Dynamic range expressed in dB does normalize for sensitivity. It is the
difference between the sensitivity and the measured degradation. In theory, a
rig with a 100 dB IMDDR of 100 dB should still have 100 dB of DR if an
attenuator is put in front of it.
The intercept point calculated from the first-order and third-order responses
will vary with either the noise floor or the dynamic range.
That is why my brain likes to think in terms of noise floor and dynamic range
rather than trying to combine them in an IP3 calculation.
Ed Hare, W1RFI
ARRL Laboratory Manager
225 Main St
Newington, CT 06013
Tel: 860-594-0318
Internet: W1RFI@arrl.org
Web: http://www.arrl.org/tis
Member: ASC C63 EMC Committee
Chairman: Subcommittee 5, Immunity
Chairman: Ad hoc BPL Working Group
Member: IEEE, Standards Association, Electromagnetic Compatibility Society
Member: IEEE SCC-28 RF Safety
Member: IEEE EMC Society Standards Development Committee
Chairman, BPL Study Project
Member: Society of Automotive Engineers EMC/EMR Committee
Board of Directors: QRP Amateur Radio Club International
> -----Original Message-----
> From: tentec-bounces@contesting.com
> [mailto:tentec-bounces@contesting.com]On Behalf Of Bill Tippett
> Sent: Wednesday, July 06, 2005 9:02 AM
> To: tentec@contesting.com
> Cc: Hallas, Joel W1ZR; Tracy, Michael, KC1SX
> Subject: [TenTec] ARRL Review of FT9000
>
>
> From ARRL's recent review:
>
> "The differences are in the details. The
> '9000D has three choices for roofing filter
> bandwidth at 3, 6 and 15 kHz, while the
> '7800 has two-6 and 15 kHz. The 3 kHz
> roofing filter and the sharp MicroTune
> preselector front-end account for the
> '9000D's 9 dB edge in third order dynamic
> range at 5 kHz spacing (an impressive 98
> dB at 14 MHz, the best we've ever seen!)."
>
> Hmmm...I wonder if "impressive"
> results are not also due to the fact that the
> MicroTune preselector further attenuates
> MDS by 9 dB beyond that measured
> with Attenuator Off. The differences indeed
> are "in the details". I wonder how Orion's
> results would compare to "the best we've ever
> seen" if another 15 dB of attenuation were
> added to its front-end (to normalize MDS)?
>
> Here are comparable data for
> the FT-9000 (14 MHz, 500 Hz BW, Preamp
> Off plus MicroTune) vs Orion (14 MHz, 500 Hz
> BW, Preamp Off):
>
> Radio MDS IMDDR3
> FT-9000 -113 dBm 98 dB
> Orion -128 dBm 92 dB
>
> Even without MicroTune, the FT-9000
> still has MDS 6 dB higher than Orion (both at
> 14 MHz, 500 Hz BW and Preamp Off) :
>
> Radio MDS IMDDR3
> FT-9000 -122 dBm 95 dB
> Orion -128 dBm 92 dB
>
> How would these compare if another 6 dB of
> attenuation were added to Orion?
>
> Normalizing for 500 Hz BW has long
> been done in rig comparisons. Maybe it's time
> to also consider normalizing for sensitivity
> differences (i.e. MDS). After all, aren't we trying
> to simulate rigs copying an identical weak DX
> signal (i.e. same MDS) under QRM conditions?
>
> 73, Bill W4ZV
>
> _______________________________________________
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>
>
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