Glenn, VK3PE, suggests that his measurements of DC levels and RF levels at various points in the PA driver section from Q90 onwards (with a 12.5v supply. ~8W out) might be of interest to some.
Ashhar Farhan tells it as it is … the problem of the TDA2822
Ashhar Farhan VU2ESE, designer of the µBITx tells us the sorry saga of the TDA2822:
“Here is the story. This is going to cause a lot of heartaches. I chose TDA2822 after listening to a lot of bad press about the LM386. Upon looking at its harmonic distortions et al, it was found to be a reasonably good device. In, it went.
“Now, unfortunately, the TDA2822 production has entirely stopped. None of the standard suppliers, including mouser, newark, element14 have no stocks left. We tried to find other source of remaining stock from our reliable supplier who has been supplying to us in the past as well.
“He turned up with a batch. We tried the ICs in burn tests for. Ten of them on ten boards at full volume for a whole day. In retrospect, we should have tested every individual IC. That batch had these WX ICs as well. About 100 to 150 of these must have shipped, there is no way to know. The way it works is like this : Not all the ICs turned out by a factory are good. So work very well, some not so well, some don’t work at all. These wafers make it to the silicon industry underground where they are cut out from the wafers and packaged and sold as low grade versions of the same parts. We got a a hundred or so of these lemons.
“We finally located a source of brand new, high quality TDA2822s that are currently being shipped. They cost almost five times as much as we were paying while this was in production. Well, such is life.
“In the meantime, we have to look for alternatives to the TDA2822. I am highly inclined towards making a discrete device amplifier. We will never run out of discrete devices, the audio would be so much better. Does the gang have any ideas?”
Initial feedback suggests that there will not be a consensus reached on a replacement. Some want to stick with the TDA2822 (assuming a reliable source of affordable devices can be found), some would prefer the ability to add in a module of the builder’s choice, and others would like to see the device replaced with discrete components. David N8DAH suggests the drop in replacement – NJM2073D-ND
Reference
KD8CEC minor firmware update v1.04
Ian Lee, KD8CEC, has released a further minor update of his firmware (v1.04). You can download it here.
The changes since version 1.01 are as follows:
– Reduce cpu usage
– Change BFO Calibration step (50Hz to 5Hz steps)
– Change CW Frequency Display (frequency is more accurate when in CWL, CWU Mode)
– Optimized source code and reduced program size (97% -> 95%)
Cooling your uBITx
Walter, W9KJO, has installed a small cooling fan (40mm) turning on with a 40 degree thermo switch located near the heat sinks of the finals in his µBITx.
Reference
Updated circuit from VA7AT for removing audio pops
Wayne, VE7HCW/VA7AT, has updated his circuit as described by Don Cantrell ND6T in his article (see the news item here).
It can be downloaded from the BITX20 file repository.
VK4PLN does it again with a Teensy 3.2 Raduino replacement
Nik VK4PLN has been thinking again … and come up with yet another Raduino replacement board (before his first board is even ready to go to market). This time it has a Teensy 3.2 marked out on it. A few more ports and most importantly more grunt to use the existing libraries for this processor to give DSP!
A familiar enclosure
E29AHU has a temporary enclosure for his µBITx. It should be familiar to all constructors of the HF Signals kit.
Reference
Remove detents from your encoder
WA6ISP uBITx replacement Raduino
Mike Hagen, WA6ISP has previously supplied Raduino X and Raduino XP alternatives to the builder community for the BITx40 units. He has been asked by many builders whether a µBitx Raduino replacement was planned.
He now has designed, built and tested a µBITx Raduino replacement. This comes with the extra feature of having an i2c 16 port I/O expander on board. The Microchip Expander IC uses the Adafruit Library MCP23017 to create 16 more Digital Pins.
This replacement board is slightly bigger than the standard Raduino and has the Ardunio Nano facing towards the left rather than to the right.
Email Mike for further information or to order. The cost of the bare board is US$12 and the built up board is $46. Note that the bare board will require you to source all parts and mount some fairly small surface mount devices.
µBITx constructors now have several alternatives to choose from in considering a replacement Raduino board: the WA6ISP uBITx Raduino, the W0EX Radi2cino and VK4PLN Raduino replacement.
External speaker and headphone jack
Generally speaking, internal speakers in a QRP transceiver, like the µBITx will be inferior. Fragile, rattly and thin sounding, and inefficient. Don Cantrell, ND6T, has written an article about how he dealt with this problem. He incorporates a headphone jack in the speaker with a switch and an associated signal limiter circuit to prevent the RX from damaging his eardrums with loud stations and static bursts.
See his blog page for details.