[Elecraft] DMM question

[Koaps]

Thanks Jack,

I wasn't sure what was going on but figured it was
something to do with RF in room. There's a repeater a
mile or two from me and my computer and TV on so maybe
that was driving it nuts.

I just figured when I was asked to do the AC checks,
setting the DMM to mV(actually is was on its
autoscaling mode) it would show the <20mV as
suggested, but instead it was going crazy.

I forced the scale to .000 V and I was able to get a
.002 to .000 reading on the pins so I figured I was
ok.

KX1 is pretty nice to build so far, in fact the KXPD
was the hardest thing I've done so far.

Now I will tackle the receiver circuits.

Thanks for the help,
-Chris

--- Jack Smith <jack.smith at cliftonlaboratories.com>
wrote:

> Chris:
> 
> A DVM has relatively high input impedance and will
> pick up stray 60 Hz 
> and other things floating around (AM broadcast,
> perhaps) when the leads 
> are open. In essence, the leads act like a small
> dipole receiving antenna.
> 
> Short the leads together and it should read a lot
> closer to zero, unless 
> you live next door to a substation or a 50 KW AM
> broadcast transmitter. 
> (You can think of this as converting the leads to a
> loop antenna, which 
> has a lot less pickup than a dipole.)
> 
> Thus, the behavior you see is normal.
> 
> Jack K8ZOA
> www.cliftonlaboratories.com
> 
> 
> 
> Koaps wrote:
> > Hello all,
> >
> > I had a question about using a digital multimeter
> for
> > AC millivolt measures.
> >
> > I have a radio shack 24-range DMM and when I set
> it to
> > mV it never seems to go to zero, its constantly
> > counting numbers from 30-100 mV with the leads not
> > connected to anything.
> >
> > If I change the range to .000 V it will show
> around
> > .020 to .009 with the leads not connected to
> anything.
> >
> > When I tested U1 pin 1 and U3 pin 6 on my KX1 on
> the
> > .000 V range I got .000, is this an ok measurement
> or
> > is my DMM too screwy to use for AC mV measures?
> >
> > All the DC and resistance measurements with it
> seemed
> > ok.
> >
> > thanks,
> > -Chris
> >
> >
> >        
> >
>
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