My Hodgepodged Morse: Audio Tone into the Mic Jack Creates J2A not A1A. BASTA!

In SolderSmoke podcast #229 Pete and I were discussing my rather flaky effort to turn the Hodgepodge BITX40 Module into a CW rig by injecting keyed 700 Hz audio into the mic jack (see video below). We got some very helpful responses from ND6T and VK2EMU:  

Hi Bill,

You mentioned generating CW by modulating SSB: Collins did that in their

first SSB transceivers, I believe, as did SGC, but the results were less

than optimal. The problem is that you are involving the audio chain and

modulator. You know from experience how difficult it is to maintain low

intermod there and the tone is no exception. So we end up with lots of

spurs within the filter passband and then also have the opposite

sideband suppression less than perfect. If you check your transmitted

signal with a spectrum analyzer or SDR you can easily see the nasties.

Listening to a CW signal thus generated makes it obvious unless it is

buried way down in the noise. It IS a valid CW signal (not MCW) since it

is (almost) a single signal. However, in actual operation it doesn't

work very well.

I know because I have done that. I bought one of Farhan's original

BITX40 boards and wanted to put it on CW. I ended up injecting a keyed

signal from one of the spare clocks on the Si5351 into the RF amplifier

chain (thus avoiding the above stated problems) but still had garbage

from the audio and IF stages. I fixed that by shorting out that signal

during transmit by a transistor to ground. That was documented on your

BITXhacks website: http://bitxhacks.blogspot.com/2017/02/ and on my

website: http://www.nd6t.com/bitx/CW.htm . It has been a while, eh?

...

Don, ND6T

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Hi Bill and Pete,

With putting an audio oscillator into you hodgepodge radio, your transmission is not the same as a standard CW rig.

If we have a transmitter as described in the ARRL handbooks from the 1940's or 1950's, (or even the Michigan Mighty Mite) it is a crystal oscillator and maybe a PA tube. By keying either the oscillator and/or the final PA on and off, then we can send Morse code as ICW Interrupted Continues Wave. If we check the list of emission designators, we have A1A.

However, if we feed a tone into a SSB transmitter, then we have J2A.

At the other end it may sound the same, but because it is created in a different way, it has a different designation. 

A quick look at Part 97 shows that J2A and J2B are classed as CW, so you are in the clear. However, if you put a tone oscillator into an AM signal to send CW, then that would be classed as A2A and not classed as CW, but as MCW. MCW can be used on 6 meters and above, but not HF.

SITS.

73 de Peter VK2EMU

-----------------------------------------------------------

So I say BASTA with the J2A!  If I want to go CW, it's all A1A for me.  I dusted off my Fish Soup 10 and am now back on 40 CW with 200 mW.... A1A all the way! 

 

SolderSmoke Podcast #229 -- G2NJ Trophy, SDR, HDR, CW! Mailbag

Soldersmoke Podcast #229 is available: 

http://soldersmoke.com/soldersmoke229.mp3

--  G2NJ Trophy is awarded to Pete Juliano, N6QW. 

 -- Get your vaccine shot as soon as you can!  

-- More from "Conquering the Electron" by Derek Cheung. 

-- Bad fire in the chip factory.  Such a shame.  Sad!  I had NOTHING to do with it.  I was home that day.  I can prove it.

 -- Bezos is not such a bad guy.  Turns out he is a space-geek.  

 -- Perseverance was the big space news.  Very cool.  

 

Pete's bench:

Raspberry Pi vs. Microcontrollers

Treedix display

Conversion of the Dentron Scout

CW rigs?

6L6 on a wooden chassis

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Bill's bench: 

Hodgepodge:   

-- BITX40 Module.  

-- Ramseykit Amp. 

-- San Jian counter,  

-- CW using 750 Hz oscillator. 

-- RF-actuated piezo buzzer.  

-- SDR!  SDR using PC and tablet.  

-- Checking the output with SDR.  

-- Moving the carrier osc frequency.  

 Also, I put the Fish Soup 10 back on the air.  Nice contacts under 200 mw.

Up next:  A rig for 80/75 and 20 meters.  Single Conversion.  Using VFO from a Yaesu FT101 that runs 8.7 – 9.2 Mhz.   Quiz question:  What IF should I use?

MAILBAG

Mark Zelesky sent me wood tokens with power and Ohm's law formulae.  Thanks!

Scott WA9WFA Built a really nice Mate for Mighty Midget RX – getting it going!

Tryg EI7CLB found board of his George Dobbs Ladybird RX.  Rebuild it OM!

Tom WX2J – We talked about “No lids, no kids, no space cadets” nastiness.

Nick M0NTV about sideband inversion.  I like the simple rule about subtraction.

Jonathan M0JGH – Always listen to Pete.  Got married, has mixing product. Leo?

Mike AE0IH.  Dad used a BC-348 in the service. Looking for one.  FB.

Adam N0ZIB – “Silent Shep” site --- with some ham radio shows I had not seen.

Walter KA4KXX in Orlando has a similar subtraction problem with San Jian counter.

Bill N5ALO sent me a really nice KLH speaker.   I’m using it now.

Jason N2NLY – interested in building SSB transceiver.  One step at a time OM…

Trevor in Annapolis sent xcsd cartoon that really hit home. 

Farhan is doing OK in India, diligently protecting his family from the virus.  

Peter VK2EMU also doing well.

Dave AA7EE Casually killed a DC receiver in Hollywood, and disposed of the remains. 

Charlie ZL2CTM doing great things with simple SSB.  Blogpost.

Phil VK8MC in Darwin sends article on "Mend not End" battle against planned obsolescence.

Bob KY3R re my SDR adventures, asked if I’ve had a recent medical/psychiatric evaluation. 

Hodgepodge: Tablet SDR with a Bluetooth Mouse (video)

I continue to find things in the shack that I can connect to the Hodgepodge.  Here it's an old Android tablet with a Bluetooth mouse.   

The waterfall is pretty, but this addition just shows why SDR is really TOO easy.  The modified RTL-SDR dongle is doing direct sampling, so there is not even any phasing circuitry to tinker with.  All the filtering and sideband selection is happening in software inside the 40 buck Android tablet.  The results look nice, but I don't find it very satisfying -- all I did was connect some cables.  So it's back to HDR for me. 

Hodgepodge: Moving the Carrier Oscillator Frequency (and a Flashback to 2002) (Video)

As explained in the video, in the course of using my RTL-SDR dongle I noticed that the signal being put out by my Hodgepodge rig had some problems.  There was poor opposite sideband rejection, and in terms of audio quality I has putting out too many lows and too few highs.  I figured the problem was the result of the carrier oscillator frequency being a bit too low, a bit too close to the flat portion of the crystal filter passband.   I needed to move that carrier oscillator frequency up a bit. 

BITX40 Module BFO 

In the actual BITX40 Modules, L5 was replaced by just a jumper wire, and the C103 trimmer was not on the board.  Farhan and his team instead selected X5 crystals to match the passband of the 12 MHz crystal filter. Mine was originally at 11.998653 MHz.  But I wanted to tweak mine a bit -- I wanted to move it up about 500 Hz.  Reducing the capacitance would move the frequency up. Putting capacitance in series with C102 would have the effect of reducing the capacitance in the circuit.  I just removed the jumper wire and used the holes for L5.  First I put in a single 30pf capacitor.  This dropped the capacitance between X5 and ground to 18 pf.  That resulted in too large a shift.  So I added another 30 pf cap in parallel with the first one.  This resulted in a total capacitance from X5 to ground of 26 pf.  This was about right -- the carrier oscillator/BFO frequency was now 11.9991 Mhz.  I had moved the carrier oscillator frequency up by 447 Hz -- just about what I was hoping for.  

This was a very satisfying fix.  it was a chance to put to use experience with other SSB rigs, to make use of the RTL-SDR dongle as a diagnostic tool, and to tinker with the BITX40 Module in the way that Farhan had intended for it to be tinkered with.  

I'd done this kind of adjustment before, but without the benefit of an SDR display.  Below is the story of one such adjustment. 

---------------------------------

A Flashback to 2001-2002

(From my book "SolderSmoke -- Global Adventures in Wireless Electronics")

Now it was time for some debugging and fine tuning.  I needed to make sure that the frequency of the carrier oscillator was in the right spot relative to the passband of the crystal filter.  If it was set too high, the filter would be chopping off high notes in my voice that were needed for communications clarity, and it would allow too much of what remained of the carrier (residuals from the balance modulator) through. If it was set too low, the voice signal transmitted would be lacking needed base notes.  I didn’t have the test gear needed to perform this adjustment properly, but my friend Rolf, SM4FQW, up in Sweden came to my aid.

One night, during a conversation with Rolf, I explained my problem and he offered to help me make the adjustments… by ear.  Performing an electronic version of open-heart surgery, with power on and Rolf on frequency, I opened the case of the new transmitter.  The carrier oscillator has a small capacitor that allows the frequency of the crystal to be moved slightly.  With Rolf listening carefully, I would take my screwdriver and give that little capacitor a quarter turn to the right.  “Better or worse?” I would ask. 

I think this little adjustment session captures much of the allure of ham radio.  There I was, out in the North Atlantic, late at night hunched over a transmitter that had been forged from old Swans and Heathkits, from cell phone chips, and from bits of design from distant members of the fraternity of solder smoke.  Pericles, the source of many of the key parts, was gone.  So was Frank Lee, the amateur whose SPRAT article had inspired the project.  But Rolf and I carried on with the core tradition of the radio fraternity: hams help their fellow hams overcome technical difficulties.  

Over the Waterfall into the Dark Side: Hodgepodge SDR

This one's for Pete. My effort to add features and modes to my Hodgepodge transceiver took a dramatic turn when I connected the rig to my computer via an RTL-SDR dongle. Woohoo! A Hodgepodge waterfall! Check it out.

The dongle was modified for direct sampling at HF. In the box with the dongle I have one amplifier stage, consisting of a 40673 dual gate MOSFET and one parallel tuned circuit, now tuned to the Hodgepodge IF of 11.998 MHz. I tap the the Hodgepodge's BITX40Module at the output of the first mixer, just before the crystal filter. This was a lot of fun. I can even check my own signal on transmit! This is like having the best of both worlds.

A Frequency Counter for the Hodgepodge -- An Analog Solution to a Digital Problem

Imagine my dismay when I discovered that I could not use my $5 San Jian PLJ6-LED frequency counter with my Hodgepodge transceiver.    The problem is described here: 

http://soldersmoke.blogspot.com/2021/02/a-problem-with-san-jian-plj6-led-counter.html

This video describes my solution.  I took some pleasure in using an analog solution to solve a very digital problem.   I know this could have been fixed with one or two changes to lines of code, but I liked doing it this way.  This was all kind of fun, and it allowed me to use yet another bit of circuitry that was sitting idle in the shack.  That is the whole point of the Hodgepodge project.  

The best is yet to come.   Especially for those of you who like waterfalls.... Stay tuned. 

Putting the Quarantine Hodgepodge Rig on CW (Video)

Putting this rig on CW posed a real Hodgepodge challenge: What did I have laying around that would let me do this? Then I remembered: Years ago I built a little 750 Hz audio tone generator. So I pressed that into service. I also needed a sidetone so I built a little RF-actuated circuit that turns on a piezo buzzer when I go key down. And I put a little DC monitoring device (recommended early in 2020 by the Ham Radio Workbench podcast) between the power supply and the rig. There is more to do! Stay tuned.

Quarantine Hodgepodge Rig -- Part 1 (Video)

More videos to follow.  I have added features, and a transmission mode.  Stay tuned.  

A Problem with the San Jian PLJ6-LED Counter

I had hoped to use this handy and cheap little frequency counter to add some glowing Juliano Blue to the frequency readout on my Quarantine Hodgepodge rig.   I've used these boards with my BITX20, my HA-600A,  and with my DX-100/HQ-100 rigs.  But guess what -- these boards do not work with the BITX40 module board that is the heart of the Quarantine Hodgepodge.  And the reason why is interesting. 

Here is what happens:  First, you plug in the IF frequency of your rig.  In my case 12 MHz.  You connect your VFO output to the signal input on the PLJ6.  You power up the PLJ6.  You then have to select one of two IF frequency options.  One of these options ADDS your IF frequency to whatever it detects at the signal input.  In my case, for a 7.2 MHz signal it would detect a VFO signal at 4.8 MHz. If it were to ADD this signal to the IF freq,  it would readout 16.8 MHz.  And it does.  But obviously that is wrong.  So you go to the other option -- this one SUBTRACTS the designated IF frequency FROM whatever it finds at the signal input.  So here we get 4.8 - 12 =  -7.2   Almost perfect right?  But here is the problem:  The PLJ6 can't handle negative numbers!  So it displays 000000.  Not helpful. 

Here is the manual: 

https://www.mpja.com/download/35057tebasic%20manual.pdf

I didn't have this trouble with any of the other rigs because none of them required the use of negative numbers.  My BITX 20 for example had an IF of 11 MHz and has the VFO running a bit above 3 MHz -- so the PLJ6 just adds the IF to the VFO signal and Bob is my uncle.  Similar problem-free addition takes place with the other rigs. 

I found some discussion on this problem on the internet.  Here is one: 

https://groups.io/g/BITX20/topic/bitx40_and_plj_6led_frequency/4330098?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,4330098 

Some of the respondents didn't seem to understand the problem.  Others hint that the ability to handle negative numbers was as some point in the code for the PLJ6 device,  and may somehow be accessible, but no further info is provided. 

I have already worked up a possible solution, but I'm interested in how you folks would approach this problem.   Any thoughts or suggestions?  I will reveal my solution in the days ahead.   

My Current Rig: The Quarantine Hodgepodge

 

As I continue to Stay In The Shack,  last week I was looking for something to do. This is what I came up with.   

Left to right: 

-- Speaker

-- Ramsey-kit QAMP20 modified for 40. I now have two MTP3055V MOSFETS in there.  

-- BITX40 Module with a solidified VFO from a Galaxy V (note the knob from a Drake 2B!)

-- Power supply 

It puts out about 15 watts SSB.  I was bracing for attacks from the 40 meter waterfall police, but no, everyone said it sounds great.  I had four very nice contacts yesterday.  It was fun. 

Still to do:  Possibly a San Jian frequency counter to give some Juliano Blue glowing numerals for the frequency readout.  This would be a step up from the Juliano Blue sticky note and  corresponding piece of black electrical tape that currently serves as the frequency indicator.