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Showing posts from March 30, 2014

Explanation of how the delay circuit works.

Om Blake Bartosh has shared with us the explanation as to how the delay circuit works as you may be eager to try it out on your Bitx. The Audio Mute circuit operates in the following way. The 555 timer is connected to the PTT switch and generates a 100 msec pulse when PTT is engaged and another 100 msec pulse when PTT is released. The 555 timer is configured as a debounce circuit, so contact bounce of the PTT switch does not initiate any new pulses. The output of the 555 timer and the PTT switch signal are combined in logic to form two signals, a mute command and a transmit command. The mute command turns on Q16 of the Exciter board which shorts the audio signal to ground, and no sound is heard from the speaker. The mute command occurs immediately upon engaging PTT, but the transmit command is delayed by 100 msec. This delay ensures audio transients due to switching from receive to transmit mode do not cause a "pop" in the speaker, but is not so long as to be noti…

Bitx3B VFO

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The Bitx3B has a Varactor tuned VFO using MV209 and the stability is controlled with the Ik3OIL FLL Freq counter which has an inbuilt software to correct the drift in the VFO.
Building a stable vfo is an art and if not built correctly it would not perform optimum.

Picture and Video  below outlines some important factors that could enhance the performance.





Audio Mute Circuit For Bitx

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Bitx had a problem of  noise being generated on pressing the PTT button. The usual way of muting the PIN 3 of LM386 did work  to solve the problem much, although to some extend, while working with Bitx3b i had discussion regarding this problem with Om Blake Bartosh from USA who was also building the Bitx Version3b  and who has also put in a great effort in bringing out the new Bitx3b construction manual.

The idea was to make a project to mute the audio of LM386 completely.
Presented below is a schematic of the audio mute circuit designed and tested by OM Blake Bartosh.

I myself build it and its working perfectly with my bitx3b. This circuit can be used for any tcvr.
The complete assembled kit will be available very soon.


SCHEMATIC OF BITX AUDIO MUTE CIRCUIT   

VIDEO OF BITX AUDIO MUTE CIRCUIT