[Elecraft] Band pass filters, was ICE

[Jim Brown]

On 4/28/2011 11:39 AM, Rick Stealey wrote:
> Actually one of the main reasons the filters are used is in DXpedition
> or FD setups to restrict the phase noise you transmit to your (phone or
> cw) part of the band so there can be other stations operating on the
> same band.  So you are protecting the other stations ability to
> use the band at the same time.

This is NOT correct.  Bandpass filters are just that -- they PASS the 
entire ham band, and only STOP signals outside the band.  They will have 
NO effect on phase noise produced by a transmitter on th SAME band. A 
MUCH narrower filter is needed.

W2VJN has published the design for a few multi-stub filters that ARE 
sharp enough to cut off between phone and CW on relatively wide bands 
like 160M, 80M, and 10M.  It would be a real challenge to make them work 
on the other bands, which are MUCH narrower as  percentage of the TX 
frequency. The W2VJN designs are in his EXCELLENT book on Managing 
Interstation Interference, available from the Inrad filter folks. It's 
worth many times the $25 cost.

An important advantage of stubs is that they can be placed at the output 
of a power amp, so they can attenuate trash produced in the amp as well 
as trash produced in the transceiver.

73, Jim Brown K9YC