EMRFD Message Archive 6300
Message Date From Subject 6300 2011-05-16 03:31:31 Adrian Scripca Audio RMS voltmeter schematic needed Hello all,
I was reading about receiver measurement in EMRFD and from what I
understand an audio rms voltmeter is helpful/needed for noise/MDS/IP3
measurements. Alas I don't seem to find any reference to such a circuit.
Can anybody please help out with a link or a schematic?
6302 2011-05-16 04:14:03 w4zcb Re: Audio RMS voltmeter schematic needed An excellent one by Bill Sabin, (W0IYH) from QST October 1992, and
also carried on the CD right here on EMRFD. (Measuring SSB/CW receiver
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6303 2011-05-16 06:30:03 Adrian Scripca Re: Audio RMS voltmeter schematic needed Thanks for the pointer, Harold. Now I only need to find my EMRFD cd.
6304 2011-05-16 07:01:37 w4zcb Re: Audio RMS voltmeter schematic needed Many of the Fluke multimeters are true RMS reading. Check your
multimeters characteristics. My Fluke 77 is one.
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6305 2011-05-16 07:11:52 Adrian Scripca Re: Audio RMS voltmeter schematic needed I do not own a Fluke multimeter but thanks for the tip.
6320 2011-05-17 11:43:56 wa9cgz Re: Audio RMS voltmeter schematic needed Adrian,
Take a look at the PC soundcard program by DG8SAQ called
Audio Meter it's a program to measure the band limited RMS of audio signals with a a sound card.
6333 2011-05-19 08:24:40 Tim Re: Audio RMS voltmeter schematic needed Here in the US it is common to get "previous generation" (err, um, probably closer to 3 or 4 generati 6350 2011-05-25 09:56:11 Adrian Scripcă Re: Audio RMS voltmeter schematic needed Hello Tim,
Thank you for your suggestion. However it is a bit harder for me to get
my hands on a lab-quality instrument in the country I live in (large
taxes and problems related to delivery). I have eventually managed to
get the QST Bill Sabin's paper (thank you Harold and Tom) so now I only
need to find time to build it.
That should also help to increase my selfesteem :-)
73 de Adrian
6353 2011-05-30 14:44:41 Kerry Re: Audio RMS voltmeter schematic needed I began with Bill Sabin's design but, as often happens with my projects, "specification creep" took-over and it became a full-feature instrument.
I have created a folder "Audio Voltmeter" in the Files section and put some information in it.
There is the draft of an article I wrote but decided not to publish; also the schematic & PCB layout.
My build works very well; its readings correspond almost exactly to those of a nice mint Trio VT-121 that I later acquired (for zero $$$s :) ).
6354 2011-05-31 05:30:36 Adrian Scripca Re: Audio RMS voltmeter schematic needed Hi Kerry,
Impressive feature creep! I think I shall build your augumented variant
or at least parts of it (such as the switchable attenuator and
selectable load). Very useful indeed!
One question though: the schematics posted in the group files do not
include the calibrator schematic. Do you happen to have it somewhere as
6355 2011-05-31 12:39:20 Gary, WB9JPS Re: Audio RMS voltmeter schematic needed Consider recycling an old instrument. I gutted an old HP400, keeping the nicely-compensated wide-range attenuator and beautiful mirrored-scale lin/log meter and other front-panel items. A couple of modern JFET opamps (fast, low noise, low drift) and an AD636, and you get flat response to 1 MHz or so, and dynamic range down to a couple microvolts rms. Ebay usually has broken "for parts" meters cheap.
6356 2011-05-31 18:36:32 Kerry Re: Audio RMS voltmeter schematic needed Sorry; I don't seem to have the power supply/calibrator schematic.
I have put another file in the folder; this shows the parts-placement overlay and a "ghost" view of the PCB side-by-side at about the same scale.
That might assist you in reconstructing the schematic; just draw the tracks on the overlay with a coloured pen.
It's just a basic circuit; a 5v regulator, an 8v regulator and a 7660 negative-rail generator.
I like Gary's idea of using the hardware from an old instrument but I appreciate that you will not have the same access to old (or new) items as our US friends enjoy.
6357 2011-05-31 19:15:04 Kerry Re: Audio RMS voltmeter schematic needed Here is a good-looking design that I found;
This site also has a lot of information on other topics; it's worth browsing.