Batboard

Could someone explain to me the purpose of the 2175 HLGT and if there is any operational risk to programming a MSF 5000 to KEY when a LOW level 2175 is detected.

Rest of the story. Attempting to extend a wirelined VHF MSF 5000 by adding a UHF control link. Probem is the VHF will not transmit upon request from console as it normally does when connected to wireline. So far the fix is to program the TRC of the VHF to stayed keyed as long as a LOW level 2175 is detected.

Are you sending the tones over the UHF link? If so, the HLGT might be getting cut off by the link's keyup time. Some remotes allow you to adjust the HLGT time to compensate for that.
As far as I understand it, the HLGT and Function Tone tell the radio to key up, and on which channel, then the LLGT holds it keyed as long as the PTT button is pressed.

jackhackett has correctly described the operation of the tone remote system.

The real issue is your RF link. It must either be keyed by hardwired PTT [e.g. E&M type connection] OR, if tone control keyed, it must be configured for guard tone keying so that PTT begins as soon as high guard is received and continues until loss of low guard.

If the link is a standard tone remote keyed device it won't start to transmit until after it has detected the function tone, thus leaving nothing for the remoted [linked] base to detect.

The optimum is hardwire keying unless the link transmitter is too far from the console, in which case guard tone keying would be employed.

Also, Motorola's Centracom II products do have the option of extending the high guard tone timing to allow time for the link to open squelch and PL to begin passing audio.

The RF Link is tone controlled via a microwave link with the same connection the VHF will be disconnected from. The plan was to pull out the VHF insert UHF in its place. Then move VHF 30 miles down the road and cross connect to far end UHF. No option for a hardwired PTT.

Some have advised the 160ms HLGT duration could be extended to 320ms at the Centracom II. Local Console Tech has not been able to figure it out so far.

Working from the field my hope is that is safe to progam the VHF TRC to key up and stay keyed from the LLGT only. Done by programming the TRC options. This seems to work in shop thats why I am little fuzzy about why the HLGT is needed. Some say its a wake up command. Perhaps this VHF never sleeps.

The HLGT is there to "prime" the AGC circuit, and is usually louder than any voice, so it adds some noise immunity incase an open mike console is on the line. The function tone that follows is 10dB lower, and the LLGT is 30dB below the HLGT level; that makes it easier to filter without the voice audio suffering in the process. At least, that's the theory.

If you can get the station to key up on just the LLGT, that would almost act as a PL decoder, although at quite a different frequency.

It would almost seem easier to put a COR on the remote receiver and have it key the station via DC or a manual PTT input. But that might not be "the Motorola way".

Bob M.

You did not say what the "far end" UHF link radio is going to be, but if it is also an MSF5000, then Bob is right. The easy way to build the system would be to "RA" connect the far end UHF MSF to the companion VHF MSF. Motorola's "RA" interface is a basic cross connect of COR and PTT signals. The CXB stations with wireline interface support this directly with simple RSS programming.

Even if you were using something as simple as a Maxtrac or CDM as a link radio, you could still connect them that way.

The only real reason to transport the entire tone remote command sequence to the far end station is if you need to implement some control command other than PTT, for example F1/F2. If you really need to do that be aware that there are notch filters in the MSF stations that would need to be disabled in order to pass the 2175 to the far end.

As far as the purpose of the high level guard, it was designed to "wake up" the tone decoding circuit to the impending function tone - i.e. open the function tone decoder window. In MSF it still alerts the microprocessor to be ready for additional activity as well as setting the initial AGC level for that transmission.

If you went to the tone control information screen in the MSF RSS and changed the top line command following "GUARD TONE" from "MORE" to "KEY", the station is still expecting that the initiation of guard tone is 'high level' and it will act accordingly to set the AGC. The KEY command then takes over and intrinsically will continue to transmit as long as guard tone is decoded OR voice activity is detected.

With regard to your microwave. If it is an analog system your 'circuit' would be implemented with channel modems. If it is a digital system, typically you would be connected to a port on a voice interface card in a channel bank.

In either case, these are usually E&M circuits and, although they are often used for voice only, the E&M capability can be used to transport contact closure keying from end to end. To use that you would install an option board in the CEB above that channel's BIM card and program the channel for BOTH tone keying and relay keying. The relay keying would connect to the E&M input which would provide a closure at the remote end to key the UHF station which would then pass the tone control sequence.

Thanks for all the help so far. I should have mentioned the UHF units are Quantars. I will look into the RA connections between MSF and Quantar.

Each of your Quantars will need to be equipped for wire-line control. At the microwave end, simply connect the station where the VHF station was and program the Quantar for tone remote control key up the same as the MSF had.

At the remote site, the Quantar wireline board will provide 600 ohm transmit and receive audio which will be cross-connected to the VHF MSF5000 wire-lines.

In the Quantar service manual you should find a section titled "System Applications" that shows where to pick up the PTT and COR connections on the 25 pair connector. By default, the Quantar should have come programmed for local PTT input and COR output. The Quantar RSS will let you change or set up these I/O's under the "wildcard" programming section.

The MSF5000 has one programmable input and one programmable output on the station accessory connector. The RSS will let you configure these I/O's so that the input is PTT and the output is COR [RX#1 Activity].

Basically, all you have to do is make a cable and do a little programming and it should work fine.