Path: csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!us.feeder.erje.net!feeder.erje.net!eu.feeder.erje.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Joerg Newsgroups: comp.arch.embedded,sci.electronics.design,comp.realtime Subject: Re: Comparing phase of physically distant signals Date: Sat, 03 Aug 2013 15:03:06 -0700 Organization: Consultant Lines: 41 Message-ID: References: <51fd247c$0$64328$c3e8da3$5e5e430d@news.astraweb.com> Reply-To: news@analogconsultants.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Trace: individual.net ZAMzMxScuqLifQcydriUZwXcnq2d6EbIgU4JMeRNCg8KvFw4Ny Cancel-Lock: sha1:Xh7IFb6uCHI7Jp5vO5EEjIJiqdM= User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.6) Gecko/20070728 Thunderbird/2.0.0.6 Mnenhy/0.7.6.666 In-Reply-To: Xref: csiph.com comp.arch.embedded:12959 comp.realtime:289 Don Y wrote: > Hi Jeff, > > On 8/3/2013 1:31 PM, Jeff Liebermann wrote: >> On Sat, 03 Aug 2013 13:21:54 -0700, Don Y wrote: >> >>> What if I sat at the "reference point" and injected a signal onto the >>> network cable. A "ping" of sorts. Prior to (or coincident with!) >>> this, I use a TDR to determine the (temporal!) length of the cable. >> >> What type of network cable? If coax, the velocity factor varies with >> temperature and humdity. >> >> See Section 3.3 and Fig 6. > > In my case, CAT5/6. But, ideally, I would prefer a methodology > that could be applied to other communications media without > relying on some characteristic of *a* medium. > As long as pulse and response for the media test (ToF) happens via the same cable it makes no difference whether its characteristics change. Provided you repeat that ToF test before every transmitted timer tick of your measurement method. > E.g., my ping could be applied to a wireless medium just as > well as wired -- if we assume propagation is at a constant > rate (over a reasonably short measurement interval) between > devices. > It normally is. Unless you are next to a busy airport, freeway or high-speed rail. You also need to make sure the frequency/carrier you are using is free of interference, regardles of whether you use cables or wireless. -- Regards, Joerg http://www.analogconsultants.com/