Upgrading to UAT
Should You Upgrade?
This page enumerates some pros and cons and other considerations relating
to upgrading an existing TBAD to dual-band operation.
For the near term, 978 MHz UAT (universal access transceiver) will
not entirely replace the requirement for 1090 MHz transponders
operating in Mode C. The eventual goal may be to scale back reliance on
Mode C, so we may see a gradual decrease in chatter—possibly toward
silence. Longer term, it is unclear whether an airplane equipped with
978 MHz UAT will still be required to carry a 1090 MHz
transponder, on a decade timescale.
Advantages to Upgrading
- Capture 3-D position information for all ADS-B compliant
airplanes, regardless of whether they elect to install ADS-B capability at
978 MHz or 1090 MHz.
- Provide additional safety by catching long 978 MHz transmissions:
more opportunities to detect a threat.
- In sparse areas, dramatically increase in-beam counts because the long
UAT transmissions count for 10 or 14 beam-counts, depending on message
type. This could be especially important if Mode C reliance wanes over
time, decreasing the rate of 1090 MHz activity.
- Less worry about future trends or rule changes: get all foreseeable
traffic for (likely) decades, even under rule changes. While your site may
not have much UAT traffic now, the trend is likely to increase with time.
- Mode A/C interrogations from other aircraft may decline with time,
instead relying on ADS-B for collision avoidance. Thus the frequency of
1090 MHz transmissions—now dominated by
Mode A/C—will likely go down. TBAD reaction time has been
assessed in the context of this frequency at each site.
Disadvantages to Upgrading
- Expense. Logistical complication of changing out; down-time.
- Potentially different antenna mechanical mounting footprint, depending
on which antenna you currently use (6-fold vs. 7-fold symmetry; the upgrade
is nominally 7-fold). See the antenna
page for details.
- Additional 5V DC requirement at discriminator (or AC and small
converter). This is necessary to get demodulated/decoded information from
UAT, but does not impact safety operation.
- You may not have appreciable 978 MHz traffic at your location.
- Opening another sensitive channel could invite interfering RF in
adjacent bands that were not present at 1090 MHz. In other words, it
is possible that false alarms increase, depending on environment.
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