Hi Group,

Many thanks for the input with the open and shorted transmission lines.

On another subject, F-connectors are used for just about everything video, with
RG-59 being 75 ohms is the F-connector designed for 75-ohms or can I use this
type of connector with 50 ohm systems?

de KJ4UO

On 16 May 2004 04:38:43 GMT, (PDRUNEN) wrote:

Hi Group,

Many thanks for the input with the open and shorted transmission lines.

On another subject, F-connectors are used for just about everything video, with
RG-59 being 75 ohms is the F-connector designed for 75-ohms or can I use this
type of connector with 50 ohm systems?

de KJ4UO

Hi OM,

It would seem to me that the connector is in large part simply a
connecting shell where the line itself does the chore of mating to a
rather unsubstantial socket. Undoubtedly these things are intended
for low power, low physical demand applications. I suppose you could
force-fit them to rg58, or just use RCA connectors and skip the
tedious threading.

73's
Richard Clark, KB7QHC

You would have trouble physically doing it. Remember, you need coax with a
skinny solid center conductor. There is such RG58, but the shield diameter
is too small. It might be possible to use 8X if you cut off part of the
strands that make up the center conductor, and tin the remaining ones to
make a rigid conductor.

Tam/WB2TT
"PDRUNEN" wrote in message
...
Hi Group,

Many thanks for the input with the open and shorted transmission lines.

On another subject, F-connectors are used for just about everything video,
with
RG-59 being 75 ohms is the F-connector designed for 75-ohms or can I use
this
type of connector with 50 ohm systems?

de KJ4UO

"PDRUNEN" wrote in message
...
Hi Group,

Many thanks for the input with the open and shorted transmission lines.

On another subject, F-connectors are used for just about everything video,
with
RG-59 being 75 ohms is the F-connector designed for 75-ohms or can I use
this
type of connector with 50 ohm systems?

de KJ4UO

Hi, the F-connector is 75 ohm, and I have had to mate it to PL-259 to
connect Belden 9913 before. This required the awkward addition of an
F-to-BNC then BNC-to-SO-239 connector. The line loss added to this
arrangement was probably significant, but the reason was to adapt an
inexpensive log periodic beam antenna. Although manufacturer claimed
transmit capable, and I did test this on vhf-marine bands, the mismatch of
connectors should be used for receive-only.

Jack Painter
Virginia Beach, Va

Provided the mechanical connection is sound, you can use any coaxial
connectors you like, regardless of nominal impedance, at frequencies less
than about 300 MHz without any observed ill effects.

"Reg Edwards" wrote
Provided the mechanical connection is sound, you can use any coaxial
connectors you like, regardless of nominal impedance, at frequencies less
than about 300 MHz without any observed ill effects.
_________________

??? Using connectors that don't maintain the characteristic impedance of the
transmission lines they connect _will_ produce undesired effects. The
effects may be negligible to amateur radio operators used to operating
transmitters into rather high mismatches, but they would never be tolerated
in most professional operations, including high-power broadcast systems.

Years ago a common impedance for rigid transmission line used in broadcast
systems was 51.5 ohms. Later the more common value was/is 50 ohms. While a
mechanical adapter was available to allow connecting a 51.5 ohm inner
conductor to 50 ohm inner conductor (SWR= 1.03), better installations
installed an RF transformer section at these interfaces.

A 1.1 SWR at the input of a TV transmit antenna using ~500 or more feet of
transmission line will produce a visible "ghost" in the transmitted picture,
as seen by a careful observer. At 1.25 SWR it can be seen, and will
objectionable to almost everyone.

RF

Visit http://rfry.org for FM broadcast RF system papers.

To save the trouble of calculating it I'll take a guess. A connector less
than 1" long of impedance 51.5 ohms in a 50 ohm system will NOT produce an
SWR of 1.03:1 or anything anywhere near to it at frequencies less than 1000
MHz.

A 1" long connector WILL produce an SWR of 1.03:1 around 3 GHz but no worse.
If you can reliably measure it.

What matters is the ratio of connector length to wavelength along the line.

For the same reason, at HF, bringing the two wires of an open wire line
close together for the purpose of drawing them through a single small hole
in the wall, will not produce any noticeable effect on line performance.
----
Reg.

=================================

"Richard Fry" wrote in message
...
"Reg Edwards" wrote
Provided the mechanical connection is sound, you can use any coaxial
connectors you like, regardless of nominal impedance, at frequencies
less
than about 300 MHz without any observed ill effects.
_________________

??? Using connectors that don't maintain the characteristic impedance of
the
transmission lines they connect _will_ produce undesired effects. The
effects may be negligible to amateur radio operators used to operating
transmitters into rather high mismatches, but they would never be
tolerated
in most professional operations, including high-power broadcast systems.

Years ago a common impedance for rigid transmission line used in broadcast
systems was 51.5 ohms. Later the more common value was/is 50 ohms. While
a
mechanical adapter was available to allow connecting a 51.5 ohm inner
conductor to 50 ohm inner conductor (SWR= 1.03), better installations
installed an RF transformer section at these interfaces.

A 1.1 SWR at the input of a TV transmit antenna using ~500 or more feet of
transmission line will produce a visible "ghost" in the transmitted
picture,
as seen by a careful observer. At 1.25 SWR it can be seen, and will
objectionable to almost everyone.

RF

Visit http://rfry.org for FM broadcast RF system papers.

Connector salesmen (and no doubt ladies) have the habit of exaggerating the
importance and magitude of SWR ON THE LINE associated with the precision of
connector manufacture. The habit transfers itself into magazine articles
without any supporting practical experiments.

Right-- but WRONG! Wouldn't be too concerned about the IMPEDENCE mismatch
at this short distance,
but, in THIS case, as the center conductor of the coax
in the CENTER PIN of the CONNECTOR, might have problem with connection, or
SPREADING the female
center connector, so as to not make good connection with the proper coax in
the future! Jim NN7K


"Richard Fry" wrote in message
...
"Reg Edwards" wrote
Provided the mechanical connection is sound, you can use any coaxial
connectors you like, regardless of nominal impedance, at frequencies
less
than about 300 MHz without any observed ill effects.
_________________

??? Using connectors that don't maintain the characteristic impedance of
the
transmission lines they connect _will_ produce undesired effects. The
effects may be negligible to amateur radio operators used to operating
transmitters into rather high mismatches, but they would never be
tolerated
in most professional operations, including high-power broadcast systems.

Years ago a common impedance for rigid transmission line used in broadcast
systems was 51.5 ohms. Later the more common value was/is 50 ohms. While
a
mechanical adapter was available to allow connecting a 51.5 ohm inner
conductor to 50 ohm inner conductor (SWR= 1.03), better installations
installed an RF transformer section at these interfaces.

A 1.1 SWR at the input of a TV transmit antenna using ~500 or more feet of
transmission line will produce a visible "ghost" in the transmitted
picture,
as seen by a careful observer. At 1.25 SWR it can be seen, and will
objectionable to almost everyone.

RF

Visit http://rfry.org for FM broadcast RF system papers.

"Richard Fry" wrote in message
...
"Reg Edwards" wrote
Provided the mechanical connection is sound, you can use any coaxial
connectors you like, regardless of nominal impedance, at frequencies
less
than about 300 MHz without any observed ill effects.
_________________

??? Using connectors that don't maintain the characteristic impedance of
the
transmission lines they connect _will_ produce undesired effects. The
effects may be negligible to amateur radio operators used to operating
transmitters into rather high mismatches, but they would never be
tolerated
in most professional operations, including high-power broadcast systems.

Connectors available off the shelf are not perfect, especially the pl259
type that are usually used by many.
While I don't doubt the problems to TV signals, this is an amateur group
type discussion.
Many antennas are nowhere near the 50 ohms that the cable is. Most any
connector will not cause any more problems than the coax/antenna mismatch
will in all but the most demanding systems (maybe EME or some satellite
work).