Convex 806A and 807A Transmission Test Sets measure Round Trip Delay and Envelope Delay Distortion. Both measurements are based on the phase shift of a (83.333 Hz) 12 mS reference.
ROUND TRIP DELAY is used to measure actual input to output transmission time of a system. It is an absolute time measurement made at a single frequency - normally 1804 Hz. The test signal is first zeroed with the test set generator directly connected to the receiver. Then the signal is passed through the system under test and returned (round trip) to the test set. The test set display is interpreted as positive milliseconds.
For reference ENVELOPE DELAY DISTORTION (EDD) is a relative
time measurement which makes no statement as to actual input to
output transmission time. It measures the difference in transmission
time of various frequencies compared to that of a "zero"
reference frequency. The test signal is passed through the system
under test, then zeroed at 1804 Hz. Delay is then measured (positive
or negative) at other frequencies relative to 1804 Hz. Zero EDD
means that all frequencies have the same delay - not zero delay.
TERMS
Round Trip Delay is also called PHASE DELAY.
Envelope Delay is also called GROUP DELAY.
FREQUENCY = radians divided by second
PHASE: The phase curve varies with frequency.
PHASE DELAY = minus phase divided by frequency in seconds
GROUP DELAY = minus slope of the phase curve in seconds
PROCEDURE - Round Trip Delay - Turn radio CTCSS off.
1. Select DELAY Measurement Mode. Select the 15 kHz Filter and set the generator to 1804 Hz.
2. Connect test set SEND directly to the RECEIVE. When the display settles, ZERO the delay reading.
3. Connect the test set to the system under test and record the delay when the display settles.
NOTE: By nature, Round Trip Delay and EDD have a 12 mS "rollover".
The test set display is configured to read between -3.000 and
+9.000 mS. The negative delay scale avoids a discontinuity when
measuring EDD near zero.
If Round Trip Delay exceeds 9 mS, use "Extended" Round Trip Delay to avoid the 12 mS ambiguity.
Related Products:
Audio: Delay module - remote
Audio: Delay voice land lines
Audio: Equalize voice land
lines or analog mux-voice channels
Last update 5/4/06.
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