[ARC5] What is a "radio range filter"?

[Kenneth G. Gordon]

On 26 Apr 2016 at 12:51, J Mcvey via ARC5 wrote:

> range filter, if used". No nomenclature given!  What is it and what what it's 
> purpose?

Yes. It is a passive audio filter with a switch which allowed three conditions, 1) sharp audio 
filter peaking sharply at the frequency of the navigation range transmitters AM modulated 
tone of 1020 Hz, 2) a sharp audio filter with a deep NULL at that same frequency allowing 
full AM audio for voice comms from the same navigation range transmitter, and 3) a 
condition with neither a null nor a peak, but still restricted audio bandwidth.

There were several versions, the most common one being a black box with two phone jacks 
on a sloping front panel and a switch marked so that the fllter could be mounted either 
upside down or right side up and still be read correctly. 
 
> I have heard that here was some kind of passive tone filter they used to use to 
> narrow the audio response, but I have never seen such a device. Anybody know 
> about it?

Most of us OT have at least one in "inventory". I have three different kinds here.

> I was wondering if it might serve as a cw filter.

It works very well as such, and has been used for that for many years, although the pitch 
(1020 Hz) is a bit high for most of OT CW ops. I prefer a tone around 750 Hz,.

Ken W7EKB