A Charming Detail About the BITX40 Module

In the BITX20 yahoo group, Farhan responded to a question about the BFO and the crystal filter in the BITX 40 Modules.  In his response we learn more about the work of the members of the women's collective.  Uma is the name of the lady who has the job of sorting the crystals. She sorts 1000 a day:

Farhan writes:

There is a longer explanation to this. The crystals we use in the BITX are microprocessor grade. This means that they are not very precise. Uma is the crystal sorter. She takes a bunch of 1000 crystals a day and sorts them by their frequency into different bags. Each board takes its five crystals from any one bag. Hence, the central frequency of each board will be slightly different from another board.

The central frequency of the ladder filter moves down from the oscillating frequency of the same crystal. That is why, in a set of matched crystals, one can be directly used as the carrier/beat frequency oscillator without needing any trimmer : it directly sits on the higher side skirt of the filter.

The BITX40 board's BFO usually ranges from 11.990.0 to 11.997.0, though in almost all cases it is very close to 11.998.0. The best way to determine the BFO frequency is to take it another ham's shack, tune in the BFO to zero beat on USB or LSB and note the frequency. I use the Rigol scope's built-in frequency counter to measure it off the modulator transformer's primary.

So, the IF offset should ideally set to the measured BFO's frequency. These are however, very subjective choices. Given that 2.2 KHz is not an ideal passband, 3 KHz is more like it, setting the BFO will determine how you would like to hear the receiver. Setting it close to the passband will make it bassy, setting it away will make it tinny. Setting it a few hundred hertz away will make it hollow. You get to choose which way you want to make your radio sound bad (harr! harr!)

- f

Boxed-up and Looking Good: An End to "HRO Al Fresco"

The "al fresco" phase has ended for my HRO receiver project.  As has happened with homebrew projects around the world, this rig was literally pushed aside on the workbench to make room for BITX-40 Module Mania.  I began to worry that the circuitry of the HRO receiver might suffer damage from the various kinds of electronic construction mayhem that take place on our workbenches.  Also, I wanted to see what it would look like in the nice big metal box that Tim Sutton had sent me (thanks again Tim.)  And I was hoping that the box would help with the AM broadcast breakthrough that I sometimes hear with this receiver.  So, as you can see, I have good excuses for declaring Basta! on the HRO Al Fresco. 

I think it looks great.  Black on silver is very cool.  It sounds great.  I'm listening to 40 right now. Thanks to Armand WA1UQO  for the very cool HRO dial that got this all started.   

TRGHS! HB2HB! Homebrew Extravaganza on 40 Meters!

AC7M HB Amp and HB Power Supply

I was flying solo last night.  Everyone else in the house was out.  So I turned to ham radio for some company.  And I was rewarded.    

I called CQ with my BITX DIGI-TIA rig and was immediately answered by Doc AC7M in far-off Twin Peaks, Idaho.   Doc was running a K3 to a homebrew solid state full gallon amp.  And get this -- Doc had also homebrewed the 3 kw switching power supply.  I looked at my store-bought supply and felt like an appliance operator.  I hang my head in shame.

As we discussed solid state amplifiers, we were joined by another builder of silicon after-burners: Don K9AQ, who called in from a beautiful cabin in rural Wisconsin. Don's amp is based on the venerable EB-104 design.   

Both Don and Doc talked about the work of W6PQL.   He has a really amazing site devoted to homebrew solid stat amps, and he is selling lots of great boards and parts for this kind of project:
http://www.w6pql.com/  

As I finishing up with Don and Doc, I got a very welcome call from an old friend from the SolderSmoke community: Dino KL0S.  He as booming in from Williamsburg, Va.  Dino has an amazing workshop.  He is building a serious vertical antenna for 160 meters.  Dino is going for the DX.

Dino's Bench

At this point Mike WA3O in Pittsburgh called in.  And get this:  Mike heard me on his new BITX 40 Module.  The Radio Gods Have Spoken! (TRGHS!).  We switched up to 7.285 MHz where I fired up my BITX 40 Module for a BITX40-BITX40 QSO (albeit not at QRP levels).
We should definitely make more use of 7.285 for BITX40 and other HB QRP SSB QSOs.  1930 EST (0030 Z) seems like a good time.

Finally, just when I was thinking that things couldn't get any better, they did:  Armand WA1UQO called in from Richmond.  Armand and I collaborate on parts acquisition at Virginia hamfests.  We specialize in the contents of the musty cardboard boxes found under the tables.  We discussed the DISRUPTIVE influence of Farhan's BITX 40: All around the world, other homebrew projects are being literally pushed aside on workbenches to make room for that fantastic little module from Hyderabad. 

I was very pleased to hear that Armand is building an analog VFO for his module, using a coil in the 4 uH range, wound on a piece of cardboard tube from a coathanger.  The inspiration for this kind of coil (which I now have in THREE rigs) came from Farhan, who used sipping straws from fast-food restaurants as coil forms in a sig generator that he built years ago.  This week, seeing a Facebook picture of my daughter and me in a restaurant with drinking glasses in front of us, Farhan asked if I had brought home the straws. 

Pete Juliano Adds Yet Another Great Word to the Homebrew Lexicon

We've talked many times about the pleasures associated with a rig that is still just a collection of parts and boards, all still spread out on the workbench, unboxed, perhaps held together by clip leads and bits of duct tape.  They seem to sound better this way.   This is the condition under which we experience that magical moment of "First Signals"  (similar to First Light with a new telescope).

We haven't had a concise way of describing this (note my long-winded description above).  Well, this morning the Sage of Newbury Park has, on his amazing blog, provided us with the words that we have so long needed: 

Al Fresco! 

That's it!  Perfect.  When a new rig is put into operation in this way, we will henceforth say that it is being run "al fresco."  Thanks Pete!

Check out the blog post that gave us this wonderful phrase:

http://n6qw.blogspot.com/2016/11/a-little-arduino-magic-for-fpm5.html

'Tis the season... To Worry about Electrostatic Discharge

Read and heed, or you'll be sorry.  The cold weather causes us to spend more time in the shack and to work on new homebrew project.  Some of these projects may involve sensitive, delicate, solid-state components that can be instantly wiped out by that little winter spark from your finger...

Take a look:

http://soldersmoke.blogspot.com/2016/01/an-electro-static-bandaid-to-protect.html
 
I have to be especially careful this year, because Northern Virginia is now officially in a drought.  So that spark-friendly dry winter air is likely to be even dryer this year.

Moonbounce on 40

Well, we were talking about it on 40.   This just proves that there is more to 40 meter SSB than the never-ending quest for audio "brilliance," "presence," "body"  and "sparkle."   I was working at the bench yesterday when I heard Frank NC1I telling another fellow about his 35 years of experience with moonbounce.  Wow, you don't hear that kind of talk on 40 every day.  Frank also said that the contact I was listening to was one of very few HF contacts that he has made in recent years.  I just had to jump in to encourage him to get on 40 more regularly.  He seemed impressed with my BITX40 Module (which I was using).  I warned him of the buffoonery that can be found on the band, but told him not to be deterred by it -- there are a lot of FB hams on 40.

Above you can see Frank's amazing antenna farm.  The dish is for 23 cm EME. Behind the you can see his 70 cm array.  That is 48 (FORTY EIGHT!) end-mounted Yagis, aimed into space. 

Check out Frank's QRZ.com page:  http://www.qrz.com/db/NC1I  He has some great pictures of his shack.  In case you are wondering why he has so many rotator control boxes, remember that the dish and the Yagi array need two each (azimuth AND elevation).

HB2HB: Butch K0BS with a KWM2 and a Hombrew 4-1000 Amp

Wow!  Now THAT is a shack! This morning I heard Butch K0BS and his friends on 40 meter SSB.  I knew I was listening to the voices of kindred spirits when I heard them talk about a drifting VFO and the need to heat up the filaments of an ART-13.   As the group was shutting down to begin their preparations for Thanksgiving dinners, I gave Bruce a call with my BITX 40 Module. He was on a KWM-2 (the rig that had been drifting a bit) and a homebrew 4-1000 amplifier.  I told him that I think a bit of VFO drift is a sign of good character. 

You really need to check out the pictures on Bruce's QRZ.com page:  

https://www.qrz.com/db/K0BS

Happy Thanksgiving to all who are celebrating the holiday.