Re: [Repeater-Builder] Re: Quantar Simulcast Issue
Optimization of a simulcast system is critical to its proper operation. Not every local Motorola shop has the equipment or experience to perform this activity. I have installed many simulcast systems over the years and it always boiled down to incorrect system optimization (excluding equipment failure of course). If it is a Motorola project a System Technologist (ST) would be assigned along with a project manager. Contact the project manager with your findings and he will assist you in rectifying the problem. Now if it is a local Motorola Shop project then all bets are off. Depending on the status of the shop they may not be able to buy the parts from Motorola to build a Motorola simulcast system. There are other simulcast designs and hardware available but they are not of the Motorola design described by WB0EMU. This is a tried and true design that has been implemented over and over with excellent results.As said below proper Quantar programming, netting, and Mod-comp adjustment are critical. Bill ex Motorola Project Manager In a message dated 6/23/2010 10:20:20 P.M. Central Daylight Time, wb0...@arrl.net writes: --- In Repeater-Builder@yahoogroups.com, wmhpowell w...@... wrote: I'm looking for some Quantar engineering level help re: an interesting simulcast issue. ... Thanks, Bill Powell -- When you say this system was set up and installed by Motorola - does that mean a 'factory direct' Motorola project or a local dealer? Is the baffled tech a shop tech or a Motorola employee [e.g. S.T.]? You say the system is GPS stabilized - do you mean what Motorola refers to as GPS Simulcast? If so, the transmit path would originate at a prime site where voted receive and/or dispatch transmit audio would be routed to a CSCI or USCI, then to an SDA, then to a Premysis TeNSr channel bank into DSM-II cards, then over T-1 paths to each remote site where channel banks with corresponding DSM cards connect to the wideband simulcast Quantar tx inputs. The GPS reference clocks, typically from Trak, provide 5 MHz reference to the Quantar stations and 1PPS timing to the DSM's which automatically time align the transmit audio. This is a proven working product. The hypothesis regarding lack of DC restoration in the modulator would suggest a design issue which is highly unlikely given the number of succcessfully fielded Quantar simulcast systems. If you are going to investigate this issue you should begin with the most current version of the Motorola GPS Simulcast manual: 6881098E65. On the other hand, it this system was implemented by a local dealer using some other form of simulcast distribution such as Harris SynchoCast - there could be any number of issues. In any case - proper Quantar programming, netting, and Mod-comp adjustment are critical. Audio phasing and level optimization is best verified using a DSA [Dynamic Signal Analyzer] such as the Agilent 35670A. Yahoo! Groups Links
[Repeater-Builder] Re: Quantar Simulcast Issue
wmhpowell w...@... wrote: I'm looking for some Quantar engineering level help re: an interesting simulcast issue. Does it have to be Quantar? I live in an area where I can hear several of high band our simulcast Quantars. The whole thing was installed and set up by Motorola including GPS stabilized time bases. All that and $3 can sometimes get you a decent latte. I'm monitoring with a true monitor: wide band IF and little limiting. When the dispatcher drops a dead carrier I hear little in the way of hetrodyne or grunge as it should be. Hopefully meaning the carriers are close to each other and not moving around a lot. However, when the dispatcher drops alert tones I hear a hetrodyne that decreases in frequency over the duration of the tone. During the tones present or after the tones go away? My guess is that the tone is somehow pulling one of the VCOs in a Quantar exciter because of a lack of DC restoration in the modulator: a capacitor is charging and slightly shifting frequency. Why would you guess that? I consider this to be abnormal and undesirable behavior - especially in a system of this caliber. How about any Simulcast System... I haven't done any field tests yet. I suppose I can set up 2 service monitors: one to receive in the AM mode and the other to provide a reference carrier and then send tone to each transmitter, in turn. That, at least would let me isolate the problem to one, two, ?? radios. Not where I'd first go/test... Has anyone else experienced a problem like this? Yes Any Motorola engineers out there? Can I be an Authorized Kenwood Service Station and Dealer Instead? Or is a retired from Motorhead Field Service person OK? Our local tech is also baffled so I'm reaching out for ideas. Thanks, Bill Powell Keyboard player for Lynyrd Skynyrd? Getting serious for a hopefully brief moment... How is the tx audio making it's way to the repeater/base stations? Have you checked and compensated for group delay on those paths? Got milk? s.
[Repeater-Builder] Re: Quantar Simulcast Issue
--- In Repeater-Builder@yahoogroups.com, wmhpowell w...@... wrote: I'm looking for some Quantar engineering level help re: an interesting simulcast issue. ... Thanks, Bill Powell -- When you say this system was set up and installed by Motorola - does that mean a 'factory direct' Motorola project or a local dealer? Is the baffled tech a shop tech or a Motorola employee [e.g. S.T.]? You say the system is GPS stabilized - do you mean what Motorola refers to as GPS Simulcast? If so, the transmit path would originate at a prime site where voted receive and/or dispatch transmit audio would be routed to a CSCI or USCI, then to an SDA, then to a Premysis TeNSr channel bank into DSM-II cards, then over T-1 paths to each remote site where channel banks with corresponding DSM cards connect to the wideband simulcast Quantar tx inputs. The GPS reference clocks, typically from Trak, provide 5 MHz reference to the Quantar stations and 1PPS timing to the DSM's which automatically time align the transmit audio. This is a proven working product. The hypothesis regarding lack of DC restoration in the modulator would suggest a design issue which is highly unlikely given the number of succcessfully fielded Quantar simulcast systems. If you are going to investigate this issue you should begin with the most current version of the Motorola GPS Simulcast manual: 6881098E65. On the other hand, it this system was implemented by a local dealer using some other form of simulcast distribution such as Harris SynchoCast - there could be any number of issues. In any case - proper Quantar programming, netting, and Mod-comp adjustment are critical. Audio phasing and level optimization is best verified using a DSA [Dynamic Signal Analyzer] such as the Agilent 35670A.
