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Radio Broadcast Technical Consulting and Sales
 
10032 Island Drive, Brainerd, MN  56401

 


Technical Tips from Mark W. Persons
Standards...Standards...How would we get along without them?


FM Composite Audio: 
For older Harris FM exciters such as the MS-15, the MX-15, and THE-1, 2.828 Volts Peak to Peak/1.0 Volts RMS will result in 100% modulation.
For Moseley STL systems, Broadcast Electronics FM Exciters, Bext, and newer Harris FM exciters, 3.5 Volts Peak to Peak/
1.237 Volts RMS will give 100% modulation.
Audio Wire Color Coding on 2-pair shielded cable:
Green = left +
White = left -
Red = right +
Black = right -

XLR-3 (A3M or A3F) Connector Audio: 
Pin 1 = Shield
Pin 2 = Audio +
Pin 3 = Audio -

Exceptions:  Marti remote pickup transmitters along with Zercom Max-Z and ZII Remote Broadcast Telephones have unbalanced audio inputs.  Pin 1 is shield, Pin 2 is ground and pin 3 is the audio. 


RJ-45 connector pin-outs found here.


For air variable capacitors, .045" plate spacing = 2kV rating  .075" plate spacing = 3kV rating  .080" plate spacing = 3.5 KV  .125" plate spacing = 4.5 kV rating.

According to a publication by Nautel, here are recommended settings of air arc-gaps when used at a 50 ohm zero reactance point in an AM transmission system:

 Radio Frequency:  Power Correction:
 540 KHz = .159 inches  1000 watts,  multiply by 1.05
 1000 KHz = .125 inches  5000 watts, multiply by 1.30
 1700 KHz = .076 inches  10,000 watts, multiply by 1.83

See examples of arc-gaps here.


Return Loss vs. Voltage Standing Wave Ratio vs. Reflected Power:

Return Loss VSWR Power Reflected With 10 KW Forward
45 dB 1.01:1 0.003% 0.3 Watts Reflected
40 dB 1.02:1 0.01% 1 Watts Reflected
35 dB 1.04:1 0.03% 3 Watts Reflected
30 dB 1.06:1 0.1% 10 Watts Reflected
25 dB 1.12:1 0.3% 30 Watts Reflected
20 dB 1.22:1 1.0% 100 Watts Reflected
15 dB 1.42:1 3.0% 30 Watts Reflected
10 dB 1.92:1 10.0% 1000 Watts Reflected
 8 dB 2.33:1 16.0% 1600 Watts Reflected
 5 dB 3.51:1 31.0% 3100 Watts Reflected

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   Ham WMH

Questions?  Email Mark Persons:  teki@mwpersons.com         

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page last edited 02/22/2016