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Saturday, February 6, 2016

Michael's Log: AA1TJ Has FIVE Contacts with the Unijunction Transistor at 1-2 milliwatts

Michael writes:

Dear Friends, The UJT transmitter circuit was improved considerably today. The power output has increased to 1.48mW and the start-up "whoosh" is now far less objectionable. It's currently running in beacon-mode at 3687.8kHz. I'll resume "CQing" as soon as I've returned from an hour's walk in the woods. I hoping to work K1QO among others. 73, Mike

Added five QSOs today. Seabury/AA1MY is in Maine...exactly 100 miles from my doorstep. It's wild to think that we made a one-hundred mile radio contact on a unijunction.

Friday, February 5, 2016

Beautiful BITX17 Presentation by Chris PA3CRX



This is a really amazing presentation on our beloved BITX rigs.  This presentation takes the viewer from block diagram to schematic to photos of the actual circuits and throws in great graphics showing spectra and filter curves etc. 

There is no sound.

Here is the link in case the embed above doesn't work:

https://prezi.com/yn2loy4mi0wo/bitx20/

Thanks Chris!

Thursday, February 4, 2016

A Probable First: First Ever Radio Contact Using Unijunction Transistor as the Transmitter


AA1TJ writes:

I spent most of a week working to raise the RF output power from my unijunction transmitter to nearly 1mW. I was rewarded this evening with two contacts.

Jim/W1PID exchanged (599/449) signal reports with me from Sanbornton, NH (112km) at 2210z!

Dave/K1SWL did the same (589/229) from Newport, NH (95km) some four minutes later!

I should think these were the first-ever radio contacts made using a unijunction transistor as the transmitter.

FYI: my receiver was comprised of a single 1N34a germanium diode mixer followed by a single 2N35 germanium transistor audio amplifier. Great signals on this end.

Wikipedia on Unijunction Transistors: https://en.wikipedia.org/wiki/Unijunction_transistor

Wednesday, February 3, 2016

New VFO for the Frankenstein R2 Phasing Receiver


I've wanted to change the VFO in my R2 phasing receiver.  The AD9850 DDS VFO with a divide by 4  I-Q generator limited me to 160, 80 and 40 meters.  But an Si5351 chip will go up to 160 MHz.  With a divide by 2 I-Q generator, this should allow me to cover 160 through 6 meters. I got the Arduino, LCD and rotary encoder all working tonight.  Thanks to Thomas LA3PNA for the code, and to Tom AK2B for help with the Arduino. The Si5351 board that you see sitting atop the Arduino is the work of Dean AC9JQ.  Thanks Dean.  

The flip-flop and inverter IC's should arrive this week.  That will allow me to finish up this VFO conversion project.

Sunday, January 31, 2016

Dead Chickens and Fake Transistors in Medellin Colombia: HK4DEI's Micro 40 DSB Rig


Daniel HK4DEI wrote to report that page 149 of the SolderSmoke book was providing some solace and comfort as he struggled to get his version of Peter Parker's Micro 40 Double Sideband rig going.  He was having problems with the amplifier.   He was almost at the point of sacrificing chickens to Papa Legba.  I wished him luck and told him to hang in there. 

Elisa saw my e-mail to Daniel and complained that I hadn't given him the solution to his amplifier woes.  I tried to explain to her that there are sometimes things in this universe that are just UNKNOWABLE.  C.F. Rockey W9SCH (who alerted us in SPRAT 22 to the chicken sacrifice option) spoke of transistors that exhibit "quantum mechanical necromancy."  Rockey explained that when this happens, "The transistor simply turns up its toes and dies. Not even an Atomic Physicist can tell you why!"  


But Daniel persisted.  And he won the battle:

Hey Bill
Did you kill some chickens already? If you did, THANK YOU!  If you don't, then please enjoy a nice sancocho de gallina for me.

But seriously... guess what?
FAKE TRANSISTORS!!!!
I knew I couldn't be screwing everything up so badly and VK3YE's circuit couldn't be so wrong.
I was getting nuts trying to understand why it wasn't working, changing a single inductor could fry the final instantly or not getting any power out at all (?) also my final BD139 was getting extremely hot, and many of them died with no apparent reason (Page 149!!!!).
I ordered a "good" deal of BD139's and BD140's combo for an incredible low price from [A WEB SITE], I've ordered many *apparently good components from that site with no problems so far... mainly resistors and capacitors. Having tried everything to get my circuit working and after some quick online search about fake transistors from china my suspicions grew considerably and I remembered some -other- BD139's I had ordered from Amazon some time ago.
I proceeded to solder the new transistors in place in my PA and Bingo! No more heating of the final and about the expected 0.5W out from my first DSB homebrew rig. I quickly reported to a fellow homebrewer in a local net and the report was amazing! 59 +10, the final transistor was comfortably warm to the touch and my mind could finally rest... lesson learned! What an electromagnetic achievement!
Just wanted to share my success Bill and thank you again for you book and you kind response.
Please say hi to Elisa and the Cristalinhos from a fellow Latin friend.
Clear Skies.
73/72 from Colombia!
Daniel
HK4DEI








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