Electronics > RF, Microwave, Ham Radio

Is is possible to repair a hairline crack in semi-rigid coax?

**biastee**:

@joeqsmith

I noticed the y-axis scale (impedance) has changed in the new graphs. Did you normalize to 50 ohm? What is the peak impedance value now?

**joeqsmith**:

--- Quote from: biastee on June 06, 2023, 01:59:54 am ---@joeqsmith

I noticed the y-axis scale (impedance) has changed in the new graphs. Did you normalize to 50 ohm? What is the peak impedance value now?

--- End quote ---

If you look at the two plots, the initial was showing the step response. The last plot shows the impulse response. The step response is calculated by taking the integral of the impulse. Z is then Z0(1+S11)/(1-S11).

There are a lot of very good papers on TDR that the main players have published.

Almost all of my math was derived from various HP papers which are readily available on-line. I have ran into mistakes in some of these papers and have posted about some of them on this site. So readers beware. It's also why I wasn't too surprised when a viewer suggested their was an error in my algorithms.

****

This short article describes the basics:

https://incompliancemag.com/article/time-domain-measurement-tdr-or-vna/

**biastee**:

--- Quote from: joeqsmith on June 06, 2023, 03:07:06 am ---

If you look at the two plots, the initial was showing the step response. The last plot shows the impulse response. The step response is calculated by taking the integral of the impulse. Z is then Z0(1+S11)/(1-S11).

--- End quote ---

I don't know how to make sense of the impulse response's y-axis (impedance). I can understand Zo = 50 ohm, but can't wrap my head around a baseline Z = 0 ohm.

Anyway, gimme your best guess: what sig-gen's parameter will be impacted? And how much? Thanks.

**joeqsmith**:

--- Quote from: biastee on June 06, 2023, 07:21:05 am ---Anyway, gimme your best guess: what sig-gen's parameter will be impacted? And how much? Thanks.

--- End quote ---

If you like guessing, maybe try finding one of these:

https://en.wikipedia.org/wiki/Magic_8_Ball

If you want data, return it to the manufacture and have them calibrate it. They can provide you with a report. Beyond the damaged cable, they may identify other problems.

**joeqsmith**:

One thing I did try was to take some very fine copper wire and wrapped it around the damaged area making sure it was laid into the cracked area. I then soldered the entire area and filed the rough spots. Looked nice but was much worse than the copper foil. I suspect the copper wire may have melted into the dielectric insulation.

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