TNC connector
- details and information about the TNC connector, - TNC socket and plug
with links to suppliers.
The TNC connector is very similar to the BNC connector
although it is not nearly as widely used. The main difference between then is
that the TNC connector has a screw fitting instead of the bayonet. The screw
fitting means that the RF connection of the TNC connector is generally more
robust and accordingly it can operate more reliably at higher frequencies.
Development
The TNC connector was developed originally to overcome
problems during vibration. As the bayonet fixing moved slightly there were small
changes to the resistance of the connections and this introduced noise. To solve
the problem a screw fixing was used and the TNC coax cable connector gains its
name from the words Threaded Neill Concelman.
TNC connector performance
Like the BNC connector, the TNC connector has a constant
impedance, and in view of the threaded connection, its frequency limit can be
extended. Most TNC connectors are specified to 11 GHz, and some are able to
operate to 18 GHz.
TNC connector formats
TNC connectors come in a variety of formats. Not only are
there plugs and sockets but there are also adapters and also other items such as
attenuators.
TNC plugs are designed not only for the required impedance,
but also to accept a particular coax cable format. In this way all the internal
piece parts are compatible with the coaxial cable used. It is therefore
necessary to specify the TNC plug for use the cable to be used. Although there
is some latitude, it is naturally best to select the correct cable format.
In addition to this there are straight and right angled
variants. Of these the straight connectors are the most widely used, although
right angled connectors where the cable leaves the plug at right angles to the
centre of the connector centre line are also available. These are ideal in many
applications where the cables need to leave the connector in this manner to
ensure cables are in a tidy fashion, or where space is at a premium.
Unfortunately right-angled connectors have a marginally higher level of loss
than their straight through counterparts. This may not be significant for most
applications, but at frequencies near the operational limit of the connector
there may be a small difference.
The sockets or female BNC connectors also come in a number of
flavours. The very basic BNC connector consists of a panel mounting assembly
with a single connection for the coax centre. The earthing is then accomplished
via the panel to which the connector is bolted using a single nut. Large washers
can be used to provide an earth connection directly to the connector. Some of
these connectors may also use four nuts and bolts to fix them to the panel.
These arrangements are only suitable for low frequency applications, and not for
RF. Where impedance matching and full screening is required. Bulkhead mounting
connectors where coaxial cable entry is provided are available for this. Again
these are available for a variety of cable dimensions and the correct type
should be used.
There are two main variants of the TNC connector assembly
method:
- Compression gland type
- Crimp type
The compression gland type has the centre pin of the
connector which is usually a solder pin and the braid and sheath of the cable
are held by an expanding compression gland fixed by a nut at the rear of the
connector. This type of connector by its nature can cope with a (limited) range
of cable sizes and requires no specialised tooling to assemble. This makes it
ideal for small quantity production, either for one off cables for laboratory
use of for limited production runs.
The crimp TNC connector has the centre pin which is normally
crimped to the centre conductor. This crimped pin is then pushed into position
through an inner ferrule which separates the inner insulation sheath and the
braid of the cable. An outer ferrule is then crimped over the braid and outer
insulation which fixes the cable to the connector. Greater accuracy is required
for the crimp style connectors and therefore the correct connector variant must
be chosen for the cable being used. This may result in a crimp style connector
not being practicable for some cable types. In addition to this the assembly
requires the use of the correct crimping tools to ensure that the connector is
correctly crimped. While these connectors are usually preferred for large
production runs because they are faster to assemble, it is not possible for them
to be reworked for obvious reasons.
For both styles of TNC connector it is essential that the
exact amount of insulation is stripped from each section to ensure accurate and
successful assembly.
The sockets or female TNC connectors also come in a number of
flavours. In view of the fact that TNC connectors are normally used for RF
applications, bulkhead mounting connectors where coaxial cable entry is provided
are normally used. Again these are available for a variety of cable dimensions
and the correct type should be used.
|
