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.

"Reg Edwards" wrote

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

AND

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.
______________________

REG: Please consider this.

Most TV transmit antenna systems have an adjustable RF transformer installed
at the antenna input connector. This transformer consists of 4 or 5 brass
"pins" of about 5/8" diameter spread evenly across a 90 degree section of
rigid transmission line. These pins can be inserted radially into the space
between the outer and inner conductors of that line section. When the pins
are withdrawn fully, they have no affect on the natural impedance of that
line section, but can produce a spatially discrete SWR as function of their
insertion distance into the line.

I, personally, and many other broadcast engineers have been involved in the
adjustment of such RF transformers to optimize the match between the main
transmission line and the antenna input [including its elbow complex(es)],
at the frequencies used in commercial VHF/UHF television -- which start at
54 MHz.

This requires (1) purchase and installation of the transformer, (2)
deployment of a tower crew to adjust it, and (3) use of a qualified field
engineer in the tx bldg with the appropriate test equipment and field
experience to direct the adjustment of that variable transformer.

Obviously, these processes are not inexpensive, and would not be undertaken
if there was no reason. The reason: to optimize the match between the main
line and the antenna, and thus to transmit the "cleanest" video.

This PRACTICAL experience illustrates that an impedance change even in a
54-60MHz TV channel occurring within a physical space of less than one inch
can produce important and commercially supportable system benefits, despite
your statements quoted above.

I invite you to post the contrary result(s) of your own "practical
experiments," and/or those of others.

RF

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