[Elecraft] K3 1500 Khz Roofing Filter

[David Gilbert]

Hi, Roy.

I've had the 1500 Hz 8-pole Inrad filter in my K3 for at least 18 months 
now, and while I don't do a lot of SSB contesting I certainly appreciate 
that filter when I do.  It works fine and gives just a bit extra margin 
of protection against really loud adjacent stations.   What DSP 
bandwidth you use is up to you.  Of course there isn't much point in 
setting it much wider than 1.5/1.6/1.8 KHz or so because the filter will 
chop it off anyway.  I have often set my DSP as narrow as 1.2 KHz or 
even sometimes 1.0/1.1 KHz, but the key to decent intelligibility with 
any of those really narrow bandwidths is to shift the center frequency 
much lower than the K3 default 1.5Khz.  I typically set the center 
frequency to about 1.1 KHz when I have the bandwidth at 1.5 KHz, and I 
drop down to a center frequency about 0.9 KHz when I have the bandwidth 
set to 1.1 KHz.

A few caveats to all of that:

a.  The optimum center frequency will probably be different depending on 
the voice you are listening to.  I sometimes have to adjust the center 
frequency depending upon the caller, occasionally as low as 700 Hz but 
usually higher than normal.  A few voices seem difficult to copy at 1.5 
KHz or less bandwidth no matter what center frequency I use.

b.  No filter on this earth is going to protect you from in-band 
splatter.  Somebody 3 KHz away with a 5 KHz wide signal is going to mess 
you up even if you're using the 1.5 KHz filter.  I'm always amazed at 
the incredibly bad, almost unintelligible signals we have to put up with 
during a major SSB contest, many of them coming from long time high 
profile contesters.  I find it to be simply pathetic.  My voice won't 
hold up during a SSB contest anymore, so I'm honestly tempted to spend 
the next CQ WW DX SSB contest just recording audio samples (both good 
and bad) identified by callsign.

c.  I bought the 1.5 KHz filters instead of buying the 1.8 KHz filters.  
If you already own the 1.8 KHZ filters I'm not sure it would be worth 
the hassle to switch, especially considering the in-band splatter issue. 
   The only thing you gain from the 1.5 KHz filters is 150 Hz additional 
protection from strong signal overload either side of you since the DSP 
can give you whatever narrow bandwidth you might want for moderate 
signal strengths.

73,
Dave   AB7E




On 5/12/2010 1:08 PM, Roy Morris wrote:
> I would like to hear from anyone who is using the #727 Inrad 1500 Khz roofing filter.  I wonder if this filter adds to razor sharp clear SSB reception when properly set in the DSP bandwidth.   What DSP bandwidth setting should be used to insert this filter?  Any comments will be appreciated.  Thanks.  Roy Morris  W4WFB
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>