Repeater Hang Time Problem

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Spatch713
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Repeater Hang Time Problem

Post by Spatch713 »

We currently have a VHF MSR2000 two site voted repeater in operation. There is one receiver at the other end of town and naturally one at the repeater site. We use phone lines for communication between the two sites. The comparator is located at the repeater site as well which I dont agree with but thats the way it is.

Here's the deal. Recently the repeaters hang time has more than doubled in length (to almost a 1500 ms) and no one knows why. No work/programming has been done to the equipment recently does anyone have an idea what is causing this?
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Dan562
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What radios do you own?: Kenwood, Yaesu, ICOM, Motorola

Post by Dan562 »

You haven't stated whether the MSR2000 has DC or Tone Remote Keying. The MSR2000 has a Delayed Drop Out Circuit on the Squelch Gate Module and the T1786B Spectra-Tac Comparator has a Delayed Drop Out Circuit on the TRN6093 Command Module which either one of the two modules's components could have changed electrical values over time, increasing the Drop Out Time. The problem could also be caused by the Remote Keying function, that's why I want to know which type is being used.

Dan
Will
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Post by Will »

The capacitor used in the drop-out timing circuit is known to leak in the MSR2000/Micor/Msy repeaters. This will increase the d-o delay and may even keep the repeater keyed. Use a tanatalum cap there.

The delay on the squelch gate in the repeater is only active when that card "wins", otherwise the external TX PTT disables the squelch gate. There are some notes in the manual on this on the squelch gate card page.

Also set each PL decoder to OR mute so any noise in the PL range does not keep the PL Decode active. Verry common in the Spectratac receiver configuration, PL forces the receiver "open".
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Spatch713
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Excellent!

Post by Spatch713 »

Ok, I will check that out when I get up to the site next time. We are using tone remote keying. It bothers me if its the cap because the last thing we need is a repeater staying keyed.
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bernie
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Post by bernie »

My two bits worth:

The Guard tone Decoder card has a circuit that causes the station to de key when the LLGT drops.

If this circuit has failed the transmitter will remain keyed until the reed stops on its own accord.

Same thing as the long squelch burst on Motorola equipment when the "Reverse Burst" is absent.

If the Spectra-Tac chassis is not co located with the station there could be a possibility that there is some cross talk on the 'phone line that happens to be 2175. Perhaps a status tone, or a "SF" tone used by telco or some other user.

Parts do fail after 25 years or so.
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Spatch713
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Post by Spatch713 »

Speaking of reverse burst I have noticed a slightly longer repeater/transmitter dekey when the cops are on their mobiles (midlands) prior to this situation happening. I cant stand that rush of static...

I will take a look into your points as well.

Thank you guys for the assistance.
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bernie
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Post by bernie »

My two bits worth:
I used to tell customers that added "off brand" units to their fleet that that was the radios way of saying "Cheap". What else did they leave out.

That was when I was customer Service Engineer for Area KW.

You could modify the system to "And " squelch.
In youur application it might even work better because you have a voting system.
Voting selectors do not like to vote between "Bad & Lousy"
Good, & great works well.

The squelch is set at at least 20DBQ.
The problem with "or Squelch" is that any time the PL is present the squelch is open.
The decoder has an inherent delay due to the decay of the reed vibration, or fade delay built into solid state decoders.

The "Reverse Burst"stops the oscillation of the reed, closing the squelch.

Both the station and the sattellite receiver need to be modified, just a jumper change.

I will look up the exact procedure if you want to modify the system.
Aloha, Bernie
Will
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Post by Will »

If I still remember, the OR mod for the RX squelch involved a couple of value changes and a transistor was removed. This was done to all the MSR2000's arround here. Most are still running just fine, even with non Motorola radios in the system.. No squelch crashes out here!!!!
Dan562
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What radios do you own?: Kenwood, Yaesu, ICOM, Motorola

Post by Dan562 »

Another thing to consider with using /\/\ equipment versus every other brand name in 2-way radio. /\/\ uses 120 mS for PL Reverse Burst and ALL other 2-way manufactures use 180 mS. Don't be surprised to hear 60mS of Reverse Burst Noise getting through the radio repeater system when the Public Safety Personnel are using Midlands versus /\/\ products.
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xmo
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Post by xmo »

I believe if you do a little research, you will find that the 120 vs. 180 reverse burst issue actually pertains to the number of degrees of phase shift rather than the duration of the burst.

Motorola uses a 120 degree phase shift whereas other manufacturers use 180, although some of the programmable Motorola radios offer a per mode choice.
Will
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Post by Will »

And to add to the confusion.... Motorola uses 240 degree phase shift for 150 to 180 MILI SECONDS, depending the Motorola model/series.

The differences are not usally "fixable", we just make the repeater receiver ignore the off brand radio's so-called reverse burst..... attempt...

That is called OR Muting in the repeater and voting receivers. It is even in the service manuals for the MSR, SpectraTac, Micor, Mitrek, ect radios.....


"We have no stinkin squelch crashess" out here!


Note: The fact is that PL is pattened by Motorola and the other mfgrs could not copy the "reverse burst".
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