开云体育

ctrl + shift + ? for shortcuts
© 2025 开云体育
  1. BITX20
  2. Topics

Pop in speaker on key-up

[email protected]
 

Just to the controls hooked up...for testing. Upon key up I get a loud "pop" in the speaker.

I searched the group and didn't see this issue.?

Ideas??

Trip - KT4WO
kt4wo67@...
 

开云体育

Trip,

I found that while I had my board sprawled all over my bench that the click on Xmit was real loud with all my cables crossing each other, when I got the wiring cleaned up and separated and the power output cable replaced by a piece of RG-174 coax it's hardly noticeable anymore.

Joel Caulkins?KB6QVI

On Dec 16, 2016, at 3:05 PM, kt4wo67@... [BITX20] <BITX20@...> wrote:

?

Just to the controls hooked up...for testing. Upon key up I get a loud "pop" in the speaker.

I searched the group and didn't see this issue.?

Ideas??

Trip - KT4WO
kt4wo67@...
Thomas Noel
 

开云体育

Trip et al,

It has been discussed before. Search for “PTT noise” or PTT transient”. Cause and solutions both simple (ignore it) and complex (Multi-transistor multi-relay switching schemes to cut the power during the crossover) have been described. Some of the discussion far predates the new SMT Bitx40 from India.

I have it with all cleaned up and in a fully shielded enclosure.

Thomas W Noel
KF7RSF

On Dec 16, 2016, at 3:27 PM, Joel Caulkins caulktel@... [BITX20] <BITX20@...> wrote:

?

Trip,

I found that while I had my board sprawled all over my bench that the click on Xmit was real loud with all my cables crossing each other, when I got the wiring cleaned up and separated and the power output cable replaced by a piece of RG-174 coax it's hardly noticeable anymore.

Joel Caulkins?KB6QVI

On Dec 16, 2016, at 3:05 PM, kt4wo67@... [BITX20] <BITX20@...> wrote:

?

Just to the controls hooked up...for testing. Upon key up I get a loud "pop" in the speaker.

I searched the group and didn't see this issue.?

Ideas??

Trip - KT4WO
kt4wo67@...
 

Trip - KT4WO

The infamous BITX-Click has been well documented on this forum, but it was mostly
some time ago.?

There is a capacitor that couples the receive audio from the BFO mixer and another
capacitor that couples the microphone amplifier to the BFO mixer.? In Rx mode and in
Tx mode these capacitors get charged to different voltages.? When you change modes
these capacitors take on different voltages.? This causes a click when going from Tx
to Rx mode, and a 20 ms carrier burst when going from Rx to Tx mode.?

There have been several methods suggested to alleviate this situation, but basically
the situation is something that most will live with as a trade-off for simplicity and low
cost.? Once you have an antenna connected the receive-mode click should be less
noticeable.? 0.1 mfd across your speaker terminals might help minimize the click.?

Some of the early BITX20 and BITX17 builders resorted to using a relay to switch
microphone and speaker circuits as a way to eliminate this situation.? That too is
documented in the forum.

It is possible to make an LTSpice simulation that documents this situation, and that
might lead to simulator experimentation to come up with a solution to the problem.
In fact, any of the BITX circuit sub-sections can be ran in LTSpice as a means for
providing better understanding how they work and to trial proposed modifications
without having to melt solder.

Arv? K7HKL
_._


On Fri, Dec 16, 2016 at 4:05 PM, kt4wo67@... [BITX20] <BITX20@...> wrote:
?

Just to the controls hooked up...for testing. Upon key up I get a loud "pop" in the speaker.

I searched the group and didn't see this issue.?

Ideas??

Trip - KT4WO
kt4wo67@...
[email protected]
 

Tnx for the help. I didn't use the right search terms.

I will dig up some of the older posts, but will prob. just live with it.

Once I have in metal case maybe it will clean up some.

My only issue so far was L3 was broken off the board when it arrived.

Fixed that and up and running!!

Tnx de Trip - KT4WO

1 - 5 of 5