[Amps] RF Chokes

[Tom W8JI]

> In my building experience over the years with this choke 
> (RF
> Parts/Ameritron), I have never seen one resonate below 
> 11.5 mhz or go above
> 12 mhz in all manners of positions and various layouts. It 
> is a non-issue.

The actual specs for that choke place the "freespace" series 
resonances at 11.8 and 16.8 MHz.
With a wall 1 inch away the series resonances move to 10.8 
and 15.4 MHz.

It is 275uH minimum on 1.8 MHz, 375uH on 3.75 MHz, and has a 
peak impedance of 30K ohms on 7 MHz.

> I think that the reason Alpha and others use 2 chokes to 
> cover all 9 bands
> is that they had a space restriction in the layout. The RF 
> Parts choke is
> larger than most.

I think they also don't believe that winding gaps can be 
used to position series resonances.

When I designed that choke I used positioned gaps to move 
unwanted resonances out of 28, 18, and 10 MHz.