I don't know how power feed for active antenna is designed in your equipment. Sometimes equipment can be back-powered through its GPS antenna port. This might be benign or not. Get at least an RF DC block for one unit (fancy name for a cap stuck between two BNC ports.) Leo On 17 Nov 2017, at 20:38, time-nuts-request@febo.com wrote: > From: Jerry Hancock <jerry@hanler.com> > Subject: Re: [time-nuts] Absolute phase > > I figured, what the heck, and just used a BNC T and it’s working.