Kevin Custer wrote:  I'm looking for someone that has modified the Spectra-TAC comparator for use outside the Motorola environment that has done away with the need of continuous links and a status tone, i.e.: modified it for COS input.  I need some opinions from folks that may be using the (newer) Motorola Spectra-TAC Comparator as a stand-alone voter, using RF links that don't transmit all the time.  I have some theories on what to do, but I thought I would see what others have done.

Some dialog followed and this is the best of the gleaned parts...
 

Kevin wrote:  What didn't you like about running the Spactra-TAC voter without the tone generators on the originating end?

Skipp  wrote:   I've done it... you really need to make and install the status tone generators. It was just a lot easier to use the tone generator adapters.  Plus we were using a combination of original method operation and local-distant located receivers with the adapters. (It was a mixed system).  The adapters were pretty easy to build once you had the information.

Someone wrote:   Kevin,  Now that I understand what you are trying to do, be advised that just because you have the link RXs co-located with the comparator your remote site Link transmitters do not have to transmit all the time.

Kevin wrote:   What keeps the Comparator from failing, then?

Skipp  wrote:  What I call the local adapter method is just a local COS/COR operated status tone generator.  The adapters were made to use non-Motorola receivers into the voting system, but you can easily locate the adapter at the voter end and just trigger it with the link rx COS/COR.
Call the status tone a non signal present idle tone that is removed with an active signal.  It's used to detect the link status/quality and set the SQM AGC action for best S-N Voting.

Here is a PDF of an aftermarket (CSC) Spectra-TAC Status Tone Encoder.

Skipp  wrote:   Also know that Motorola came out with a modification to the Spectra-Tac Current Generator Module, which improves the vote performance quite a bit.  I also have that paper-work if you burn to have it.

Kevin wrote:   Yes, please..  It may be the same mod that Dan talked about  (SRN-1068), but it would be interesting to see if they are the same mod.

Skipp wrote:  The update was related to running lots of SQM (Signal Quality Module) units and the current generator becoming unstable. The fix was the addition of a small daughter board, with an updated current generator.  If you're only running a few modules in one shelf, you probably won't notice the problem.  If you're running more than one voter shelf, you should think about the mod if the programmed type of operation has hunting problems.

Here is a PDF of the Motorola Voter Update document talked about.

Then comes John Sichert's reply:

Kevin Custer, at 08:54 AM 1/20/06, wrote:

John,
Jeff DePolo said you might have some information I am looking for...

I'm looking for someone that has modified the Spectra-TAC comparator for use outside the Motorola environment that has done away with the need of continuous links and a status tone, i.e.: modified it for COS input.  I need some opinions from folks that may be using the (newer) Motorola Spectra-TAC Comparator as a stand-alone voter, using RF links that don't transmit all the time.  I have some theories on what to do, but I thought I would see what others have done.

Thanks for any assistance you can provide...

----------------------------------------------

John Sichert KA3LAO wrote:

I was going to post this sometime back, but someone made me mad when I tried to help him.
He basically wanted the same information. When I told him what to do, he said, I don't want to modify it, it was too much trouble.
At least, that was the drift I got.
So, I crawled back in my shell.

Remove the AGC shunt diodes.
Where one of the diodes were, add a 330 ohm resistor.
Remove the tone detector toroid.  From the center terminal of the coil, add a 10k resistor to the spare pin on the edge connector.
I am doing this from memory, I believe it is pin 9. Whatever, there is only one pin that is unused.
That is the COR input, active high. Ground it, the module goes idle; open the connection, the module shows an unsquelched indication.
To set levels, put 1000 Hz at 5 kc in the remote receiver. The level across the 600 ohm terminals should be -14 dBm.
The comparator is very sensitive to distortion and audio response. I kept the response between links, +/- 2db from 50-4000.

This is what I found worked best:
No hang time at the remote site.
The remote site TX must be true FM, that means mod the TA-451 with a MV-1604 diode and associated resistors & caps.
That thing will be flat as a pancake. I like to decode PL at the link RX. Even though I have done it since 1984, I have been told, it cannot be done.
Add the cap across the short tail cap in the remote Micor RX, to prevent unwanted squelch closing. It is not usually needed on the UHF link RX.
The voter is designed for de-emphasized audio. I have never tried one flat.
Just in case you are using Spectra-Tac RXs, replace the 25k pots on the Audio Control Module if they are on a White substrate, they drift in value.

To check the amplifier string in the SQM.
Put a 3000 Hz tone into all the SQMs, (parallel the 600 ohm inputs). Use a low level to start with, monitor the Signal Quality line of each module.
Bring up the level, verify the modules all track with one another to about 11 volts. If a module does not make it to 11 volts, it is defective.
Good luck finding the trouble, lots of  "thick film hybrids".

Now the good news,
If you have it set up correctly, the users should never know it voted, or worse, what RX is voted.
The system using this setup has been operational since 1984.

I took me about 5 years of grief to find all this out.
It only took me 15 minutes to tell you.

Copyright KA3LAO 1980-2006

You have my permission to straighten this out and reprint it. (If you think it was worth anything)  Just give me credit.
I don't have time to tell you how poor it will work if you don't follow these guidelines. But I can tell you a few that have not listened.

John

SpectraTac Signal Quality Module Modification For COR Operation

This modification will permit SpectraTac comparators to be used in the conventional “status tone” type of operation but will also permit remote receivers to be linked in over RF paths using carrier operated relay detection instead of status tone. This mod will eliminate the need for link transmitters to be constantly keyed. Every effort was made to keep this modification simple and easy to reverse if so desired.

Steps one, two and three eliminate the status tone level controlled agc and replaces it with a fixed value. In normal operation using phone line linking the agc is required to keep the levels constant under varying phone line conditions. Using RF links are this is not normally necessary as the losses are constant.

Steps four and five isolate the status tone detector and allow it to become a simple dc switch controlled by the cor input.

Steps six and seven provide diode isolation of the detector and activity checker and route them out to an unused pin (21) on the edge connector to be used as the cor input (active low).

Below are the seven steps required for this modification. Please refer to both the schematic and board layouts to view the modified areas. Any input as to help make this a better modification is always welcome.

Steps:

1—Remove C9 and replace with a 22K ohm resistor.

2—Jumper U4a pins 1 and 2.

3—Remove or cut Q2 collector lead.

4—Remove CR6.

5—Remove R66.

6—Add a 1N914 or similar diode from the base of Q6 to edge connector pin 21.

7—Add a 1N914 or similar diode from U3 pin 8 to edge connector pin 21.
 

*Note---Check your board for a female connector on pin 21. This will be the new COR input. Some boards do not have the female pin on unused terminals, if this is the case remove a pin from an old module and install at position 21.

Copyright 2007   Glenn Hochwalt  W8AK        w8ak  at  arrl.net

By the way, the Spectra-TAC Total Area Coverage Comparator Reference Manual, 6881039E50 is still available from Motorola, brand new, for $12.25 as of February 2007. The manual has revisions through 12/31/03 and is revision A.

HTML © Copyright and last updated February 23, 2007, Kevin K Custer   W3KKC
Text, concept, images, etc., Copyright John Sichert, Jeff DePolo, Skipp May, Dan Babilla, Glenn Hochwalt, and Kevin Custer, January 2007.
All Rights Reserved!