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Thread: Comparators GE vs Motorola

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    Default Comparators GE vs Motorola

    I want to set up an analog voting system for a local ham repeater that has poor inbound coverage. Outbound is fine and I have access to a couple of sites for remote receivers. I'd like to keep this project as cheap as possible and want it to remain invisible to the end-users. My plan is to locate the comparator at the repeater site and use RF links to get back to the comparator from the remote receivers. I have seen GE and Motorola on Ebay. Is one better than the other? Is one less prone to need alignment all the time? Specifically, I was looking at the Spectra TAC. I have some contacts on the Harris side of the house, but I don't know what to ask for if the Harris is a better product. What do you guys recommend?


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    Quote Originally Posted by rescue161 View Post
    I want to set up an analog voting system for a local ham repeater that has poor inbound coverage. Outbound is fine and I have access to a couple of sites for remote receivers. I'd like to keep this project as cheap as possible and want it to remain invisible to the end-users. My plan is to locate the comparator at the repeater site and use RF links to get back to the comparator from the remote receivers. I have seen GE and Motorola on Ebay. Is one better than the other? Is one less prone to need alignment all the time? Specifically, I was looking at the Spectra TAC. I have some contacts on the Harris side of the house, but I don't know what to ask for if the Harris is a better product. What do you guys recommend?
    I recommend JPS /Raytheon SNV-12 voters. They are the most flexible to configure. Also JPS made an earlier SNV-4 that is nice, except documentation is slim and you may have to drive a controller with it to get the repeater drop out delay and PTT logic.

    Motorola SpectraTac and DigiTac voters require the receiver to have a 2175 Hz pilot tone. A lot of hams have lashed up brand x receivers with Spectra Tac and fail to notice that 1) the audio needs to be muted for about 15 ms after the COR activates and the 2175 Hz tone drops. Otherwise the AGC keeps hunting and the voter won't work properly. 2) you need a 2175 Hz notch filter in the receiver or the voter will react to 2175 Hz energy in the speech and will mute. In short, you need the C269 line driver option that is part of a Micor satellite receiver.

    RF Links can be a problem with Motorola voters. I say this because there are some limitations with respect to the signalling per above. If the links are to remain up 100% of the time and simply serve as an audio and pilot tone path, they will work. Once you start configuring them to key up and down, you add complexties.

    I can't speak for old GE voters, but Harris uses JPS Raytheon for analog voters these days,

    Here is an idea to keep costs down. Buy the SNV-12 voter and co locate all the receivers and voter at the repeater site. Use antenna diversity to improve talk back from the portables. Two or more antennas mounted with a few wavelength vertical separation on the tower will provide about a 5 dB improvement. If you have the means, three receive antennas, in horizontal plane, in a triangular pattern will yield a lot of diversity gain perhaps 9 dB. Go with four and have the fourth antenna horizontally polarized (UHF halo) and you will gain additional improvement.




    You will have to consider additional filtering on each of these antennas to provide duplex operation. But you will save on site rentals, back haul RF Links or microwave etc.

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    Doug Hall used to make the 4RV/2 voting comparator. They worked very reliably for analog once the levels and pre/de-emphasis was setup correctly. I have several sites that have been in service for more than 15 years. eBay may be your only source now.
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    Quote Originally Posted by RFI-EMI-GUY View Post
    Use antenna diversity to improve talk back from the portables. Two or more antennas mounted with a few wavelength vertical separation on the tower will provide about a 5 dB improvement. If you have the means, three receive antennas, in horizontal plane, in a triangular pattern will yield a lot of diversity gain perhaps 9 dB. Go with four and have the fourth antenna horizontally polarized (UHF halo) and you will gain additional improvement.
    That's what Motorola Eng did for the iDEN sites - three moderate gain collinears in the same plane in a triangular pattern.
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    Quote Originally Posted by rescue161 View Post
    I want to set up an analog voting system for a local ham repeater that has poor inbound coverage. Outbound is fine and I have access to a couple of sites for remote receivers. I'd like to keep this project as cheap as possible and want it to remain invisible to the end-users. My plan is to locate the comparator at the repeater site and use RF links to get back to the comparator from the remote receivers. I have seen GE and Motorola on Ebay. Is one better than the other? Is one less prone to need alignment all the time? Specifically, I was looking at the Spectra TAC. I have some contacts on the Harris side of the house, but I don't know what to ask for if the Harris is a better product. What do you guys recommend?
    You want the product requiring the least alignment, and cheap as possible, but you also want to use older equipment with dried out caps, card pin contacts known to go flaky, and uses discrete logic with RC time constants to accomplish the job. Over RF links.

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    SNV-12 is the way to go and they can be had used for reasonable prices if you keep your eye out. The Spectra-TAC's are getting too old, but they are cheap if you don't mind working on them regularly. Stay away from Digi-TAC's.

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    Quote Originally Posted by Magnus View Post
    SNV-12 is the way to go and they can be had used for reasonable prices if you keep your eye out. The Spectra-TAC's are getting too old, but they are cheap if you don't mind working on them regularly. Stay away from Digi-TAC's.
    Magnus, what is your opinion on Digi Tac as a direct replacement for Spectra Tac in an all Motorola environment? What weaknesses?

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    Quote Originally Posted by com501 View Post
    Doug Hall used to make the 4RV/2 voting comparator. They worked very reliably for analog once the levels and pre/de-emphasis was setup correctly. I have several sites that have been in service for more than 15 years. eBay may be your only source now.
    LDG sold an inexpensive product, the RVS-8 which, though no longer available was an 8 channel analog/microprocessor controlled voter meant for the ham market. It has some nice features. But it has unbalanced inputs and is a bit cheaply finished, and might pose some integration issues.

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    Quote Originally Posted by RFI-EMI-GUY View Post
    Magnus, what is your opinion on Digi Tac as a direct replacement for Spectra Tac in an all Motorola environment? What weaknesses?

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    I think it's over engineered and over complicated. Unless you have specific need of one of its features I would steer clear of them. Unless your using Securenet or analog trunking I don't see any reason to replace a Spectra TAC with one.

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    Quote Originally Posted by Magnus View Post
    I think it's over engineered and over complicated. Unless you have specific need of one of its features I would steer clear of them. Unless your using Securenet or analog trunking I don't see any reason to replace a Spectra TAC with one.

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    It is definitely not very suitable for integration with RF links or non Motorola receivers.

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    Quote Originally Posted by Magnus View Post
    I think it's over engineered and over complicated. Unless you have specific need of one of its features I would steer clear of them. Unless your using Securenet or analog trunking I don't see any reason to replace a Spectra TAC with one.
    Let's say a fully-loaded DigiTAC crosses my path at a reasonable enough price that I'm willing to buy it just to screw around with it... what all goes into the configuration of one of those? Is unobtainum RSS involved or is it all done with DIP switches and analog pots?

    Status tone and keying delay caveats would not be an issue as the interfaced stations would most likely be MSF5000 repeaters (I've been hacking away at MSFs for 10+ years so "over-engineered" doesn't scare me) and backhaul would be via analog E&M cards in Cisco routers.
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    Quote Originally Posted by motorola_otaku View Post
    Let's say a fully-loaded DigiTAC crosses my path at a reasonable enough price that I'm willing to buy it just to screw around with it... what all goes into the configuration of one of those? Is unobtainum RSS involved or is it all done with DIP switches and analog pots?

    Status tone and keying delay caveats would not be an issue as the interfaced stations would most likely be MSF5000 repeaters (I've been hacking away at MSFs for 10+ years so "over-engineered" doesn't scare me) and backhaul would be via analog E&M cards in Cisco routers.
    You just need Hyperterm or equivalent serial terminal to talk to it. Chances are no changes will have to be made if it's been in service set up by someone competent. It has two Amphenol 25pr connectors on the back for audio pairs and I/O. So, all your work is done on 66 blocks. Pretty straight forward product. I put in dozens of them in the 90's and then took them out as people migrated to P25 I&II with zero failures over their service life. They went in once, did their job, and never caused any problems. Console integration was easy too. You could even put elements on the desktop to monitor voter activity, and enable/disable sites if links / phone lines dropped out, or a site channel got clobbered.
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    Quote Originally Posted by motorola_otaku View Post
    Let's say a fully-loaded DigiTAC crosses my path at a reasonable enough price that I'm willing to buy it just to screw around with it... what all goes into the configuration of one of those? Is unobtainum RSS involved or is it all done with DIP switches and analog pots?

    Status tone and keying delay caveats would not be an issue as the interfaced stations would most likely be MSF5000 repeaters (I've been hacking away at MSFs for 10+ years so "over-engineered" doesn't scare me) and backhaul would be via analog E&M cards in Cisco routers.
    Coincidentally, I have one arriving tomorrow. They can be had for $200 shipped on e bay. Prices will probably come down further as sellers find a weak market. The value to me is the SECURENET capability. I will be using a JPS SNV-4 DSP for the analog. Most of the settings are via hyper terminal. There are some jumpers and switches that probably can stay at factory default. I have a lot of work ahead...

    Not sure they would support E&M from the receivers instead of pilot tone. If there were a way, it would be good to know. You can get logic outputs to key a transmitter in clear or coded mode. But as far as I/Os to replace pilot tone, I don't see it. You would have to hack the input boards and then the AGC would have to be spoofed in order to get a S/N ratio. I am sure someone has done it, but I haven't seen any documentation to that effect.

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    Quote Originally Posted by RFI-EMI-GUY View Post
    Not sure they would support E&M from the receivers instead of pilot tone...
    E&M is just the transport... the Ciscos are just providing a 4-wire analog audio pipe via IP. When the latency is reasonable the audio quality is broadcast quality excellent.
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    Quote Originally Posted by motorola_otaku View Post
    E&M is just the transport... the Ciscos are just providing a 4-wire analog audio pipe via IP. When the latency is reasonable the audio quality is broadcast quality excellent.

    I'll second motorola_otaku's comment. I have an AstroTac system deployed here, in mixed mode, with Cisco's sending the audio back and forth. On Analog, once I got the audio balanced out between all sites, the audio sounds broadcast quality to my ears.
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