On Wednesday, October 10, 2012 9:30:25 AM UTC-7, Jeff Liebermann wrote:
On Tue, 09 Oct 2012 16:02:33 -0500, John S

wrote:



On 10/9/2012 2:16 PM, Jeff Liebermann wrote:

Also look on eBay for a Tekronix 1502, 1503c or similar TDR.



I have a 1502. I want something which will give me info within tenth of

an inch on a PCB.



That's not going to happen with my home made TDR. The speed-o-lite is

about 1ft per nanosecond. To see 0.1 inches, you'll need a resolution

of:

0.1in / 12in/nsec = 8.3 picoseconds

That can be done, but not with commodity hardware.

Hmmm. Has to go round-trip, and depending on the PC board dielectric, the velocity will likely be about half the vacuum SOL. ~33psec?? Still kinda fast for most scopes you'd find in a hamshack, though. OTOH, if you're worried about that sort of effect, maybe you DO have a fast enough scope. Pretty much guaranteed it will be a 50 ohm input, though, and that will require you to rethink the setup a bit.



--

Jeff Liebermann

150 Felker St #D http://www.LearnByDestroying.com

Santa Cruz CA 95060 http://802.11junk.com

Skype: JeffLiebermann AE6KS 831-336-2558