[arm-allstar] Telemetry volume

[Nate Bargmann]

* On 2020 15 Dec 13:24 -0600, "David McGough via ARM-allstar" wrote:
> 
> Remember that the RX level setting (option 2 in simpleusb-tune-menu) is
> the most important, since this is the level sent across the network and
> back out to the local TX.  When running option 2, there is a real-time
> graphic showing the audio level, with the 3KHz point on this graphic being
> the target level to aim for, keeping peaks below 5KHz (and cerainly NOT
> off the end of the scale!).
> 
> Once the RX level is correct, then adjust the TX settings, which are only
> heard via the local transmitter.  There should be no distortion on any
> telemetry with the default telemetry levels.

David is exactly correct.

Lacking a proper signal generator, I employed a "poor hams" version of
the same utilizing an extra radio, a sound fob, and an RTL-SDR to
monitor deviation with the svxlink-calibration-tools Debian package (I
use Debian on my desktop and laptop).

On the desktop I installed the aforementioned svxlink package and
followed these instructions to read deviation with the RTL-SDR and the
devcal utility (since I used a Debian package it was already installed
in the normal path, i.e. /usr/bin):

https://xastir.org/index.php/HowTo:Set_Deviation_via_RTL

The radio was an Alinco DR-635 and I wired the mic input to a 3.5 mm
plug that would plug into the fob line out jack (the impedance mismatch
didn't seem to matter).  Two other wires went to PTT and ground and I
was lazy and simply used a clip lead to key the transmitter.  Audacity
has a timeout by default so be aware of that when the tone goes silent!

On the laptop I set up Audacity to generate a 1 kHz tone through the
fob.  I set the audio level and the output device using the pavucontrol
GUI desktop app to achieve 3 kHz deviation from the Alinco transmitting
on the repeater input frequency as received by the RTL-SDR.

At that point was was a simple matter of setting levels using the Simple
USB utility.  Just keep in mind that setting the transmit level from
AllStar to the repeater to set the devcal configuration file for the
repeater's transmit frequency.

One caveat is to be sure that the signal into the repeater's receiver is
full quieting at a minimum.  When I had a paying job setting levels into
such equipment levels were set by injecting a modulated signal at -50
dBm using a service monitor which is a quite strong signal when a
receiver's sensitivity might be between -117 and -120 dBm.  With this
setup the object is to avoid having any noise on the repeater's
receiveri so I made sure the dummy load the Alinco was transmitting into
was close to the repeater's input port which I left open for maximum
signal leakage.

Finally, I set levels without PL tones as tone deviation will often vary
from radio to radio even though devcal is only supposed to be measuring
just the specified tone frequency.

73, Nate, N0NB

-- 

"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."

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