[1000mp] mark v hum

[Jim Smith]

Hi John,

The function of speech compression is to reduce the dynamic range of the 
transmitted audio so that the ratio of peak transmitted power to average 
transmitted power is reduced.  The maximum peak power you can transmit 
is determined by the transmitter design.  Compression, then, increases 
the average power that you can transmit.  This makes you louder.  Please 
don't use compression near my run frequency unless you're calling me.

A necessary consequence of using compression is that all the background 
noise picked up by your mike or already existing in the audio system is 
also now louder.  No doubt you have heard a few signals where the noise 
from the logging computer or the Tx cooling fan is very noticeable.  We 
won't talk about the contest stations with the two horsepower fan 
cooling the shack.

Some tests you could perform to try to find where the hum is coming from.

Key the rig in SSB mode with the mike on but don't say anything.  Note 
the reading of the power output meter.  Listening on a separate Rx and 
noting the S meter reading would be a good thing too.  Oh yes, if you 
don't hear any hum in the separate Rx there probably isn't any and you 
could spend the time allocated to hum trouble shooting to put up another 
antenna.

Now wrap the mike with a towel or something (or switch it off if that's 
possibe) so that no background shack noises get picked up by the mike 
and transmitted.  If you notice that the power out is reduced, hum or 
not, you need to reduce either the background noise in the shack or the 
amount of compression.

If the above test makes no change in the power output all I can say is 
Hummm.... it's in the rig somewhere or you've got something plugged into 
the patch input or you've got a towel you should throw away.  You could 
try unplugging the mike and test again.  You could also try turning the 
MIC gain all the way down.

These are late night, top-of-the-head ideas which may or may not be of 
use to you.  RF feedback might be the culprit.  Is your mic connected 
directly to the rig or, as I mine is, through the computer sound card?

If what's here doesn't help solve your problem give us more detail as to 
your setup and what you found when performing the above tests.

73 de Jim Smith   VE7FO




n3drk wrote:

>Whenever the speech processor is activated I receive reports of a hum. Any
>comments on what may be going on here?
>thanks
>john
>
>_______________________________________________
>List Moderator: Richard Lubash N1VXW
>1000mp mailing list
>1000mp@mailman.qth.net
>To Change Options or Unsubscribe:
>http://mailman.qth.net/mailman/listinfo/1000mp
>
>  
>