Re: Digest Number 925

At 20:25 01/05/2003 +0000, you wrote:
>   From: Dan Jacobson <[email protected]>
>Subject: Re: priority watch and power save
>
>But it might not be worth buying a fresh radio. I.e. I indeed
>connected a milliamp meter in series to the R2, but got all kinds of
>funky reactions, probably related to my $10 multi meter slowing down
>battery responsiveness.  Don't try it at home, kids.

A meter in current mode operates by putting a resistance in series with the 
circuit being measured, and then measuring the voltage dropped across that 
resistance (more or less).  The more sensitive the meter scale, the larger 
the resistance, and the more voltage drop for a given current.  With 
something like the R2, where the voltage is only  2.4 V in the first place, 
and "battery low" shutdown is probably around 2 V, you can't afford to drop 
much voltage across the meter.  As the radio cycles the receiver on and off 
in power save mode, current varies, and voltage drop across the meter 
varies, and this is likely the cause of the strange behaviour you saw.  
However, it's unlikely to have harmed the radio in any way.

I'll bet if you switch to a higher current scale on your multimeter, the R2 
would work fine, because this reduces the series resistance.  The needle 
deflection might be smaller than you'd like, on an analog meter.  Digital 
multimeters with a 10 or 20 amp scale are fine.  On that scale, the series 
resistance is around 0.01 ohm, and voltage drop at R2-size currents is only 
a few millivolts, yet you still have 2 useful digits of current measurement 
on a 3.5 digit meter.  A 2 amp scale would be even better, but most DMMs 
don't have one.  (You can make your own my putting a 0.1 ohm resistor in 
series with the radio, and measuring the voltage across it with the 200 mV 
scale).

Even better is to build a small 2.5 to 3 V regulated power supply using a 
LM317.  Connect the output to the radio.  The input to the regulator can be 
5-20 V or so.  Connect the ammeter in series with the input of the 3V power 
supply, set to whatever scale you want.  Now the voltage drop across the 
meter doesn't matter because the regulator always provides 3 V to the radio 
even as the current drawn changes.  The ammeter measures the input to the 
regulator, which is almost identical to the output current - the regulator's 
standby current is low (and predictable, so you can subtract it off if you 
want higher accuracy).

The most convenient way of doing this is with a bench power supply, but it 
isn't necessary.

>I indeed saw the savings on the meter when just leaving the VFO on one
>channel.  So the same batteries that provided one day of scanning
>enjoyment before needing recharge perhaps can provide oh 5 days of
>single-channel monitoring, [assuming in both cases the transmissions
>are few]?

The current during "receiver shutdown" state is still close to half what it 
is in "receiver on" state (45 vs. 110 ma).  Even if the radio spends 
virtually all of its time in the low-power state, the average power 
consumption will be about half that when scanning.  So you'll get 2 days 
instead of 1, but not 5.

>Well, if my experiment was correct, I am hereby sorry to inform you
>that no saving were seen. Not even the first rest phase was
>entered. It was the same worst case ("500mA" according to my
>tinsletown meter) that one sees during intensive scanning. This was
>for "Memory channel watch".

Sounds like Icom didn't bother to implement power save mode when doing 
priority watch.

        Dave  


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