Any Field Strength Guys Here?

On Saturday, December 3, 2022 at 5:09:02 PM UTC-5, whit3rd wrote:
> On Saturday, December 3, 2022 at 11:58:09 AM UTC-8, Tauno Voipio wrote: 
> > On 3.12.2022 19.49, Mike Monett VE3BTI wrote: 
> > > I am trying to find the field strength of a 1 Watt (30 dBm) signal with an 
> > > isotropic antenna at a distance of 15 kilometers. 
> > > 
> > > I need to compare this to a GPS signal of -125 dBm. 
> > > 
> > > Anyone know how to find this? 
> > Calculate the surface area of a sphere of 15 km radius 
> > and divide your transmitting power onto it.
> If the radiation is 'isotropic' in the ground plane, it might have a factor of three 
> more power intensity than that calculation recognizes, because it's a vertical 
> dipole. It isn't much gain, but that's the implication I'd draw from 'isotropic'.

More likely to use these commodity monopoles:
https://www.digikey.com/en/products/detail/TG.08.0113/931-1379-ND/5120279
They list gain as nearly 4dB- take that to mean dBi.

On 03/12/2022 5:49 pm, Mike Monett VE3BTI wrote:
> I am trying to find the field strength of a 1 Watt (30 dBm) signal with an
> isotropic antenna at a distance of 15 kilometers.
> 
> I need to compare this to a GPS signal of -125 dBm.
> 
> Anyone know how to find this?
> 
> 
> 
> 
> 

467uV/m

piglet

piglet <erichpwagner@hotmail.com> wrote:

> On 03/12/2022 5:49 pm, Mike Monett VE3BTI wrote:
>> I am trying to find the field strength of a 1 Watt (30 dBm) signal with
>> an isotropic antenna at a distance of 15 kilometers.
>> 
>> I need to compare this to a GPS signal of -125 dBm.
>> 
>> Anyone know how to find this?
>> 
>> 
>> 
>> 
>> 
> 
> 467uV/m
> 
> piglet

Fantastic. That is a lot more than I expected. Very interesting. Can you
show your calculations? 

If my calculations are correct, that is 
(467e-6)^2 / 377 = 5.78e-10 W/m = -62.381 dBm, or 63 db above the GPS
signal. 

Perfect. Thanks.




-- 
MRM

On 04/12/2022 14:31, Mike Monett VE3BTI wrote:
> piglet <erichpwagner@hotmail.com> wrote:
> 
>> On 03/12/2022 5:49 pm, Mike Monett VE3BTI wrote:
>>> I am trying to find the field strength of a 1 Watt (30 dBm) signal with
>>> an isotropic antenna at a distance of 15 kilometers.
>>>
>>> I need to compare this to a GPS signal of -125 dBm.
>>>
>>> Anyone know how to find this?
>>>
>>>
>>>
>>>
>>>
>>
>> 467uV/m
>>
>> piglet
> 
> Fantastic. That is a lot more than I expected. Very interesting. Can you
> show your calculations?
> 
> If my calculations are correct, that is
> (467e-6)^2 / 377 = 5.78e-10 W/m = -62.381 dBm, or 63 db above the GPS
> signal.
> 
> Perfect. Thanks.
> 
> 
> 
> 

The one I know is E = (7*sqrt(P))/d which gives higher results so tends 
to get used for exposure compliance calcs

E in V/m; P in W; d in m

1W at 15km = 467uV/m

see:
<https://ham.stackexchange.com/questions/10076/how-do-you-calculate-the-field-strength-at-a-given-distance>

But there is another formula often seen which is ballpark same:

<https://www.rfwireless-world.com/calculators/Electric-and-magnetic-Field-Strength-calculator.html>

E = sqrt(30*P)/d

1W at 15km = 365uV/m

Real life may be wildly different.

Isn't this stuff Ham Radio 101 that you needed to get your call?

piglet

Piglet <erichpwagner@hotmail.com> wrote:

> On 04/12/2022 14:31, Mike Monett VE3BTI wrote:
>> piglet <erichpwagner@hotmail.com> wrote:
>> 
>>> On 03/12/2022 5:49 pm, Mike Monett VE3BTI wrote:
>>>> I am trying to find the field strength of a 1 Watt (30 dBm) signal
>>>> with an isotropic antenna at a distance of 15 kilometers.
>>>>
>>>> I need to compare this to a GPS signal of -125 dBm.
>>>>
>>>> Anyone know how to find this?
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>> 467uV/m
>>>
>>> piglet
>> 
>> Fantastic. That is a lot more than I expected. Very interesting. Can
>> you show your calculations?
>> 
>> If my calculations are correct, that is
>> (467e-6)^2 / 377 = 5.78e-10 W/m = -62.381 dBm, or 63 db above the GPS
>> signal. 
>> 
>> Perfect. Thanks.
>> 
>> 
>> 
>> 
> 
> The one I know is E = (7*sqrt(P))/d which gives higher results so tends 
> to get used for exposure compliance calcs
> 
> E in V/m; P in W; d in m
> 
> 1W at 15km = 467uV/m
> 
> see:
> <https://ham.stackexchange.com/questions/10076/how-do-you-calculate-the-f
> ield-strength-at-a-given-distance> 
> 
> But there is another formula often seen which is ballpark same:
> 
> <https://www.rfwireless-world.com/calculators/Electric-and-magnetic-Field
> -Strength-calculator.html> 
> 
> E = sqrt(30*P)/d
> 
> 1W at 15km = 365uV/m
> 
> Real life may be wildly different.

This is very valuable information. Thank you for taking the time, and for 
the links.

> Isn't this stuff Ham Radio 101 that you needed to get your call?

I got my first license in 1958. There was not much to the exam, mostly 
regulations and a code test at 5 wpm. A kid could have passed it. Come to 
think of, I was a kid then:)
 
> piglet

Thanks,

Mike 
 



-- 
MRM

In article <XnsAF63A56E02B61idtokenpost@88.198.57.247>, spamme@not.com 
says...
> 
> I got my first license in 1958. There was not much to the exam, mostly 
> regulations and a code test at 5 wpm. A kid could have passed it. Come to 
> think of, I was a kid then:)
>  
> 
> 

Many licenses are a joke.  I got my first class license radiotelephone 
when I was 22 and had never seen a TV transmitter, but was licensed to 
work on them.

Ralph Mowery wrote:
>  Mike Monett VE3BTI says...
>>
>> I got my first license in 1958. There was not much to the exam, mostly
>> regulations and a code test at 5 wpm. A kid could have passed it. Come to
>> think of, I was a kid then:)
>
> Many licenses are a joke.  I got my first class license radiotelephone
> when I was 22 and had never seen a TV transmitter, but was licensed to
> work on them.

My FCC /Restricted/ Radiotelephone Operator Permit allows me to operate 
aircraft radios and instruments. It doesn't license me to work on them.
    
Danke,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.