[aprssig] Re: aprssig Digest, Vol 43, Issue 27

[Alex Carver]

> Message: 7
> Date: Wed, 23 Jan 2008 09:24:02 -0000
> From: "Dave Baxter"
> Subject: RE: [aprssig] info for TM-D710E in car

> Nope, that is NOT the solution to the radio loosing
> it's settings and
> not updating it's postion data from the GPS, after a
> power dip during
> engine cranking.
> 
> That device will however as it says prevent the main
> battery from being
> emptied if an accessory (that is powered via it) is
> left on while the
> engine is not running.   That is not the issue here.
>  That is that the
> D710 locks up when the "12V" input drops below
> 11.45V.
> 
> They are asking if this has been seen by others, and
> if there are plans
> for an updated (or modified) D710 that does not
> suffer in that way...
> I suspect there are cascaded regulators used, 12V>8V
> then 8V>5V etc, so
> when the first drops out, they all do.
>  
> IK1AQI and IZ1CQY also state they had found a
> temporary solution, by the
> sound of it a 12V UPS of sorts (an extra battery in
> paralel with the
> radio!)
> 
> But you have to wonder about the mentality of a
> maker who produces a
> piece of kit that if not specificaly designed for
> vehicle use, will be
> used by many in vehicles, that does not tolerate, or
> behave sensibly
> when the power momentarily dip's below a certain
> value.  There again,
> that's nothing new, is it.
> 

The mentality is that they are trying to meet certain
transmission specifications to get the regulatory
licensing.  The D700 and D710 (and many other radios)
use multiple power sources not just regulators.  The
final transistor amplifiers use filtered, but not
regulated, power.  Only the CPUs and related control
circuitry uses the regulated power from the voltage
regulators.

Even if the engineers replaced every voltage regulator
with a low dropout unit, it's not the regulator that's
dropping out, it's the CPU commanding the receiver to
power down because it will be unsafe (to the
electronics) to transmit.  None of the final
transistors will be biased properly in a low voltage
situation.  This can easily cause anything from low
transmission power to spurious emissions or even
failure of the transistors.

Basically the radio is turning itself off, it's not
the regulators dropping out.  The power in is
regulated down to 5 volts by one regulator for the
CPUs (cascaded down to 3.3 volts for the main CPU) and
a second, parallel regulator provides 8 volts for
backlighting and audio circuits.  The rest of it is
filtered, unregulated input voltage within the
operating range.  Note that the radio does have an
overvoltage detector, too.  It will shut off for input
voltage over about 14 volts.  Same thing as the
undervolt condition, the CPU made the decision to shut
itself down, not regulator drop out.


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