I'll try to take it one by one; First, a quick reference on Tone remotes, at wiki: http://en.wikipedia.org/wiki/Tone_remote
(including wav samples. listen to them.) --- In Repeater-Builder@yahoogroups.com, "ve7ltd" <dcame...@...> wrote: > > All, > > I am trying to help a local group with a remote TX/RX site they have which is > remoted to their office with a leased phone line and some Motorola tone > remote equipment. I know the radio end has a Motorola L3276A adapter, and > the office end has a "telephone style" handset (don't have the model number). > > As of last week, this system will no longer transmit. It still receives fine, > but will not activate the PTT on the remote radio, or at least there is no > transmitted signal. The fact that is receives tells me that at least the line > is intact. > > I have not yet been to the remote site (several miles away) to look at the > radio, but I want to know a little more about this tone remote system before > I go: > > 1) Can I plug a regular telephone into the pair to monitor the signaling? > You can monitor it, but it really won't tell you anything useful. What you need to know is what levels are going out, at the office end. If you can just put a good, TRUE RMS digital Multimeter on the line, especially if it will read in dBm, you can find out what level of tone you're sending out. Has to be a high-impedance meter, so you don't load the line. Since the tone-remote sequence is 120ms of 2175 Hz, and 40 mS. of function tone (typically 1950 Hz for F1, frequency 1, transmit,) at 10 dB below the level of the first burst of 2175 Hz, followed by a sustained tone of 2175 Hz, another 20 dB below that; let's say your sequence starts out at 0 dBm, then the Function Tone will be at -10 dBm, then the last 2175 Hz will be at -30 dBm. (these are good levels to have; the function tone is supposed to be about the same level as average voice, so there is enough headroom above the voice so nothing clips in the telephone system). > 2) How is the signaling done for TX and RX on the 2 wires? 1950Hz tone or > something similar? See the wiki.... > > 3) What should I hear on the line when the PTT on the handset is pressed? > Again, wiki. > 4) Is there a way to passively monitor the leased line audio for the > signaling from either end with my HP 8920A service monitor? > If your scope input has an 'isolated' ground connection, this might be possible. Also, there is a thing called a TIMS, transmission impairment measurement set, which should give you such info. It will measure in dBm, show you level & frequency. But not the piece of equipment the average person has; pretty pricey new. That's why you can work with the good DMM. > I don't fully understand the concept of balanced lines, and I don't want to > damage any of the equipment by connecting something I shouldn't to it. The line should not have any voltage on it at all, DC, and only those small amounts of AC for signalling and voice. Getting to the end of it, if you're sending at the office end, as I mentioned above, and at the radio end, you'll have (let's pick a value) 10 dB loss thru the phone lines. Looking for your Low Level Guard Tone of -30 dBm at the office end, then 10 dB of loss, should give you LLGT of -40 dBm. You can also look at this with a (storage) scope, to catch the rapid tone sequence, and levels. Best quick check is to look for your levels at each end. If you've got too much loss in the line, or it's unbalanced (one side has more or less resistance to ground than the other side; it should be almost infinite Resistance to ground from either side), then the Tone Remote Adapter at the radio end won't decode the sequence properly, and it won't generate the PTT signal. Clear like mud? Chuk > Dave Cameron - VE7LTD > IRLP System Designer >
