[R-390] Line Level meter

[ka9egw at britewerkz.com]

I can do the math if it was a simple sine-wave power supply, no problem.
Assuming, of course, the line's ability to source without being loaded
down...which I kind of doubt given the low levels we're talking about...

Wikipedia says "The typical VU scale is from -20 to +3. The rise and fall
times of the meter are both 300 milliseconds, meaning that if a constant
sine wave of amplitude 0 VU is applied suddenly, the meter will take 300
milliseconds to reach the 0 on the scale. It behaves as a full-wave
averaging instrument, and is not optimal for measuring peak levels."  AH-HA.
Til now I guess I've been trying to figure the deal for a peak-reading
meter.

Another good reference [which unfortunately adds little value to my design
process] is at http://www.aes.org/aeshc/pdf/mcknight_qa-on-the-svi-6.pdf

In either case, a 1mA FS, 100-ohm internal-resistance, non-radioactive meter
movement is what I have to work with.  I kept two out of the batch I offered
to the list maybe a year or so ago.

Here's another go at it:

Sanity check: figure zero forward drop with a [Cu2O] fullwave bridge,
.775/.00067=1156 ohms, still a long ways to go to get to the 3K-plus in the
original spec.  I can only figure the original meter's movement was
something *significantly* more sensitive than 1mA FS.

Looks like I'm going to have to put an op-amp in there.  Dadburn it.  After
opening up the meter to check for any internal resistance, natch...

Or I may just plug the meter in the hole for looks and say the heck with it.
Or configure it as an S-meter to read the AGC line.  But I haven't given up
yet.  More thought is indicated.

73, Brian KA9EGW

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of Roy Morgan
Sent: Wednesday, August 25, 2010 12:57 AM
To: r390 list
Subject: Re: [R-390] Line Level meter



On Aug 24, 2010, at 9:48 PM, <ka9egw at britewerkz.com> <ka9egw at britewerkz.com
 > wrote:

> OK, so...to get a 2/3 reading at .775Vrms... let me see--
> My brain hurts.

A slide rule. You need a slide rule.

Or, a copy of the Radiotron Designers Handbook (nice Db tables and
such.)

Do carry on and let us all know how you make out.

Roy

Roy Morgan
k1lky at earthlink.net
K1LKY Since 1958 - Keep 'em Glowing!



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