[Elecraft] FTDX5000 Design Flaw

[John, KI6WX]

The ARRL is aware of this issue.  This problem was discussed in my 1988
articles on phase noise in QST (March & April issues).  The article notes
that a high phase noise transmitter degrades the performance of a low phase
noise receiver to that of the transmitter.  This article started the ARRL
making composite transmit noise measurements.

A strong signal (>S9+50dB) from a transmitter with broadband -130 dBc
composite noise in a 500 Hz bandwidth reduces the receiver's blocking
dynamic range to 103 dB.  Most top notch receivers show a blocking dynamic
range of around 140 dB.  In this case, the dynamic range is reduced because
the noise floor is increased.

I don't think most hams are aware of the problem.  If you have a nearby ham
running high power and your receiver doesn't work well when they are
transmitting, you just assume that the signal is too strong for your
receiver.

This problem is like splatter or key clicks.  It doesn't impact the owner of
the transmitter, but instead degrades the receiving environment of those who
live near them.  There is little incentive for the owner of the high
composite noise transmitter to improve their equipment.

-John
 KI6WX

> 
> The FTDX500 wouldn't be the only one, if a -130 dBc composite noise
> number defines failure. If you have access to QST reviews, compare:
> 
> Flex 5000
> FT-2000
> Orion II
> IC-7700
> K3
> 
> all of which plot tx composite noise at 100 or 200 W out to 1 Mhz. You
> can draw your own conclusions, but the FTDX5000 apparently isn't
> exceptional in that regard.  The Flex is no better than -120 dBc out
> to 1 MHz, the FT-2000 is slightly worse than the FTDX-5000, and the
> Orion II is no better than -130 dBc out to 100 kHz. The Icom rigs seem
> to do a little better. The K3 performance indeed far surpasses the
> others. I could find no comment on these numbers in the reviews.
> 
> Bob NW8L
> 
> > Why is this not sent to the Editor and Technical Editor or QST as
> > well as the lead test engineer at the ARRL lab?  What was their
> > response?
> >
> > If the radio's transmitted phase noise is that bad, Yaesu should be
> > forced to recall all units currently in the field.
> >
> >
> > 73,
> >
> >    ... Joe, W4TV
> >