Response is flattened through gain controlling the pre-amp from a look-up
table held in the micro's EEPROM. The alignment procedure is automated using
the HB-IP bus from the spectrum analyzer and a computer. The
computer/analyzer also looks for harmonic content and spurious emissions
during this procedure. Think it takes about ten seconds to do this.

"Richard Clark" wrote in message
...
On Fri, 04 Mar 2005 01:13:39 GMT, "Thomas Magma"
wrote:

Wow this is a long thread. Don't really know where I should put my two
bits
in, but here it goes.

I have designed several RF PA sections in the past. 500MHz at about 50W.
Pretty easy stuff if you have the right tools and know how to use them.
The
tools I like using for matching the power output FET is two triple stub
tuners. One on the input of the FET and one on the output. So it
goes...pre-amp (50 ohm output) - stub tuner - FET - stub tuner - 50
ohm
dummy pad - spectrum analyzer. Then just tune the stubs for the
performance
you desire, these include: efficiency (thermal issues), harmonic content,
spurious emissions, load VSWR considerations, cold start, ect. Then
remove
the FET and look into the triple stub tuners with the network analyzer.
Model and duplicate the network out of discrete components that can
handle
the voltage/power, send the design off to the enviro test lab, and head
home
early for the day.

Cheers,
Thomas

Hi Thomas,

Thanx, your two bits were worth more than the academic plug nickel.
This is something that our original poster should hearken to as his
needs were obviously production oriented. Bench experience will trump
cut-and-paste theory in a heart-beat.

However, triple stub is pretty aggressive. How long did it take you
to flatten response?

73's
Richard Clark, KB7QHC

On Fri, 04 Mar 2005 16:47:05 GMT, "Thomas Magma"
wrote:

Response is flattened through gain controlling the pre-amp from a look-up
table held in the micro's EEPROM. The alignment procedure is automated using
the HB-IP bus from the spectrum analyzer and a computer. The
computer/analyzer also looks for harmonic content and spurious emissions
during this procedure. Think it takes about ten seconds to do this.


Hi Thomas,

10 seconds to adjust all 6 stubs?

73's
Richard Clark, KB7QHC

No the triple stub tuners are only for development. Production boards have
discrete components to form the match network. Power levelling or
"flattening the response" is computer adjusting the output power to
compensate for the reactive components to ensure a constant output power
over the entire band of the radio. We also put in a small temperature
compensation coefficient into the EEPROM because the PA tends to put out
more power when it is cold.

"Richard Clark" wrote in message
...
On Fri, 04 Mar 2005 16:47:05 GMT, "Thomas Magma"
wrote:

Response is flattened through gain controlling the pre-amp from a look-up
table held in the micro's EEPROM. The alignment procedure is automated
using
the HB-IP bus from the spectrum analyzer and a computer. The
computer/analyzer also looks for harmonic content and spurious emissions
during this procedure. Think it takes about ten seconds to do this.


Hi Thomas,

10 seconds to adjust all 6 stubs?

73's
Richard Clark, KB7QHC

On Fri, 04 Mar 2005 17:39:04 GMT, "Thomas Magma"
wrote:

No the triple stub tuners are only for development.

Hi Thomas,

I thought 10 seconds was awful quick. How long would it take to
flatten the response when manually adjusting the triple stub tuners?

What merit did you find with triple that could not be found with
double stub tuners?

73's
Richard Clark, KB7QHC

If your amp has to operate over a wide frequency range it is not likely that
you can flatten the response just with stubs. Stubs should be looked at as
more single frequency devices than broadband networks. But you can use the
stubs to plot out the appropriate impedance curve on the Smith Chart to
ensure a flat response when you model in the discretes.

I usually just try to get the flatness of the response as close as possible
and rely on a software calibration routine to flatten it off. Saves a lot of
time.

It's my understanding that a triple stub tuner of the right length can reach
anywhere on the Smith Chart where as a double stub can not.

"Richard Clark" wrote in message
...
On Fri, 04 Mar 2005 17:39:04 GMT, "Thomas Magma"
wrote:

No the triple stub tuners are only for development.

Hi Thomas,

I thought 10 seconds was awful quick. How long would it take to
flatten the response when manually adjusting the triple stub tuners?

What merit did you find with triple that could not be found with
double stub tuners?

73's
Richard Clark, KB7QHC

On Fri, 04 Mar 2005 19:09:20 GMT, "Thomas Magma"
wrote:
If your amp has to operate over a wide frequency range it is not likely that
you can flatten the response just with stubs.

Hi Thomas,

Certainly not as conventional Triple Stubs. However, care to provide
some of the cogent details of that particular project? Any
interesting insights?

73's
Richard Clark, KB7QHC

Thomas Magma wrote:
No the triple stub tuners are only for development. Production boards have
discrete components to form the match network. Power levelling or
"flattening the response" is computer adjusting the output power to
compensate for the reactive components to ensure a constant output power
over the entire band of the radio. We also put in a small temperature
compensation coefficient into the EEPROM because the PA tends to put out
more power when it is cold.

Richard was asking how long it took you to tune the triple stub filters
during devolpment.

I am curious about the exact nature of the impedance transmformation
these devices provided.

jk

"Richard Clark" wrote in message
...

On Fri, 04 Mar 2005 16:47:05 GMT, "Thomas Magma"
wrote:


Response is flattened through gain controlling the pre-amp from a look-up
table held in the micro's EEPROM. The alignment procedure is automated

using

the HB-IP bus from the spectrum analyzer and a computer. The
computer/analyzer also looks for harmonic content and spurious emissions
during this procedure. Think it takes about ten seconds to do this.


Hi Thomas,

10 seconds to adjust all 6 stubs?

73's
Richard Clark, KB7QHC