BITX 20/40 BUILD UPDATE #4: 11MHz SSB Ladder Filter

As reported yesterday I have the 20 meter receiver portion of my BITX 20/40 rig up and running.  I decided to take a closer look at the crystal filter I built.  

Here is my method:  

1) Using an Arduino/DDS sig generator, I put 11 Mhz energy into the base of Q2 (the stage immediately prior to the crystal filter).   

2) Using my Rigol 1052E oscilloscope, I measured RMS voltage at the output of Q3/Q3A (the stage immediately following the filter).   

3) I looked at Vrms as I MANUALLY varied the input frequency in 100 Hz increments.

4) I took the results and plugged them into a spreadsheet.  I then used the spreadsheet to calculate the db drop from the peak Vrms value (So I wasn't looking at insertion loss, just the filter shape).  

I used 20*LOG(Vrms/276)

5)  I ended up with the chart displayed above. 

I have a few questions: 

1) What do you folks think about my methodology for evaluating the filter? 

2)  Where would you guys put the BFO frequency? 

3)  I know the ripple looks ugly, but the receiver sounds great.  Should I attempt to get rid of the ripple? 

Here is the filter I used (as prescribed by the AADE software):  I estimated Q at 10000 and used LM and CM values derived by the G3UUR method, and made no effort to match impedances going into the filter:   

Here is what GPLA predicted.  I estimated Rin and Rout values.  That probably accounts for the difference between the GPLA prediction and what I measured. 

  

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BITX 2040 Build Update #3 Receiver Sounds Great!

There it is,  my second BITX transceiver, this one for 20 and 40.   Once I got the VFO sorted out, this one went together very quickly.  Obviously experienced gained on the first project was a big help.

I followed Farhan's advice and characterized the 11 MHz crystals in the filter.  Then I used the AADE filter design software to build a 3 KHz filter.  Using my Arduino DDS signal generator and the new Rigol 'scope, I was able to do a manual sweep across the passband -- it looked very close to what was predicted by the software. 

This morning I built the bandpass filter for 20. As soon as that was done, I fired up the receiver.  This was an amazing experience for me: a homebrew receiver that worked right away!  That never happened before.   I'm listening to 20 meters now.  It sounds great.  I even managed to demodulate and display some SSTV.  The VFO seems very stable.

I still have to build the RF amplifier stages, the bandpass filter for 40 and low pass filters for 20 and 40 (I know Steve Smith is watching!).  Then it will be time for cabinetry.   I guess I should put some paint or varnish on that walnut box.   Any recommendations?   I'll line it (on the inside) with copper flashing material.     

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Happy New Year! Straight Key Night

 

For the first time in years I got on the air on New Year's eve.  I fired up the HT-37 and Drake 2-B on 20 meters last night right at 0001 UTC  (well, with these rigs I should say GMT!).  There was a moment of stress when, as I was trying to adjust the key, the whole thing fell apart and the little ball bearings spilled out.  Yikes!  It was as if the radio gods were trying to tell me something.  It took me a few minutes to re-assemble my straight key, then I called CQ.  The HT-37 puts out a lot more power than I normally emit,  and it caused the Carbon Monoxide detector to go off, sparking a minor panic among family members.  (See, this never happens with QRP!)  With that resolved I had nice QSOs with K5KFK in Texas, W6VNR in California, and N1WPU in Maine.  This morning I worked WA0ZDE in Missouri.  The old HT-37 was drifting a bit, but Rick said he kind of liked that.  (I put a muffin fan on top of the transmitter -- that should settle it down a bit).   By the way, my key is a bit unusual: it is just a cheapo key, but I have it mounted on the base from a Vibroplex bug.  I never mastered the Vibroplex, and ended up giving the bug parts to HI8G in Santo Domingo -- Gustavo planned on using them to fix another bug that had been given to him years before by Fred Laun (K3ZO). 

 

Rick, WA0ZDE ( who I talked to on 20 this morning) sent me a VERY SKN photo collage (see below).  I see that Rick also tends to hold onto his gear for a long time. 

 

HNY to all!   GL in 14.  73! 

 



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SolderSmoke Podcast #157: Peter Parker on Phasing Rigs

SolderSmoke Podcast #157 is available for download.
http://soldersmoke.com/soldersmoke157.mp3

December 27, 2013

-- Santa Report:  Rigol Scope at SolderSmoke HQ.  Kites at VK3YE.
-- Project updates:   Bill's BITX 40/20 build. 
-- Peter finishing up BITX40  (in a big box)
-- BITX 17 (5 watts SSB) works JA, ZD7, ZS!
-- The mystery, elegance, and gentleness of phasing SSB
-- Phasing explained in 1970 ARRL SSB book
-- Phasing SSB: From Hallicrafters HT-37 to SDR
-- The SP5AHT Phasing Rig
-- I & Q for you:  The Binaural Experience
-- Direct Conversion receivers and Software Defined Radios
-- Simple DC receivers plugging into sound cards 
-- The joy of receiver building
-- 144 MHz aircraft bounce (Melbourne to Sydney)
-- VHF Across The Great Australian Bight  

HAPPY NEW YEAR TO ALL!

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Santa Arrives at SolderSmoke HQ! Rigol and Black&Decker

Santa Claus obviously heard my distress call when the TEK 465 gave up the ghost.  This morning it was replaced by a RIGOL digital scope.   I'm going through the tutorials.  Wow, lots of features.  A Black&Decker jig saw also arrived -- this will help in my cabinetry efforts. 

Last night just before dinner I talked to Kiyo, JH1MDJ, in Tokyo on 17 meter SSB with the 5 watt BITX.   I kind of broke through a small pile-up and we then had one of those "please repeat your power level... I can't believe that is 5 watts to a dipole" conversations.  

Happy Holidays to all!

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

How they took the iconic Apollo 8 Earthrise Photo (Amazing Video)

I was ten years old and totally obsessed with the space program.  This video brought back a lot of the magic. Wow. You really have to see this one.


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Where to send all those LM386 chips: Make them BEAM robot brains!

Over in the BITX20 yahoo group there have been some comments about the shortcomings of the widely used LM386 audio amplifier chip.  Many people don't like it because it is noisy.  I don't like it because it is a chip. (In my BITX rigs I have replaced it with a simple discrete component audio amplifier.)  So this morning I was pleased to find this video on the Maker blog that presents a very good use for all those LM386 devices:  We can turn them into robot brains!

Make's video and web page on this project are both very good.   One paragraph in the page kind of captures the reasons I dislike the LM386:

How It Works

The core of the “Herbie” circuit is the LM386 power amplifier chip. To simplify a bit, we can think of the chip as a “black box” with inputs and outputs that respond in predictable ways, and don’t have to completely understand what’s going on inside. 

 http://makezine.com/projects/sunbeam-seeker-bot/

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20