On 3/4/2015 6:54 AM, Brian Morrison wrote:
On Wed, 04 Mar 2015 06:39:20 -0500
Jerry Stuckle wrote:

On 3/4/2015 6:11 AM, Brian Morrison wrote:
On Wed, 04 Mar 2015 05:50:02 -0500
Jerry Stuckle wrote:

On 3/4/2015 2:29 AM, Jeff wrote:

Coax can NEVER be spliced without causing a huge impedance
mismatch at the point of the splice. This is not 60hz or DC.
But any ham with even a minor bit of technical knowledge should
understand this.


We are talking about 200kHz here not 200MHz!! Use could join the
coax with a bit of choc-block at that frequency and not see any
significant performance degradation.

Jeff


It doesn't matter if it's 200kHz. The problem remains.

It depends what you mean by 'problem'.


And yes, there WOULD be s"significant performance degradation" if
he used a bit of choc-block.

That is only true if the discontinuity is a significant fraction of
a wavelength, 200kHz is about a 1.5km wavelength, in coax that
would be about 1km with typical velocity factors. A choc block is
about 10mm long, so it is 1/100,000th of a wavelength. I would not
expect any major problem but it could be used to experiment and
cleaned up later if necessary.


Incorrect. It all depends on the amount of the impedance bump. The
larger the bump (and there always will be one, even if connectors are
used), the greater the effect on the signal.

You are correct, but in my opinion you would need a very large change
in impedance over 10mm for it to make any difference at 200kHz.


And just how big is the change being proposed?

And while the change in
impedance has a greater effect as you get a higher proportion of a
wavelength, a bump that's even small percentages of a wavelength can
create a significant loss.

Shouldn't be too difficult to calculate the impedance of the choc
block, it's pretty much a balanced line.


And a coax is an unbalanced line - which complicates the calculations.


In extreme cases, a short or open (which is much less than 1/100,000
of a wavelength) would allow no signal through.

We were not discussing either a short or an open.


As I said it is an extreme - but it shows that even a small percentage
of a wavelength can have an effect, contrary to your previous statement.



But if you understood ANYTHING about transmission lines, you
wouldn't make such a stupid statement.


Actually it's because Jeff understands about transmission lines
that he makes the statement, it isn't a stupid statement at all in
the context of the OP's question and the technical details of the
installation.


It is a stupid statement, showing how little he understand
transmission lines.


I don't agree, there is plenty of latitude using imperfect connectors
at low frequencies. People have been using PL259/SO239 connectors for
frequencies as high as 500MHz for decades and yet on the VNA they most
certainly are not 50 ohm connectors above 10MHz or so. A VSWR of 2:1
creates a mismatch loss of 0.5dB, at 3:1 it's still only 1.2dB.


Connector impedance doesn't change with frequency, just as coax
impedance doesn't change with frequency. Loss will increase as
frequency increases, however.

And yes, PL259/SO239 was never meant to be an "all purpose connector"
and has greater loss than many other connectors - at any frequency.

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