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Voting Brush Up - Primer

Posted: Sun Feb 15, 2009 9:26 am
Please excuse me, I am going to ask some question and brush up on a topic that my skills were not so sharp on to begin with.

I am helping fix up a mess of a voting system. It is a analog UHF repeater system with a quantar as the repeater. Currently it has one remote RX site with a spectra tac interfaced to it. The remote RX site is a series of UHF mobiles that get it back to the spectra tac. It works, but not well.

I am re doing this system to include three remote sites. I will be getting the signals back to the repeater via VHF links. I have at my disposal three new astro tac rx's and possibly and astro tac comparator. Assume that we are still going to use the spectra tac comparator.

1) At the rx site I am thinking about intefacing the astro tac rx's to a VHF CDM tuned down in power (maybe about 1 watt is all that is needed). I would assume that the audio +/- out of J10 of the astro tac rx'r would go into the rear 16 pin of the CDM mic input and ground. I would tie PTT to ground so the radio is always in TX.

2) At the repeater site I would have a V mobile rx'r with the audio out intefaced into the spectra tac.

3) Do I need to use the guard tone 2175, or can it be that when the astrotac recieves a signal it toggles PTT on the rx site mobile, and at the repeater site I can use COR on the mobile to go into the spectra tac?

Advantages and disadvantages?

4) Throw the astro tac comparator in the mix. Pros/cons. This will only be a convetional analog system. Is interfacing the astro tac to the quantar easy?

5) Is it easy to interface the mobile rx radio into the astro tac comparator?

6) I want to make a provision for in cabinet fall back repeat. I know this has been discussed before. Can some one re eloborate on this a bit.

7) Before any one asks, I have the astro tac RX'r and Comparator manuals on order, and I am diggin up the old spectra tac comparator manual. I am just trying to get some other insight. And yes, I plan on reading the manuals.

Thanks, Rob

Re: Voting Brush Up - Primer

Posted: Sun Feb 15, 2009 10:15 am
by The Pager Geek
My suggestion is to read the manuals first, then ask the questions. Most of your questions will be answered in there.

For example:
- Using the RF links you specify prevents you from using the Astrotac comparator. Not only will it not pass signals from the Astro Modem or V.24, but it will not take an analog input from the mobile radio.

- Using the RF links you named, the best way is to have a crossband repeater type setup at the remote receive sites. Astrotac Rx causes a transmit to the Tx CDM. (Read: it's not transmitting all the time.) At the comparator, you would have the RX CDM with a pilot tone generator (JPS PTG-10) that would drop tone on Rx activation. Feed that into the Analog comparator. Either Spectratac or Digitac.

- As for fallback, it's easy since you are only doing analog. Just enable it per the Quantar Programming manual.

Good luck....

Re: Voting Brush Up - Primer

Posted: Sun Feb 15, 2009 11:19 am
by xmo
The Motorola Spectra-TAC system is not designed to work the way you propose do this. It is designed for full time status tone from the remote receivers to the comparator such as with dedicated phone line links or microwave paths.

You can make it work with keyed RF links. The hammies often do it this way because they usually don't have the money for leased lines and continuously keyed RF links are not a good fit for FCC part 97. It will be a PIA to configure and level set - and you must be very careful with your design. One big problem with locally injecting a status tone replacement at the comparator site is that it is very hard to replicate the almost immediate transfer from signal to status tone that takes place at a true Spectra-TAC remote receiver.

If you inject the status tone locally, you have to switch it based on COR. Assuming your links are PL protected, you will have delays in the process. When the remote receiver looses the signal it will de-key the link, however, the status tone won't return at the comparator until the link TX reverse burst is partially complete.

During that delay the comparator will see a very quiet input and will switch to it, thus causing audio holes. This gets very annoying if a user is at threshold on one of your receivers causing it to open and close rapidly.

There are ways to deal with these issues - you should look on the repeater builder site for ideas. You might want to do away with status tone altogether. Either get a different comparator or modify the Spectra-TAC.

Re: Voting Brush Up - Primer

Posted: Sun Feb 15, 2009 12:57 pm
Ok, So I am a little lost.

The one RX site is currently rigged with a two mobiles that shoot to a cdm with pilot tone generator at the site. Needless to say it does not switch properly between the quantar rx and the remote site. I always thought that injecting 2175 at the shack was not a great way of doing things and would cause a delay, which is exactly what happens.

Some Questions

1) If I use a Astro Tac Rx'r and a CDM vhf radio at the remote site that is set to constantly transmit 2175 I would have no issues with the spectra tac voter?? We have the channels so it would not be an issues. Any pitfalls with this?

2) I have not worked much with the Astro Tac Comparator. If I understand TPG post, I can not interface a mobile radio, or line level audio into the unit? What is Moto currently solution for analog voting then.

3) As far as a voter, we have all brandnew equipment just hanging around, in addition to the spectra tac that is being used now. What else would I use a Doug Hall or JPS. They all basically work the same way with pilot tone, so what would be the advantage with changing out voters?


Re: Voting Brush Up - Primer

Posted: Sun Feb 15, 2009 6:09 pm
by nmfire10
The astrotac comparator is connected to the astrotac receivers by v.24 modems, essentially a serial data link that passes the received audio as data across the the phone lines or microwave or whatever. Clearly, that isn't going to work with RF link radios. So you need to use a voter that can take in plain old audio pairs.

I highly recommend the JPS SNV12 voter. You can use COR out of your link receivers rather than status tone. Or you could use links that always on send the status tone from the remote receiver over the air and vote the conventional way. The SNV12 will use that status tone to drive its AGC making up for fluctuating levels automatically. Its a very powerful machine.

Re: Voting Brush Up - Primer

Posted: Sun Feb 15, 2009 6:21 pm
by MassFD

I cannot comment on the voter setup but I do not think you can tie the PTT to ground on a CDM. It will not power up keyed.

You may be able to tie it to another accessory pin programed to go low after a programed power up delay

Re: Voting Brush Up - Primer

Posted: Sun Feb 15, 2009 6:21 pm
I have heard very good things about the JPS unit. I use their NXU units and love them.

So motorola makes no analog voter anymore. Do they still make the digitac or astro tac 3000. Did those do analog?

Thanks, Rob

Re: Voting Brush Up - Primer

Posted: Sun Feb 15, 2009 7:18 pm
by xmo
If you google "Motorola Digitac", the first two hits come back to product pages on Motorola's web site.

This tends to suggest that it is still a current product.

You said you have an Astro-TAC voter. If that is the original Astro-TAC and not an Astro-TAC 3000, it might do analog voting using status tone. Read it with your RSS and see what your choices are.

The Astro-TAC 3000 does analog voting without the 2175 status tone but requires the V.24 links for communication between the receivers and the voter [in addition to the audio path]

Re: Voting Brush Up - Primer

Posted: Mon Feb 16, 2009 5:28 am
Ok guys Thank you for the replys. I could always see if I can program in a delay or maybe program the P button to toggle PTT, so after power up just depress the P button and it would toggle PTT.

XMO, I will check out the voter ad see what they have. They told me it was an astro tac. I tis boxed up in storage at the fire house. So I will go on a treasure hunt. The only units I have are the astro tac rx units. I wil have to go and take a look.

Thanks, Rob