[Yaesu] FT-920 Transmit IMD

[Christian von Wechmar]

Hi Everyone,

I'm considering getting a Yaesu FT-920. Together with the INRAD filter
boards, it seems to be a very nice rig. The man-sized dimensions are also a
big plus for me.

However, the ARRL test (October 1997) has the following comments about the
transmitter:

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Somewhat disconcerting were the results of the transmit intermodulation
distortion (IMD) tests (see Figures 1 and 2). Almost as disturbing as the
prominence of third and fifthorder products was the prominence of
higherorder (ie, seventh, ninth, eleventh) products.  Yaesu specified a
third-order IMD figure of -31 dBc (see Table 1), a specification it met on
15, 17, 20, 40, 80 and 160 meters, where IMD performance was much better but
not spectacular. For comparison, the best case was 40 meters, where
third-order products were 32 dB down, and fifth-order were 45 dB down, and
higher-order products were almost non-existent.

On HF, the ARRL Lab measured worstcase performance on 12 meters, where
thirdorder products were just 25 dB down and fifthorder 31 dB down. That's
marginal in comparison to other transceivers in this price class that we've
looked at recently. Exacerbating this performance was the fact that
higher-order products do not drop below 50 dB until the 13th order!

The worst-case performance on 50 MHz was only a shade better. Third-order
products were down by 27 dB and fifth-order products by 33 dB, but, once
again, higher-order products remain prominent through the 13th order.  As we
've said in past reviews, this is the kind of IMD performance that may lead
to problems with splatter and "wide" signals, especially when the
transceiver is used with an amplifier.

The ARRL Lab measured comparable IMD performance on a second FT-920. This
marginal IMD performance was the only serious problem we encountered with
this transceiver.  Yaesu advised that its production units as of mid-August
were "displaying less variation in performance, due to tightening of
production part tolerances." Yaesu supplied one of these units for us to
test. The unit barely met its third-order IMD specification on the HF bands
but not on 6 meters; higher-order products overall were less prominent,
however.

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Does anyone know if Yaesu fixed the transmitter? Sadly, the only other real
option would be to get the (more expensive) Mark V Field. Another concern is
the reputed wide CW keying bandwidth. Anyone know if this was indeed a
problem, and if it has been addressed?

73 ES DX,
Chris ZS1DX