Kenwood TH-D72A/E - Manual (Page 69)

7 APRS NETWORKS
TH-D72A/E CONTENTS 61
the same time also hit the WIDEn-N network when they are in good coverage areas. For this reason,
the usual 2 hop recommendation for mobiles is not WIDE2-2. This is because those packets would
not be recognized by these fill-in digis. Instead, we encourage all mobiles to use the 2-hop path of
WIDE1-1, WIDE2-1.
WIDE1-1, WIDE2-1 Mobile Path:
WIDE1-1, WIDE2-1 Mobile Path: To assure that mobiles can get 2 hops no matter where they are and
no matter what digi hears them first, we recommend the WIDE1-1, WIDE2-1 path. Notice how the
second entry is already decremented to 2-1 so that the result of this combination is still the national 2
hop recommendation. The reason we do not suggest a 2 hop pair of WIDE1-1,WIDE1-1 is because it
causes unnecessary dupes in those fill-in areas which are incapable of recognizing dupes. Also, we
strongly discourage any fixed station from using WIDE1-1 as the first hop. Because it is not necessary
and causes the same problems with multiple dupes.
The SSn-N path:
The SSn-N path (which can also be SSSn-N or SSSSn-N) is a special path for a given
communications geographical area. Typically SS is the standard abbreviation for States in the USA,
but many large states are divided into two or more ARRL communication sections. So, a 3 or 4 letter
SSSn-N designation is also appropriate. These paths are used by these special communications
organizations for state or section-wide nets or for drills or for emergencies. Depending on N, these
packets can hit every digipeater in the state or section, but will not go into other areas no matter how
big N is. A typical value is SS3-3 or more.
For example, using WIDE3-3 from the middle of Maryland would not only hit all digipeaters in
Maryland but also dozens of digipeaters in the 5 surrounding states. This would be very bad
practice. But using MD3-3 would hit every digi in Maryland and nowhere else. In fact, MD5-5 would
be no worse than MD3-3. In either case, all digis in the state would be hit and any left over hops will
not go anywhere. This is because no digi will repeat the same packet twice.
TEMPn-N Backup/Emergency Path:
We also needed a special come-as-you-are emergency backup path system for when there is no
existing infrastructure and when we needed to implement a system in a hurry in the field.
The two standardized paths, WIDEn-N and SSn-N provide good APRS operation everywhere for
most applications. Except, if the power to the digipeaters is lost, and then there is no backup system.
To meet this need, we defined the special path of TEMPn-N to be used when either WIDEn-N or SSn-
N does not work.
To implement this ubiquitous backup system, we took advantage of the fact that every existing
Kenwood Mobile APRS radio can be a digipeater. But it would be a huge problem if all these mobiles
drove around routinely with their digipeaters enabled as WIDEn-N or SSn-N. Human fallibility
suggests that once turned on (by the hundreds), many would forget to turn them back off, and we
would destroy the national channel with unwanted interference. We solved that problem by defining
this special TEMPn-N path. This path can be enabled in ALL mobiles ALL the time, because no one
uses it for routine operations. Thus, it is available to everyone at any time if there is a mobile
Kenwood nearby and there is no danger of any QRM to existing operations.
Unfortunately, the original TM-D700A/E did not come factory set to enable automatic TEMPn-N
operation. As a result, not many TM-D700A/E operators have remembered to do this themselves.
But in the TM-D710A/E, Kenwood has enabled TEMPn-N digipeating from the factory, thus assuring
that this backup system is readily available everywhere there is a TM-D700A/E. The new TH-D72A/E
also comes pre-loaded to support TEMPn-N digipeating but it defaults to OFF so that these
handhelds do not automatically start digipeating when someone uses the TEMPn-N system. But they
can be enabled at any time with a simple menu item so that a TH-D72A/E handheld in a high location
can act as a digipeater by anyone that needs it.