Re: Receiver sensitivity parameter


mediumwavedx
 

Hi Phillips,

Millivots per meter (mV/m) is a way of defining a station's expected (or measured) field strength at a receiving location. It matters little whether that signal is ultimately impressed on a ferrite bar or rod, or a long wire, in that the receiver will take whatever tiny voltage induced and convert it into intelligible audio if it is strong enough. The iron core ferrite rod is basically a signal concentrator. The longer the rod and thus the more iron ferrite, the more the concentration, and the greater signal voltage, at least to a point.

A mediumwave station's expected field strength at a receiving location (daytime hours) also depends on other factors, one being the ground conductivity between the transmitter and receiver path.

I did some articles on ferrite antennas and signal measurements on my blog a couple of years ago. Maybe they will help with introducing some of this material.

Field Strength Calculations (3 parts):

An Unassuming Antenna - The Ferrite Loopstick:

Field Strength Calculations: A History:
Bill
RADIO-TIMETRAVELLER
http://radio-timetraveller.blogspot.com

---In ultralightdx@..., <phillicom@...> wrote :


I am still trying to get my cotton wool stuffed brain around this parameter.

Does this parameter only apply to receivers with ferrite antennas?  Is this the "missing" piece of the puzzle that has eluded me?  It would explain why a barefoot short ferrite antenna receiver generally has lower specified sensitivity than a long ferrite.

If I follow this line of logic then it would suggest that a ferrite antenna receiver operating at 150KHz would need to be in a field 10 times greater than the same receiver operating at 1,500KHz to deliver the same degree of performance.  This would, in turn, suggest that a ferrite antenna receiver will be roughly three times more effective at the top end of the BCB than at the bottom when operating in fields of the same amplitude.

Am I reasonably correct in following this line or am I talking through a cocked hat?





To: ultralightdx@...
From: ultralightdx@...
Date: Wed, 3 Sep 2014 22:17:13 -0400
Subject: [ultralightdx] Re: Receiver sensitivity parameter

 

Whatis.com says it better then me! "The standard unit of electric field (E-field) strength is the volt per meter (V/m). An E field of 1 V/m is represented by a potential difference of 1 V existing between two points that are 1 m apart. 

The volt per meter, or some fractional unit based on it, is used as a means of specifying the intensity of the electromagnetic field (EM field) produced by a radio transmitter. Although an EM field contains a magnetic (M) component as well as an electric (E) component, the relative field strength of radio signals is easier to measure in free space by sampling only the E component. The magnitude of the E component from a distant radio transmitter is often much less than 1 V/m, and in such cases, fractional units are preferred. One millivolt per meter (mV/m) is equal to 10 -3 V/m; one microvolt per meter (? V/m) is equal to 10 -6 V/m; one nanovolt per meter (nV/m) is equal to 10 -9 V/m; one picovolt per meter (pV/m) is equal to 10 -12V/m.
The magnitude of the E component of a radio wave varies inversely with the distance from the transmitter in a free-space, line-of-sight link. If the distance is doubled, the E-field intensity is cut in half; if the distance increases by a factor of 10, the E-field intensity becomes 1/10 (0.1 times) as great. The E component of an EM field is measured in a single dimension, so the intensity-versus-distance relation is a straight inverse rule, not the inverse-square law."





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