[Elecraft] TX IMD

[Robert Friess]

The RD06HHF1 used in the Low Power Amplifier in the K3  is NOT rated
to only 30 MHz.  It does carry a specification for 6 watts power
output and 16dB gain at 30 MHz, perhaps for services at 27 MHz,   but
further down the data sheet are S parameters all the way to 1000 MHz
indicating a much wider range of useful operation.  The RD06HHF1 as
used in the K3 operates at an output power of only about 1 watt.
Furthermore, when the K3 is equipped with the 100 watt KPA3, the low
power amplifier operates at about 5 watts output.  At this level the
contribution to total IMD is negligible.

73,
Bob, N6CM

On Mon, Jan 26, 2009 at 1:14 PM, Joe Subich, W4TV <lists at subich.com> wrote:
>
> Unfortunately neither the Toshiba or ASI datasheets for the
> 2SC2782 used in the KPA3 provide any IMD specifications.
> Unlike the information available for the 2SC2879.
>
> The 2SC2879 has a distinct "sweet spot" at 60 Watts output
> with 12.5V and 100 mA idle current.  A push pull pair of
> 2SC2879 (e.g., FT-990) would be expected to produce -38dB
> IMD at 120 watts at the collector (100 W from the LPF) with
> 8 - 10 W of drive and Vcc 12.5V at 28 MHz.  Note that the
> 2SC2879 is also rated for -24dB IMD at 100 Watts per device
> (or 200 W PEP from a pair) ... there is no such specification
> for the 2SC2782.
>
> I haven't been able to find IMD data on the low level devices
> for either the FT-990 (2SC2166 predriver, 2SC3133 drivers) or
> K3 (RD06HHF1 predriver, RD15HVF1 drivers).  However, I am a
> bit concerned that the K3 predriver is only rated for 30 MHz
> operation!
>
> 73,
>
>   ... Joe, W4TV
>
>
>
>
> > -----Original Message-----
> > From: elecraft-bounces at mailman.qth.net
> > [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Dave
> > Hachadorian
> > Sent: Monday, January 26, 2009 11:42 AM
> > To: Elecraft reflector
> > Subject: Re: [Elecraft] TX IMD
> >
> >
> > There is something that has been puzzling me for the last 17 years.
> >
> > In November of 1991, QST reviewed the Yaesu FT-990, which
> > used a 13.8 vdc PA. Worst case measured 3rd order IMD
> > was -38 dB, 5th order was -47 dB. This measurement was at
> > 100 watts output. The review is available on ARRL's
> > members-only web site.
> >
> > ARRL had this comment, "It's refreshing to see that it's
> > possible to make a 100-W MF/HF radio with low voltage finals
> > AND such low-distortion transmitter performance".
> >
> > As far as I know, no ham 13.8 volt radio has even come close
> > to this TX IMD performance ever since.  Looking at the 990
> > PA, there's a 2sc2166 predriver, a pair of 2sc3133
> > drivers, and a pair of 2sc2879 finals, all npn transistors,
> > nothing exotic.
> >
> > So what was Yaesu's secret, and why hasn't anyone else even
> > come close?
> >
> > Dave Hachadorian, K6LL
> > Yuma, AZ
> >
> >
> >
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> >
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> >
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> >
> > .
> >
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