[Elecraft] RSGB RadCom K3 review posted on RSGB Members web page

[Bill W4ZV]

Jan Erik Holm wrote:
> 
> Interesting review.
> 
> Considering IMDDR3 it seems like one should stay
> way from the 500 Hz filter, looks like the 400 Hz
> is the filter to get.
> 

I haven't read the review but he must have had a bad 500 Hz filter from what
I've heard reported (i.e. the 2.7k better than the 500 Hz).  That makes no
sense and is contradictory to previous measurements by both Elecraft and
Sherwood:

Elecraft:

Filter            20kHz  10kHz  5kHz  2kHz
200 Hz, 5 pole    100+   100+   100+   95
250 Hz, 8 pole    100+   100+   100+   95
400 Hz, 8 pole    100+   100+   100+   95
500 Hz, 5 pole    100+   100+   100+   94
1 kHz, 8 pole     100+   100+   100    94
2.7 kHz, 5 pole   100+   98      92    n/a
2.8 kHz, 8 pole   100+   100     93    n/a

http://www.zerobeat.net/mediawiki/index.php/K3_Roofing_Filters


Sherwood:

Filter - IMD @ 2 kHz
500 Hz - 95 dB
400 Hz - 96 dB
200 Hz - 101 dB*

*I listed the 200 Hz because it's a 5-pole filter (just like the 500 Hz) in
case some believe there is an inherent problem with 5-pole filters.

http://www.sherweng.com/table.html


It's odd but Peter Hart reported something similar when he did Orion's
review.  The 2.4k filter was much better than the 1.0k, which again makes no
sense unless the 1.0k was defective.  I'm sure Peter reported what he
measured but common sense would dictate that one should suspect something
was wrong with the filter and request another when anomalous results like
this are measured.  It also reminds me when ARRL once reported better IMD
performance with Preamp ON versus Preamp OFF.  Common sense would say
"TILT"!

73,  Bill  W4ZV
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