[Elecraft] 250 Hz and 400 Hz Filter Measurements

[Bob Naumann]

FWIW - I have the 5-pole 500 and the 5-pole 200 in my K3 and I find that
they cover all contest conditions thus far. 

I have not felt that I needed any additional filtering at all under any
circumstances and I rarely use the 200. 

When things are light - I switch to the 1kHz or even the 2.1 sometimes on CW
when conditions allow.

73,

Bob W5OV
  
-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Craig D. Smith
Sent: Friday, July 16, 2010 7:36 AM
To: 'Jim Brown'; elecraft at mailman.qth.net
Subject: Re: [Elecraft] 250 Hz and 400 Hz Filter Measurements

Good Morning Jim ...

Thank you for the detailed measurements.  That helps substantiate some of
the word-of-mouth on the forum.

I have done no measurements, but do have a 400 Hz filter both in my main RX
and in the sub.  My main interest is CW contesting and I have found them
more than adequate for everything except for conditions sometimes
experienced in the 160 meter contests.  On 160 the 200 Hz 5 pole filter in
my main RX occasionally improves the situation with a very strong local
station.  But I agree with you that there is no need for the 250 Hz 8 pole
option.

73   Craig  AC0DS 

Craig D. Smith
PowerSmith Consulting
1009 Alder Way
Longmont, CO  80503
phone:  303-834-7712      email:  Craig at PowerSmith.net
web:  www.PowerSmithConsulting.com
 

<> -----Original Message-----
<> From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net]
<> On Behalf Of Jim Brown
<> Sent: Friday, July 16, 2010 12:48 AM
<> To: Elecraft List
<> Subject: [Elecraft] 250 Hz and 400 Hz Filter Measurements
<> 
<> Crew,
<> 
<> I finally got around to dragging out my precision audio spectrum
<> analzyer to check out the 250 Hz filters. I have two K3s, one
<> with a single RX and one with two RS. I have 250 Hz and 400 Hz
<> filters in all three RX.
<> 
<> First, I tweaked the centering of each filter (that is, the
<> offset), then I measured bandwidth at -6dB, -30dB, and -60dB with
<> IF bandwidths of 1kHz and 250 Hz.
<> 
<> Results: There was some variation from one filter to another, but
<> trends are quite consistent. The only significant difference
<> between the 250 and 400 Hz filters is at their -6dB points with a
<> 1kHz IF, where the average bandwidths were 311 and 412 Hz
<> respectively. This is essentially the bandwidth of the roofing
<> filters themselves.
<> 
<> Once you crank the IF down to 250Hz, there is no significant
<> difference between the two filters. The average -6dB bandwidths
<> were 193 and 200 Hz; at -30 dB, both filters averaged 300 Hz; at
<> -60dB, they averaged 381 and 397 Hz respectively.
<> 
<> There IS one repeatable difference between the 250Hz and 400Hz
<> filters -- their insertion loss, which is 3dB. That is, the 250Hz
<> filters have 3dB more insertion loss.
<> 
<> After doing these measurements, I firmly agree with W4ZV, W0YK,
<> and others, who have noted that there is no good reason for
<> having both of these filters in a radio. Indeed, there is no good
<> reason for the EXISTENCE of this particular 250 Hz filter,
<> primarily because it is NOT a 250Hz filter by any reasonable
<> measure.
<> 
<> It is long past time for Inrad to lean on their filter supplier
<> and get them to ship 250 Hz filters. Failing that, I want my
<> money back for three filters. BTW -- all of these were purchased
<> from Inrad, not Elecraft.
<> 
<> 73, Jim Brown K9YC
<> 
<> 
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