[Elecraft] Band pass filters

[Jim Brown]

On 7/27/2021 12:53 PM, Morgan Bailey wrote:
> 80 to 100 dB band to band attenuation is necessary for a contest station.

That depends a LOT on the radios and the amps.

> Reviewing Contest University the RA6LBS talk from a few years ago is the
> basis for this decision. He probably has the most experience in this field
> beside that of VA6AM. Both make great filters. Just having a filter is not
> enough. One needs a multiplexer in conjunction with the band pass filter to
> get to that DB level. One could stack 2 band pass filters and attain
> whatever is needed to get the job done. The multi switchable boxes that run
> about 500 to 900 dollars only give about 30 to maybe 40 db of rejection.

That also depends a LOT on the boxes, and some are far better than 
others. See this study I did about 8 years ago for National Contest 
Journal. http://k9yc.com/BandpassFilterSurvey.pdf Several of the units 
are 10-20 dB better than that.
  It
> is just not enough to keep the other radio quiet and SAFE from front in
> overload and toasting the receiver circuits. I use transmitting band pass
> filters rated at 3500 watts on the output of my amp. 

This is a very good way to do it. Most hams overlook the harmonics and 
IMD generated in power amps.
This coupled with
> multiplexers on 160/80/40 and 20/15/10 makes for a multi two or an SO2R
> setup quiet on each radio. Between the multiplexer and associated band pass
> filters I am able to run 1.5KW 160-10 with an antenna farm that takes up 68
> linear feet total for 160-10. Additionally, 160/80/40 are vertical
> polarized and 20/15/10 are horizontal polarized adding more rejection. It
> works and works well.
> 
> One problem that many stations on a small lot have is ignoring Common Mode
> pick up off the shield of the coax. Grounding all shields before entering
> the shack 

YES! AND seriously bonding everything in the shack and the building that 
contains it.

and using 1:1 choke baluns is a necessary step to prevent
> interstation interference. 

Yes, it's quite important to have a SERIOUS common mode choke at the 
feedpoint of EVERY antenna. http://k9yc.com/2018Cookbook.pdf
> 
> Having radios with very low composite/Phase noise is necessary. 

YES!

At the last Visalia DX Convention, gave an overview talk on a dozen or 
so mechanisms that contribute to inter-station interference, and how to 
minimize each. It's here. http://k9yc.com/Multi-Station.pdf

And W2VJN's book on the subject is excellent.

73, Jim K9YC