> 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.
Reply by Ralph Mowery●December 4, 20222022-12-04
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.
Reply by Mike Monett VE3BTI●December 4, 20222022-12-04
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
Reply by Piglet●December 4, 20222022-12-04
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.
>
>
>
>
Reply by Mike Monett VE3BTI●December 4, 20222022-12-04
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
Reply by piglet●December 4, 20222022-12-04
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
Reply by Fred Bloggs●December 3, 20222022-12-03
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'.
On Saturday, December 3, 2022 at 6:00:51 PM UTC-5, Jasen Betts wrote:
> On 2022-12-03, Fred Bloggs <bloggs.fred...@gmail.com> wrote:
> > On Saturday, December 3, 2022 at 2:58:09 PM UTC-5, 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.
> >>
> >> To compare, the radiating power of a GPS satellite is about
> >> 500 W, including antenna gain. The radius of its sphere is
> >> about 20000 km.
> >
> > Where are you getting that 500W bullshit? This source says 45W.
> > https://www.nxp.com/docs/en/brochure/75016740.pdf
> says
> "It’s transmit power is 44.8 Watt at 1575.43 MHz and the antenna gain
> is 12 dBi."
>
> Thus about 500W as an isotropic radiator as seen from inside the
> antenna beam.
Getting back to that 1W isotropic radiator at 15km, incident on the -21dB gain antenna ( 4dBi gain and L-Band wavelength) gives an receiver input power of -65 dBm -21 dB= -86 dBm.
>
>
>
>
>
> --
> Jasen.
Reply by Fred Bloggs●December 3, 20222022-12-03
On Saturday, December 3, 2022 at 6:00:51 PM UTC-5, Jasen Betts wrote:
> On 2022-12-03, Fred Bloggs <bloggs.fred...@gmail.com> wrote:
> > On Saturday, December 3, 2022 at 2:58:09 PM UTC-5, 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.
> >>
> >> To compare, the radiating power of a GPS satellite is about
> >> 500 W, including antenna gain. The radius of its sphere is
> >> about 20000 km.
> >
> > Where are you getting that 500W bullshit? This source says 45W.
> > https://www.nxp.com/docs/en/brochure/75016740.pdf
> says
> "It’s transmit power is 44.8 Watt at 1575.43 MHz and the antenna gain
> is 12 dBi."
>
> Thus about 500W as an isotropic radiator as seen from inside the
> antenna beam.
I see it now. Looks like they upgraded the L-band antennas a few years ago to broaden the pattern 3dB knees to cover the entire hemisphere of the Earth with a single interception, with a line of sight elevation no less than 5o.
https://www.gpsworld.com/gps-iir-iir-m-satellite-antenna-patterns-released-for-worldwide/
In that 3-D illustration they list the distance to satellite as 26,553 km, but that's from Earth center. They list Earth radius as 6,378 km, so that leaves 26,553-6378=20,175 of propagation distance to Earth's surface. NPX article says 20,200, so take that as a match. Then the angle subtended by the Earth as seen from the satellite is 2x6378/26,553x180/pi=27.5o, confirming they're illuminating an entire hemispheric surface.
That 44.8W at 12dBi makes for xmit power of 10Log(44.8 x 1000) + 12dBi=58.5 dBm, over the Earth hemisphere with range loss 10Log((20200 x 1000)^2x4pi) (range squared)= 157 dB, making for an incident power of 58.5-157=-98.5 dBm. Then plugging into the receive antenna with 4 dBi gain and taking lambda to be 0.19m ( at 1575 MHz nominal) gets -21dB receive antenna aperture and directivity gain, Gain x Lamda squared/4pi. Total input power to the receiver is then or -98.5 dBm -21= -120dBm as stated in NPX article, which is a match. Add in another 6dB atmospheric loss for -125dBm, not that even 6dB is all that significant. This was a calculation for a receiver looking straight up, 90o elevation, and the power levels won't be that much different at the Earth edges- distance is not that significant but beam pattern being down 3dB is, a little.
Fact check on NPX write-up: TRUE
https://www.nxp.com/docs/en/brochure/75016740.pdf
Thanks for your input.
>
>
>
>
>
> --
> Jasen.
Reply by Dave Platt●December 3, 20222022-12-03
In article <d851b90a-4faa-493f-a1ca-fc0d1afaec5en@googlegroups.com>,
whit3rd <whit3rd@gmail.com> wrote:
>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'.
Traditionally, "isotropic" is used to refer to antennas which are truly
isotropic, radiating equal power in all directions. This is a useful
fiction - no such antenna actually exists - but it's the "least common
denominator" in antenna patterns because it has no directional bias at
all.
A vertical dipole would (in principle) have 2.15 dB of gain (in its preferred
direction) over an isotropic reference.