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    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

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 Post subject: Voltage measurement on RF cable
Posted: Thu Oct 20, 2005 4:03 pm 
I have a piece of RG58 going into an into an o-scope with a 100 MHz BW. The signal is a sinewave (almost) and I know the power out of my source (10 MHz) is +10 dBm. Problem is the o-scope is reading about exactly twice the voltage I expect to see (which is 2 Vpk-pk). I'm measuring 4 Vpk-pk. Any ideas what might be going on. Thanks.

--- Ted

 Post subject:
Posted: Thu Oct 20, 2005 4:08 pm 
User avatar

Joined: Mon Jul 18, 2005 4:31 pm

Posts: 40

Location: Baltimore, MD

I'll bet your scope's input is set to the high impedance mode. Make sure it is set to be a 50 Ohm load. You are exactly right to be expecting about 2 Vpp.

 Post subject:
Posted: Fri Oct 21, 2005 7:17 am 
Agreed, your scope impedance is not 50 ohms. If you do not have an option for 50 ohms, place a 50 ohm resistor in parallel between clip leads.

 Post subject:
Posted: Fri Oct 21, 2005 10:24 am 
kanling wrote:
I'll bet your scope's input is set to the high impedance mode. Make sure it is set to be a 50 Ohm load. You are exactly right to be expecting about 2 Vpp.

Thanks kanling - you are exactly right :!:

I can't believe I was dumb enough to not think of that. :D


Posted  11/12/2012

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