Avionics News April 2013 - 63

1
Airplanes at the VOR checkpoint in Modesto, Calif., should see the 093/273 radial.

accurately the transmitter synchronizes the rotating directional beam and time signal. This is generally controlled to
produce an error well under 1 degree.
2. Receiver error: VOR is basically an analog technology initially implemented using tube-based circuits and
unstabilized oscillators, with significant frequency drift and
less-than-perfect gain control. While modern equipment is
crystal-controlled (and in the latest implementations, digital),
it’s frequently coupled to cabling and antennas that may be as
old as the aircraft. And with an aging general aviation fleet,
this is a major issue.
3. Propagation error: Even assuming a perfect transmitter and receiver, there are still errors that may be introduced
depending on what happens to the signal between the transmitter and receiver. Interference between the space and ground
components of the radiated signal, multipath effects due to signals being reflected by objects including other aircraft, buildings and other surface features, and polarization errors can
all lead to a receiver working with a corrupted version of the
signal originally radiated from the transmitter; which is why
the tolerances of the system are so loose.
For example, consider a recent VOR check performed in a
1975 Cessna Skylane I co-own with four other private pilots.
Modesto has a VOR checkpoint on the North-West ramp,
several hundred feet from the approach end of runway 28R.
I requested a taxi to the checkpoint, and placed the circle
directly under the cockpit. The results are shown in photos
1, 2, 3 and 4. According to the sign, that location should be
in the 093/273 radial for Modesto VOR (114.6 MHz) at 0.6
nm. The Garmin GNS 530 receiver in our cockpit reported
that we were on the 105/285 radial. The CDI connected to the
GNS 530 reported radial 106, and a separate CDI connected
to a King KX-155 receiver used as nav/comm No. 2 reported
radial 102… all well out of IFR tolerance.
You may imagine my reaction. The airplane has been routinely used for IFR flights with those radios, and my partners
had logged errors between nav 1 and nav 2 of 4 degrees or less
for many years. Thinking things through, I unlatched the parking brake and pulled forward to put the vertical stabilizer and
Continued on following page

2
A Garmin GNS 530 at Modesto VOR checkpoint sees radial 105 —
out of IFR tolerance.

3
The CDI attached to the GNS 530 reports radial 106.

4
The CDI attached to the King KX-155 reports radial 102.
avionics news

•

april

2013

63



Avionics News April 2013

Table of Contents for the Digital Edition of Avionics News April 2013

Point of Communication
AEA Now
The View From Washington
International News and Regulatory Updates
Breakthrough
Member Profile
Digital Displacement and Fusion
Avionics News Through the Years
A Conversation With...
The Race to ADS-B Out
AEAviators
NextGen Status Report
Member Profile
Esterline CMC Electronics
What Radial Are We On?
AEA Offers Free NCATT Certifications and Endorsements at 2013 Convention
Work On Your Business, Not In Your Business
Business Basics
Survey Reveals Hiring Trends for the Aviation Industry
Meet the AEA Awards Nominees
What's New
Before & After
Avionics News April 2013 - Intro
Avionics News April 2013 - Cover1
Avionics News April 2013 - Cover2
Avionics News April 2013 - 1
Avionics News April 2013 - 2
Avionics News April 2013 - 3
Avionics News April 2013 - Point of Communication
Avionics News April 2013 - 5
Avionics News April 2013 - AEA Now
Avionics News April 2013 - 7
Avionics News April 2013 - 8
Avionics News April 2013 - 9
Avionics News April 2013 - 10
Avionics News April 2013 - 11
Avionics News April 2013 - 12
Avionics News April 2013 - 13
Avionics News April 2013 - The View From Washington
Avionics News April 2013 - 15
Avionics News April 2013 - International News and Regulatory Updates
Avionics News April 2013 - 17
Avionics News April 2013 - 18
Avionics News April 2013 - 19
Avionics News April 2013 - Breakthrough
Avionics News April 2013 - 21
Avionics News April 2013 - 22
Avionics News April 2013 - 23
Avionics News April 2013 - 24
Avionics News April 2013 - 25
Avionics News April 2013 - Member Profile
Avionics News April 2013 - 27
Avionics News April 2013 - 28
Avionics News April 2013 - 29
Avionics News April 2013 - Digital Displacement and Fusion
Avionics News April 2013 - 31
Avionics News April 2013 - 32
Avionics News April 2013 - 33
Avionics News April 2013 - 34
Avionics News April 2013 - 35
Avionics News April 2013 - Avionics News Through the Years
Avionics News April 2013 - 37
Avionics News April 2013 - A Conversation With...
Avionics News April 2013 - 39
Avionics News April 2013 - The Race to ADS-B Out
Avionics News April 2013 - 41
Avionics News April 2013 - 42
Avionics News April 2013 - 43
Avionics News April 2013 - AEAviators
Avionics News April 2013 - 45
Avionics News April 2013 - NextGen Status Report
Avionics News April 2013 - 47
Avionics News April 2013 - 48
Avionics News April 2013 - 49
Avionics News April 2013 - 50
Avionics News April 2013 - 51
Avionics News April 2013 - Member Profile
Avionics News April 2013 - 53
Avionics News April 2013 - 54
Avionics News April 2013 - 55
Avionics News April 2013 - Esterline CMC Electronics
Avionics News April 2013 - 57
Avionics News April 2013 - 58
Avionics News April 2013 - 59
Avionics News April 2013 - 60
Avionics News April 2013 - 61
Avionics News April 2013 - What Radial Are We On?
Avionics News April 2013 - 63
Avionics News April 2013 - 64
Avionics News April 2013 - 65
Avionics News April 2013 - 66
Avionics News April 2013 - 67
Avionics News April 2013 - AEA Offers Free NCATT Certifications and Endorsements at 2013 Convention
Avionics News April 2013 - 69
Avionics News April 2013 - 70
Avionics News April 2013 - 71
Avionics News April 2013 - Work On Your Business, Not In Your Business
Avionics News April 2013 - 73
Avionics News April 2013 - 74
Avionics News April 2013 - 75
Avionics News April 2013 - 76
Avionics News April 2013 - 77
Avionics News April 2013 - Business Basics
Avionics News April 2013 - 79
Avionics News April 2013 - 80
Avionics News April 2013 - 81
Avionics News April 2013 - 82
Avionics News April 2013 - 83
Avionics News April 2013 - Survey Reveals Hiring Trends for the Aviation Industry
Avionics News April 2013 - 85
Avionics News April 2013 - Meet the AEA Awards Nominees
Avionics News April 2013 - 87
Avionics News April 2013 - 88
Avionics News April 2013 - 89
Avionics News April 2013 - 90
Avionics News April 2013 - 91
Avionics News April 2013 - 92
Avionics News April 2013 - 93
Avionics News April 2013 - 94
Avionics News April 2013 - 95
Avionics News April 2013 - What's New
Avionics News April 2013 - 97
Avionics News April 2013 - 98
Avionics News April 2013 - 99
Avionics News April 2013 - 100
Avionics News April 2013 - Before & After
Avionics News April 2013 - 102
Avionics News April 2013 - 103
Avionics News April 2013 - 104
Avionics News April 2013 - Cover3
Avionics News April 2013 - Cover4
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