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Seasonal Change of Soil Conductivity vs. AM Broadcast Reception

R

rfry

From another website:

>»seeing measured values as low as 2 to 4 mS isn't uncommon during the summer months.
>With that amount of variation in ground conductivity, how does that affect coverage and interference variation between seasons?
__________

My response there ...

A 5000 watt station on 1000 kHz produces a groundwave field intensity of 0.5 mV/m at the end of a complete, 59-mile path of 8 mS/m soil.

With other things equal ...

If the soil conductivity of that complete path was 4 mS/m, the distance to its 0.5 mV/m groundwave field would be 42.2 miles.

To produce a 0.5 mV/m groundwave field at 59 miles for a complete path of 4 mS/m conductivity would take an applied output power of 24,500 watts.

RF
 
rfry said:
To produce a 0.5 mV/m groundwave field at 59 miles for a complete path of 4 mS/m conductivity would take an applied output power of 24,500 watts.
Click to expand...
But in reality, few if most listeners wouldn't be able to adequately receive a listenable .5mV/m MW signal.
Especially true with modern noise conditions.
 
I would say that the main function of M-3 Maps is as a best case scenario for the sales department or as a worst case scenario to simplify AM applications. I don't think there is anyone clamoring for new maps, because 1) It would eliminate the work for consulting engineers to do conductivity and contour measurements to squeeze in new stations and upgrades, and 2) Because of the usefulness of the 2 mV/m contour prediction in translator applications where the 2 mV/m contour goes out more than 25 miles in some or all directions.
 
Last edited:
Kelly A said:
But in reality, few if most listeners wouldn't be able to adequately receive a listenable .5mV/m MW signal.
Especially true with modern noise conditions.
Click to expand...
A MEASURED 0.5 mV/m signal is very listenable on a good car radio outside city and suburban areas. However, the M-3 PREDICTED 0.5 mV/m contour often overestimates the real 0.5 mV/m contour. Managers, salespeople, on air talent, and even many younger engineers who grew up on FM, act like M-3 is written in stone.
 
Schroedingers Cat said:
A MEASURED 0.5 mV/m signal is very listenable on a good car radio outside city and suburban areas. However, the M-3 PREDICTED 0.5 mV/m contour often overestimates the real 0.5 mV/m contour. Managers, salespeople, on air talent, and even many younger engineers who grew up on FM, act like M-3 is written in stone.
Click to expand...
But, given the increase in noise floor over the years, even the ITU specifies 10mV/m for reliable listening. Not everyone is a DX'er, nor has a quality AM radio with equal quality antenna, at least for MW frequencies.
 
When away from the city noise, I can easily listen to a .5 mV/m AM signal. In the city ... not a chance.
 
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