Author Topic: does radiowaves' range depend on frequency?  (Read 1893 times)

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GreekMan

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does radiowaves' range depend on frequency?
« on: October 25, 2015, 08:25:16 AM »
I heard this somewhere but It does not sound right.
We are assuming propagation into space/vacuum.

So, I tried to find any applicable formulas by googling to no end.
Other than the energy decaying per the square of the distance, of course.

ghrit

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Re: does radiowaves' range depend on frequency?
« Reply #1 on: October 25, 2015, 11:04:23 AM »
I heard this somewhere but It does not sound right.
We are assuming propagation into space/vacuum.

So, I tried to find any applicable formulas by googling to no end.
Other than the energy decaying per the square of the distance, of course.
Given your airless and no physical interferences situation, the correct answer is no.  Like all photons, speed is independent of frequency (or energy, which is directly related.)
There are two kinds of ships.  Submarines and targets.
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GreekMan

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Re: does radiowaves' range depend on frequency?
« Reply #2 on: October 25, 2015, 11:59:46 AM »
thanks!

btw...I am totally downloading many of the resources in your site. good job!

AD

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Re: does radiowaves' range depend on frequency?
« Reply #3 on: October 25, 2015, 05:32:25 PM »
thanks!

btw...I am totally downloading many of the resources in your site. good job!

Yep he is a "Good Monkey"
The only dumb question is the one that did not get asked!!

spacecase0

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Re: does radiowaves' range depend on frequency?
« Reply #4 on: October 25, 2015, 09:18:18 PM »
I would assume that antenna design would be the next thing that would mess with things even in space

ghrit

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Re: does radiowaves' range depend on frequency?
« Reply #5 on: October 25, 2015, 10:57:37 PM »
I would assume that antenna design would be the next thing that would mess with things even in space
Well, yes and no.  It makes no change in speed.  Once you get away from the theoretical isotropic antenna, the pattern changes.
There are two kinds of ships.  Submarines and targets.
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Tevin

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Re: does radiowaves' range depend on frequency?
« Reply #6 on: October 26, 2015, 12:06:10 AM »
I heard this somewhere but It does not sound right.
We are assuming propagation into space/vacuum.

So, I tried to find any applicable formulas by googling to no end.
Other than the energy decaying per the square of the distance, of course.

This is an interesting question I had never thought of. My gut says that, given the conditions you set forward, all radio waves should have the same range. Radio waves are physics, and with no physical limitations they should all act the same, just as a 50 ton space ship and sheet of tissue paper both weigh the same (zero) in outer space.

But it seems almost too simple. Instead of googling for a variation of "do all radio frequencies have the same range in space" I instead googled "Why does NASA use microwaves." If it's all the same, then why don't they talk to the Mars rover on, say, 40 meters? I figured there must be a reason why microwave frequencies are used for space comms and was hoping to find information that verifies not all frequencies are the same.

As it turns out, NASA prefers microwave frequencies for a lot of reasons and none of them have anything to do with range across a vacuum. So I'm going to agree with ghrit, not because I can prove the theory, but because i can't disprove it. I realize that accepting something as true solely because you can't prove it's false is really bad science, but that's the best I can do without researching deeper into this than I care. 

Thanks for the great post.





spacecase0

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Re: does radiowaves' range depend on frequency?
« Reply #7 on: October 26, 2015, 12:40:46 AM »
this is a fantastic thread

I think NASA uses microwaves due to low QRN
and that it is easy and small to build a small antenna to cover microwaves,
and not that possible to set up a 40M antenna for a rover...
also all the HF frequencies can be directed by the earth's ionosphere, and somewhere 2M and shorter go straight through into space

anyone else here tried AM on 440MHZ ?
you don't even need squelch
possibly my favorite band and mode
to bad almost no one uses it there


Tevin

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Re: does radiowaves' range depend on frequency?
« Reply #8 on: October 26, 2015, 07:08:14 AM »
this is a fantastic thread

I think NASA uses microwaves due to low QRN
and that it is easy and small to build a small antenna to cover microwaves,
and not that possible to set up a 40M antenna for a rover...
also all the HF frequencies can be directed by the earth's ionosphere, and somewhere 2M and shorter go straight through into space

anyone else here tried AM on 440MHZ ?
you don't even need squelch
possibly my favorite band and mode
to bad almost no one uses it there

From what I found, microwaves are preferred because the antennas are smaller and also because microwaves penetrate clouds and atmospheric interference better. So the benefit of microwaves is mostly about what they do once they reach Earth more than what they do out in space.

And yeah, this is a great topic.

BTPost

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Re: does radiowaves' range depend on frequency?
« Reply #9 on: October 30, 2015, 01:51:44 PM »
Microwaves are used, because Antennas are smaller, and Antenna Gain is easier to come by, with shorter wavelengths... This is how NASA can talk to a Space Probe (That only puts out 10 Watts) at such great distances, by using BIG Dish Antennas, with Massive Antenna Gains, and very Low Noise Figure FrontEnds.... Try getting that kind of Antenna Gain at 40Meters.....
Bruce in alaska AL7AQ

GreekMan

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Re: does radiowaves' range depend on frequency?
« Reply #10 on: November 27, 2015, 12:46:01 AM »
I found soemthing interesting in this document
http://www.qsl.net/va3iul/Antenna/Basics_of_Radio_Wave_Propagation.pdf

Quote
Free Space Loss
Radio waves travel from a source into the surrounding space at the “speed of light”
(approximately 3.0 x 108 meters per second) when in “free space”. Literally, “free
space” should mean a vacuum, but clear air is a good approximation to this.
Free Space Path Loss(dB) = 27.6(dB) – 20*LOG[Frequency(MHz)] – 20*LOG[Distance(m)]

but with this document I have reached the limit of comprehension.