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[aprssig] Help setting up a new TM-D710 for APRS

Stephen H. Smith wa8lmf2 at aol.com
Mon Dec 31 04:54:33 UTC 2007


Steve Noskowicz wrote:
>  Bob,
>
>    You may have said before...   Would you provide some details on this.
>
> Does the S-Meter go up any on this "hash"?
> Does the S-Meter control threshold setting change due to this noise?
> Does the unsquelched noise (with hash vs. without) sound any different (to you)
> ?
>
> 73, Steve
>
>
>   


This is totally broadband white noise that blankets all of the HF and 
VHF spectrum. It is not discrete carriers, hash,  or "birdies" with 
grinding noises or audible whine.  (I suspect diode noise effect from 
high DC currents flowing through semiconductor junctions in the hybrid 
power converter system.)  

Since it is broadband band white noise,  the unsquelched radio on an 
empty channel sounds exactly the same as without the noise.   The effect 
is to mask weak signals and make them sound noisier than they would be 
otherwise, and to raise the thresh-hold of the noise-activated FM 
squelch; i.e. stronger signal and more quieting required to open the 
squelch. 

The result is very similar to the type of white-noise receiver desense 
that base stations on crowded sites sometimes experience.  The net 
effect is to reduce the effective sensitivity of the radio from .25-.3 
microvolts to more like 1-2 microvolts.  







--

Stephen H. Smith    wa8lmf (at) aol.com
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