Tone Remote system holds PTT on after dekey...

blueboy · Post by **blueboy** » Mon Jan 26, 2004 4:40 pm

I'm working with a Motorola L1548 Tone remote adapter and several (4) L1475 tone remote controls. These were a drop ship type item circa 1997-1999 era and were made by Instrument Associates. The problem is that intermittently, after one of the remotes dekeys it's PTT or monitor or function (channel) button, the transmitter (Radius SM50) stays stuck on for 3, 4, 5 or up to 20 seconds. Sometimes it does it, sometimes not. Seems to go in waves where it gets really bad and does it at all remotes. Tried unplugging the wall-wart power pack immediatley after dekey and system still gets hung up. This makes me feel that the remotes are not the cause but the remote adapter, radio or in building phone lines. Audio on lines seems clean and unloaded. Take a remote upstairs and hook directly to the remote adapter and the problem seems to go away... Maybe. It is quite intermittent. I have seen this type of problem on the DC remote version of this product and found that the remote adapter wasn't "dissipating" the DC current after dekey. I fixed it with a 480 ohm resistor across the phone line at the remote adapter. Because this device uses audio instead of DC current this won't work.

Any ideas would be appreciated!

Thanks, Blueboy

jim · Post by **jim** » Mon Jan 26, 2004 4:53 pm

By chance, is the phone line nearby any other line that may carry an identical tone such as another local radio system? If your line were to get another tone induced from close proximity to another (via induction or direct/ndirect leakage), it's possible for this to happen.

This can also happen with data causing cross-communications.

blueboy · Post by **blueboy** » Mon Jan 26, 2004 5:10 pm

Nope. It's all by itself in a clock tower in a little town hall. There is a slim possibility it's RF interferance coming from our own antenna (40 ft. away).

I should mention that we are using about 10 watts, good coax\connectors and it's a VHF 158 meg. system.

I rebooted radio and remote adapter several times and the problem still shows up. Customer notices the problem 1 or times per month.....AAAARGH!

I don't think RF is to blame as this problem has existed for maybe 6 months. System in place since 1997....

Post by **wavetar** » Mon Jan 26, 2004 5:34 pm

Gotta love those intermittant problems! I agree it isn't the tone remotes themselves that are causing the problem. My first suggestion is to try another tone for PTT. The remotes & adaptor should be capable of using a number of non-standard tones for PTT. I do recall reading somewhere that 2175 isn't always the best choice, for whatever the reasons. It's success or failure might also give an indication of whether it's another 2175 tone being inducted onto the lines. If that doesn't seem to help, my next step would be to replace the tone adaptor, as I've seen them do any number of strange things.

Todd

RKG · Post by **RKG** » Mon Jan 26, 2004 5:35 pm

Just a guess, but the key function is held in at the termination panel by the present of the LLGT. Once you have verified that the remotes are dropping LLGT, I'd look for two things: first, does the adapter drop coil current in the key relay as it should? Second, could the relay itself be sticking, so that it holds in even without current on the coil?

The EM relays used in more remote termination panels are pretty robust sealed units, and they are not carrying much current, but they have been known to fail. Replacing them isn't much of a problem.

MSS-Dave · Post by **MSS-Dave** » Mon Jan 26, 2004 5:59 pm

Another thing to try....make SURE the termination panel is grounded to the radio, the power supply and to ground (everything common) and not just through the control cables. I had some problems like this, LLGT would go away but the radio stayed keyed, RF feedback was holding the PTT relay partially closed.

Dave

Post by **xmo** » Mon Jan 26, 2004 6:00 pm

Tone remote systems initiate PTT on receipt of high guard tone followed by function tone and then low level guard tone. They are supposed to stay keyed until the low guard drops. Some systems stay keyed with either low guard OR audio activity. This avoids drop out if transmit audio falses the decoder off. It also creates the possibility of the transmit staying on if some noise is picked up on the control line. That is the first thing I would look for.

There does not appear to be any input level control on the L1548 - it relys entirely on its AGC. That means you can't make it less sensitive by turning down the input and turning up the output of the remotes. However - the way it works is that it is supposed to set the gain for a given transmission based on the high level guard tone. You could check to see that the high guard is at the upper part of the level range rather than the low end - that could cause the adapter to operate with lower gain in its AGC circuit - with a [hopefully] corresponding reduction in its succeptability to any noise on the line.

When you go to check it again - make sure your termination jumpers are correctly set. With multiple remotes you are only supposed to have one terminated. If they are all terminated - it could drag the line level down. The one to terminate should be the one farthest [electrically] from the L1548. The L1548 should also be terminated [SWA-7 down]

kurt meltzer · Post by **kurt meltzer** » Mon Jan 26, 2004 6:04 pm

I'm currently using several of those same tone remotes and tone remote adaptors, in campus style systems with on-premise wirelines. They have been in continuous service since 1996, but I've never experienced the symptom you describe on any of them.

If you can get the symptom to occur while you are at the site, perhaps you can listen to the wireline with a butt set after all desk sets have dekeyed but while the xmtr is still stuck in a keyed state. Do you hear low level guard tone? (you shouldn't). If you do, I'd suspect maybe the transmit key on one of the remotes is sticking.

If xmtr remains keyed after LLGT ceases then I'd suspect either the adaptor or the xmtr itself. Perhaps try disconnecting adaptor from xmtr and see if the adaptor's PTT line (pin 6) stays low even after all desk sets have dekeyd and LLGT has ceased. L1548 adaptors, when new, all came with a pre-made cable asssembly for use between the adaptor and radio, and if you are using this cable, then PTT will be the green wire. You could also try hard-keying the xmtr on and off, locally, while it is disconnected from the adaptor. Does the radio ever hang up in transmit after you have ungrounded its ptt line? This of course, would point to the xmtr as the source of the problem.

I hope this helps. I have extra manuals for both the L1475 and L1548, which you are welcome to if you need them.

commtek · Post by **commtek** » Mon Jan 26, 2004 7:27 pm

I actually saw a similar problem caused by a bad superflex jumper between the radio and the hard line. RF was getting into the controller and holding the PTT.

blueboy · Post by **blueboy** » Mon Jan 26, 2004 7:40 pm

Ok. No relay on the PTT output to replace. It's an open collector NPN that's held high with a suitable resistor and a zener across the output and ground to look after transients. Myself, I doubt the radio is at fault nor is the PTT output on the adapter panel.

So far I like MSS Dave's ground everything idea as I know that the components are not all grounded together. Sloppy,I know but this is what happens when you NEVER get lightening strikes. He is right though. There is an antenna 40 ft. away, the problem is intermittent and variable, there is lots of lengthy, loose wire\cable connections etc. It's really got RF spelled all over it....

I do have a new adapter panel in a box to try. If I get another complaint I'll try grounding everthing and install a different adapter panel and see what happens.

PS this board is truly great. I'm a long time listener and first time caller so to speak...

Amazing the intelligence and experience out there. I can just imagine Motorola's tech response centre's line if I phoned this in.... "I'm sorry, that product is no longer supported. Is there anything else I can help you with today??? No? Would you like to participate in a survey???" !@$#$^%^&&*%

It's really too bad that the 2-way industry is going the way it is. At least for the "small guys"

I guess that's another topic. Thanks for the help. I'll keep watching if anyone else has ideas.

Jim202 · Post by **Jim202** » Mon Jan 26, 2004 8:20 pm

I don't remember anyone mentioning the point of checking the output level of each of the remotes. After making sure that only one unit has the termination installed, measure the tone level output of each remote in transmit.

You might also ask if it seems to happen from one remote more than the others. Hopefully the operators that are using the system can point you to the unit that it seems to be happening from. Like maybe several are rarely used and can be eliminated on just the useage.

One remote might show up with a low line output and is causing the issue here.

This may not be the answer, but you will at least know the status of each remote when you through.

Jim

RESCUE161 · Post by **RESCUE161** » Tue Jan 27, 2004 6:47 am

I posted a problem a several weeks ago about a repeater here that does the same thing. It's very annoying to have to monitor several channels and the radio is hung up because the tx is stuck. I don't have access to the transmitter site though, so I have no idea what is going on.