Icom IC-7800 review

[Bill W4ZV]

G3VVT wrote:
 >Reading through the article it appears that the problem occurs when
you  test
for frequency offsets inside the 64.455MHz 1st IF 6kHz roofing  filter. The
measurements on some of the tests of 5kHz offset and below were  apparently
noise limited to -60db region.

 >With this in mind, for close in frequency offsets only, the K2 should  be
showing a better performance than the Icom IC-7800. No doubt
technical  reviews
will be appearing from the ARRL which may answer the question for N.  American
amateurs who do not have access to the RSGB magazine.

         Bob, indeed the IC-7800's close-in phase noise is so bad that
measurements
of IMD and BDR are "noise limited".  As is detailed in the August QST article
about Product Testing, ARRL chooses to measure the composite result including
phase noise issues (see 3rd paragraph under both BDR and IMD sections on page
34 of August 2004 QST).  G3SJX simply lists "noise limited" but ARRL's Expanded
Test Reports shows the composite result.  Indeed the K2 beats the IC-7800 for
BDR but is equal for IMD at 1 kHz spacings.  As has been discussed here
previously, the K2's close-in performance also degrades quite a
bit for signal spacings under 5 kHz.  I'm not sure whether this is
due to filter blow-by or phase noise.  Here are the comparative
measurements from ARRL's ETR's for the K2, IC-7800 and Orion at
5 and 1 kHz spacings respectively:

Rig             IMD             BDR     (at 5/1 kHz spacings)
K2              91/67   134/116
IC-7800 89/67   115/96
Orion   92/84   130/118

Sources: http://www2.arrl.org/members-only/prodrev/reports.html

The comparison between the phase noise plots of the IC-7800 (page 21
of the IC-7800 ETR) and Orion (page 22 of the Orion ETR) are
especially striking, but unfortunately a plot of the K2's phase noise
was not done.

                                                         73,  Bill  W4ZV

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[John, KI6WX]

>          Bob, indeed the IC-7800's close-in phase noise is so bad that
> measurements
> of IMD and BDR are "noise limited".  As is detailed in the August QST
article
> about Product Testing, ARRL chooses to measure the composite result
including
> phase noise issues (see 3rd paragraph under both BDR and IMD sections on
page
> 34 of August 2004 QST).  G3SJX simply lists "noise limited" but ARRL's
Expanded
> Test Reports shows the composite result.  Indeed the K2 beats the IC-7800
for

> BDR but is equal for IMD at 1 kHz spacings.  As has been discussed here
> previously, the K2's close-in performance also degrades quite a
> bit for signal spacings under 5 kHz.  I'm not sure whether this is
> due to filter blow-by or phase noise.  Here are the comparative
> measurements from ARRL's ETR's for the K2, IC-7800 and Orion at
> 5 and 1 kHz spacings respectively:
>
> Rig             IMD             BDR     (at 5/1 kHz spacings)
> K2              91/67   134/116
> IC-7800 89/67   115/96
> Orion   92/84   130/118
>

Bill;
I have extensive measurements of the K2 phase noise on all bands.  On 20
meters at a 20 kHz spacing, both the oscillator phase noise and the mixer
IP3 contribute to the overall dynamic range.  At less than 10 kHz, the phase
noise is dominate and limits the DR3.  I know that filter blow-by is not an
issue at 5 kHz with the CW filter.  Greater than 20 kHz, the K2 DR3 is
primarily limited by the mixer IP3 and the DR3 gets up to about 100 dB.
-John
 KI6WX


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