[Elecraft] [KPA500] Rear power switch thread

[Andrew McNamara]

>Hogwash, at least with the current/recent rigs from ALL the major 
>players. Many of the controls on these radios, just like the K3, are 
>rotary encoders or push buttons that have no 'position'. When the radios 
>start up, they go back to where they were because they stored the 
>operating conditions IMMEDIATELY when changes were made.

The issue is that if you power off the radio as it updates the
non-volatile memory, you can corrupt the memory. This is just as true for
Icoms, Yaesus as the K3. The window in which this can happen is very,
very small, but it does happen (the subject comes up often enough on
the corresponding Icom and Yaesu mailing lists).

What's worse is that most modern radios are "soft calibrated", so you
can end up losing your calibration as well. Not such a big problem with
the K3, since you can recalibrate it yourself, just inconvenient.

There's another related problem - power doesn't just go away, it
decays. Without very careful hardware design, the CPU "goes crazy" as the
voltage drops and can write to random locations (modern microcontrollers,
like the PIC used in the K3, have some built-in protection against this).

BTW, radios (and appliances) don't usually write their settings out to
non-volatile storage with every button push and knob twiddle - the write
is usually deferred for a short period. There are three reasons for this:

  - writing to flash memory is slow; writing immediately would make
    the radio sluggish.

  - flash has a limited write-cycle life; by deferring the update for a
    short time, you get to merge or skip updates due to later activity
    by the user making the earlier update superfluous.

  - the more frequently you write, the more likely you are to win the
    "back to the factory for recalibration" lottery.

None of this is unique to amateur transceivers; it applies to just about
every modern appliance to some degree or other, although  it can be
mitigated in various ways (put calibration in a different flash page,
retain backup copies, etc).  Turn your flat-screen TV off at the wall
often enough, and you may well scrag it too (assuming the switch-mode
power supply survives the experience).

-- 
Andrew McNamara - VK2TAN