Re: [CQ-Contest] Sept/Oct NCJ article on DX Prowess of Receivers

[Bill Coleman <aa4lr@arrl.net>]

On Sep 1, 2004, at 11:45 PM, Bill Tippett wrote:

> AA4LR:
> >The primary reason the K2 and K2/100 rigs do so well on these 
> receiver tests is because they use a very simple single-conversion 
> design. Although the first (and only) IF filter isn't a particularly 
> sharp-skirted design, it is sufficient to knock out most all adjacent 
> channel interference.
>
>         Sufficient only for 5 kHz spacings and above.  The K2
> falls apart very badly at closer spacings.  IMD performance
> is mediocre at best for 1-2 kHz spacings.

I'm afraid it is all relative, Bill. IMD performance may degrade at 
closer spacings, due to the modest skirts of the filter -- but it is 
still substantially better than many older designs using a 15 kHz 
roofing filter.

> IMD: 91 dB @ 5 kHz.....67 dB @ 1 kHz   (graph on page 19)
> BDR: 135 dB @ 5 kHz.....116 dB @ 1 kHz   (graph on page 20)
> http://www.arrl.org/members-only/prodrev/pdf/lab/k2.pdf
>
> Also note where it falls on Sherwood's 2 kHz IMD rankings here:
> http://www.sherweng.com/Dayton_2004/Dynamic_Range_Data.pdf

Two things to note: the ARRL figures for the K2 and K2/100 are 
substantially different. This is not due to any circuitry change when 
adding the 100 watt PA, but due to circuit refinements made in all 
later model K2s.

Second, in the Sherwood measurements (which don't indicate what vintage 
of K2 they tested), the k2 at 2 kHz is only 6-9 dB worse than rigs 
costing many, many thousands more, and is better than many rigs in use 
today.

> As I said previously, how many contests have you heard
> recently with signals spaced 5 kHz or more?

Usually, during a contest, there are strong signals all across the band.

My K2/100, in comparison with my older Kenwood TS-430S beats it hands 
down. When conditions on the Kenwood seem really noisy, the K2 presents 
a nice, quiet band.

While the K2/100 may not be the ultimate in contest rig performance, it 
is a great performer, and beats all others on performance for a given 
price.

PS - how well would the K2 fare if Sherwood or some other company would 
come up with some sharp IF filters for it?

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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