Do any Motorola services sound choppy?

[dwebb210]

I work for a company that has a 9 UHF frequencies on three licenses.
A Motorola XPR-5550e is in the office next to mine.
It has six channels. Four are Digital DMR. One is analog.
The sixth is a mystery.

The frequency of the sixth channel is on the same license as two of the DMR services.

I assumed it would be DMR, but there is something different about it.

I have a Uniden BCD396xt and a TYT MD-380 on my desk.

When I listen to the analog signal of the sixth channel, it is choppy.
It acts like full signal strength, then zero signal, then full signal.
Maybe 15 cycles per second. Give or take a bunch.
But it is consistent.

It doesn't sound anything like the analog signal of the other DMR channels.

I thought maybe it was reflection interference.
I took the scanner for a drive.
It sounded the same for more than a mile away.
And sounded the same until there was no signal to hear.

I changed the base radio to Channel 6 and keyed the mic.
My radios heard the same choppy signal.

The other channels all sound normal from the base radio.

Any thoughts?

FYI, the reason for the MD-380 (set to RX ONLY) is because
my position is partially responsible for one area of production
that gets a lot of radio traffic, but they consider my position
low priority and not worthy of my own radio. Listening to what
is going on in that department gives me insight to production
issues. Nobody cares about me listening.

And before I'm asked, the reason I'm not going to our electricians
and asking about the "mystery channel", management of that department
is very protective of "his" stuff. His first response would be
"who wants to know, and why". At this point, it is just curiosity.
The mystery channel should be the lowest importance of all of them,
but it is just weird it is the most problematic.

I thought a quick Google of "choppy radio service"
would point me in the right direction. But no.

 

[com501]

The channel you are trying to hear is set for 2-slot simplex. A Moto radio could decode this if you knew how it was setup. Your scanner and MD-380 cannot.

 

[Ubbe]

Set your MD380 to simplex by entering the RX frequency also as TX and it will change mode to simplex.
Make two channels the same with different slots. I assume you know the CC and TG being used on channel 6.

/Ubbe

 

[dwebb210]

I thought I had already tried all possible combinations with the MD-380, but to make sure I set two channels identical except for the two time slots. Both simplex. Still no audio when keying the mic on the base radio.

EDIT BEFORE SENDING: I thought I had decoded the color code. When set up as a duplex frequency, the color code decoded to ZERO. But now when I try decoding the color code in simplex, the decoder is all over the place. No big deal. I'll just sit here and try each code.

I'm not doubting that the MD-380 can't decode this.

But I'm curious now, why would the analog audio of 2-slot simplex sound different than the analog audio of a 2-slot repeater output?

Also, as far as receiving on the MD-380, why would it care if it was set to simplex or not when receiving a signal?

Finally, not that it really means anything, just an interesting note that the frequencies on the license have offset frequencies, as though they intended to have a repeater associated with them, including this one. But when I key the mic of the base radio, there is obviously no repeater. Is it possible this particular base is simplex on that time slot, but a different base radio has a repeater on the other slot? There is another base radio somewhere. Probably in the electrician's office.

 

[dwebb210]

Ubbe was correct.

Simplex DMR, slot 2, CC:15. I get audio now.

Now I need to investigate why there appears to be a repeater input frequency.

Thanks!

 

[dwebb210]

Another update.

There is audio on both slots with the same color code and talk group.
I can't change channels between the slots and tell if it is the same conversation. At least not yet.
The nature of the radio traffic doesn't support that. It is often just one word statements, and it could be from any of a dozen people.
I'm sure I'll figure it out given enough monitoring.

Anyway, thanks for the response.

 

[Ubbe]

A DMR radio has two modes, one infrastructure and one simplex.
The only way to switch between them are to set the TX frequency exactly the same as the RX to select simplex mode.
Any other frequency combination sets infrastructure mode to the received digital protocol.

/Ubbe