HT813 FXO AC Termination settings

#1

Hi, noob here. I have an HT813. Could someone please explain what AC Termination is? I tried Googling but couldn’t find any definite answer.

I tried two different AC Termination country settings, comparing the FXO and Advanced Settings pages for the USA option with those of the Australia/New Zealand option. I rebooted the device, as directed, each time I switched the country setting. However, I did not notice any difference when I compared the settings side by side. I expected the country setting to be a kind of a profile setting that auto-sets multiple configuration entries, such as the dial tone frequency, but there was no difference.

Any help would be appreciated.

#2

The manual explains what the setting is. It has to do with the impedance settings of the FXO line and the HT has the standard for some countries already preprogrammed and failing that you can select the impedance type for most of the world standards by selecting the impedance itself.

While a country may have a given standard, it could be that your country is not listed or the provider being used may not follow the country standard. There is no mention in the manual that any other setting is adjusted by setting the AC Termination by country other than the impedance setting.

The impedance is a design specification used to standardize the delivery of a telecom signal taking into account the line length, gauge of wire, current, voltage and other factors such that there is a reasonably good chance of providing a workable solution over a fairly broad range of the aforementioned variables.

Of course, what is actually seen is rarely spot on to the spec as things change over time. Nevertheless, one such factor of impedance is echo. If the device (HT) is sending too much energy into the line, then the excess energy will be reflected back into the HT resulting in the person on the HT hearing echo. Hence, the setting can be quite important.

#3

Thank you for explaining that so clearly. I’m in Australia and have set the country-specific impedance accordingly to Australia / New Zealand. As a test to troubleshoot a noisy PSTN dial tone from the HT’s FXO port, I set AC Termination to Impedance Based and picked the closest impedance I could find for Australia “220 + (820 || 115nF)”. It seemed to have made a difference, which mystifies me a bit.