[arm-allstar] Yet another USB FOB Modification

[Doug Crompton]

Yes, we will clearly agree to disagree on this. 

73 Doug
WA3DSP
http://www.crompton.com/hamradio


Date: Sun, 16 Nov 2014 14:16:52 -0500
From: kuggie at kuggie.com
To: arm-allstar at hamvoip.org
Subject: Re: [arm-allstar] Yet another USB FOB Modification


  
    
  
  
    On 11/16/2014 12:58 PM, Doug Crompton
      wrote:

    
    
      
      My definition of users is individual
          simplex nodes which I would suspect is the overwhelming
          majority especially in the BBB world.

        
    
    

    

    We'll have to agree to disagree there.....

    

      

    
    
      

          I lost track of what we are even talking about here.
    
    

    

    I'll get you back on track.

    

    

    
       If it is pre/deemphasis then that
          can be done in the radio or in SW.
    
    

    

    I never said anything about pre or deemphasis.  

    

    
        In my opinion characteristically
          distorted usbradio audio is much more of an annoying problem
          than improper equalization. 

        
    
    

    

    By definition, systems that have double pre-emphasis or any other
    equalization problem are distorted.   Generalizing that ALL usbradio
    installations have distorted audio is not factual.  If a usbradio
    system has distortion which is offensive, something is wrong with
    the deployment.  

    

    
      

          Most radios can be made to work with simpleusb and with
          pre/deempahsis done in the radio. 
    
    

    

    Suitable audio usually isn't the problem.  Getting quality logic to
    the radio interface is.  But, there is a new solution to that
    problem.

    

    
      That is using fixed level speaker
          audio and mic input. It works fine. Mototorla's can do it and
          so can most all commercial ham equipment.
    
    

    Many commercial radios have high pass filtering on the MIC input. 
    This is for good reason, to eliminate voice energy that can mix with
    the PL tone and cause 'talk off'.  As such, these filters keep you
    from effectively using the MIC input for CTCSS.  In some instances,
    you can crank the CTCSS audio up to overcome the losses of the
    filtering, only to create problems with the dynamic range of the
    clipper/limiter, creating distortion.  PL distortion of even the
    slightest amount will cause harmonics which 'sound' louder than they
    are comparing deviation.  "PL" buzz is a big problem when using MIC
    audio on radios that have HPF'ing.  Jamming the CTCSS into the MIC
    jack creates another problem.  When you modulate voice peaks which
    are clipped by the limiter, the CTCSS tone gets chopped off, causing
    the decoder to drop on the users end.

    

     The right way is to get to the modulator, so the CTCSS tone
    injection is after the clipper/filter.

    

    

    
       It makes no difference what type of
          FM modulation is being used if you let the radio do the
          pre/deemphasis.
    
    

    

    It's evident you don't have a lot of experience with modulators in
    FM radio.  Some modulators are PM (phase modulated).  These
    modulators are present in many Motorola and GE radios don't have the
    ability to modulate with the same index across the entire PL and
    voice range.  As such, it takes a greater amount of voltage to get
    industry standard PL deviation.  

    

    
       Why make things more difficult at
          the expense of a dB or two more flatness that most people
          can't even hear.

        
    
    

    

    Because not doing it correctly is bad news.  Creating spurious
    emissions can get you a pink slip.  Besides, people know the
    difference - believe me.

    

    
      

          Our local network typically has 15 to 20 nodes connected and a
          mixture of radios, many Alinco, a few Motorola, and a others.
          They are all running simpleusb and all typically have good
          audio. I find that most audio problems arise with the users
          handhelds. Listen to any repeater and you will find audio all
          over the place in quality and level. You can't correct
          something that is bad to begin with.  

        
    
    

    While I agree that you can do anything with poorly designed and
    aligned user radios, by maximizing the dynamic range and minimizing
    the distortion introduced, the better you can tolerate it.  Why make
    it worse than it already is?  I'll agree that it is more difficult
    to deploy a system where the audio is taken from the discriminator
    and feeds the modulator directly, but there is no substitute for the
    amount of dynamic range and lower distortion that results.  Like
    anything, taking the easy way out usually works okay, but I'm not
    one that is generally satisfied with it just being okay.

    

    Kevin

    

    

    

  


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