J
John Larkin
Guest
On Sat, 11 Dec 2010 12:47:06 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:
John
wrote:
Too scared to try it?
John
P
Phil Allison
Guest
"John Larkin is a LYING CUNT "
** Done it many times.
FFS look up the matter on the net
- you FUCKING RAVING NUT CASE !!!
.... Phil
** Done it many times.
FFS look up the matter on the net
- you FUCKING RAVING NUT CASE !!!
.... Phil
J
John Larkin
Guest
On Sat, 11 Dec 2010 13:39:35 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:
John
wrote:
Then you did it wrong.
John
P
Phil Allison
Guest
"John Larkin is a NUTCASE LYING CUNT "
** FFS look up the matter on the net
- you FUCKING RAVING NUT CASE !!!
.... Phil
** FFS look up the matter on the net
- you FUCKING RAVING NUT CASE !!!
.... Phil
J
John Larkin
Guest
On Sat, 11 Dec 2010 16:50:46 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:
Or try it?
John
wrote:
You can't google "source termination" ?
Or try it?
John
P
Phil Allison
Guest
John Larkin is a TOTALLY INSANE autistic pig.
** Fraid he has been that way since birth.
..... Phil
** Fraid he has been that way since birth.
..... Phil
J
John Larkin
Guest
On Sat, 11 Dec 2010 17:02:42 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:
Cursing and shrieking won't help you understand transmission lines.
Quite the opposite.
John
wrote:
Cursing and shrieking won't help you understand transmission lines.
Quite the opposite.
John
J
John Larkin
Guest
On Fri, 10 Dec 2010 06:04:29 -0500, JW <none@dev.null> wrote:
load will form a simple voltage divider with gain of 0.5.
The frequency response is the same either way, flat until the scope
capacitance or the scope bandwidth starts to roll it off.
RF signal generators are usually spec'd/calibrated to deliver some
voltage or power into a 50 ohm load. Function generators are usually
spec'd/calibrated to deliver some voltage into an open circuit. The
difference is 2:1 voltage.
As Phil said, get a 50
John
Right. The end of the coax looks like a 50 ohm source, so a 50 ohm
load will form a simple voltage divider with gain of 0.5.
The frequency response is the same either way, flat until the scope
capacitance or the scope bandwidth starts to roll it off.
RF signal generators are usually spec'd/calibrated to deliver some
voltage or power into a 50 ohm load. Function generators are usually
spec'd/calibrated to deliver some voltage into an open circuit. The
difference is 2:1 voltage.
As Phil said, get a 50
The waveform will be the same, just different amplitude.
John
P
Phil Allison
Guest
John Larkin is a TOTALLY INSANE autistic pig.
** Fraid he has been that way since birth.
The sooner the pig dies the better.
..... Phil
** Fraid he has been that way since birth.
The sooner the pig dies the better.
..... Phil
P
Phil Allison
Guest
"Jamie" = Maynard A. Philbrook
Radio ham: KA1LPA
Maynard is a grossly autistic mental retard.
Maynard is a fucking troll too.
..... Phil
Radio ham: KA1LPA
Maynard is a grossly autistic mental retard.
Maynard is a fucking troll too.
..... Phil
J
Jamie
Guest
John Larkin wrote:
J
Jamie
Guest
Phil Allison wrote:
I say friend because I don't know if you have a fetish
for girls of guys!
Being from down under, you may prefer kangaroo,
that sure would make it seem you got a real work out!
Jamie..
take care of you lately ?
I say friend because I don't know if you have a fetish
for girls of guys!
Being from down under, you may prefer kangaroo,
that sure would make it seem you got a real work out!
Jamie..
P
Phil Allison
Guest
"Jamie" = Maynard A. Philbrook
Radio ham: KA1LPA
Maynard is a grossly autistic mental retard.
Maynard is a fucking troll too.
Maynard is fucking arsehole.
..... Phil
Radio ham: KA1LPA
Maynard is a grossly autistic mental retard.
Maynard is a fucking troll too.
Maynard is fucking arsehole.
..... Phil
J
John Fields
Guest
On Fri, 10 Dec 2010 17:02:42 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
An ideal transmission line will exhibit only delay and insertion loss,
the insertion loss qualifying it as an attenuator, albeit a tiny one
for a short line at a low frequency.
---
At the capacitive end of the cable that's true, but you don't get the
-6dB rolloff that you'd expect, you get the corner at -3dB and the
skirt falls off at -3dB per octave.
---
Yes, but in the process of being absorbed, the voltage across the
source resistance will be exalted or diminished by the current in the
wave reflected from the load, causing unexpected variations from
nominal in the voltage across the load when the exalting/diminishing
wave from the source returns to the load.
---
I did, and got some interesting results, among them that with the
capacitance you specified the knee was at about -3 dB at 200MHz and
the rolloff was -3dB per octave.
Possibly because of the "feedback" from the reflections?
I don't know. My models blew up after a while and left me with the
feeling that maybe I was hooking up to the coax incorrectly.
Seems strange, since it worked for a while, so I sent a request for
clarification to the LTspice user group.
They're excellent with feedback, so when I get an answer I'll modify
my circuit, as required, and post it.
---
Yes, of course.
We all know that, but a signal generator with an attenuator designed
and legended to drive a resistive load will only be accurate at the
frequency where the capacitor's reactance is such that the voltage
across it will be half that of the open-circuit voltage of the
generator.
And, even at that, the attenuator will only be useful in determining
the voltage across the load, not the power into it, as displayed,
since the load is reactive.
---
JF
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
---
An ideal transmission line will exhibit only delay and insertion loss,
the insertion loss qualifying it as an attenuator, albeit a tiny one
for a short line at a low frequency.
---
---
At the capacitive end of the cable that's true, but you don't get the
-6dB rolloff that you'd expect, you get the corner at -3dB and the
skirt falls off at -3dB per octave.
---
---
Yes, but in the process of being absorbed, the voltage across the
source resistance will be exalted or diminished by the current in the
wave reflected from the load, causing unexpected variations from
nominal in the voltage across the load when the exalting/diminishing
wave from the source returns to the load.
---
---
I did, and got some interesting results, among them that with the
capacitance you specified the knee was at about -3 dB at 200MHz and
the rolloff was -3dB per octave.
Possibly because of the "feedback" from the reflections?
I don't know. My models blew up after a while and left me with the
feeling that maybe I was hooking up to the coax incorrectly.
Seems strange, since it worked for a while, so I sent a request for
clarification to the LTspice user group.
They're excellent with feedback, so when I get an answer I'll modify
my circuit, as required, and post it.
---
---
Yes, of course.
We all know that, but a signal generator with an attenuator designed
and legended to drive a resistive load will only be accurate at the
frequency where the capacitor's reactance is such that the voltage
across it will be half that of the open-circuit voltage of the
generator.
And, even at that, the attenuator will only be useful in determining
the voltage across the load, not the power into it, as displayed,
since the load is reactive.
---
JF
J
Jamie
Guest
Phil Allison wrote:
SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5
SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5
P
Phil Allison
Guest
"John Fields"
** I set up the same conditions as the OP described - ie an RF generator,
1.5 meters of RG58 co-ax and a 60MHz scope with 1 Mohm //20pF input.
AS EXPECTED the input impedance of the cable dips sharply at the quarter
wave frequency, 22MHz for my set up - or 28 MHz if the cable is left
completely unterminated. This was determined by monitoring the signal at the
output connector of the RF gen with a 10:1 probe.
However, at the scope end of the cable there is little sign of any dipping
or peaking.
So, the cable acts like a quarter wave stub all right, but the unterminated
end has a fairly consistent signal level since peaking and dipping occur
simultaneously at opposite ends.
Sue as hell looks like standing waves at play to me.
..... Phil
** I set up the same conditions as the OP described - ie an RF generator,
1.5 meters of RG58 co-ax and a 60MHz scope with 1 Mohm //20pF input.
AS EXPECTED the input impedance of the cable dips sharply at the quarter
wave frequency, 22MHz for my set up - or 28 MHz if the cable is left
completely unterminated. This was determined by monitoring the signal at the
output connector of the RF gen with a 10:1 probe.
However, at the scope end of the cable there is little sign of any dipping
or peaking.
So, the cable acts like a quarter wave stub all right, but the unterminated
end has a fairly consistent signal level since peaking and dipping occur
simultaneously at opposite ends.
Sue as hell looks like standing waves at play to me.
..... Phil
J
John Larkin
Guest
On Sat, 11 Dec 2010 17:41:22 -0600, John Fields
<jfields@austininstruments.com> wrote:
inductance and capacitance, so it can't dissipate power.
An ideal 50 ohm transmission line, used to extend the output of a 50
ohm signal generator, adds time delay. Nothing else.
scope was flat, no frequency whoopie-doos, from DC up to there. But it
is 6 dB/octave after the corner.
generator gobbles them all up.
some reason, the lossy-line model seems to work better, even if you
crank the losses down to invisibility.
John
<jfields@austininstruments.com> wrote:
How could an ideal transmission line have loss? It only includes
inductance and capacitance, so it can't dissipate power.
An ideal 50 ohm transmission line, used to extend the output of a 50
ohm signal generator, adds time delay. Nothing else.
Insane. Sorry to say so, but insane.
Nope.
The 200 MHz corner was where I predicted. And I bet the voltage at the
scope was flat, no frequency whoopie-doos, from DC up to there. But it
is 6 dB/octave after the corner.
If it's source terminated, there are no secondary reflections. The
generator gobbles them all up.
Spice seems to have two txline models, the ideal and the lossy. For
some reason, the lossy-line model seems to work better, even if you
crank the losses down to invisibility.
Gibberish.
Ditto.
John
J
John Larkin
Guest
On Sun, 12 Dec 2010 12:04:34 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:
nothing but time delay to the 50 ohm generator.
will be flat over frequency until the 160 MHz -3 dB point, and then
roll off nicely at -6/octave, unless the scope itself craps out first.
Your 60 MHz scope will roll off before the 50r+20 pF corner hits. You
shouldn't see any frequency peaks or dips at the scope, regardless of
the cable length.
You might see some wobbles if the generator isn't a clean 50 ohm
source. In that case, you can get multiple reflections.
Thanks for trying it.
John
wrote:
Yes.
Also yes. That was the point. As seen from the end, the coax adds
nothing but time delay to the 50 ohm generator.
Sure, but you don't see them at the scope. The signal at the scope
will be flat over frequency until the 160 MHz -3 dB point, and then
roll off nicely at -6/octave, unless the scope itself craps out first.
Your 60 MHz scope will roll off before the 50r+20 pF corner hits. You
shouldn't see any frequency peaks or dips at the scope, regardless of
the cable length.
You might see some wobbles if the generator isn't a clean 50 ohm
source. In that case, you can get multiple reflections.
Thanks for trying it.
John
P
Phil Allison
Guest
"John Larkin is a CRIMINAL LIAR "
Phil Allison
** The LIAR claimed there were no standing wave effects - quote:
" No standing waves or resonances at all. "
Then he denied that the "quarter wave stub " was relevant to the case.
Wot a blatant fucking LIAR !!!
..... Phil
Phil Allison
** The LIAR claimed there were no standing wave effects - quote:
" No standing waves or resonances at all. "
Then he denied that the "quarter wave stub " was relevant to the case.
Wot a blatant fucking LIAR !!!
..... Phil
J
John Larkin
Guest
On Sun, 12 Dec 2010 12:43:51 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:
above 200 MHz, as predicted. No bumps or resonances will be visible at
the scope. As I noted in a previous post, any standing wave effects
are buried inside the cable and invisible at the load.
I made no comments about a quarter-wave stub.
Read your own posts. You said:
"The real situation is that of an unterminated transmission line of
operating over a very wide frequency range.
Will exhibit more peaks and dips than the Himalayas."
There are no such peaks or dips at the end of the line, at the scope,
as you observed yourself.
John
wrote:
The frequency response is flat at the scope, with just the rolloff
above 200 MHz, as predicted. No bumps or resonances will be visible at
the scope. As I noted in a previous post, any standing wave effects
are buried inside the cable and invisible at the load.
I made no comments about a quarter-wave stub.
Read your own posts. You said:
"The real situation is that of an unterminated transmission line of
operating over a very wide frequency range.
Will exhibit more peaks and dips than the Himalayas."
There are no such peaks or dips at the end of the line, at the scope,
as you observed yourself.
John