[CQ-Contest] Band Pass Filters

[Pavel Perchine]

Joe,


> 1- To have the filters provide the ultimate best rejection they can
> provide the impedance must be as close to 50 ohms as possible.
> Is this true? If it is, is there any published data showing how much is
> lost on performance due to "X" SWR?
>

There is no relationship between the filter SWR and  maximum filter
attenuation but there is a tight connection between SWR and Insertion
filter loss. You can have  very good filter rejection and very bad  filter
SWR (return Loss) at the same time.

>
> 2- This one is even more important. They are rated 200 watt units. "At
> 50 Ohms"
> Now SWR that is NOT 50 Ohms Can make some pretty high voltages true?
> And I am assuming these voltages are what gives each unit it's power
> rating.
>
> With High SWR some filter parts inside will be under the stress and also
the dissipation heat (with increased filter insertion loss) will go up too.
Both factors can destroy the filter.

I would keep an antenna SWR below 1:2.
SWR =2 is not the best, it is 25 or 100 Ohms but some filters can handle it
without any issue.
With SWR going higher the chance  to smoke your filters is very high and
the tuner addition will help for sure.

Pavel
VA6AM
https://va6am.com/

Go too high and fry a cap.
>
> Now Our Station, (The only CW station) will be running a K3 with the
> Roofing filters. My Partner in this station says,,,,,
>
> Picking up a K3 tomorrow.
> We will be using it at field day. It has a 400 Hz roofing filter, 100
> Watts, internal tuner, USB interface, upgraded synth and the nice IO board.
> Should be on the air for SST Sunday night.
> Jim
>
>   Now I know we will be clean on Transmit, To an OCFD.
> That 400Hz roofing filter, How much will that protect US, see we will be
> surrounded by several IC-7300's
>
> Would like to use the Band Pass filters to help but not sure if they can
> handle the not perfect SWR that a typical OCFD will give us.
>
> I assume if we had to we can add an external manual tuner, to make the
> SWR flat then go to the filter and rig.
> And the external manual tuner would also add in some band pass filtering
> effect too.
>
> Joe WB9SBD
>
>
>
>
>
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