EMRFD Message Archive 1167

Message Date From Subject
1167 2007-11-20 06:39:53 patt896 Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
ref: QST 12/07 (W. Hayward) & QST 5/96 (W. Carver)

Comparison, comments?

Richard Patten
1168 2007-11-20 08:17:47 Allison Parent Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
1170 2007-11-20 12:10:28 michael taylor Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
On Nov 20, 2007 9:39 AM, patt896 <d.patten@att.net> wrote:
> ref: QST 12/07 (W. Hayward) & QST 5/96 (W. Carver)


The older article is "A High Performance AGC/IF Subsystem",
QST May 1996 p.39-44 by Bill Carver K6OLG (now W7AAZ)

I believe the article is included on the EMRFD CD and perhaps ARRL Handbook CDs.

I don't have any practical experience with either, so I cannot comment.

-Michael, VE3TIX
1171 2007-11-20 12:23:23 Baruch Zilbershat... Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
1172 2007-11-20 19:47:42 Wes Hayward Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
Hi Richard and group,

You ask us to compare and contrast the latest offering from QST with
the classic design of W7AAZ. There are dramatic differences between
the two IF amplifiers, which become apparent upon a reading of the
two papers. Bill's paper, like the amplifier, is extensive with a
lot to it. This is not the casual design that the hybrid cascode
is, but is an effort aimed at coming up with the best IF amplifier
that he could at the time. That was in 1996 and the design still
holds up well.

There are several facets to Bill Carver's amplifier that make it
stand out. First is the wonderfully accurate relationship between
the applied control voltage and the gain reduction in dB. This
turns a control system into a measurement tool. Imagine! An S-
meter that has meaning. This is all the result of the Analog
Devices integrated circuits used. The second thing that makes the
system standout is the careful design work that Bill did to get the
most from the AD parts. I urge you to look at the paper not just as
a potentially good design to duplicate, but as a tutorial on elegant
analog design.

But there are complications. First, the noise figure of the AD
parts is not very good. Bill had to precede the amplifiers with a
FET just to come up with something suitable for weak signal
communications applications. Second, the amplifier has exceedingly
high gain. This was in line with Bill's early requirements. He
needed to use three stages of the AD parts to get the required
control range and gain, but had to put a crystal filter part way
through the system to keep the noise within limits. This leads to
some complication in the system dynamics. Filters in the middle of a
control system always do. Finally, the AD parts have become quite
expensive.

The final analysis is that a comparis
1174 2007-11-21 07:07:56 cwfingertalker Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
Richard

Speaking as a home brewer I think it comes down to what is it you want at the end of
your project. What is your design philosophy. Are you looking for a simple circuit for
casual operating or something with all the advantages bar none no matter what the
cost. I think sometimes you can not compare these circuits on the same plane
because they appeal to different needs, wants and desires of a
builder.

The trouble with circuit designs using exotic electronic parts for me is that period of
time between the "inspiration" of the designer to the when the last letter is printed in
the article at "publication". It can be months and in some cases years. In that time
IC's may disappear altogether or become very expensive to buy in small lots. Circuits
like the Cascode IF system can be reproduced reliably at a lower cost and over a
longer period of time because of better parts availability and less cost. This may not
be an "electronic" advantage but for me living in a rural area 300 miles from the
nearest parts store it sure helps my projects get finished.

Some of the best articles I enjoy incorporates the old adage of teaching me how to
"fish" instead of feeding my hunger. What I mean by this is that telling me to use a
part like a 2N2222 in a circuit is far different than teaching me the parameters why
this transistor was chosen in the first place. So by teaching me this I may learn how
to choose another similar part in the future or adapt an old circuit design with
currently available parts. I must admit I still manage to "get the smoke out" of a lot of
transistors.

Best Regards

Bill Martin N7EU

Sam's Valley Oregon.
1176 2007-11-21 07:07:59 Johan H. Bodin Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
Hi Wes and the group,

another way of obtaining fair to good S-meter accuracy is to use a
microcontroller as a "calibration block". Many microcontrollers have an on-chip
A/D converter which can be used to measure the AGC voltage. The linearization
can be done in software by fitting a polynom to the AGC response curve or by
using a table with piecewise linear interpolation, for example. It doesn't take
many lines of code. An analog panel S-meter can then be driven with PWM from a
microcontroller pin. Even a "sloppy" panel meter will give good results if
included in the calibration process. In cases where 8-bit input resolution is
sufficient, a minimalistic QRP approach would be to use the PIC10F222 which is a
Flash microcontroller with A/D and on-chip clock oscillator in a 6-pin SOT23
package (!), about the same size as a normal solder blob ;-)

72/73
Johan SM6LKM

-
1177 2007-11-21 07:51:25 Hari G Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
Hi ,
I have done similar approach with 16F876 , it kind of mimics the Hang
AGC.Its ok i would way i used MC1350 which kind of limited the range but as
a casual operator i was happy with that.But later i moved to STAR !

Best Regards
Hari
VU2GHB



On 11/21/07, Johan H. Bodin <jh.bodin@telia.com> wrote:
>
> Hi Wes and the group,
>
> another way of obtaining fair to good S-meter accuracy is to use a
> microcontroller as a "calibration block". Many microcontrollers have an
> on-chip
> A/D converter which can be used to measure the AGC voltage. The
> linearization
> can be done in software by fitting a polynom to the AGC response curve or
> by
> using a table with piecewise linear interpolation, for example. It doesn't
> take
> many lines of code. An analog panel S-meter can then be driven with PWM
> from a
> microcontroller pin. Even a "sloppy" panel meter will give good results if
>
> included in the calibration process. In cases where 8-bit input resolution
> is
> sufficient, a minimalistic QRP approach would be to use the PIC10F222
> which is a
> Flash microcontroller with A/D and on-chip clock oscillator in a 6-pin
> SOT23
> package (!), about the same size as a normal solder blob ;-)
>
> 72/73
> Johan SM6LKM
>
> -
1178 2007-11-21 15:47:35 patt896 Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
Bingo!! Thanks everyone for your replies.

Six Degrees of Separation, here. W. Carver and I were both military
Brats in Formosa during 1957/1958; but I dont recall meeting him.
Perhaps he was down south; we lived in Taipai.

Richard Patten



1179 2007-11-21 17:26:59 Hari G Re: Hybrid Cascode GP AGC IF Amp vs HP AGC/IF Subsystem
Richard ,

He is busy building (finishing) the chasis of his Star clone.

Best Regards
Hari

On 11/22/07, patt896 <d.patten@att.net> wrote:
>
> Bingo!! Thanks everyone for your replies.
>
> Six Degrees of Separation, here. W. Carver and I were both military
> Brats in Formosa during 1957/1958; but I dont recall meeting him.
> Perhaps he was down south; we lived in Taipai.
>
> Richard Patten
>
>