Railroads ready to occupy the 220MHz band

Karl W4KRL W4KRL at arrl.net
Wed Mar 10 13:05:47 CST 2010

As a result of some catastrophic accidents, Congress has mandated that
American railroads install a system to provide Positive Train Control (PTC)
that will override the manual operation of the train to enforce safe train
separation. Several systems are under test and all use radio combined with
GPS to locate and control trains from wayside units. The Association of
American Railroads (AAR) estimates that 19,000 locomotives and 50,000
wayside radio units will be required in a total system cost of $9 billion.
The railroads are currently planning to use the 220/221MHz band. Let's hope
this isn't a new threat to one of our bands. Ultimately, a large commercial
base of 220MHz equipment may be a benefit to us when surplus units show up.


Here is a white paper about the system. I've extracted some interesting
comments related to the 220MHz band.




73 Karl W4KRL


15.0 Digital Mobile Radio Communications Systems

Digital mobile radio communications systems present a number of challenges;
there are no

similar systems in operation on which these new sub-systems can be modeled.
This will most

likely be the less deterministic, highest technical risk area in the entire
PTC development. It is

assumed the 220/221 MHz radio frequency band will be used for wireless PTC.

Antennas, Antenna Coupling Units, and Antenna Tower Structures Issues:

- Mobile and Fixed Antennas pose several challenges. The 220 MHz is a
relatively new band

and there are no established product lines for these bands. Several vendors
are just now

starting to produce new 220 MHz antennas. One year ago, TESSCOR, a leading

distributor in this field, only had one 220 MHz antenna listed. This was an
NMO mount

omnidirectional antenna. In comparison, antennas for the 150 MHz band filled
numerous pages

in the TESSCOR catalog.

- Antenna Coupling Units Unlike the traditional 50, 150, 450, 800 and 900
MHz bands,

antenna filters, duplexers, combiners, amplifiers, signal distributors and
other similar

components are not readily available, even though there is a small selection
that is starting to

grow as more vendors take an interest in the 220 MHz band. There is no data
or knowledge

base to forecast how a new 220 MHz radio will behave/interact with other
co-located radios

operating on the 50, 150 and 450 MHz bands. Most railroad radio towers are

crowded with multiple antennas from radios operating on many bands, except
in 220 MHz.

While 220 MHz antenna performance and interaction/interference can be
forecasted by

modeling, there is no guarantee that actual field performance will match the
forecasted results.

This is a high technical risk area, since it will be difficult/impossible in
most cases to re-locate,

remove or change other antennas and antenna coupling units already installed
in thousands of

base station towers.


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