HW/SB Questions..

[Kenneth G. Gordon]

On 13 Jun 2006 at 13:21, jflan at tampabay.rr.com wrote:

> The pop noise in my radio occurs when going
> from receive to transmit.  It doesn't matter whether you are in SSB or
> CW.  In fact placing the unit into TUNE exhibits the same result.  As
> far as how loud the noise is, it is quite objectionable in my opinion.
>  The sound is a solid THUMP.  If you have headphones on, it will wear
> on you.  If you look at your schematic, parts R339,R340... in that
> area comprise the so called 'filter' which is used to supply the
> squelch pulse to the grid of V14a (through C323).  If I remove C323,
> the thump noise is actually better.  The best way to describe the
> sound is to think of hitting a deep bass drum once during the
> switching action.

Ah! I ***think*** I know what it is: first of all, as far as the headphones 
are concerned, I'll bet you are using some high-quality, or music-quality 
headphones. Those have a very wide frequency response, probably 
extending from 10 Hz through 10 Khz or more.

Communications headphones have a very limited frequency response. 
One of the reasons for this is that they naturally discriminate against 
some types of noise. Usually, their frequency range is limited to 300 to 
3000 Hz or so, thereby automatically limiting both low and high 
frequency noise components.

Your description of the noise as a "deep bass drum" sound tends to 
reinforce this idea in my mind. The noise **I** hear from my HW-101 is 
more of a sharp "pop", or " click", although not particularly loud, and of 
short duration. For that to be translated to a "boom" would indicate 
something enhancing the sound. I.e. wide frequency response 
transducers such as good quality headphones, or a good or better 
quality speaker, or possibly a low-frequency parasitic oscillation in an 
audio stage somewhere.

The original Heathkit speaker mounted in the SP-600 cabinet also has 
a specifically "tailored" frequency response, designed specifically to 
ignore frequencies below and above fairly precise limits.

If you are using a better quality speaker, like, say a Radio Shack 
Minimus 8 or something, these low frequency noises would be 
drastically enhanced.

As far as headphones are concerned, I don't know what to advise you, 
but some designed especially for "communications" might reduce the 
problem to a very low level.

Please let us know about your headphones and speaker.

Ken W7EKB

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