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Monday, March 22, 2021

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


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.


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! 


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