> The Yaesu Mk V in class A, on the other hand is astoundingly clean.
> http://nc0b.com/documents/NC0B-Contest-U-2008-9.pdf
That's true enough. Unfortunately, as you also point out in
your presentation, most transceivers do not offer 24, 32, or 48
volt amplifiers capable of 200 in class B and 50 to 60 watts in
class A. Any amplifier other than a high gain triode like the
8877 or pair of 3CX800s is going to require more power than
any of the transceivers can provide in class A to reach 1500
watts out.
The example I gave is for the Mark V Field. Even though it has a
Class A mode, its power is limited to 25 watts - not enough to
drive even an 8877 to 1500 watts out.
73,
... Joe, W4TV
> -----Original Message-----
> From: Rob & Terri Sherwood [mailto:rob@sherweng.com]
> Sent: Tuesday, September 09, 2008 9:56 AM
> To: Joe Subich, W4TV
> Cc: 'Robert Kirkland'; amps@contesting.com
> Subject: Re: [Amps] IMD and driving power
>
>
> The Yaesu Mk V in class A, on the other hand is astoundingly clean.
> http://nc0b.com/documents/NC0B-Contest-U-2008-9.pdf
>
> Joe Subich, W4TV wrote:
> >
> >
> >> As a general rule if you can reduce your amp driving power in
> >> half you gain a 3db reduction in the transceiver IMD.
> >>
> >
> > This is one of those "general rules" that is very wrong when it
> > comes to solid state transceivers. Almost all modern power
> > transistors have a "saddle shaped" IMD curve. When power output
> > is reduced significantly below the optimum point IMD increases.
> > If power is increased above optimum IMD increases rapidly.
> >
> > For example, look at the 2SC2879 used in the Yaesu Mark V Field:
> > http://www.datasheet4u.com/download.php?id=71199. The IMD
> vs. Power
> > Output curves show a "sweet spot" around 55 to 65 watts per
> transistor
> > before filter and transformer losses of about -38 dB. With
> the losses
> > in the transformer, lowpass filter and antenna tuner, this
> represents
> > just about the transceiver's rated 100 watt output.
> Decreasing power
> > to 40 watts per transistor (1.4 dB) increases IMD by more
> than 6 dB!
> > Increasing power output to 80 watts per transistor (~1 dB)
> results in
> > an 8 dB IMD increase and pushing to 100 watts (~2 dB) per
> transistor
> > results in a nearly 14 dB increase in IMD.
> >
> > If your amplifier requires substantially less drive than your
> > transceiver produces you are better off using an attenuator on
> > its input rather than reducing the drive in the transceiver.
> >
> > 73,
> >
> > ... Joe, W4TV
> >
> >
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: amps-bounces@contesting.com
> >> [mailto:amps-bounces@contesting.com] On Behalf Of Robert Kirkland
> >> Sent: Sunday, August 31, 2008 9:04 AM
> >> To: amps
> >> Subject: [Amps] IMD and driving power
> >>
> >>
> >> As a general rule if you can reduce your amp driving power in
> >> half you gain
> >> a 3db reduction in the transceiver IMD. Less in, less out.
> Bob,w5pvr
> >>
> >> _______________________________________________
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> >> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> >>
> >
> > _______________________________________________
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> >
> >
> >
> > --
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