[arm-allstar] Yet another USB FOB Modification

Sun Nov 16 12:58:12 EST 2014

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

I lost track of what we are even talking about here. If it is pre/deemphasis then that can be done in the radio or in SW. Yes it is more difficult to do that in simpleusb but that wil change with a future new channel driver for the BBB. In the past things were driven by the way Allstar was delivered basically forcing people into using usbradio as thats the way the Acid release installs. The user would have to find and install simpleusb if they wanted to switch. In my opinion characteristically distorted usbradio audio is much more of an annoying problem than improper equalization. 

Most radios can be made to work with simpleusb and with pre/deempahsis done in the radio. 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. It makes no difference what type of FM modulation is being used if you let the radio do the pre/deemphasis. Why make things more difficult at the expense of a dB or two more flatness that most people can't even hear.

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

Date: Sun, 16 Nov 2014 11:47:02 -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 1:34 AM, Doug Crompton
      wrote:

      I suppose any of those items could be
          true in about 5% or less of the situations encountered by the
          average Allstar user.

    Since you said user, and not operator, let's put that into
    prospective.  Most every transmitter on WAN uses direct FM, the same
    goes for the WIN system.  These two systems make up a whole lot more
    than 5% of the AllStar users.  You are generalizing and comparing
    apples to oranges.  Even if you really meant operators, your math
    isn't close to reality.

       For the average user a standard FOB,
          whether it be DMK or modified Chinese, works just fine.

    Again, that depends on what exactly the average user is doing.  If
    he's using MIC audio only - yes.  If he's also using channel B and
    dumping PL into the modulator to get good sub-audible, then a
    standard FOB job isn't fine.

       I don't want people to get the idea
          this is going to do something special for them and they need
          to spend the extra money and buy it. 

    And I don't want people to think they can get by with a $2.00 FOB
    when they need the additional circuitry of a better device. 
    Education is what is needed here, not some half-cocked response that
    doesn't take into account all of the circumstances of the
    situation.  

      Most all radios have TX timeouts so
          that point is taken care of. 

    Time out timers in radios?  You aren't serious?  I don't know of any
    situation were I would knowingly enable a TX timer 'on the radio'. 
    That surely wouldn't fly on our network.

      The other issues don't apply to most
          radios. 

    Again, you are generalizing.  There are plenty of folks that hack
    into the radios circuitry to get adequate deviation, especially on
    PL tones.  

      I don't understand the cos/ctcss one
          because like PTT this is SW switchable.

    Just because the logic state is switchable in software doesn't
    guarantee that it will be properly recognized by the hardware.  The
    two logic states are logic high and logic low.  The FOB requires a
    logic low (a pull to near ground potential) because the logic the
    device is looking for was supplied by a hardware switch to ground. 
    The maximum voltage on the GPIO's is 3.3 V, that's why the Schottky
    diodes exist.  The thing you have to remember is that many radios
    supply a positive logic source and they may not have the ability to
    source a low.  This situation happens where the device in the radio
    is a PNP transistor or other active high circuit, and while it has
    the ability to pull to a high, but cannot source a ground without a
    pull-down resistor.  Pull down's can be a problem and is why Mark
    Herson commented on why he prefers to have a pull to +5 so when the
    system is protected by an incorrect COR condition if the radio is
    turned off or otherwise disconnected.  

        Most hams are cheap and
          building, modifying etc. are a large part of our hobby.

    You are generalizing again.  Many (most?) hams cannot do the
    modifications to the FOB's.  Out of the 13 core members of the WAN
    system, 3 of them have the ability to do FOB modifications.  The
    others wouldn't even consider it.

       We usually
          don't put dollars and cents on our time. It's the fun of doing
          it. Anyone can buy something and throw it on the air. Everyone
          has to make the decision what's best for them. 

    Misinformation destroys a hobby.  Education is best, but getting
    people to read and understand what it takes to make an educated
    decision isn't easy.  Believe me, I know.  I have authored hundreds
    of articles on this hobby.

          The FOB mod I described in the how-to on the web page is
          really a piece of cake. All you need to do is solder some
          wires on the FOB and build a minimal amount of external
          circuitry. I made it harder (mechanically) because I put it in
          a nice box which is not necessary. For $10 or less worth of
          parts and a few hours of your time you have an interface.

    While I agree that you have an interface, that interface doesn't
    take into account every installation.  The URI and RIM handle the
    extra LPF'ing needed when driving a modulator directly.  The RIM has
    buffer circuitry on the COS and PL inputs to take whatever the radio
    can give it, and convert it to a solid pull to ground, just the the
    mechanical switch the CM108/119 was designed for.  Your $2 FOB will
    not work with all types of radios.  You have to know what you need
    and source the equipment accordingly.  

    The RIM isn't some poorly thought through copy of a URI.  It has
    additional circuitry for those instances where they are required.  I
    have nothing against the URI.  I have more of them deployed than any
    other radio interface.  I simply got tired of having to put a
    resistor divider in the discriminator line to get the audio in range
    of the software, adding amplification beyond the ability of the URI
    to sufficiently drive the modulator, and putting transistor
    switching in between the radio and URI so the hardware inputs worked
    reliably.  Nothing more, nothing less.

    Whether a user of this technology needs the special things the
    commercial interfaces provide depends on the situation, and making
    generalizations doesn't help.  I'm sure you are proud of your work
    converting a FOB, but understand there are fewer hams than you might
    expect with the skills and equipments needed to do a successful FOB
    job.

    Kevin

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