On Sun, 18 Jun 2006 16:34:19 +1200, "David & Margaret McBeth"
wrote:

If I join 2 lengths of 93 ohm coax to give 46.5 ohm impedance will the db
loss on the line be greater,less or the same as a single lengthof the coax?
ZL2DG


Presumably by "join 2 lengths" you mean to connect two lengths in
parallel.

If the loss factor L is the loss in one length of the cable, won't the
loss in two parallel lengths be Plost=Pin/2*L+Pin/2*L, so Plost/Pin=L?

Owen
--

On Sun, 18 Jun 2006 05:10:58 GMT, Owen Duffy wrote:

On Sun, 18 Jun 2006 16:34:19 +1200, "David & Margaret McBeth"
wrote:

If I join 2 lengths of 93 ohm coax to give 46.5 ohm impedance will the db
loss on the line be greater,less or the same as a single lengthof the coax?
ZL2DG


Presumably by "join 2 lengths" you mean to connect two lengths in
parallel.

If the loss factor L is the loss in one length of the cable, won't the
loss in two parallel lengths be Plost=Pin/2*L+Pin/2*L, so Plost/Pin=L?


Hi Owen,

Hmm, each time I look at these equations, something is missing, but I
don't know what (probably because it is missing).

Simply put, two lines in parallel lose as much power as one line.
Nothing to be gained in that regard.

73's
Richard Clark, KB7QHC

On Sat, 17 Jun 2006 22:16:58 -0700, Richard Clark
wrote:


If the loss factor L is the loss in one length of the cable, won't the
loss in two parallel lengths be Plost=Pin/2*L+Pin/2*L, so Plost/Pin=L?


Hi Owen,

Hmm, each time I look at these equations, something is missing, but I
don't know what (probably because it is missing).

Devilishly clever technique that. I can't really help, I didn't see it
even after I pressed the send button!


Simply put, two lines in parallel lose as much power as one line.

Of course, we both assumed the lines operates with VSWR=1.

Nothing to be gained in that regard.

Pardon the pun!

Owen
--

On Sun, 18 Jun 2006 05:33:00 GMT, Owen Duffy wrote:

Simply put, two lines in parallel lose as much power as one line.

Of course, we both assumed the lines operates with VSWR=1.

Hi Owen,

You assumed twice. SWR will only mean more loss - the same loss for
one or two lines either way.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
Simply put, two lines in parallel lose as much power as one line.
Nothing to be gained in that regard.

Doesn't it depend on the value of the load impedance,
i.e. upon the SWR?
--
73, Cecil http://www.qsl.net/w5dxp

It is perfectly obvious, at DC and low frequencies, the resistances of
the two inner conductors are in parallel with each other. So with a
fixed voltage at one end there will be a greater power dissipated in a
load resistance at the receiving end.

Outer conductor resistance has a secondary effect.

By connecting two cables in parallel the resulting attenuation will be
smaller. But as Cecil implies, for exact calculations, cable
impedance, cable length, generator and load resistances, and SWR enter
the argument.

In general, it is a complete waste of time, trouble and cost to
connect coaxial cables in parallel merely to obtain a different Zo
impedance.

If a reduction in line loss is the objective, then the most economic
and effective procedure is to use thicker wires in the transmission
line and let line impedance look after itself.
----
Reg. G4FGQ

Reg Edwards wrote:
In general, it is a complete waste of time, trouble and cost to
connect coaxial cables in parallel merely to obtain a different Zo
impedance.

Sounds like someone might have some free 93 ohm coax
and be wanting to use it on a dipole.
--
73, Cecil http://www.qsl.net/w5dxp