[SOC] 'Scope question

[Paul Playford]

Congratulations on your efforts with an oscilloscope Tom.  My scope is the 
first thing I turn on when sitting down at my test bench.

It sounds like you are doing everything as good as you can with the 
equipment you have.

The 20 MHz bandwidth means your observations of a sine wave (rf carrier) at 
20 MHz will be down 3 dB from what they really are.  So if you observe 6 vpp 
at 20 MHz your are actually looking at 8.5 vpp.

The observed frequency will be the same as the actual frequency, depending 
on your scopes calibration.

Depending on your 'scope probe, it can get worse.  If you are using an 
inexpensive probe (not Tektronix or H-P that is matched to your scope) that 
is rated at 20 MHz, then you are actually looking at 12.0 vpp.

Which also means if you see 6 vpp at 10 MHz you are actually looking at a 9 
vpp signal.

I own a Tektronix 465 and three Tektronix 7000 series oscilloscopes that are 
all rated to 100 MHz and I use Tektronix probes with them and I feel very 
comfortable making observations below 30 MHz.  But when I get above 50 MHz I 
have to allow a little windage for the bandwidth.

Most of what I look at when using an oscilloscope is the shape and frequency 
of the waveform.  If I want an accurate rf voltage measurement I will use an 
rf probe and my Fluke digital multimeter.

de Paul, W8AEF

ZF2JL/ZF2TA  FO8DX/FO8PLA  8Q7AA  XZ0A  VU7RG
soon to be TX5C


----- Original Message ----- 
From: "Tom McCulloch" <thom2 at att.net>
To: <thom2 at att.net>
Cc: <soc at mailman.qth.net>
Sent: Sunday, November 11, 2007 6:48 PM
Subject: [-] [SOC] 'Scope question


> snip

>    OK, so I wasn't able to get good Voltage P-P readings on the scope for 
> any of the bands I tried (80 through 10 meters) -- they all seemed too 
> low.