A follow up for others:
The E-bay, Chinese "RG400" has a steel core, which is OK at VHF, but
questionable at low HF.
73, Mac N8TT

"Jeff Liebermann" wrote in message
...

On Mon, 8 Oct 2012 23:34:11 -0400, "J. C. Mc Laughlin"
wrote:

One such coax appears to be the expensive RG-400. Only need a few feet.
Question: What might be a source for short lengths of RG-400? I have tried
Newark, Mouser, and the like. . . .

http://www.ebay.com/itm/230756316444
http://www.ebay.com/itm/160856544191
http://www.ebay.com/itm/380086386242


J. C. Mc Laughlin
Michigan U.S.A.
Home:

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.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Tue, 09 Oct 2012 16:02:33 -0500, John S
wrote:

I have a 1502. I want something which will give me info within tenth of
an inch on a PCB.

Thanks for the two emails asking for details. Too bad that your email
address is invalid. If you want answers, kindly supply a working
email address.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 10/10/2012 11:08 PM, Jeff Liebermann wrote:
On Tue, 09 Oct 2012 16:02:33 -0500, John S
wrote:

I have a 1502. I want something which will give me info within tenth of
an inch on a PCB.

Thanks for the two emails asking for details. Too bad that your email
address is invalid. If you want answers, kindly supply a working
email address.


My fault. I'm using Thunderbird and they added an additional button when
I last updated. They now have a "Followup" button to which I have not
yet become accustomed. It was always "Reply" before this last update.

I apologize for my confusion.

John

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