Batboard

In our wireless group we are developing some standards for tone levels. We don't follow the rest of the world when it comes to tone levels. Our current infrastructure is old analog microwave. TT is 0dBm in and out. My question has to do with Motorola standards on adusting base stations. At what line input level does Motorola recomend to use to deviate a transmitter and what is the deviation set to? Also at what deviation do you input to a reciever for the correct line ouput? Any help would be appreciated.

There was an extended discussion of this exact subject some time ago here on this Board; do a search for it and you'll find it easily.

Best I can recall the gist of the posts was that, while there may be some set standards, in practice no one really follows them .

One common standard calls for 2/3 system deviation to correspond to -10 dbm on the wireline. Receiver status tone for voters is usually -13 dbm.

Wow... analog mw. How fun for you!

Tom in D.C. wrote:There was an extended discussion of this exact subject some time ago here on this Board; do a search for it and you'll find it easily.

Best I can recall the gist of the posts was that, while there may be some set standards, in practice no one really follows them .

Here's the thread:

http://batboard.batlabs.com/viewtopic.p ... guard+tone

My two bits worth:

It seems you wish to make a "Block & Level" diagram for your system.
From a functional view point you want the signal that is transmitted from one of your stations to re produce the received signal from one of your subscriber units. (Buzz word for a radio)

To accomplish this you must pay very strict attention to the operating parameters of the various system elements.

Consider the analog microwave.
Depending on the base band loading the per channel level setting can become very critical. If all channels are active "hot levels" can cause the entire base band to be over driven causing cross talk, distortion, as well as other problems.

As I recall Starplex, as well as many other channel modems use Telco standards of -17 TX, +7 RX., the attenuators on the term card set the line levels to the base station (or what ever).

You must use a selective level meter to set the base band levels. (By the way, I have a new, as in never used Cushman CE 24 A Selective Level meter for sale very CHEAP)

The Base station (or whatever) line input is set to match the output of the Multiplex, or what ever your connectivity specs.
(Telco, Channel bank, voting comparator, etc.)

The line out of the base is normally set with 1kc tone at 2/3 system deviation, 3kc for us old timers.
The line out level is set to satisfy the input of what ever it is connected to. (Trunking systems are -10DBM, wire line stations are commonly set to 0 DBM input and output. )

Motorola SpectraTac voting comparators use a "Status Tone" @-13DBM0 (13 DB below test tone)
The "A" version SpectraTac used Status Tone @ Test tone level. This caused overloading of analog base band in analog microwave systems so "B" and later use the -13DBM status tone level.
The output of the comparator card level is set by the status tone, a sample & hold circuit sets the input attenuator.

There may be other modules such as line amplifiers that also must be considered.

I have been called on to trouble shoot systems that were never properly designed in the first place, or where some genius decided to fix a particular problem in the system by mis adjusting a level that seems to fix the problem at hand, but created many problems for other parts of the system.

In conclusion, the audio levels in any given part of the system are arbitrary. The important thing is that all of the various components in the audio path operate within their parameters to avoid distortion.

Motorola systems generally have a 3db audio boost to improve the signal to noise figure. 2 kc in, 3 kc out.
The modulator input voltage calculation for Motorola transmitters take this into consideration.
See a MICOR or MOTRAC manual for details

Very well put Bernie.

Now if only we could get the radio shops around the country to follow these steps. It seems with the
outcropping of new radios, the average field technician doing the work has never been mentored in
how to do this or how important it is to do this.

With what I have seen over the last few months, I could almost say your lucky the average field
tech even knows how to use a digital voltmeter.

Jim

bernie wrote:My two bits worth:

It seems you wish to make a "Block & Level" diagram for your system.
From a functional view point you want the signal that is transmitted from one of your stations to re produce the received signal from one of your subscriber units. (Buzz word for a radio)

To accomplish this you must pay very strict attention to the operating parameters of the various system elements.

Consider the analog microwave.
Depending on the base band loading the per channel level setting can become very critical. If all channels are active "hot levels" can cause the entire base band to be over driven causing cross talk, distortion, as well as other problems.

As I recall Starplex, as well as many other channel modems use Telco standards of -17 TX, +7 RX., the attenuators on the term card set the line levels to the base station (or what ever).

You must use a selective level meter to set the base band levels. (By the way, I have a new, as in never used Cushman CE 24 A Selective Level meter for sale very CHEAP)

The Base station (or whatever) line input is set to match the output of the Multiplex, or what ever your connectivity specs.
(Telco, Channel bank, voting comparator, etc.)

The line out of the base is normally set with 1kc tone at 2/3 system deviation, 3kc for us old timers.
The line out level is set to satisfy the input of what ever it is connected to. (Trunking systems are -10DBM, wire line stations are commonly set to 0 DBM input and output. )

Motorola SpectraTac voting comparators use a "Status Tone" @-13DBM0 (13 DB below test tone)
The "A" version SpectraTac used Status Tone @ Test tone level. This caused overloading of analog base band in analog microwave systems so "B" and later use the -13DBM status tone level.
The output of the comparator card level is set by the status tone, a sample & hold circuit sets the input attenuator.

There may be other modules such as line amplifiers that also must be considered.

I have been called on to trouble shoot systems that were never properly designed in the first place, or where some genius decided to fix a particular problem in the system by mis adjusting a level that seems to fix the problem at hand, but created many problems for other parts of the system.

In conclusion, the audio levels in any given part of the system are arbitrary. The important thing is that all of the various components in the audio path operate within their parameters to avoid distortion.

Motorola systems generally have a 3db audio boost to improve the signal to noise figure. 2 kc in, 3 kc out.
The modulator input voltage calculation for Motorola transmitters take this into consideration.
See a MICOR or MOTRAC manual for details

OK, let me throw this out there: is automating the settings of baseband signaling something that you'd pay for?

In other words, should I throw this over to the marketing guys as a potential optional application for the 3920?