[opendtv] F-Type Connectors Now used past 2GHz What Standard?
- From: "Colin R Wright" <colinrwright@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 13 Feb 2005 23:47:56 +1100
Hi everyone,
To change the subject from MPEG licensing and the FCC, there might be
someone out there able to help us with a question we have about
F-connectors.
One of our Australian Standards work groups is updating the standard for TV
(MATV) distribution systems. This covers terrestrial, cable and satellite
distribution of analog and digital television and sound signals in single
and multiple (hi-rise apartment) domestic dwellings.
The current standards for F-connectors appear to be IEC 60169-24 and
ANSI/SCTE 01 1996 but they seriously lack necessary detail (See below).
Since F-connectors are now being used for systems going up to 2150MHz (Some
say to 3GHz), the tolerances given in the old standards don't seem to stack
up for suitable return loss etc.
To provide improved return loss and extended frequency response we are
suggesting some recommendations-
1. All F-Type male connectors shall use cable with an inner solid core
conductor or have an integral inner pin, the diameter of which is not less
than 0.85mm and not more than 1.15 mm.
2. The characteristic impedance of these connectors be 75 ohms (plus minus
?) and that the return loss of a mated pair be better than 20dB over the VHF
and UHF bands and better than 14dB in the range 950MHz to 2150MHz.
3. The contact reliability of a F-type male-female connection shall not
exceed 20 milliohms as measured by the total series resistance of the inner
and outer.
Note: Specifications 2 and 3 shall be met after 10 insertions/extractions
Some Background:
IEC 60169-24 was published in 1991 when the connector was generally used for
analog signals over a more restricted frequency range. It is now also being
used for digital signals with a frequency range extending above 2GHz.
Although IEC 60169-24 states that it is "typically for use in 75 ohm cable
distribution systems", that standard does not include any return loss
requirements; it includes only mechanical dimensions.
The return loss of the coaxial connectors used throughout the distribution
system has become very important, now that they are used over a wide
frequency range. Intrinsically the return loss of the male part of most "F"
connectors is very good because it consists basically of the coaxial cable
centre conductor and insulation.
Unfortunately however IEC 60169-24 allows the centre pin diameter to have
the very large diameter range of 0.51 to 1.69mm in order to accommodate
variations in the centre conductor diameter of different sizes of 75 ohm
coaxial cable and also variations in the dielectric constant of the cable
insulation (eg. solid or foamed polyethylene). Because of this large centre
pin diameter range the centre female part of the socket is depicted in IEC
60169-24 as a pair of "fingers".
However a socket with such a structure probably would have either a
significant roll off at frequencies above about 1GHz and/or poor return
loss.
Noting that the type of cables now used for antenna distribution systems
normally have a centre conductor diameter of 1.0 +/- 0.15mm many modern "F"
connectors use a different structure for the centre female socket with a
restricted range. Such connectors can have very good return loss figures
over the full frequency range required by this specification.
The related American standard ANSI/SCTE 01 1996 recommends that the centre
conductor have a maximum diameter of 1.30mm but what tolerance and which
cable types?
======================
Someone out there should be able to advise us.
Regards from downunder,
Colin Wright
Seven Network Australia
38-42 Pirrama Road
Pyrmont (Sydney) NSW 2009
AUSTRALIA
cwright@xxxxxxxxxxxx
colinrwright@xxxxxxxxxxxxxxx
Tele: +61 2 8777 7710
Cell: +61 (0) 419 477 777
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