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Setting Audio Levels through a Repeater
White Paper
A Step-by-Step procedure
By Shorty, K6JSI
September, 2005 This White
Paper describes the proper audio alignment procedure for WIN System
repeaters and links, and may be useful to others who want good, clean
audio through their repeaters and links.
Assumptions:
4)
Verify the test gear you are using for accuracy.
Connect your Signal Generator output to your Service Monitor
input and generate a full-quieting (must not contain
any noise whatsoever, usually
1000 uv or more) on-frequency signal with a 1000 Hz audio tone at 3.0
kHz deviation from the Generator into the Monitor.
Be certain that both Instruments agree on the deviation level.
This is a critical step in measuring the performance of your
repeater/link audio through-put.
If there is a
discrepancy between the instruments, the priority is given to the
Monitor, to be certain the Monitor is reading 3.0 kHz deviation, and
adjust the output level of the Generator to make the Monitor display 3.0
kHz deviation, noting the adjustment level differential necessary to be
made in the Generator in order to achieve that 3.0 kHz reading on the
Monitor. Write it
down. You’ll need it later.
If you can do
the sweep test in 100 Hz steps it is best, however even 500 Hz steps
would at least give you an idea of your repeater system’s audio
flatness. If your Monitor
does not read a consistent 3.0 kHz during the audio sweep test, then
adjust your Generator where necessary to achieve the desired deviation
reading of 3.0 kHz on the Monitor at each frequency step between 300 and
3,000 Hz you are using, noting the adjustment necessary in the generator
to achieve the 3.0 kHz reading on the monitor at all steps.
Write them
down. You’ll need them
later. This assures
an accurate audio through-put test on the repeater/link under test. At a minimum,
perform the sweep test at the following steps:
Tone at 500 Hz
at Generator = 500 Hz
at the Monitor
Tone at 1000 Hz at Generator = 1000 Hz at the Monitor
Tone at 1500 Hz at Generator = 1500 Hz at the Monitor
Tone at 2000 Hz at Generator = 2000 Hz at the Monitor
Tone at 2500 Hz at Generator = 2500 Hz at the Monitor
Tone at 3000 Hz at Generator = 3000 Hz at the Monitor Receiver Set Up
1)
Make certain your Repeater RX
is on frequency. You
accomplish this by measuring the LO (Local Oscillator) frequency, which
should be labeled on the RX ICOM.
If it is not, take the operating frequency and deduct the IF
frequency from it (GE is 11.2 MHz), eg:
RX operating frequency is 448.900 MHz,
minus the IF frequency of
11.2 MHz = 437.700 MHz for the LO.
If it is a
High-Side injection crystal, you must
add the IF frequency to the
operating frequency to get the LO frequency, eg:
RX operating frequency is 448.900 MHz, plus the IF frequency of
11.2 MHz = 460.100 MHz for the LO. Net, or
adjust, the crystal to the proper LO frequency.
This sets your receiver operating frequency to the proper
frequency.
2)
Disable the CTCSS requirement
at your Repeater.
3)
Turn OFF the CTCSS (PL) on
your source radio or Signal Generator.
4)
When we ask you to inject a
full-quieting signal into the
Repeater RX, be certain there is
no noise on the signal.
That is what full-quieting means…
No Noise. Typically
this is 1,000 micro-volts (uv), or -47 dBm at a minimum.
5)
When we ask you to inject an
on-frequency signal into the
Repeater RX, be certain that it is the correct RX operating frequency.
That is what on-frequency means…
Transmitter Set Up
1)
First, we need to measure the amount of noise contributed by the
transmitter itself. Inject
a full-quieting, on-channel signal into the RX with your signal
generator. Then connect
your service monitor to the TX operating on the correct frequency.
Then turn off
the 1000 Hz tone generator so no tone is being sent into the RX.
Also be certain you are
not generating a CTCSS tone into the RX.
Then carefully measure the deviation of the TX.
If necessary, ground the Mic and the CTCSS input lines.
The TX always generates a small amount of noise that can be
measured, typically around 0.05 to 0.15 kHz of deviation, with no audio
present on the audio inputs (Mic and CTCSS).
This deviation must be added to all future measurements on the
TX. Write it down.
You’ll need it later.
Repeat this process for all transmitters connected to the
controller.
2)
Next, we need to be certain the TX is
not sending out a CTCSS tone,
by either de-soldering the YEL CTCSS wire to the exciter at Pin 2, or by
cutting it. If this is not
possible, carefully measure the CTCSS deviation and add this number to
the target deviation levels specified in this procedure.
For example: If the
CTCSS deviation is 600 Hz and the target audio deviation out of the TX
is 3.0 kHz, the corrected
deviation will be 0.6 + 3.0 = 3.6 kHz.
Also, it should be noted that CTCSS and program audio do not
simply add together well, so it would
really be a lot better to
disable the CTCSS on the TX.
3)
Finally, we need to set the absolute maximum deviation the TX can make,
by adjusting the Clipper on the exciter.
In a GE MASTR II this is the on-edge pot (potentiometer) that is
vertically mounted near the crystal ICOM.
The other on-edge pot is closer to the RF output connector, and
is the CTCSS level adjustment pot.
Inject a full-quieting, on-channel signal into the RX with your
signal generator. First you
need to clean the two pots, as they get rather dirty, and they are about
30 to 40 years old! So, I
usually carefully clean the two on-edge pots with a good contact cleaner
(be sure the power is off) then rotate the pots from minimum to maximum
several times to clean the windings.
Then set the pot to about the middle setting. Then connect
your service monitor to the TX, on the correct frequency.
Then turn on the 1000 Hz tone on your Generator, and set your
deviation for 7-8 kHz into the RX.
Then turn up the RX level adjustment pot on the controller to
maximum, and also the TX level adjustment pot on the controller to
maximum. We want to get as
much audio into the Mic line as possible.
Note the deviation level coming out of the TX, and set it to the
maximum deviation level you want your transmitters to operate at.
We usually run our TX clipper deviation at somewhere between 5.0
and 5.5 kHz. This sets your
overall maximum deviation level for the TX.
Repeat this process for all transmitters connected to the
controller.
Controller Set Up
1)
First, you need to deal with pre-emphasized or de-emphasized audio from
your receiver(s) to your transmitter(s).
If you are using GE MASTR II radios, the GE exciter is a phase
modulated transmitter, meaning that it automatically pre-emphasizes the
audio at a 6 dB per octave rate.
So, in order for the audio to sound correct you must de-emphasize
the audio coming into the transmitter(s) somewhere in the audio chain
before it gets to the transmitter.
As we
normally use discriminator audio out of our receivers, and it is not
de-emphasized, we must de-emphasize it somewhere.
If you are using an MOT fast-acting Squelch Board, you can order
them with C-18 installed (a .01 mf cap), and you will have perfectly
de-emphasized audio. Or,
you can install C-18 yourself.
Or, you can grab de-emphasized, squelched audio from the RX;
however the stock squelch crash is really annoying.
The bottom
line is that you must de-emphasize the incoming audio somewhere before
it gets to the transmitter.
If you are using an FM transmitter, then it will not pre-emphasize the
audio automatically, unless it does this in the low-level audio section.
Check your manual to determine if your transmitter pre-emphasizes
the audio or not. If it
does not, then you do not need to de-emphasized the audio ahead of the
TX as it is already pre-emphasized by the users radio, and discriminator
audio does not normally de-emphasized the users audio.
The bottom line here is that the audio coming out of the
connected repeater or link transmitter must be pre-emphasized, either by
the user or by the TX.
2)
Next, determine where you are going to de-emphasize the discriminator
audio coming from your RX, if you need to de-emphasize it at all.
If you have not already de-emphasized the RX audio ahead of the
controller, then it needs to be done by the controller at this step.
Most controllers have an audio de-emphasis circuit in them, and
you will want to use that circuit now (some work better than others).
3)
After you have chosen your audio de-emphasis scheme, inject a
full-quieting, on-channel signal into the RX with your Signal Generator.
Find the input audio test points for each port on your controller
(if none exist use the de-emphasis jumper as a test point).
Set the tone generator at 1000 Hz with an FSD signal (5 kHz) and
set the RX 1 input level pot on the controller such that the port 1
audio test point is at 2.0 volts peak-to-peak at FSD on your Scope.
4)
Repeat this very important step with all RX’s and audio input sources on
each port to the controller, such as IRLP audio, for instance.
They should all be the same 2.0 volts p-p with FSD at the audio
test point for each port used.
Transmitter Audio Path:
1)
Once you have all the RX input levels to the controller properly set at
2.0 v p-p for FSD, then inject a full-quieting, on-channel signal into
the Repeater RX 1 with your Signal Generator.
Then connect your Service Monitor to the output of TX 1 on the
correct frequency. Then
turn on the 1000 Hz tone generator, and adjust the deviation level of
your generator to 3.0 kHz of deviation.
If you still have your Scope hooked up, you should see 1.2 v p-p
at the controller RX 1 test point.
2)
While observing the TX 1 deviation, adjust the controller TX 1 audio
adjustment pot for 3.0 kHz of deviation out of the TX, plus add in the
TX noise contribution you wrote down earlier; let’s say it was 0.15 kHz,
so the total deviation reading on your Service Monitor should be 3.15
kHz. Your repeater audio
through-put on port 1 is now properly adjusted.
This assumes you are not
running CTCSS on the TX output.
If you are, then it needs to be disconnected for this step, or
added to the target TX deviation.
Please remove the CTCSS though if possible, as the program audio
and low frequency audio really do not add well together very well.
Disconnect the PL. If you
are running CTCSS on the TX output, be sure and add it into this level
adjustment also, or 3.0 + 0.15 + 0.500 = 3.65 kHz.
3)
Be sure to add or subtract any differences (if any) that you measured
and wrote down when you previously verified your test equipment to 2
above.
4)
The next item is the sweep test, to verify your frequency response
through the repeater and/or links.
With the set up outlined in steps 1, 2 & 3 above, turn the
frequency control for the audio from 100 Hz to 3000 Hz in 100 Hz steps,
or 500 Hz steps, and
note the TX deviation at each audio frequency step.
Again 100 Hz steps are preferred; however 500 Hz steps would
still give you some idea of the audio through-put flatness.
It should not
vary more than 10% throughout the entire audio band, 300 to 3000 Hz.
At 3.15 kHz of output deviation, that would be 0.315 kHz up or
down from your 3.15 kHz starting point at 1000 Hz, or 2.835 kHz to 3.465
kHz TX output deviation for a 3.0 kHz RX input.
After you
have measured the audio through-put at 300 Hz tone, move the frequency
to 400 Hz, and note the TX output deviation.
Repeat this step every 100 Hz, or 500 Hz, and plot the data.
5)
Once you have completed this sweep test, including any adjustments you
had to make for any differences you noted during the preliminary
verification test of the test equipment above, you will have a good idea
of just how flat your audio will sound.
The practical limits are +/- 10% from the center deviation, or in
this case, 3.15 kHz TX deviation.
This is the step that makes for a great sounding repeater.
6)
Repeat the above set up and testing for all TX’s, fed by all RX’s and
audio sources. I usually
leave the Monitor on the port 1 TX, and move the signal generator to the
other inputs being used on the controller, making sure we get the same
deviation results… 3
kHz IN = 3 kHz out. Then
move the service monitor to the next transmitter, and repeat the audio
through-put tests beginning the port 1 Repeater RX and moving through
all the other RX’s feeding that TX.
7)
If you are running CTCSS on the output of any of your TX’s then we will
now adjust it. Remember
that we must include the noise contribution of the TX itself in this
adjustment. The average
deviation for CTCSS is between 400 and 600 Hz for the CTCSS output tone
deviation level. That means
on the low side it would be 0.400 + 0.150 = 0.550 kHz (if your TX noise
contribution was .15 kHz).
You can adjust the on-edge pot closest to the RF output on the exciter.
On the high side it would be 0.600 + 0.150 = 0.750 kHz.
You now have your TX CTCSS adjusted.
Repeat this process for each TX running CTCSS on its output.
Tones and Courtesy Beeps
Audio Adjustments for the Palomar
Telecom RBC-700 Controller
Repeater Setup Procedure
1)
Send the ‘Interface Normal’ command and trip the Interface Telemetry by
momentarily providing a signal to the Repeater receiver input.
This provides the normal audio load to the CW ID audio.
2)
Send the ‘Start Identifier’ (*868) command or the ‘CW ID to Repeater
Only’ command and adjust the tone deviation to 1 kHz deviation at the TX
using the Master Gain pot, P8 on the Audio Mixer Card 1 (AM1).
This is the bottom pot on the Card, and the left-most Audio Mixer
Card.
3)
If this deviation level cannot be reached, DO NOT increase the software
volume level. Either change
the way the transmitter is fed or increase the value of the 1 megohm
feedback resistor on the U6 summing Op Amp on the Audio Mixer Card.
This is the resistor just to the
right of C1. The value should not be any higher than necessary, but in
no case should it be higher than 3.6 megohms.
If the transmitter is unusually sensitive, reduce the value of
the 1 megohm feedback resistor or attenuate the level at the
transmitter. NOTE:
After a power on reset or a software reboot,
the CW ID the CW will sound loud and clicky.
The deviation will be approximately 1.5 kHz to 1.8 kHz
until the Interface Telemetry is tripped.
The CW ID will
4)
Send the ‘CW ID to Interfaced Links’ (*869) command and adjust the
interfaced CW ID to 2.5 kHz deviation using the Tone Buss pot, P7 on the
Audio Mixer card 1 (AM1).
This is the second pot up from the bottom of the Card.
Expect this pot to be close to its maximum gain value.
If you desire the level to be lower, adjust the level using the
CW Telemetry software volume adjustment after all the levels have been
set.
NOTE:
The “A” series Audio Mixer cards may not be able to obtain
the proper CW Telemetry level.
If this happens, leave the pot in the maximum gain value
and continue with the adjustment setup.
5)
Step 4 should be repeated for all Link transmitters on the controller.
Send a *869 command and adjust the interfaced CW ID to 2.5 kHz
deviation using the Tone Buss pot, P7 on the Audio Mixer card 1 (AM1).
This is the second pot up from the bottom of the Card.
Expect this pot to be close to its maximum gain value.
If you desire the level to be lower, adjust the level using the
CW Telemetry software volume adjustment after all the levels have been
set.
Receive Audio to Transmitter
Audio Setup Procedure
1)
All levels are set using a
900 Hz reference audio
signal, or test tone. Do
NOT use a 1000 Hz reference audio signal.
The notch filters in the controller will slightly attenuate the
1000 Hz tone audio level as it passes through the controller.
2)
Be sure and take all receivers using CTCSS out of decode mode and set
all levels without the CTCSS active.
3)
Be sure and take all transmitters using CTCSS out of encode mode.
This is a must, as these measurements must be performed
without PL on RX or TX.
4)
Set the controller Power Switch to “Off.”
Remove the first (of two) Squelch Card (SQ1), insert an extender
card, and insert the SQ1 card into the extender card.
Turn the controller Power Switch to “On” and wait for the
controller to boot up. Be
certain that
all CTCSS
circuitry is off.
5)
Inject a full quieting, on channel signal into the Repeater RX.
Set the reference audio signal of the Signal Generator to
900 Hz (NOT 1000 Hz) and set
the deviation to FSD (5.0 kHz) into the RX.
Using an oscilloscope, check the amplitude of the audio signal at
TP1 on the squelch card and adjust the Level Adjust pot for ‘port 1’ to
2 volts peak to peak on the scope.
6)
Repeat this procedure for each receiver in the system, verifying the
appropriate Squelch Card test point and adjusting the appropriate Level
Adjust pot for 2 volts p-p.
Turn the Power Switch off and remove the card extender from SQ1, and
replace SQ1 in its normal position.
7)
Next we need to measure the amount of noise contributed by the
transmitter itself. Turn
the Power Switch back on, wait for the controller to boot up.
Inject a full-quieting, on-channel signal into the Repeaters RX
with your Signal Generator.
Then connect your Service Monitor to the TX on the correct frequency.
Then turn off the 900 Hz
tone generator so no tone is being sent to the RX.
Also be certain you are not generating a CTCSS tone.
Then carefully measure the deviation of the TX.
If necessary, ground the Mic and the CTCSS input lines.
The TX always generates a small amount of noise that can be
measured, usually around 0.05 to 0.15 kHz of deviation, with no audio
present on the audio inputs (Mic or CTCSS).
This deviation must be added to all future measurements on the
TX. Write it down.
You will need it later.
Repeat this process for all transmitters connected to the
controller.
8)
Inject a full-quieting, on-channel signal into the Repeater RX and while
observing the TX 1 deviation, adjust the controller TX deviation, using
the P1 audio adjustment pot on Audio Mixer Card 1 (AM1), this is the top
pot on the card, for 3.0 kHz of deviation out of the TX, plus add in the
TX noise contribution you wrote down earlier, let’s say it was 0.15 kHz,
for a total deviation reading on your service monitor of 3.15 kHz.
Your repeater audio through-put on port 1 is now properly
adjusted. This
assumes you are not running CTCSS on the TX output.
If you are, then it needs to be disconnected for this step, or
added to the target TX deviation.
Please remove the CTCSS though, as the program audio and low
frequency audio really do not add well together.
Disconnect the PL. If you
are running CTCSS on the TX output, be sure and add it into this level
adjustment also, or 3.0 + 0.15 + 0.500 = 3.65 kHz.
9)
Next we will adjust the next receiver’s audio into the Repeater TX
(Repeater port). Move the
signal generator to the next port (Link port 1, usually) and inject a
full-quieting, on-channel signal into the Link port 1 RX, and while
observing the TX 1 deviation, adjust the controller TX deviation, using
the P2 audio adjustment pot on Audio Mixer Card 1 (AM1), this is the
second pot down from the top on the card, for 3.0 kHz of deviation out
of the TX, plus add in the TX noise contribution you wrote down earlier,
let’s say it was 0.15 kHz, for a total deviation reading on your service
monitor of 3.15 kHz. Your
link-to-repeater audio through-put on port 1 is now properly adjusted.
Repeat this process for each input port to the Repeater TX.
10)
Next we will adjust the next Link TX output deviation.
Move the signal generator to the repeater port and inject a
full-quieting, on-channel signal into the Repeater
1 RX, and while observing the
Link 1 TX deviation, adjust the controller TX deviation, using the P1
audio adjustment pot on Audio Mixer Card 2 (AM2), this is the top pot on
the card, for 3.0 kHz of deviation out of the TX, plus add in the TX
noise contribution you wrote down earlier, let’s say it was 0.15 kHz,
for a total deviation reading on your service monitor of 3.15 kHz.
If you are running CTCSS on the TX output, be sure and add it
into this level adjustment also, or 3.0 + 0.15 + 0.500 = 3.65 kHz.
Your repeater-to-link audio through-put on link port 1 is now
properly adjusted.
Repeat this process for each input port to the Link port 1 TX. |