Re: [LAD] [ot] rme fireface: weird balanced output measurements

On Saturday, February 18, 2012 08:29:11 AM Jörn Nettingsmeier did opine:

> fons, gene,
>
>
> thanks for your insights, particularly about the problems of AC rms
> meters at audio frequencies - i was totally ignorant of this, and i'd
> have shot myself in the foot with this eventually.
>
> fons, after i read your remark i asked around, and yes, the ff800 does
> indeed use servo-driven outputs, so the voltage difference is
> intentional and no cause for concern. i'll definitely investigate the
> level differences between channels, but as you said, i'd better do that
> with a sound card rather than a meter.
>
> gene, would love to follow your scope advice (particularly for the
> beneficial effects on gonads),

Chuckle. Its caught me by surprise a couple of times. I've had a scope
probe in one hand since around 1950. Its a very informative tool.

> and i'm looking out for one, but i'm not
> really prepared to pay much. in any case, it's way sexier than one of
> those usb sampling gadgets sold for a scope these days... maybe i'll
> find a nice, simple one in a dumpster somewhere.

Some of those usb gizmo's come with some truly useful software. If it can
digitize to 16 bits (most of that stuff is only 8 bits), then the
possibilities of doing some truly useful investigations under steady state
signal excitation becomes available. Sadly, one of those that does 8 bits
only, and claims to be able to an FTT, just doesn't have the bit depth to
make that FFT's output of more than casual interest.

My own scope, a Hitachi V1065, 100 mhz dual trace, is somewhat
computerized, enough that it can measure p-p voltages, or time from point a
to point b, and conversely a good estimate of the frequency by taking the
reciprocal. Also a dual time base with what seems to be excellent time
base stabilty. Still usable, despite its 100 mhz rating, at 185 mhz
although not to claim it is still calibrated at nearly an octave above its
ratings, I can at least chase through a ch 8 transmitters rf chain with it.
Fairly light, I paid $1200 for it used when it was till available new for
around 2G's about 21 years ago. I should think that a clone of it could be
had from fleabay for 250-500 today. Expect to buy probes, I get decent
ones rated for 200 mhz at a decent price from MPJones @ $40/copy.

Personal opinion: Stay away from the low end stuff from even the major
makers, its bound to be out of calibration AND non-repairable if its more
than 10 years old. The majors simply do not support older stuff.
Generally, Sencor does but it will spend the holidays in Sioux Falls too,
HP will till they are out of custom parts.

The only thing my old Hitachi has needed over the years was opened up and
all the assembly screws snugged up and one missing one replaced, too many
miles on too many vibrating airplanes in its history. Otherwise, at 20
some years, the tube is still factory bright and it Just Works(TM). The
switches need some exercise occasionally but that's expected.

> nice to get you two guys into another discussion about signal
> transmission - very instructive!

I enjoy discussing things with Fons, I think in some sense we compliment
each other, filling in the gaps so to speak. He has the theory better than
I, and likely has at least 8 years more schooling than I, where I've been
in the ditches making it work for almost 65 years. I have an 8th grade
education, a GED, am a C.E.T., and have had what used to be a 1st phone for
50 years. But the commish threw that under the buss 30 years, so its not
worth a lot in bragging rights today.
> best,
>
>
> jِrn
>
>
> btw: yes, the folkwang address seems to have expired at last. the la*
> lists were the last things i used it for, and i have now resubscribed
> from my own mail domain. so please ditch that old one from your address
> books if you want to get in touch off-list.

Cheers, Gene

-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: <http://coyoteden.dyndns-free.com:85/gene>
The key elements in human thinking are not numbers but labels of fuzzy 
sets.
		-- L. Zadeh
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