Feature request -- TDR

[kc0ws]

How about adding TDR functionality? A friend sent me a printout from the TAPR unit showing the length of the line, and any impedance bumps or changes. It would help with a situation like I was trying to diagnose (long distance) that turned out to be a kink in a coax cable, which was causing a VSWR of 2:1. We didn't have our AIM yet, but it wouldn't have helped, because short provided by the antenna would have gotten all the attention on the "Distance to Fault" calculation, ignoring the kink in the cable. Problem was near where the cable started up the tower.

[Bob]

That's a nice feature alright.
What is the spatial resolution of the TAPR unit?

-- Bob

[kc0ws]

From the online manual (I don't have a unit, but will be using a borrowed one later this month):
"The TDR resolution is 4.1 nanoseconds. This limits the resolution of the cable fault to about 1.3 feet (or about 0.4 meters). The TDR mode ignores the Start and Stop frequencies, it needs to setup a custom grid."

If I understand the process correctly, the resolution will depend on how close together the frequency readings are. I think the process goes like:
Take a series of evenly spaced readings, recording the Z magnitude.
Do an Inverse FFT on that series.
Scale the results to impedance units.
May need a step for DC restoration.

Basically any impedance bump in the line will cause a recurring set of Z bumps in the frequency sweep, which the FFT picks out. If so, the resolution is related to twice the frequency sample spacing.

I may be all wrong on this, as I have not done it myself. Consider it no more trustworthy than smoke or hand-waving until independently verified.

P.S. I did find that the TAPR site mentions doing and IFFT on the reflection measurement.

[g3rep]

Apologies for late posting, new to the forum but when I saw your comment on TDRs I was hopeful for a similar facilty.
I have use TDRs on long feeder runs and they are incredible since they see all the discontinuities on the way. Barrel connectors on long coax runs, on openwire feeder you could see all the spreeders and any poor ones.
I believe TDRs use pulse technology and not swept RF so I guess it is wishful thinking.
73s
Bob

[k9fv]

This feature would be GREAT!!!! and "IF" it is possible, I for one applaud the effort and suggetion. Bob - pretty please<

73 de Ken H>

[tf4m]

Some of my coax runs are more than 2,000 feet in length and some of my open wire feeders are up to 4,000 feet in length.

Today I was visited by telephone technicians who demonstrated their RiserBond Model 1270A TDR meter by measuring some of my feedlines.

If this funcionality could be added to the VNA2180 it would be great.

73 de Thor, TF4M
tf4m.com/

[k7vo]

Is the measuring method of the "non TDR analyzers" give usable/comparable accuracy to cable faults or kinks? I get the impression that the TDR feature is more accurate but is the extra feature and cost worth the improved accuracy? The rig Expert 230 Pro has TDR capability. I am about to purchase one or the other (AIM 4150 vs rig Expert).
Bob
K7VO

[Bob]

The new AIM software with the TDR function was shown at the Visalia Hamfest last weekend. It will be ready to release in about a week. It works with the AIM4170 and the AIMuhf. There is no extra cost.

Here's a sample screen shot:
www.w5big.com/RG58&RG59.gif
Anyone who would like to be a beta tester, please send me an email.

73/ Bob

[k9fv]

I'm waiting patiently for the release, but it's hard all this waiting:) I did drop you a email concerning the beta testing. That screen shot is IMPRESSIVE!!

73 de Ken H>