[aprssig] KISS TNC - Calibration function to set deviation correctly

John Langner WB2OSZ wb2osz at comcast.net
Wed Aug 19 21:51:19 CDT 2015


> I am looking for a way ... to set the deviation correctly.


Consider the following approach.

(1) Put your TNC into normal operation so that it will transmit
occasionally.

(2) Set up a receive-only instance of direwolf using a different receiver
and a good antenna.

(3) Observe the audio level lines for stations heard directly.  


Example: 


$ direwolf -t 0 | grep -v "^Digipeater" | grep -A 2 "audio level ="


W1MHL audio level = 96(53/33)   [NONE]   _||||||||
[0.4] W1MHL>APN382:!4223.32N/07115.23W#PHG3640/Waltham Amateur Radio
Association - N1OMJ Digipeater NoW1<0x0d> 
Position, DIGI (white center), Kantronics KPC-3 rom versions, 9 W height=640
4dBi omni 

...

W1CCE-1 audio level = 82(40/22)   [SINGLE]   ____:____
[0.4] W1CCE-1>TR2S0S,WIDE,WIDE2-2:'c4cl#H>/]"4p}<0x0d>
MIC-E, normal car (side view), Kenwood TM-D700, En Route 

...

KB1JKJ-8 audio level = 32(13/7)   [NONE]   __|||||||
[0.5] KB1JKJ-8>T2SS5R,WIDE1-1,WIDE2-1:`c+ll \(/"5'}
MIC-E, Mobile Satellite Station, Unknown manufacturer, In Service

...

W1WCI-11 audio level = 99(58/34)   [NONE]   ___|||||:
[0.5] W1WCI-11>APX200,WIDE2-2:=4243.14N/07106.12W-XASTIR-TNC-PI<0x0d>
Position, House, Xastir

...

KB1QV-10 audio level = 34(11/13)   [NONE]   ||||||___
[0.2] KB1QV-10>APTT4,WIDE2-1:!4305.18N/07131.34W#<0x16>PHG34803/Bow,NH
Position, DIGI (white center), Tiny Track

...

KB1ZSE-8 audio level = 79(39/28)   [NONE]   ___:::|:_
[0.6] KB1ZSE-8>TRTU7P,WIDE1-1:`cPso|m>0]"8,}MOBILE=<0x0d>
MIC-E, OVERLAYED CAR w/overlay 0, Kenwood TM-D710, Off Duty 

...

K1ABC-9 audio level = 75(41/26)   [NONE]   __:::|||_
[0.5] K1ABC-9>T2SX6X,WIDE1-1:`c4~r-8>/`"4G}146.520MHz de Paul from Nashua,
NH_%<0x0d> 
MIC-E, normal car (side view), Yaesu FTM-400DR, In Service 

...


(4) Notice how the audio levels vary all over the place.  32 to 99 and
everywhere in between.   

Kenwood and Yaesu fall near the middle, 75 to 82.  Assuming these have the
factory settings, that level should be close to ideal.  If you don't see any
of them, just take the average of the crowd.

(5) Adjust your transmitter to have a similar level.





Exercise for the reader:   

(a) What is the impact of setting the transmit volume level too high?

(b) What are the other two numbers and the vertical bars after the audio
level?

Hint:  See http://www.tapr.org/psr/psr128.pdf page 13









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