An RF based AGC design from K P S Kang

K P S Kang VU2KR / VU2OWF has an item on his blog showing an RF AGC for BITx designs.  The AGC is apparently very effective at calming those 9+20dB signals that on the uBITx will damage your hearing!

The design is for the BITx40, but can be readily adapted for the uBITx – probably not at the antenna (because it is best to avoid diodes at the front end of the uBITx), but at the 45MHz IF stage.  Are there any takers to adapt this design for the uBITx?

Nice looking case

Sajeesh VU3PSZ shows off his new uBITx case design alongside his older BITx40.   A nice pair of rigs.   His blog item shows all the details, including a home made jig to achieve the folds in the aluminium.   This is definitely worth a look if you are considering a home-brew aluminium case for your uBITx.

Reference

Front panel layout ideas

Vic WA4THRI always enjoy seeing how others have built their BitX’s and has pointed out ideas that others might find useful:

1. Almost everyone places their tuning control to the right, but if you place the Raduino to the right you can easily update and play with the software by just plugging your computer into the USB port [EDITOR:  With a penetration on the right hand side wall of the enclosure for insertion of a mini-USB-B connector.]

2. It is hard to beat the value of the Banggood EF01 instrument case. If you turn it upside down and eliminate attaching the hard plastic feet you have a smoother mounting surface for circuit boards and can use the vent holes for a speaker grille.  Add some stick-on soft plastic feet on the “new” bottom.

3. Using the second line of the BitX display to label switches and controls saves having to find a way to place labels on the front panel.

Reference

 

Raduino Repair Service

Jim Sheldon W0EB is offering a new service to uBITX owners in the US (sorry no service is provided to foreign owners) to repair Raduinos.

Jim has just finished designing and building a Raduino test fixture that allows him to look at all the signals coming out of the board and also hook up all the digital controls to the board. He has the equipment in his shack to replace the Si5351 clock chip if it is bad and he can also replace a bad Nano (but the customer must provide the Nano).

He’s not sure how long he will be able to offer this, but he is aware that there are a few BITx owners out there that have somehow blown up their Raduino.  It is not that easy to get a replacement at the moment.

DO NOT send Jim your Raduino in need of repair without first contacting him and discussing the problem.  He may refuse to work on it if it appears too badly damaged – that’s at Jim’s discretion.

The offered service is ONLY Raduino repair, not complete uBITX repair.

Contact Jim via his QRZ.com  address (his email address is listed as well).

Convert your uBITx display to an I2C Display

Andy KB1OIQ has posted a file on the [BITX20] IO Group files page: kb1oiq_i2c_mod.pdf that describes the hardware and software modifications that he performed on his uBITX to free up digital pins on his arduino.  You will need to be logged in to the Group page to access the file.

Andy converts the LCD to use the I2C bus, thus freeing 6 Arduino digital pins for other uses.   Only very minor modifications are required to the Raduino sketch (and you will need to install a different library).  He documents every step involved with photos.   Well done!

[EDITOR Comment – removal of the two pull-up resistors on the additional board and direct connection to the I2C A4 and A5 ardunio pins should suffice without use of a level converter board.  However, the cost of adding in the level converter is negligible and will work well!]

Reference

New Software Release for TFT Colour Touch Screen

VU2SPF – Dr. SP Bhatnagar (India) and VE1BWV Joe Basque (CD)  are pleased to announce the initial public release of the UBITX Colour Touch Display Controller v2.72u.   
This is essentially  the same as the one for BITX, but modified to work with the UBITX.   The new software provides  a Colour Touch Display Controller with a no menu approach  to control your ubitx .
More info  can be found in the following locations:

The website contains information on how to download the code.

Features:
  1.  Low cost for parts – Suggested parts –  1 atmega2560 – approx $8.00US, 1 Addafruit dds Si5351 – $10.00  –  2.8 TFT  touch colour display     $12.00 US
  2. All bands, band selectivity, USB LSB  -Works well with digital modes
  3. All Display buttons are touch control – and no menus
  4. Any button can have a physical button and a TFT touch or any combination.
  5. 100 memory channels
  6. Tunable BFO’s
  7. 3 VFO’S – A  B  and  MEM
  8. USB / LSB
  9. TX  timeout control
  10. Touch TX button and or physical TX control – for ptt mike or digital modes (vox input low)

Next : New Feature – Working on adding  CAT Control

Connections diagram

Joe VE1BWV subsequently uploaded the connection diagram to show how the Arduino Mega 2560 connects to the display, the si5351a and the main board.

Typical current draw on the uBITx

Greggory N5WLF  observes that he gets in the range of 1.4-1.8 amps current draw on transmit, SWR depending and asks if this correct.

Feedback from the group suggests that:

  • on receive current draw is around 0.16A for an unmodified uBITx; and
  • on transmit it runs around 1.4-1.8 amps depending on the SWR.  On high SWR the finals can draw up to 2.2A approximately.A 2A fuse on the TX line and 0.5A on the main board seems about right in order to protect your uBITx.

Reference

BCI filter in the RX line

Nick Pullen VK4PLN has inserted his 3 stage BCI filter into the RX line.

Filter Details: https://groups.io/g/BITX20/wiki/uBITX-AM-BCI-Filter

Nick cut the trace either side of the new HPF board, exposed a bit of the trace and jumpered onto that.   You need to cut the second trace from the PA side (3rd trace down from the 45MHz roofing filter with the crystal).

Taken from the top trace to the bottom in the photo below, starting from the relay on the left and the PA circuit on top:

1: TX pwr to the PA circuits via R89
2: RX path (between K1 and K3 relays. (CUT AND INSERT HERE)
3: TX pwr to the LPF bank.
4: RX pwr to the receive circuit (R18,R38…)

Nick picked up GND from the 2 unused caps C216 and C210 as can be seen in Nick’s photo above.

Reference

IRF510 bias current

Jerry KE7ER says:

“Farhan recommends 100ma for the push-pull IRF510’s on the uBitx. More is better, you get into a more linear region of the FET. But more means more power getting sucked from the battery if portable, that power gets dissipated as heat in the FET’s.  I’m going with 100ma.

“With a 500ma quiescent drain current when using a 24v supply, each FET is dissipating 24*0.5 = 12 Watts.   That’s a lot of heat. Back off to 100ma and it is only 24*0.1 = 2.4 Watts.   Which still seems plenty.

“You want to be very careful when adjusting IRF510 gate bias trim-pots, take it too far and the IRF510’s might be trying to dump 100 Watts or so.”

Note that a Mitsubishi D16HHF1 in push-pull requires a higher bias current setting (perhaps 250 mA or 300aA).