A-3
B.
Determine if the image frequency for the VHF Comm falls within the range of the TFM-556.
If so, select a set of frequencies that will cause the TFM-556 to be set as close as possible to
the image frequency. Any one of the many possible sets will suffice. Record those values in
the spaces provided in the following chart. Modulate the TFM-556 transmitter on the following
frequencies for at least 20 seconds. Listen for any noise or detected audio signals on the VHF
comm.
Example - Bendix/King KY 196A:
The first IF frequency is 11.4 MHz. The L.O. is above the received frequency (high side
injection), therefore the image frequency is 22.8 MHz above the selected frequency. Set the
KY 196A to 120.000 MHz and the TFM-556 to 142.8000 MHz.
(Note: Where indicated by an asterisk (*), required action is to switch ATC-550 on and off as
often as necessary.)
FREQUENCIES
RESULTS
VHF #1
TFM-556
PASS
FAIL
132.000
66.0000
135.975
67.9875
135.975
138.0000
121.15
157.5000
131.25
157.5000
128
*
Image:
FREQUENCIES
RESULTS
VHF #2
TFM-556
PASS
FAIL
132.000
66.0000
135.975
67.9875
135.975
138
121.15
157.5
131.25
157.5
128
*
Image:
NOTES:
