APRS / HAM RADIO Standard Connectors
By Knut, N1QKP
Last Updated 02/18/97
In an effort to enable various radio, GPS and TNC equipment to easily be interfaced, a
standardized set of cables is recommended. It is recognized that most equipment are of
different brands and/or models. Therefore we have come up with a set of cables that
terminates in easily accessible connectors. This article is based on ideas taken in part
from from several sources including ARRL and Baker to Vegas APRS Setup. It also attempts
to use the features of the most common equipment in our group, and uses connectors
that are available at local stores, no mail-order-parts are required. Please feel free to comment and/or ask questions.
DC POWER CABLES:
There are 3 basic parts to a complete cable.
1) Source Cable from power source.
2) Distribution Cable and Y-Splitters.
3) Conversion cable to the radio or other equipment.
(Note: To ensure good connections, all joints must be soldered.)
Connectors:
All DC Cables should be terminated with Molex type. This was chosen due to
its readily availability in local stores. There are other, probably better type of
connectors available, but not as readily available. The positive lead (red wire) shall be
connected to the pointed end. All Power will be terminated in a Female Connector. This
type of connector is readily available at Radio Shack as Heavy Duty 20 amp rating. The
price is about 99 cents each.
 
(Male RS 274-151, Female RS 274-154)
Other plugs used in this setup are:
 Coaxial
Power Connector as required by the TNC,
(RS 274-1567 or as appropriate for your TNC)
BLACK Phono Connector for GPS Power,
 RED Phono
Connector for GPS Data.
(RS 274-451)
Source Cable:
The Source Cable can take several forms. The purpose for this cable is to
provide a short (6 - 24") fused link from the vehicle's power to this cable-system.
The key to this cable is that it can comfortably supply a 50 Watt Transceiver and its
accessories with 20 amp. The cable should be made of a minimum of 12 gauge wire. Fuses
should be inline in both the positive (red) and negative (black) wire. The only exception
to this would be with a Cigarette Lighter Plug charging a smaller battery. The Cigarette
Connection in the vehicle will typically be fused at 10 - 15 Amp. The Fuse between the
portable battery should again be rated 20 Amp. The blocking diode should be rated greater
than the fuse in the Cigarette Plug, since a fuse can typically accept surges above its
rating. An optional pair of Male-Female pair of Molex connectors may be placed between the
cigarette lighter plug and the blocking diode. A conversion cable from your AC - DC Power
Supply is also recommended. This will simply be a short cable from tinned ends to a Female
Connector.
Extension Cable:
A 6 - 10' long extension cable should be a part of this kit. This will
allow for connection directly to the vehicle's battery while the equipment is located
inside the vehicle. The minimum wire-size is 12 gauge.
Splitter Cable:
A splitter cable will allow several items to be connected to one feed.
Again, all connections must be soldered.
End Cable:
The End Cable will allow the generic cable system to interface with the particular
brand of equipment. This is where standardization becomes difficult. The recommendation is
to:
Terminate your Radio's Power Cable in a Male Connector as described here.
Terminate the GPS 45 Power-cable in a Male BLACK Phono Plug for Power (P = center, N =
shield).
We recommend that the GPS receives Power via a Molex Plug or Black Male Phono Plug (as
described). We also recommend that Data is available on a RED Female Phono Connector (see
below).
The above cable can also be separated for more flexibility. Even if the above cable is
used, an additional set of these cables are great to have in the cable box. Some HTs (like
my Standards) uses a 'non-standard' plug configuration of Negative in the Center. When a
cable is wired with Negative Power in the Center, a RED CAP or RED TAPE Shall be used to
identify this.
Garmin 45 to TNC DATA CABLES:
The Data Cables will all terminate in RED PHONO type connectors. Generally, the GPS
end which provides data will be of Female type (to protect against shorts on the data
output). We recommend that in lieu of having a hardwired 25 or 9 pin data plug on the GPS
Data Cable, the GPS Cable terminate in a RED FEMALE PHONO Connector, while the TNC or
Computer cable picks up with a RED MALE PHONO plug to the appropriate connector for the
TNC or Computer. Data Signal will be wired to the center connector, while Data Ground to
the shield.
GPS ANTENNAs:
Again, there are many types of GPS in use. Some models use BNC connectors.
The ultimate is that the owner of the GPS supply a remote antenna. An amplified
weather-proof exterior antenna works very well. Some of these are sensitive to overloading
from the 2m transmitter, so the GPS and the 2m antenna should be mounted as far apart as
possible. An acceptable, inexpensive alternative for the Garmin GPS-45 is to use a BNC
extension cable with suction cups available from Radio Shack (about $10). This allows the
original antenna to be mounted outside the vehicle for 360 degree view of the horizon,
something that is very important during a race in a city with tall buildings
blocking the view.
COMPLETE SETUP:
This picture shows how a Garmin 45 would be interfaced. As of the right
now, most of us use the KPC-3 TNCs for APRS. Therefore we do not have a problem
interfacing the radios to the TNC. Those of us that use other brands of TNCs, typically
also provide a Transceiver and the cables required between the TNC and Transceiver. We
are, however, discussing the simplest way to generalize the interface between the TNC and
the Radio. Both DB9 and DIN connectors are usable. The key is that they are readily
available (at Radio Shack or equivalent).
LINKS:
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