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SB2 on 75/80m

Don, ND6T
 

Aside from some remaining software issues and final "casing it up" serial number 144 is working nicely on 75/80m !
I configured maximum output at the high end (3.8 to 4 MHz) achieving an easy 10 W. PEP, Bottom of the CW band is a healthy 7.6 Watts at 13.8 V.
Worst case spurious and harmonics is -52 dBC. Quite good!  The receiver is quite sensitive and, for a 5 crystal filter, sounds very nice!
Modification sheet in .pdf form is attached.
Great job, Steve! Thank you.
73, Don

Don, ND6T
 

I always have to make at least one error, it seems. The notation about minimum working voltage applies only to the transmit low pass filter and should be up in that section. The voltages in the band pass section can be anything above 6 volts. -Don

John AE5X
 

Good job, Don. I'm curious what microphone you're using?

Tnx/73,
John AE5X

Don, ND6T
 

John,
Those that I made for the BITX series. I removed the dynamic elements from some old CB hand held microphones and replaced them with electret elements. I used rubber grommets, drilled out the proper size holes for the new elements and installed. The rubber makes a tight fit to the old element holding structure and provides a degree of acoustic isolation. I found that I had to crank the gain back on the SB2 considerably to prevent overdriving. I would think that it might have enough gain to accommodate a dynamic microphone if one removed R34.  You are going to have some serious fun! 73, Don

Don, ND6T
 

Thanks to Steve the firmware issues are resolved. Installed it in the case and put it on the air. First contact was T31EU, the Kanton Island, Kiribati DXpedition. Nice for 80m! Love the smooth QSK. 73, Don