On Mon, 19 Feb 2007 01:09:52 GMT, james wrote
in :

On Sun, 18 Feb 2007 09:21:02 -0600, "Pete KE9OA"
wrote:

+++I understand what you are saying, but the RF amplifier should be conjugate
+++matched to 50 ohms anyway, in order to have uncondisional stability. I am
+++not sure what the noise figure of this system is, but it seems that the gain
+++distribution is such that most of the gain is in the 2nd I.F. strip anyway.
+++Even so, under 30MHz, in most areas the excess environmental noise is in the
+++15dB region so a receiver with a 12dB noise figure does just fine.
+++I remember the old Allied Model 2568 CB radio. This thing had quite a bit of
+++RF gain and relatively low I.F. gain. As soon as you connected an antenna,
+++it sounded like an FM unit. The problem with that design is that the AGC
+++voltage was derived from the RF stage with its relatively low selectivity,
+++in addition to the I.F. strip. Strong off channel signals would capture the
+++AGC loop and desense the whole system. Remember the old term "bleed over"?
+++You do have a good point about keeping the RF gain ahead of the mixer as low
+++as possible, since any gain ahead of the 1st mixer degrades the dynamic
+++range by that same amount. In my last contract with Motorola, we were using
+++mixers that had an IP3 of +40dBm so we were able to get away with having
+++some gain ahead of that mixer.
+++
***********

Conjugate match is needed for maximum power transfer.


IMPEDANCE match... for maximum power transfer. A 'conjugate' match is
when the impedances are complex, which isn't always the case.


Nuetralization
helps extend stability over various mismatch condistions.


Lots of things can improve stability, but unless the amp/mixer is
oscillating the point is moot.


In a receiver RF front end it is preferable to match for best noise
figure and accept the gain. The less gain before the mixer the better.
The RF front end sets the noise figure for the whole receiver. The
gain of the RF Front end need only be high enough to overcome the
noise figure of the next stage and any losses it may present if any.


All true. But the point I was trying to make (which I incorrectly
assumed was already understood) is that any impedance matching device
or network between the antenna and the 1st RF can cause more noise
from IMD than the noise from the 1st RF or mixer, -especially- if that
matching device/circuit uses a ferrite core or solid dielectric, which
includes almost all CB radios. That's why strong signals can sometimes
be heard even when the source is several MHz away (often mistaken for
receiver overload).

The concept here is to reduce (or, ideally, eliminate) that impedance
transformation stage. A long time ago I built a common base (voltage
follower) RF preamp using eight transistors in parallel followed by
the impedance transformation stage (transformer). The input impedance
directly to the transistors is about 100 ohms, but I feed it directly
anyway. The difference is like night and day. I use it for lowfer work
these days.


More often than not,CB calibur radios places far to much gain in the
first stages so that more simple IF stages can be used. Thereby
lowering costs.


Like you said before, the first RF is all that matters.

On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland
wrote:

+++Conjugate match is needed for maximum power transfer.
+++
+++
+++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is
+++when the impedances are complex, which isn't always the case.
***********

I have found that it is rare in the real world that impeadances are
not complex. Outside transimission lines, there is little that is not
complex. Then again when you conjugate match, the imaginary part of
the complex impedances is nulified and you are then left with the real
part.

james

On Mon, 19 Feb 2007 19:12:33 GMT, james wrote
in :

On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland
wrote:

+++Conjugate match is needed for maximum power transfer.
+++
+++
+++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is
+++when the impedances are complex, which isn't always the case.
***********

I have found that it is rare in the real world that impeadances are
not complex. Outside transimission lines, there is little that is not
complex.


You just said that resistors have complex impedance and transmission
lines are flat.


Then again when you conjugate match, the imaginary part of
the complex impedances is nulified and you are then left with the real
part.


Reactances don't just disappear. They create a current between the
source and load that must be assessed to see if it is going to cause
any problems. Sometimes it doesn't and sometimes it does.

On Mon, 19 Feb 2007 12:43:12 -0800, Frank Gilliland
wrote:

+++On Mon, 19 Feb 2007 19:12:33 GMT, james wrote
+++in :
+++
+++On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland
wrote:
+++
++++++Conjugate match is needed for maximum power transfer.
++++++
++++++
++++++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is
++++++when the impedances are complex, which isn't always the case.
+++***********
+++
+++I have found that it is rare in the real world that impeadances are
+++not complex. Outside transimission lines, there is little that is not
+++complex.
+++
+++
+++You just said that resistors have complex impedance and transmission
+++lines are flat.
+++
************

No I did not. Besides Resistors can have complex impedances depending
upon constrtuctinand frequency in which they are used.

+++
+++ Then again when you conjugate match, the imaginary part of
+++the complex impedances is nulified and you are then left with the real
+++part.
+++
+++
+++Reactances don't just disappear. They create a current between the
+++source and load that must be assessed to see if it is going to cause
+++any problems. Sometimes it doesn't and sometimes it does.
+++
+++
***********

I did not say they disappeared. At resonance the conjugate match
causes the net reactance to be zero. Thus nulify. The reactance are
always there.


james

On Tue, 20 Feb 2007 03:13:52 GMT, james wrote
in :

On Mon, 19 Feb 2007 12:43:12 -0800, Frank Gilliland
wrote:

+++On Mon, 19 Feb 2007 19:12:33 GMT, james wrote
+++in :
+++
+++On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland
wrote:
+++
++++++Conjugate match is needed for maximum power transfer.
++++++
++++++
++++++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is
++++++when the impedances are complex, which isn't always the case.
+++***********
+++
+++I have found that it is rare in the real world that impeadances are
+++not complex. Outside transimission lines, there is little that is not
+++complex.
+++
+++
+++You just said that resistors have complex impedance and transmission
+++lines are flat.
+++
************

No I did not.


Go back and read your own words again.


Besides Resistors can have complex impedances depending
upon constrtuctinand frequency in which they are used.


When a resistor is used at its intended frequency, any reactance is
insignificant. If it wasn't then it would be called an 'inductor' or
'capacitor'.


+++
+++ Then again when you conjugate match, the imaginary part of
+++the complex impedances is nulified and you are then left with the real
+++part.
+++
+++
+++Reactances don't just disappear. They create a current between the
+++source and load that must be assessed to see if it is going to cause
+++any problems. Sometimes it doesn't and sometimes it does.
+++
+++
***********

I did not say they disappeared. At resonance the conjugate match
causes the net reactance to be zero. Thus nulify. The reactance are
always there.


Notwithstanding the fact that the non-reactive component of impedance
changes at or near resonance, maximum power transfer (due to matched
impedances) occurs regardless of whether those impedances are reactive
or not. Hence "impedance match" instead of the more limited "conjugate
match". As for your assertion that non-reactive impedances are rare in
the "real world", maybe you should describe -your- "real world" and
how it differs from the rest of reality.

On Mon, 19 Feb 2007 22:52:40 -0800, Frank Gilliland
wrote:

+++Notwithstanding the fact that the non-reactive component of impedance
+++changes at or near resonance, maximum power transfer (due to matched
+++impedances) occurs regardless of whether those impedances are reactive
+++or not. Hence "impedance match" instead of the more limited "conjugate
+++match". As for your assertion that non-reactive impedances are rare in
+++the "real world", maybe you should describe -your- "real world" and
+++how it differs from the rest of reality.

**********
I am not saying that the real portion of impendances are rare. I am
saying that pure resistance is but a subset of complex impedance. Pure
resistance is where the reactive part of the complex impedance is
zero. In the real world no component has a "zero" reactive component
as does it not have zero resistive part.

In conjugate matching, the nodal point where the output of the
transform network terminates with the load will have a net reactance
of zero. The real part is still there. It does not go away. The net
real part should be half that of the real part of the load.

All components have complex impedances. In cases where frequency of
operation is well below the self resonance frequency, discrete passive
components can be thought of as purely resistive or purely reactive
dending on construction of the passive part. That be whether it is a
resistor or a capacitor or inductor. Non passive components have
complex impedances.

All the above is valid only when you are dealing with time varying
signals. Complex impedance has no definition when dealing with a non
time varying signal(ie. DC).

james

On Tue, 20 Feb 2007 18:52:07 GMT, james wrote
in :

On Mon, 19 Feb 2007 22:52:40 -0800, Frank Gilliland
wrote:

+++Notwithstanding the fact that the non-reactive component of impedance
+++changes at or near resonance, maximum power transfer (due to matched
+++impedances) occurs regardless of whether those impedances are reactive
+++or not. Hence "impedance match" instead of the more limited "conjugate
+++match". As for your assertion that non-reactive impedances are rare in
+++the "real world", maybe you should describe -your- "real world" and
+++how it differs from the rest of reality.

**********
I am not saying that the real portion of impendances are rare. I am
saying that pure resistance is but a subset of complex impedance. Pure
resistance is where the reactive part of the complex impedance is
zero. In the real world no component has a "zero" reactive component
as does it not have zero resistive part.


Well, in my "real world" there are many components with reactances so
small as to be insignificant and are therefore ignored.


In conjugate matching, the nodal point where the output of the
transform network terminates with the load will have a net reactance
of zero. The real part is still there. It does not go away.


Okay....


The net
real part should be half that of the real part of the load.


Huh?


All components have complex impedances. In cases where frequency of
operation is well below the self resonance frequency, discrete passive
components can be thought of as purely resistive or purely reactive
dending on construction of the passive part. That be whether it is a
resistor or a capacitor or inductor.


Thank you. And I should add that it is more often the case where an
intended reactive component is measured for resistive impedance than
an intended resistive component is measured for reactive impedance.


Non passive components have
complex impedances.


Not necessarily, for the very same reasons mentioned above.


All the above is valid only when you are dealing with time varying
signals. Complex impedance has no definition when dealing with a non
time varying signal(ie. DC).


For all practical purposes, true.

But you are still ignoring the fact that a conjugate match is nothing
more than an impedance match using a conjugate impedance, which is
often not necessary. Just because some comp resistors -- or even the
wires or PCB traces -- in an audio amp or power supply may have a very
slight inductive reactance doesn't mean you waste your time trying to
load them all with sub-pF caps. That's why, here in the real world,
the term "impedance match" is used to include any necessary conjugate
match that may (or may not) be necessary, and why you don't hear the
term "resistance match" used very often (i.e, never).

How about the real world above 1GHz? It is very easy to model these
"insignificant" reactances in a program such as ADS and see the effects on a
real world circuit design.

Pete

"Frank Gilliland" wrote in message
...
On Tue, 20 Feb 2007 03:13:52 GMT, james wrote
in :

On Mon, 19 Feb 2007 12:43:12 -0800, Frank Gilliland
wrote:

+++On Mon, 19 Feb 2007 19:12:33 GMT, james wrote
+++in :
+++
+++On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland
wrote:
+++
++++++Conjugate match is needed for maximum power transfer.
++++++
++++++
++++++IMPEDANCE match... for maximum power transfer. A 'conjugate'
match is
++++++when the impedances are complex, which isn't always the case.
+++***********
+++
+++I have found that it is rare in the real world that impeadances are
+++not complex. Outside transimission lines, there is little that is not
+++complex.
+++
+++
+++You just said that resistors have complex impedance and transmission
+++lines are flat.
+++
************

No I did not.


Go back and read your own words again.


Besides Resistors can have complex impedances depending
upon constrtuctinand frequency in which they are used.


When a resistor is used at its intended frequency, any reactance is
insignificant. If it wasn't then it would be called an 'inductor' or
'capacitor'.


+++
+++ Then again when you conjugate match, the imaginary part of
+++the complex impedances is nulified and you are then left with the
real
+++part.
+++
+++
+++Reactances don't just disappear. They create a current between the
+++source and load that must be assessed to see if it is going to cause
+++any problems. Sometimes it doesn't and sometimes it does.
+++
+++
***********

I did not say they disappeared. At resonance the conjugate match
causes the net reactance to be zero. Thus nulify. The reactance are
always there.


Notwithstanding the fact that the non-reactive component of impedance
changes at or near resonance, maximum power transfer (due to matched
impedances) occurs regardless of whether those impedances are reactive
or not. Hence "impedance match" instead of the more limited "conjugate
match". As for your assertion that non-reactive impedances are rare in
the "real world", maybe you should describe -your- "real world" and
how it differs from the rest of reality.

On Sat, 24 Feb 2007 18:03:18 -0600, "Pete KE9OA"
wrote in
:

How about the real world above 1GHz? It is very easy to model these
"insignificant" reactances in a program such as ADS and see the effects on a
real world circuit design.


Did you miss this part?


When a resistor is used at its intended frequency.....

Resistors can have complex impedances, especially film resistors. Carbon
film resistors can get by up to 30MHz or so, and metal film resistors
shouln't be used above 10MHz. The problem with these devices is that they
consist of a sprial etched resistance material that has a fair amount of
reactance as you go up in frequency.
Carbon composition resistors are preferable in RF applications, but even
their lead length becomes too reactive at higher frequencies.
Nowadays, we use 0603 or smaller size components at higher frequencies. 0402
geometry is presently being used at higher frequencies, with 0201 size soon
to become the norm. This is what I have been working with for the last
couple of years.

Pete

"Frank Gilliland" wrote in message
...
On Mon, 19 Feb 2007 19:12:33 GMT, james wrote
in :

On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland
wrote:

+++Conjugate match is needed for maximum power transfer.
+++
+++
+++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is
+++when the impedances are complex, which isn't always the case.
***********

I have found that it is rare in the real world that impeadances are
not complex. Outside transimission lines, there is little that is not
complex.


You just said that resistors have complex impedance and transmission
lines are flat.


Then again when you conjugate match, the imaginary part of
the complex impedances is nulified and you are then left with the real
part.


Reactances don't just disappear. They create a current between the
source and load that must be assessed to see if it is going to cause
any problems. Sometimes it doesn't and sometimes it does.