Gold Elite BIM Card Levels
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Gold Elite BIM Card Levels
Greetings, some co-workers and I were having a discussion over setting levels on the TX pots of the Gold Elite era BIM cards. We're trying to determine if the test tone levels achieved by pressing the reset button on the card produces an average voice test tone or if it basically sets a limiter for peak level. A look through the manual wasn't really clear on this. Does anyone know if you set the TX pot to produce a -10 dB test tone if you have room to reach 0 dB peak or is what you set here the maximum limit?
Re: Gold Elite BIM Card Levels
It is not a peak limiter. A perfect example is the paging tones generated from the BIM. With the pot set to -10dB, generated paging tone levels will range from approximately -1dB to -8dB.
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kb4mdz
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Re: Gold Elite BIM Card Levels
From Centracom Manual 68P81074E58; pp 2-3:
"3.3 transmit Audio Level Set (refer to figures 1)
Step 1. Select a channel for level setting
Step 2. Connecta na ac voltmeter to the selected channel terminals at the punch block.
Step 3. Briefly press and release the reset switch on the base interface module (BIM). This starts the generation of the following tones at high guard tone level; 5 seconds of 1000 Hz, 3 seconds of 300 Hz, and 3 seconds of 3000 Hz,. The green LED is lit for the duration of these tones.
Note: Depressing the reset button too long results in an error message on the printer. This error clears itself when the reset switch is released.
Step 4. Set the transmit level adjust potentiometer (R113) to the level required by the customer. The level was set at the factory for 0dBm. The tones are transmitted at the same level as average voice, so they can be used to set the transmit level of the BIM. This level should not be set above 0dBm. To repeat the tone generation, momentarily depress the reset switch.
Note: Both low frequency paging tones and peak voice levels can be as great as +10 dB above average audio level. If the transmit level is set too high, the output of the line driver clips and distorts the transmit audio.
Step 5. Repeat steps 3 and 4 at the base station. The three tones generated at the BIM cover the usable audio spectrum and can be used to check the frequency response of the telephone line connecting the BIM and Base Station. The level of 1000 Hz tone received at the base station should be used to set its deviation to approximately 3 kHz. {note: yes, this was written before narrowbanding! Adjust to 1.5 KHz accordingly!}. This insures that peak voice levels are transmitted at the full 5 kHz. {2.5 kHz for narrowbanded} deviation without hitting the limiter too hard. The 1000 Hz tone is used because most of the voice energy is in a band around this frequency and phone lines are usually designed to pass band with higher amplitude. "
Disquoth.
There is a nice diagram of frequency response of Relative Transmit Tones with 0 dBm Test Tone, but I don't know how to post it here. Basically, it shows one level for Alert Tones, and Test Tones at 0 dBm, from 300 Hz to 1KHz, to 3000 Hz. Function Tone is at -4 dBm, and the area in between those two levels is shaded and called "Average Voice"; High Guard Tone is at +6 dBm. Paging Tones are de-emphasised, with 1000 Hz tone crossing the 0 dBm line, and at 300 Hz paging tone about +9 dBm, and 3000 Hz paging tones are down about -9 dBm.
Yes, it's really deeply buried in old manuals. But it's critical if you want your radio system to work properly. I helped one boss spend just one day going around to all base stations, and resetting levels so that when he pressed reset it gave the 0 dBm test tone (or maybe he adjusted it to -10 dBm, can't quite remember) and then I adjusted each transmitter for proper deviation. This cleaned up voice, paging tones and we got a "This is the best this radio system ever sounded!"
"3.3 transmit Audio Level Set (refer to figures 1)
Step 1. Select a channel for level setting
Step 2. Connecta na ac voltmeter to the selected channel terminals at the punch block.
Step 3. Briefly press and release the reset switch on the base interface module (BIM). This starts the generation of the following tones at high guard tone level; 5 seconds of 1000 Hz, 3 seconds of 300 Hz, and 3 seconds of 3000 Hz,. The green LED is lit for the duration of these tones.
Note: Depressing the reset button too long results in an error message on the printer. This error clears itself when the reset switch is released.
Step 4. Set the transmit level adjust potentiometer (R113) to the level required by the customer. The level was set at the factory for 0dBm. The tones are transmitted at the same level as average voice, so they can be used to set the transmit level of the BIM. This level should not be set above 0dBm. To repeat the tone generation, momentarily depress the reset switch.
Note: Both low frequency paging tones and peak voice levels can be as great as +10 dB above average audio level. If the transmit level is set too high, the output of the line driver clips and distorts the transmit audio.
Step 5. Repeat steps 3 and 4 at the base station. The three tones generated at the BIM cover the usable audio spectrum and can be used to check the frequency response of the telephone line connecting the BIM and Base Station. The level of 1000 Hz tone received at the base station should be used to set its deviation to approximately 3 kHz. {note: yes, this was written before narrowbanding! Adjust to 1.5 KHz accordingly!}. This insures that peak voice levels are transmitted at the full 5 kHz. {2.5 kHz for narrowbanded} deviation without hitting the limiter too hard. The 1000 Hz tone is used because most of the voice energy is in a band around this frequency and phone lines are usually designed to pass band with higher amplitude. "
Disquoth.
There is a nice diagram of frequency response of Relative Transmit Tones with 0 dBm Test Tone, but I don't know how to post it here. Basically, it shows one level for Alert Tones, and Test Tones at 0 dBm, from 300 Hz to 1KHz, to 3000 Hz. Function Tone is at -4 dBm, and the area in between those two levels is shaded and called "Average Voice"; High Guard Tone is at +6 dBm. Paging Tones are de-emphasised, with 1000 Hz tone crossing the 0 dBm line, and at 300 Hz paging tone about +9 dBm, and 3000 Hz paging tones are down about -9 dBm.
Yes, it's really deeply buried in old manuals. But it's critical if you want your radio system to work properly. I helped one boss spend just one day going around to all base stations, and resetting levels so that when he pressed reset it gave the 0 dBm test tone (or maybe he adjusted it to -10 dBm, can't quite remember) and then I adjusted each transmitter for proper deviation. This cleaned up voice, paging tones and we got a "This is the best this radio system ever sounded!"
Re: Gold Elite BIM Card Levels
One comment that I would include here is that this adjustment pot does get dirty with time. I normally rock it back and forth with the effort on a number of back and forth movements. The pot is also a course adjustment, so if you breath wrong, the setting will move on you.
If this is a tone controlled circuit, which these days probably is, you can cheat and use just the the console and just keying it with no audio. Set the low level guard tone to about a -27 to a -30. This should work out just fine for most set ups. Check the tone audio deviation out of the transmitter to proof your adjustment. once you find the correct setting point, you shouldn't have to measure the transmitter the next time. Record the setting level and leave a note as to what level it needs to be at.
This becomes a fast, easy way of setting the output pot adjustment without driving everyone crazy having to listen to the tones going over the air. All the users out in the field hear it a dead carrier.
Jim
If this is a tone controlled circuit, which these days probably is, you can cheat and use just the the console and just keying it with no audio. Set the low level guard tone to about a -27 to a -30. This should work out just fine for most set ups. Check the tone audio deviation out of the transmitter to proof your adjustment. once you find the correct setting point, you shouldn't have to measure the transmitter the next time. Record the setting level and leave a note as to what level it needs to be at.
This becomes a fast, easy way of setting the output pot adjustment without driving everyone crazy having to listen to the tones going over the air. All the users out in the field hear it a dead carrier.
Jim