[TowerTalk] Inner conductor migration in Heliax(TM)

[David Aslin G3WGN]

Thanks Jim.
I learned about the DG8SAQ device after I'd already bought the AIM4170C.  The AIM is a fine analyser but it tops out at 180MHz so I won't see quite such fine detail.  May be time to upgrade!
73, David G3WGN  M6O

On Tue,4/12/2016 12:17 PM, David Aslin G3WGN wrote:
> I do have a short length (maybe 60ft or so) of properly stored near-new LDF4-50 so I can use that as the baseline.
> Anyone actually attempted impedance or another measurement to check for performance change?

Hi Dave,

The best way I know of to measure coax parameters is to do an open and short Z measurement with a vector analyzer and import both into ZPlots, which is an Excel spreadsheet. You also need to enter the length if you want Vf and attenuation/ft (or /m). ZPlots will yield a graph of Zo, Vf, and attenuation vs. frequency.

My weapon of choice for measurement is DG8SAQ-designed VNWA, built and sold in the UK by SDR Kits. About $700 shipped to the US with calibration kit. It also does excellent TDR by sweeping over whatever frequency range you choose and taking the inverse FFT. For best detail (and to see "little" issues, I usually sweep 100-500 MHz. For even better detail, sweep 600-1,300 MHz.

73, Jim K9YC