Cecil Moore wrote:
On Apr 27, 10:30 am, Wimpie wrote:
Depending on the frequency resolution of your VSA, the frequency of
the injected signal can be well within 1 kHz of the carrier, so LC
filters in the PA will not distort the measurement. In case of a 100W
PA and injection of about 100 mW, the difference in wanted signal and
signal to be rejected is 30 dB (not that large).

Would any competent optical physicist suggest that it is valid to
study the conditions associated with interfering coherent light waves
inside an interferometer by introducing an incoherent light source
into the system? Why would any competent RF engineer suggest that the
system source conditions associated with interfering coherent RF waves
can be studied by introducing an incoherent test signal?

Interestingly, it's NOT an incoherent test signal. It's a carefully
chosen coherent test signal with a frequency difference. It's the same
idea as having an interferometer with dithering piezo transducer on a
mirror or a modulator in one of the paths.

Wimpie wrote:
Hello Cecil,

On 27 abr, 20:13, Cecil Moore wrote:
On Apr 27, 10:30 am, Wimpie wrote:

Depending on the frequency resolution of your VSA, the frequency of
the injected signal can be well within 1 kHz of the carrier, so LC
filters in the PA will not distort the measurement. In case of a 100W
PA and injection of about 100 mW, the difference in wanted signal and
signal to be rejected is 30 dB (not that large).
Would any competent optical physicist suggest that it is valid to
study the conditions associated with interfering coherent light waves
inside an interferometer by introducing an incoherent light source
into the system? Why would any competent RF engineer suggest that the
system source conditions associated with interfering coherent RF waves
can be studied by introducing an incoherent test signal?

As this slightly off-carrier frequency signal behaves like a load with
very low VSWR with a cable in between that extends with constant
speed. In other words, the amplifier sees a constant VSWR, but with
changing phase. Small frequency difference results in slow phase
change of VSWR.


to the device under test, this isn't much different than a electrically
controlled line stretcher (a classic automated load pull setup... see
the stuff from Maury Microwave, for instance)

It's a very clever technique. A variant is used in antenna ranges where
you have a probe with a mismatch in it.

On 27 abr, 23:18, Cecil Moore wrote:
On Apr 27, 1:43*pm, Wimpie wrote:

In other words, the amplifier sees a constant VSWR, but with
changing phase. Small frequency difference results in slow phase
change of VSWR.

From the IEEE Dictionary:

"impedance -

(1)(A) The corresponding impedance function with p
replaced by jw in which w is real. Note: Definitions
(A) and (B) are equivalent.

(1)(B) The ratio of the phasor equivalent of a steady-
state sine wave voltage ... to the phasor equivalent
of a steady-state sine wave current ...

(1)(C) A physical device or combination of devices
whose impedance as defined in definition (A) or (B)
can be determined. Note: This sentence illustrates
the double use of the word impedance ... Definition
(C) is a second use of 'impedance' and is independent
of definitions (A) and (B)."

The pinging experiment seems to be measuring a physical impedance (1)
(C) the nature of which is unclear. When the amplifier is outputting
power, it seems that the source impedance would be a V/I ratio (1)(B)
which doesn't respond to incoherent signals. Seems to me, you guys are
pinging something other than the source impedance.
--
73, Cecil, w5dxp.com
"Halitosis is better than no breath at all.", Don, KE6AJH/SK

Hello Cecil,

You may try to figure out how the signal injection method functions
(it is a form of active load pulling).

Can you agree with:

it doesn't matter whether:
-power reflect towards the amplifier is caused by load mismatch, or
-power is sent towards the amplifier by means of a phase synchronized
source.

This source is phase synchronized with the PA's exciter, so we have a
steady state system.

We assume small load mismatch (or low injected power towards the PA)
so that the operating point of the PA just changes slightly (to allow
linear approximation).

Now we insert a coupler between the amplifier and the load. This
coupler will measure the forward voltage generated by the PA, plus the
reflected part of the voltage that originates from the phase
synchronised source. Depending on the phase relationship, it can be
more or less then the forward voltage of the PA. If the PA shows 50
Ohms, the coupler's output would not change due to the signal
injection (as no signal is reflected by the PA).


We note the forward coupler's output voltage (both phase and
amplitude).

Now we change the phase relationship between the exciter and the
source that transmits some power toward the PA. Lets change 180
degrees and keep the amplitude the same. We again note the coupler's
output voltage (both phase and amplitude).

The voltage that is reflected by the PA equals half the complex
voltage change because of the phase change. Off course you have to
correct the readings because of the coupler loss. If you know the
signal that is send toward the PA, you can now calculate the complex
output impedance of the PA for small load change around 50 Ohms.

Instead of changing the phase of the source manually, you can do that
continuously and note the couplers output continuously. If you change
the phase of a signal continuously (with certain constant rad/s), the
result is a decrease or increase of frequency.

Assuming some reflection by the PA, the complex output from coupler
rotates around a certain point. That certain point is the result of
the PA's output power and the rotating vector is the result from the
injected signal that is reflected by the PA (back towards the load).

With a VSA you can discriminate between the voltage component from the
PA itself and the reflected component (with slightly different
frequency). With a normal spectrum analyser, you can only determine
the magnitude of the PA's reflection coefficient (or VSWR as you
like). Given the dynamic range of today's equipment, you can inject a
very low level signal that may mimic load mismatch well below VSWR =
1.1.

With respect to the impedance concept, we as amateurs do not use
steady state signals, as they contain no information. We modulate them
and are still using the impedance concept, despite the definitiones
you showed.

As long as the signal that is injected is well within the pass band of
the PA and it sufficiently low to allow linear approximation, the
concept of superposition and concept of impedance still holds. But if
you feel more confident with the manual phase change, or using two
known loads with known slight mismatch, I have nothing against it.
But if you have a VSA, some couplers and signal source at hand, it
may save lots of time.

With kind regard,

Wim
PA3DJS
www.tetech.nl

Wimpie wrote:

With a VSA you can discriminate between the voltage component from the
PA itself and the reflected component (with slightly different
frequency). With a normal spectrum analyser, you can only determine
the magnitude of the PA's reflection coefficient (or VSWR as you
like). Given the dynamic range of today's equipment, you can inject a
very low level signal that may mimic load mismatch well below VSWR =
1.1.



One needs to have an analyzer with a narrow band detector for this, though.

Inexpensive analyzers like the TAPR VNA have untuned detectors, so the
PA's main signal will screw things up.

The N2PK uses a form of direct conversion detector, so your test signal
would have to be far enough away from the main signal so that the LPF in
the detector filters it out. The original N2PK design uses, I think, a
100 Hz filter, and the adc samples at 15.36 kHz with a digital filter.
The overall BW is something like 5 Hz, so putting your test signal 1kHz
away would probably work.

On 4/26/2011 7:52 PM, Richard Clark wrote:
On Tue, 26 Apr 2011 15:27:28 -0700, Jim
wrote:

(If I had a very efficient op amp, I could simulate any arbitrary output
impedance, without dissipating any power in the source)

I can see why this is parenthetical, because it covers a lot of sins
of omission.

yep.. not possible to build such a thing, anymore than one can build a
zero ohm output impedance RF source with any signficant power.
Suggested more as an example that the power dissipation in the source
doesn't necessarily correlate with match, load Z, or anything else in
general.

(You can get pretty darn close at powers less than a watt and HF, though..)

OP AMPs are a constant of my admiration in the possibilities offered.
That and the signal processing you suggest (plus digital oscillators)
"could" change the playing field - if conventional design weren't so
universally fallen back upon.

73's
Richard Clark, KB7QHC

I wonder if this should be applied to these sorts of projects -

https://www.kb9yig.com/

I have a 1 watt kit that I haven't put together yet. Several others in
our club have and they love them. Especially nice for CW.

tom
K0TAR

On 4/27/2011 6:33 PM, Wimpie wrote:
it doesn't matter whether:
-power reflect towards the amplifier is caused by load mismatch, or
-power is sent towards the amplifier by means of a phase synchronized
source.

This source is phase synchronized with the PA's exciter, so we have a
steady state system.

We assume small load mismatch (or low injected power towards the PA)
so that the operating point of the PA just changes slightly (to allow
linear approximation).

Thanks Wimpie.

It sometimes takes a bit to get me to realize this type of thing isn't
hard, it's actually simple. My old brain tries to obfuscate things from
itself sometimes.

It Calc 100. Make the difference small.

tom
K0TAR

On Apr 27, 6:33*pm, Wimpie wrote:
With respect to the impedance concept, we as amateurs do not use
steady state signals, as they contain no information. We modulate them
and are still using the impedance concept, despite the definitiones
you showed.

Trouble is, the impedance in IEEE definition (1)(B) doesn't *cause*
reflections. If the actual source impedance matches IEEE definition (1)
(B), the presumption that source impedance will *cause* a reflection
is invalid.

Walter Maxwell argues that the actual source impedance of an RF
amplifier is in reality a V/I ratio, i.e. it agrees with IEEE
definition (1)(B).
--
73, Cecil, w5dxp.com
"Halitosis is better than no breath at all.", Don, KE6AJH/SK

On Apr 27, 2:13*pm, Cecil Moore wrote:
On Apr 27, 10:30*am, Wimpie wrote:

Depending *on the frequency resolution of your VSA, the frequency of
the injected signal can be well within 1 kHz of the carrier, so LC
filters in the PA will not distort the measurement. *In case of a 100W
PA and injection of about 100 mW, the difference in wanted signal and
signal to be rejected is 30 dB (not that large).

Would any competent optical physicist suggest that it is valid to
study the conditions associated with interfering coherent light waves
inside an interferometer by introducing an incoherent light source
into the system? Why would any competent RF engineer suggest that the
system source conditions associated with interfering coherent RF waves
can be studied by introducing an incoherent test signal?
--
73, Cecil, w5dxp.com
"Halitosis is better than no breath at all.", Don, KE6AJH/SK

Cecil suggested reading Chapter 19A in Reflections to view the results
of my extensive measurements of the output resistance (impedance) of
RF power amps, but except for Jim and Richard, it appears that the
others have not. Actually, Chapter19A is an addition to Chapter 19,
which when taken completely will provide some information that will
hopefully change some minds concerning the maximum power delivered. It
should be understood that 'maximum' power delivered is that power
delivered with a specified level of drive.

For example, if the drive level is set to deliver a maximum of 100w,
and the pi-network is adjusted to deliver that maximum power into its
load, the source resistance (impedance) will be the (complex)
conjugate of the load impedance. We're not talking here about the
very maximum power that the amp can deliver, with max drive, max plate
current, etc.

If you review the 19A portion of you will see beyond a doubt that the
conjugate match exists between the output of the pi-network and its
complex load impedance, and that the maximum power delivered at the
drive level that allows only 100w to be delivered as the maximum.

Further review of all the data presented there will also show that the
output resistance of the amp is non-dissipative, while the dissipative
resistance is that between the cathode and plate. The reason the
efficiency of the amps can exceed 50 percent is because the cathode to-
plate resistance is less than the non-dissipative output resistance,
where that R = E/I appearing at the output of the pi-network.

Walt, W2DU

I hope the review of my measured data will clear up some of the
confusion concerning the output resistance (impedance) of the RF power
amp.

Walt, W2DU

On Apr 27, 2:13*pm, Cecil Moore wrote:
On Apr 27, 10:30*am, Wimpie wrote:

Depending *on the frequency resolution of your VSA, the frequency of
the injected signal can be well within 1 kHz of the carrier, so LC
filters in the PA will not distort the measurement. *In case of a 100W
PA and injection of about 100 mW, the difference in wanted signal and
signal to be rejected is 30 dB (not that large).

Would any competent optical physicist suggest that it is valid to
study the conditions associated with interfering coherent light waves
inside an interferometer by introducing an incoherent light source
into the system? Why would any competent RF engineer suggest that the
system source conditions associated with interfering coherent RF waves
can be studied by introducing an incoherent test signal?
--
73, Cecil, w5dxp.com
"Halitosis is better than no breath at all.", Don, KE6AJH/SK

Cecil suggested reading Chapter 19A in Reflections to view the results
of my extensive measurements of the output resistance (impedance) of
RF power amps, but except for Jim and Richard, it appears that the
others have not. Actually, Chapter19A is an addition to Chapter 19,
which when taken completely will provide some information that will
hopefully change some minds concerning the maximum power delivered. It
should be understood that 'maximum' power delivered is that power
delivered with a specified level of drive.

For example, if the drive level is set to deliver a maximum of 100w,
and the pi-network is adjusted to deliver that maximum power into its
load, the source resistance (impedance) will be the (complex)
conjugate of the load impedance. We're not talking here about the
very maximum power that the amp can deliver, with max drive, max plate
current, etc.

If you review the 19A portion of you will see beyond a doubt that the
conjugate match exists between the output of the pi-network and its
complex load impedance, and that the maximum power delivered at the
drive level that allows only 100w to be delivered as the maximum.

Further review of all the data presented there will also show that the
output resistance of the amp is non-dissipative, while the dissipative
resistance is that between the cathode and plate. The reason the
efficiency of the amps can exceed 50 percent is because the cathode to-
plate resistance is less than the non-dissipative output resistance,
where that R = E/I appearing at the output of the pi-network.

The earlier portion of Chapter 19, that appears in Reflections 2, can
be downloaded from my web page at www.w2du.com, click on 'Read
Chapters from Reflections 2', and select Chapter 19.

I hope the review of my measured data will clear up some of the
confusion concerning the output resistance (impedance) of the RF power
amp.

Walt, W2DU

On 28 abr, 14:39, Cecil Moore wrote:
On Apr 27, 6:33*pm, Wimpie wrote:

With respect to the impedance concept, we as amateurs do not use
steady state signals, as they contain no information. We modulate them
and are still using the impedance concept, despite the definitiones
you showed.

Trouble is, the impedance in IEEE definition (1)(B) doesn't *cause*
reflections. If the actual source impedance matches IEEE definition (1)
(B), the presumption that source impedance will *cause* a reflection
is invalid.

Are you familiar with the concept of S-parameters where you determine
impedance by measuring of reflection coefficient?

Walter Maxwell argues that the actual source impedance of an RF
amplifier is in reality a V/I ratio, i.e. it agrees with IEEE
definition (1)(B).
--
73, Cecil, w5dxp.com
"Halitosis is better than no breath at all.", Don, KE6AJH/SK

Wim