Re: Vpp question
- From: redbelly <redbelly98@xxxxxxxxx>
- Date: Sun, 17 Jun 2007 10:40:08 -0700
On Jun 16, 2:28 pm, willwestw...@xxxxxxxxx wrote:
I have something simple but I can't seem to find an answer to it.
I am getting a different Vpp measurement on the scope from the signal
generator. When put in a 1Vpp 200KHz square wave from my signal
generator, while the frequency is dead on at 200KHz, I got a reading
of 2 Vpp on the scope. I think my voltage output from signal generator
is Vpp because there's a light on the generator which is lighted.
There's also RMS light but it's off. The scope is on DC Coupling.
Does anyone know why my Vpp reading on the scope is doubled?
Many thanks.
As others have said, the sig gen is expecting a 50-ohm terminator on
the other end of the cable.
If your scope doesn't have a "50 ohm" setting, you could get one of
these:
http://www.thorlabs.com//thorProduct.cfm?partNumber=T4119
If you're just doing low frequency stuff, you're probably OK without
the 50 ohm terminator, you just need to remember your setting is off
by a factor of 2. But as you approach RF frequencies ***, you'll get
weird wave-interference effects in your cabling, and the output
amplitude will vary with frequency.
Regards,
Mark
*** problems happen at frequencies where the signal's wavelength (in
the cable) is comparable or less than the cable length. You're okay
if the wavelength is a lot longer than the cable length:
Wavelength >> Cable
or
(Signal velocity)/frequency >> Cable
or
Frequency << (Signal velocity)/(Cable length)
A typical coax has a signal velocity of (2/3)c, so this gives
Frequency << (200 MHz) / (Cable length, in meters)
Regards,
Mark
Mark
.
- References:
- Vpp question
- From: willwestward
- Vpp question
- Prev by Date: Re: DIY CNC Machine How Hard Can It Be?
- Next by Date: Re: Pull down resistors on bus of microcontroller board
- Previous by thread: Re: Vpp question
- Next by thread: Western Digital "MyBook" as RAID?
- Index(es):
Relevant Pages
|
