Re: noise canceling Elevator /HF?

On Wed, 27 Feb 2008 11:28:42 GMT, ml <m@xxxxxx> wrote:

the companies that make these noice devices say the above you
proposed won't work at all, however your idea is ceartainly worth
trying and a fun experiment only way i'll learn and know fer sure

Hi Myles,

What they may be talking about is noise that arrives over the air
(radiation) won't be materially affected by chokes - or at least not
enough. However, where chokes do work best is with noise over the
wire (conduction) and your sense antenna sitting right on top of the
elevator shack is tightly coupled (and why I suggested putting it
further away).

and the chokes are easy to do can't hurt

However, knowing their impedance characteristic is important because
you may end up thinking they weren't useful for the wrong reason (they
didn't present enough impedance).

A ferrite choke at the feed point consisting of 50 mixed beads of
Amidon types #75 and #73 (or #77) over RG58 will be about a foot
long. A couple more of these along the line (one a quarter wave away
from the feed point for a low band, and another a quarter wave away at
the high band) will help decouple it further. At a minimum, over the
HF band it will present something on the order of 1000 Ohms to those
noise currents traveling on the braid outer surface. The attenuation
ratio of this Z to your front end Z is not very considerable (low
teens of dB) but still useful. At the proximity you are with sitting
on top of the elevator shack, distance with the square law will help
far more - you only want to sense the noise, not pull it into your ham
shack.

You will need to choke ALL lines going topside in this manner (your
principle antenna, your sense antenna, your control leads to your SGC)
such that this sounds like an investment of roughly 150-450 beads.

I would move the sense antenna first as that is the cheapest test for
noise reduction that could bring the greatest return - pick the low
hanging fruit first.

73's
Richard Clark, KB7QHC
.

Relevant Pages

  • Re: AM radio receiver - design
    ... The OP is making a radio for the standard AM band. ... frequencies from 20Hz to roughly 7KHz. ... The fn1 and fn2 are two parts of the noise. ... cared about the signals out of the demodulator at high frequencies, ...
    (sci.electronics.design)
  • IBOC Digital "Hash" {Noise} - It is a "Additive" Problem that Grows . . .
    ... Maybe Adds One S-Unit of Added Noise to the S/N Across the Band ...
    (rec.radio.shortwave)
  • Re: 40M band closed ?
    ... Yesterday evening at around 8PM IST, i took my receiver to ... antenna and switched on the receiver and there was no noise. ... this noise present in the 49m shortwave broadcasting band? ... Today morning i brought the receiver down and hung a wire antenna ...
    (rec.radio.amateur.dx)
  • Re: Outdoor concert recordings
    ... > that AT sells specifically for these mics go for about 10% of that. ... cardiods never gave me wind noise that I could notice in context, ... It really bugs me when I see a band on TV and when they ... which helps keep the noise floor down. ...
    (rec.audio.pro)
  • Re: noise canceling Elevator /HF?
    ... What they may be talking about is noise that arrives over the air ... where chokes do work best is with noise over the ... on top of the elevator shack, distance with the square law will help ... principle antenna, your sense antenna, your control leads to your SGC) ...
    (rec.radio.amateur.antenna)