[Elecraft] low pass filters

[Ken G Kopp]

OT:  A caution related to external low-pass filters …

Many were made with cutoff frequencies -below- 6M and these
exhibited high reflected power above 10M.

Trivia, FWIW

73!

Ken - K0PP

On Sun, Feb 17, 2019 at 4:26 PM Don Wilhelm <donwilh at embarqmail.com> wrote:

> A low-pass filter will not change RFI either coming into the shack or
> going out.  There are low-pass filters in all transceivers produced by
> Elecraft (and most other manufacturers), and they are in both the
> transmit and receive path.
> The current FCC requirement is for the 2nd harmonic be suppressed by 43
> dB over the fundamental.
> Low pass filters come from a past era when the FCC requirements were not
> as stringent and TVs responded to those higher order harmonics from
> amateur transmitters.  That is no longer the case.
>
> Considering receive, we do have many sources of unintentional radiation
> which is present in the HF spectrum, and other than locating and having
> the offending device turned off, there is not much we can do about it.
> Although if it is interfering with licensed operation, there is recourse
> by cooperation with the FCC.  The products giving problems range from
> inexpensive switching power sources (read wall-warts) to control
> circuits in many household appliances and other consumer devices, and
> even some lighting products.
>
> If you are operating in an environment like Field Day where there are
> multiple transmitters operating in close proximity, bandpass filters and
> single band antennas are the normal "cure" as well as physical
> separation of the antennas.
>
> 73,
> Don W3FPR
>
>
>
> On 2/17/2019 5:59 PM, Richards wrote:
> > Good day -   What is the consensus concerning low-pass filters to
> > minimize RFI both coming in and going out  of the shack?   Is there a
> > type or size, brand or model that comes highly recommended?  Is it
> > prudent to employ one, regardless of whether or not there is a known,
> > identified problem , i.e., just in case?  Does it assist reception as
> > well as transmission?
> >
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