[Icom] PW1 ?

Thu, 26 Jun 2003 18:10:38 -0700

Bruce, Andy,

What I could do is put my IC-756Pro2 on the spectrum analyser and run a
2-tone test at 12W PEP output. The Quadra requires 75 ~ 80W drive for 1 kW
PEP output; at that drive level, the IMD3 of the Pro2 is probably around -33
dBc.

The contribution of exciter IMD to total system IMD is not all that
significant unless the exciter exhibits severe IMD. To run some rough
"numbers":

The exciter output is 100W PEP, with -30 dBc IMD3. This equates to 0.1W PEP
total IMD3 power.

The amplifier has 10dB power gain, i.e. 100W PEP drive yields 1kW PEP
output.

Let us assume that the amplifier has -30 dBc IMD3 at 1 kW PEP output, i.e.
total IMD power to the antenna is 1W. Now, the amplifier's 10dB power gain
amplifies the exciter's 0.1W contribution by a factor of 10, i.e. to 1W. If
we assume that the IMD3 products are always additive (they may not be; they
can also cancel each other), the total IMD3 power output from the amplifier
is 2W, i.e. -27 dBc. Still none too shabby within the context of the example
given.

In practice, amplifiers and exciters often yield better IMD figures than in
my example, and amplifier power gains range from 9 dB (for some solid-state
amplifiers) to as much as 18 dB  (for grid-driven tube amplifiers with a
swamped input circuit). With a higher  amplifier power gain, the lower drive
requirement goes along with better exciter linearity. The bottom line is
that the exciter may degrade the overall IMD3 "numbers" by anything from 1
to 3 dB in an average case.

Wow! I have just saved myself a whole lot of data-sheet lookups and two-tone
tests, and can go back to playing ball with Big Max!

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Bruce Marton
Sent: Thursday, June 26, 2003 14:01
To: [email protected]
Subject: RE: [Icom] PW1 ?

Yeah,
I have been waiting for Adam to send me the latest results on the
distortion figures of solid state devices as used in the 781 at low
output levels.
--Adam stop petting the new dog and start working on those numbers--
Bruce

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of [email protected]
Sent: Thursday, June 26, 2003 4:17 PM
To: [email protected]
Subject: Re: [Icom] PW1 ?

Bruce-

Thanks for the very valuable information on the Acom. I had thought the
Alpha 87A had been around a long time and the Acom sure looks similar in
execution. And I know you would never run 2,000 watts :-)

Now if we could just get you out of that old technology 781 ( I had one
)
and into a 756 Pro II, you could really utilize the potential of that
amp!
:-) Bet Adam Farson has some good thoughts on the quality of the signal
put
out by a 756 Pro II at 12 watts.

Andy K5VM

----- Original Message -----
From: "Bruce Marton" <[email protected]>
To: <[email protected]>
Sent: Thursday, June 26, 2003 1:14 PM
Subject: RE: [Icom] PW1 ?

| Andy,
| The Acom is not based on the Alpha.  It's really the other way around.
| Acom was producing a stripped down version of their amp and putting
| Alpha's name on it.  Since Alpha is not really in the business like
they
| were, Acom moved on to build their own amp as they see fit to make it,
| and hence the Acom's of today.  They are not Alpha's, they are better
| than Alpha's, at least that's what I keep hearing.
| As far as service is concerned, you send the amp to Acom in Boston, MA
| for service.  That's where I picked up my new amp and had the pleasure
| of spending most of a Saturday with Krassy himself, who fully
| demonstrated the amp and all of it's internal workings to me in
person.
| Not to mention we set up the 10/12 meter operation while the amp was
| open.  The amp is fully computer controlled, can be diagnosed remotely
| via an internet link from the amp if you ever have any troubles, and
can
| be upgraded as such.
|
| As far as distortion goes, the solid state devices appear to just make
| the grade in passing FCC minimum requirements, so there is no danger
of
| running illegally, but the tubes run much beyond the minimum
| requirements, hence much cleaner and I like to have things run without
| heavy breathing myself.
| Just like the output levels.  I can run the Acom with about 40 watts
of
| drive and do an easy 1500 watts.  The tubes aren't even hot.  The amp
| can do well over 2kw with less than normal full output from an
exciter,
| say about 70 watts.  I usually run my amp with about 12 watts of drive
| or so, this gives me about 500+ watts out and everything is very cool.
| Now the question is what is the distortion from the exciter (solid
state
| 781), with 12 watts of output.  I have been told they lower output
| levels from the ratings lead to higher distortion in solid state
| devices??
|
| Bruce

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Icom Users Net: Sundays, 1700Z, 14.315 MHz
Icom FAQ: http://www.qsl.net/icom/

----
Your Moderator: Dick Flanagan W6OLD, [email protected]
Icom Users Net: Sundays, 1700Z, 14.315 MHz
Icom FAQ: http://www.qsl.net/icom/