Ashhar Farhan VU2ESE inducted into CQ Magazine Hall of Fame

Doug AC9RZ has alerted constructors to the big news of the day – Ashhar Farhan VU2ESE, designer of the BITx series of kitset transceivers has been inducted into the CQ Amateur Radio Hall of Fame!  The announcement from CQ Magazine follows:

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(Xenia, Ohio – May 18, 2018) – The CQ Amateur Radio Hall of Fame has 11 new members for 2018, CQ magazine announced today. This brings to 321 the total number of members inducted since the hall’s establishment in 2001.

The CQ Amateur Radio Hall of Fame honors those individuals, whether licensed hams or not, who have made significant contributions to amateur radio; and those amateurs who have made significant contributions either to amateur radio, to their professional careers or to some other aspect of life on our planet. The 2018 inductees (listed alphabetically) are:

  • Marlon Brando, FO5GJ (SK), iconic movie actor
  • David Brown, KC5ZTC (SK), NASA astronaut killed in 2003 Columbia disaster
  • Kalpana Chawla, KD5ESI (SK), NASA astronaut killed in 2003 Columbia disaster
  • Laurel Clark, KC5ZSU (SK), NASA astronaut killed in 2003 Columbia disaster
  • Ashhar Farhan, VU2ESE, pioneer in popularizing open-source Bit-X “semi-kits” using Arduinos for affordable QRP transceivers

  • Grady Fox, W4FRM (SK), SSB pioneer; worked on Manhattan Project during World War II and the camera for NASA’s lunar landers
  • Wendell King, ex-2ADD (SK), African-American pioneer of broadcasting and college radio
  • Fred Lloyd, AA7BQ, founder of QRZ.com, the most widely-accessed amateur radio website
  • Mark Pecen, KC9X/VE3QAM, wireless communication and networking pioneer, inventor, cybersecurity expert
  • Carole Perry, WB2MGP, longtime advocate for youth in amateur radio; moderator of Dayton youth forum for more than 30 years
  • Ed Westcott, W4UVS, photographer who chronicled the Manhattan Project during World War II and later helped the FBI with its investigation of the Jonestown massacre

Two new members each are also being inducted into the CQ DX and Contest Halls of Fame at the respective Dayton DX and Contest dinners. Their names will be announced separately.

CQ Communications, Inc. / 17 West John St. / Hicksville, NY 11801 USA / 516-681-2922

The world’s premier independent amateur radio publisher.

Publishers of:
CQ Amateur Radio, CQ Books, the CQ Video Library

Reference

VU2ESE power mod for 10m operation


Ashhar Farhan VU2ESE notes that 28 Mhz has, unusually, been open for the last week.  As a result, he realised that the ubitx output was woefully low on 10m.  Hence the experiment below:

Ashhar suggests the following final fix, and asks for others to try it out and see if it is replicable:

Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well)
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262.
So, what happens is that removing the C261 and C262 increases the gain of the finals. They are run open. Hence greater gain at 28 mhz.
However, the gain is very high at lower frequencies. So, in order to reduce the gain at the lower frequencies, the 0.1 uf cap is replaced by the 470 pf. As the frequency of the signal drops, less and less RF flows through the 470 pf, decreasing the gain of the predriver. 470 pf is not a magical value, 220 pf works almost as well.

Step #1 Increase the predriver gain towards the higher frequencies

The predriver Q90 has a emitter degeneration capacitor C81 (0.1uf) and and R83 (10 ohms). Replace C81 with a 470 pf and R83 with 2.2 ohms. Altenatively, short R83.

With this, the emitter reactance decreases with increasing frequency, yielding higher gain beyond 14 MHz.

Step #2 Take off the feedback from the IRF510s.

a) Replace the existing  R97 and R98 with a value of 47 ohms  with 220 ohm resistors.
b) Remove C261, C262.
Reference #1
Reference #2

Updates made to HF Signals website

Ashhar Farhan VU2ESE, designer of the µBITx, has posted to the BITX20 IO Group to say that there have been changes made to the wire up diagram to fix the errors.  This is good news as there will be fewer mistakes made by constructors meaning more happy customers!

While many will have moved on to one or other of the other firmware versions available for the µBITx, those wanting updated factory firmware will be pleased to know that a bug fix release will be coming soon.   uBITx.net will let you know when this happens.

A further comment from Ashhar suggests that he may use the PTT line as one of the keying lines (for the straight key).   This will mean a change to the wire up in line with the approach taken by the W0EB software team.

Reference

Replacement to TDA2822 coming soon!

Sajid, VA3QY asked Ashhar Farhan where he could source a new and reliable TDA2822 audio chip.

Ashhar Farhan has replied, “I am working on an audio amp.  I am testing it live. I always personally use circuits on the air before recommending them. I hope that by Tuesday I will have something you can use.   About 100 out of 4000 boards have had this problem. and less than 20 of them have reported the blow out.”

Reference

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

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).