[R-390] No Peak on T701

[n4buq at knology.net]

On Mon, 01 May 2006 10:28:12 -0400, "Tim  Shoppa" <tshoppa at wmata.com> 
wrote :

> > I attempted to perform the "ground E211 and measure the output on the
> plate 
> > of V204" test.  I'm not sure, but I may have 'scope problems.  In
> order to 
> > see the signal, I have to select a very small vertical deflection
> value 
> > (say 0.1V/div or less).  When I do this, the 'scope "wobulates" up and
> down 
> > on the screen on the order of 0.05V or more.  If I look at the output
> of 
> > the RF-IF output at F103, it is doing the same thing.
> > I don't know if the power is dirty, the power supply is acting weird, 
> > the 'scope is flaking, or what. 
> 
> Is the wobulation 60Hz/120Hz?
> 
> Could be anything from real 60Hz power supply hum in the radio, in
> the scope, ground dfference between the two, etc.
> 
> As long as the wobulation isn't inside the scope, isolating the 60Hz
> hum can make a world of difference.
> 
> Standard workaround is use smallish capacitors in series with the scope
> probe
> that will block 60Hz you do not want to see but not block the MHz
> signals you want to see.
> 
> Typical values might be 100pF to 0.005uF.
> 
> Tim.

No, it isn't steady.  That's why I called it "wobulating".  It's almost 
like some component is randomly, but rapidly, changing value causing the 
pattern to shift up and down at a varying rate and varying amplitude.  
Looks kind of like it needs to check in down at the "nervious hospital" 
(reference to the movie Slingblade).

Thanks,

Barry - N4BUQ