITx to show a meter, but which is not used in the firmware because there are no components to sense signal strength on the main board.


New release of KD8CEC firmware (v1.061)

Ian KD8CEC has released version 1.061  of his KD8CEC Firmware for the µBITx.  This adds the WSPR mode to your µBITx.   If  you use Ian’s uBITX Manager  to put WSPR information into uBITX (using your PC),  the µBITX no longer needs any external device to transmit WSPR.

Ian says, “Beta testers have been very helpful when embedding the WSPR functionality. WSPR mode will continue to improve in the future.

“By using WSPR before or after having a QSO, you can check where your uBITX is getting to around the world.”

Added or improved in version 1.061:

  1. 1.Added WSPR function to uBITX
  2. Update uBITX Manager to Version 1.0
  3. Reduced program size
  4. Fixed IF Shift Bug
  5. Other bugs fixed
  6. CWL, CWU mode are more friendly.  Two options are displayed for shifting frequency.

Please see the link below for details.

You can download a HEX file (no need to use the Arduino IDE to load the firmware) and uBITX Manager from the link above.

You can also download the source code at https://github.com/phdlee/ubitx and see all the changes I’ve made so far.

LPF switching

Mike KU4QO suggests that how the relays select the relevant output low pass filter is done in a very clever way.

Control switching of LPFs

Three relays control four different filters.

  • When KT1, KT2 and KT3 are not energized, the 21-30MHz filter is selected.
  • With KT1 energized it bypasses the 21-30MHz filter and selects the 14-21MHz filter.
  • With KT1 and KT2 energized it bypasses both of those filters and selects the 7-10MHz filter.
  • With KT1, KT2 and KT3 energized it bypasses all filters except for the 3.5-5MHz filter.

The relays are only energized when transmitting (and only when needed).  It is an unusual configuration, saving the expense of a 4th relay.

Mike had a problem where he had no power out on 30m or 40m. Receive was fine. It ended up that one of the legs on relay KT2 was not soldered. A quick soldering of the pin and he was back in business.

Raj VU2ZAP responded, “Farhan has his mysterious ways of being thrifty. The real reason is as I think is to save one data out control line from Raduino.”

“The relays are known to fail, so I cut the TX line to filter ralays and linked it to +12V . The relays remain on during RX and  when you tune across bands you can hear them clicking! This affects power consumption but I can live with that.”

RF Path analysis

Jerry Gaffke KE7ER, provided an analysis of the RF path through the relays and suggested:

“With no relays energized as shown in the uBitx schematic,  RF power from the finals goes through KT1-14 to the 30m lowpass filter then through KT1-3 out to the antenna.   That’s as short as it can get.

“With KT1 energized and KT2 not, RF power goes through KT1-16 and KT2-14 to go through the 20m lowpass filter.  Still pretty short.

“With KT1 and KT2 both energized, we get the 40m lowpass filter through KT3-14.

“With KT1,KT2,KT3 all energized, we get the 80m lowpass filter through KT3-16.

“That’s getting to be a pretty long path for that RF, going through all three relays.  But at 3.5 – 4mhz it simply doesn’t matter.”


Another nice build: N8GGI’s uBITx

This is a rather nice µBITx build from Dennis N8GGI.

Dennis says, “Finished wiring up the UBITX today and downloaded the KD8CEC firmware. I took my time with the case. Old retired industrial designers still like to design (and build).

“I added a keyer circuit which has a speed pot…I don’t like to run through menus to match someone’s speed. I also added a Hi-per-Mite audio filter which really makes it a nice CW rig.

“First 40 meter CW contact was New Hampshire from my QTH on Lake Erie in north central Ohio.  Second 20 Meter CW QSO was from Portugal getting a 559 report using a tri-bander at 60 feet. I tried 20 meter SSB and worked the gulf coast of Florida with a 5×6 report. It’s a great little radio! Now I still have to tackle the TX pop and try to tame down the sidetone volume issue. I hope the 1,500 watt linear doesn’t get lonesome from lack of use.”

And what lies beneath the paint!   The “see-through” version!  Dennis says, “Kinda looks like the old ‘visible V-8’ from the ’70s.”

Calibrating your uBITx

Many constructors have had issues calibrating their µBITx.

To begin with, you have to figure out how to get into the expanded “Settings” menu.  Push on the encoder, and select “Settings”.  Wait for the menu to exit automatically.  Then press the encoder again and in turning the dial you should see the additional menu items displayed.

Jacob AG7CT has documented the steps he takes to calibrate his µBITx:

  1. Tune to WWV on the dial
  2. Enter menu
  3. Turn setup on
  4. Reenter menu turn to and select calibrate
  5. Zerobeat the WWV carrier. (May be difficult if BFO is too far off.)
  6. Click PTT.
  7. Click encoder, select set BFO.
  8. Zero the sideband off WWV.
  9. Click PTT to set.
  10. Click encoder, turn setup off.
  11. Wait more than 10 seconds to ensure setting are saved before removing power.

Replacement encoder

Jim W0EB  suggests a replacement encoder for the µBITx from Digi-Key :

part# PEC11R-4020F-S0012-ND

This appears to be a direct replacement for the original encoder and works really well. It’s a genuine Bourns encoder and not that expensive.


Drive control – 2 methods

Bill K9HZ who we have already reported had developed a relay control system driven by the Low Pass Filter I/O lines.  In addition, Glenn VK3PE has also come up with a circuit that could be adapted using a digital potentiometer module to be driven by the Raduino using a digital I/O line.

Relay drive control

Bill K9HZ has now drawn up the circuit he used to allow for relay switching of drive levels by band grouping, driven by the LPF band grouping I/O lines of the Raduino.  No firmware mod is required to deliver even drive power across all of the bands.

RV1 in the yellow circle is the existing drive pot in the uBITx.  Remove it and connect the wires from the relay as shown.  Q17C, Q18C, and Q19C references connect to the transistor Q17, Q18, and Q19 collectors.  Then set RV1A, RV1B,  RV1C  and RV1D on the basis of the appropriate band grouping selected to keep the power out flat.


Digital drive control

Glenn VK3PE has come up with an old circuit that could be used to work with a digital potentiometer module to use as adrive control set by the NANO  firmware on a band by band basis.

The original drive control, RV1, would need to be removed and a few parts added, along with a digital pot (I2C control) in place of R3 below to form an attenuator in the RF path.

With some careful work it should be possible to design a small PCB that fits into the holes vacated by RV1, either vertically or horizontally.

The schematic is from page 62 of the book by Randy L. Henerson on designing a Transveiver. Its a very old book (1997) ISBN 0-07-028263-3


Additional PCBs for Sunil’s Case

Sunil VU3SUA  is providing extra PCBs with his uBitx case.

See http://amateurradiokits.in to purchase the case and PCBs.

1. Encoder PCB
This pcb will save you from the clutter of wiring up the encoder.

2. USB.D9. PCB
Use this board if you wish to. if you do not want to use this board then cut a small plexi glass sheet and close the open area.

3.Power Connector PCB
The DC Power supply connections are easy to install with a board to assist. The On/Off switch, Fuse, IN4007 diode and power connector are mounted on a small board again removing wiring clutter.

Care has to be taken in mounting the On/Off switch, as excessive use of soldering heat or bending of the pins on the switch may damage it.

Sunil says that he will be making further improvements in the µBITx products to make it easier to wire in kit components into the case.