(This weirdly came up as a new message--silly me.)

Phil Hobbs wrote:
> Les Cargill wrote:
>> Marcel Mueller wrote:
>>> On 26.05.18 07.40, Randy Yates wrote:
>>>> I was miffed initially by this statement since, as far as I know,
>>>> there is nothing inherent in wavelength that impacts how RF waves
>>>> travel through space.
>>>
>>> If you are talking about vacuum then yes. In all other media the 
>>> velocity of propagation depends on the frequency. E.g. water
>>> molecules in the air interact frequency dependent.
>>>
>>>> But I guess this was just a way (a confusing one, IMO) of referring
>>>> to the wavelength dependency of antenna aperture, as explained
>>>> nicely in this article on the Friis equation?
>>>
>>> The coupling of the antenna to the free space also introduces a 
>>> frequency dependent group delay. 
>>
>> All necessary apologies in advance.
>>
>> All group delay is inherently frequency dependent:
>>
>> " Group delay is the actual transit time of a signal through a device 
>> under test as a function of frequency."
>>
>> http://na.support.keysight.com/pna/help/latest/Tutorials/Group_Delay6_5.htm 
>>
>>
>> A reasonable definition.
> 
> But unfortunately dead wrong because it ignores causality.
> Group delay != true delay, in general.
> 
> Group delay is d phi / d omega, and is useful as a leading-order 
> approximation to how a nice wide smooth pulse propagates through a 
> network.� It's exactly analogous with group velocity in radio or optical 
> propagation, which is d(omega)/d k, where k is the wave vector.
> 
> You can see the distinction in two ways.� First, group delay can be 
> negative, which true delay cannot.
> 
> Second, networks can have group delay without having true delay.� You 
> can undo the effect of a 1-pole RC lowpass with an RC highpass, for 
> instance.
> 
>>
>> I have the conceit that I'm not picking nits here so much as heading
>> off one potentially confusing interpretation of that
>> sentence :) The� "quantifiers" for "a group delay" sort of leaves
>> the phrase "for all group delay" dangling.
>>
>>
>>> And last but not least a short
>>> distance link has some frequencies with poor performance due to
>>> eigenvalues of the overall geometry.
>>>
>>
>> Aka comb filtering/multipath/cosite interference?
>>
>>>
>>> Marcel
>>
> Cheers
> 
> Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Les Cargill wrote:
> Marcel Mueller wrote:
>> On 26.05.18 07.40, Randy Yates wrote:
>>> I was miffed initially by this statement since, as far as I know,
>>> there is nothing inherent in wavelength that impacts how RF waves
>>> travel through space.
>>
>> If you are talking about vacuum then yes. In all other media the 
>> velocity of propagation depends on the frequency. E.g. water
>> molecules in the air interact frequency dependent.
>>
>>> But I guess this was just a way (a confusing one, IMO) of referring
>>> to the wavelength dependency of antenna aperture, as explained
>>> nicely in this article on the Friis equation?
>>
>> The coupling of the antenna to the free space also introduces a 
>> frequency dependent group delay. 
> 
> All necessary apologies in advance.
> 
> All group delay is inherently frequency dependent:
> 
> " Group delay is the actual transit time of a signal through a device 
> under test as a function of frequency."
> 
> http://na.support.keysight.com/pna/help/latest/Tutorials/Group_Delay6_5.htm
> 
> A reasonable definition.

But unfortunately dead wrong because it ignores causality.
Group delay != true delay, in general.

Group delay is d phi / d omega, and is useful as a leading-order 
approximation to how a nice wide smooth pulse propagates through a 
network.  It's exactly analogous with group velocity in radio or optical 
propagation, which is d(omega)/d k, where k is the wave vector.

You can see the distinction in two ways.  First, group delay can be 
negative, which true delay cannot.

Second, networks can have group delay without having true delay.  You 
can undo the effect of a 1-pole RC lowpass with an RC highpass, for 
instance.

> 
> I have the conceit that I'm not picking nits here so much as heading
> off one potentially confusing interpretation of that
> sentence :) The� "quantifiers" for "a group delay" sort of leaves
> the phrase "for all group delay" dangling.
> 
> 
>> And last but not least a short
>> distance link has some frequencies with poor performance due to
>> eigenvalues of the overall geometry.
>>
> 
> Aka comb filtering/multipath/cosite interference?
> 
>>
>> Marcel
> 
Cheers

Phil Hobbs

> 
> With a reflective, i.e., dish, antenna, higher frequencies means MORE
> gain.   Satellite and many fixed point-to-point applications that use
> reflective, directive antennas like to go to higher frequency because
> of this.   In the old days the limitation was that the rf electronics
> got prohibitively expensive as the frequency went up.


here is marks rule of thumb.. 
depends on the type of antenna at each end of the link

omni to omni, lower frequencies are better
omni to dish   frequency independent
dish to dish  higher frequencies are better

(better means less  spreading loss)

mark

On Mon, 25 Jun 2018 11:54:01 -0700 (PDT), gyansorova@gmail.com wrote:

>On Sunday, May 27, 2018 at 8:56:21 AM UTC+12, Eric Jacobsen wrote:
>> On Sat, 26 May 2018 01:40:39 -0400, Randy Yates
>> <yates@digitalsignallabs.com> wrote:
>> 
>> >In an article in a recent issue of Microwaves & RF magazine, Jack
>> >Browne makes the following statement:
>> >
>> >  Frequency plays a part in any link budget, especially for longer links,
>> >  since long-distance links require the LONGER PROPAGATION DISTANCES of
>> >  larger-wave-length, lower-frequency signals rather than
>> >  smaller-wavelength, higher-frequency signals.
>> >
>> >(emphasis mine). 
>> >
>> >I was miffed initially by this statement since, as far as I know, there
>> >is nothing inherent in wavelength that impacts how RF waves travel
>> >through space.
>> >
>> >But I guess this was just a way (a confusing one, IMO) of referring to
>> >the wavelength dependency of antenna aperture, as explained nicely
>> >in this article on the Friis equation? 
>> >
>> >  http://www.antenna-theory.com/basics/friis.php
>> >
>> 
>> For the most part you're right, the frequency effects are
>> predominantly associated with antenna characteristics.   I wrote and
>> article about it about a decade ago:
>> 
>> https://www.dsprelated.com/showarticle/62.php
>> 
>> There are some atmospheric effects, etc., that are frequency
>> dependent, and materials penetration/reflection is frequency
>> dependent, but for the most part free space propagation is independent
>> of frequency.
>
>I find that interesting. I am always told that using higher frequencies means lower distances. So what must you do to the antenna to fix things? eg if you are using wi-fi at 5 gig versus 2.4, the 2.4 one has greater coverage

Regulatory effects often matter more.   e.g., in many regions the
maximum amount of allowed transmitted power for unlicensed devices is
different at 2.4GHz than it is at 5GHz.   This can make more
difference in coverage area than propagation effects.

Nevertheless, a good 5GHz stick antenna will be smaller than a 2.4GHz
antenna, so it will collect less energy.

With a reflective, i.e., dish, antenna, higher frequencies means MORE
gain.   Satellite and many fixed point-to-point applications that use
reflective, directive antennas like to go to higher frequency because
of this.   In the old days the limitation was that the rf electronics
got prohibitively expensive as the frequency went up.

On Sunday, May 27, 2018 at 8:56:21 AM UTC+12, Eric Jacobsen wrote:
> On Sat, 26 May 2018 01:40:39 -0400, Randy Yates
> <yates@digitalsignallabs.com> wrote:
> 
> >In an article in a recent issue of Microwaves & RF magazine, Jack
> >Browne makes the following statement:
> >
> >  Frequency plays a part in any link budget, especially for longer links,
> >  since long-distance links require the LONGER PROPAGATION DISTANCES of
> >  larger-wave-length, lower-frequency signals rather than
> >  smaller-wavelength, higher-frequency signals.
> >
> >(emphasis mine). 
> >
> >I was miffed initially by this statement since, as far as I know, there
> >is nothing inherent in wavelength that impacts how RF waves travel
> >through space.
> >
> >But I guess this was just a way (a confusing one, IMO) of referring to
> >the wavelength dependency of antenna aperture, as explained nicely
> >in this article on the Friis equation? 
> >
> >  http://www.antenna-theory.com/basics/friis.php
> >
> 
> For the most part you're right, the frequency effects are
> predominantly associated with antenna characteristics.   I wrote and
> article about it about a decade ago:
> 
> https://www.dsprelated.com/showarticle/62.php
> 
> There are some atmospheric effects, etc., that are frequency
> dependent, and materials penetration/reflection is frequency
> dependent, but for the most part free space propagation is independent
> of frequency.

I find that interesting. I am always told that using higher frequencies means lower distances. So what must you do to the antenna to fix things? eg if you are using wi-fi at 5 gig versus 2.4, the 2.4 one has greater coverage

Marcel Mueller wrote:
> On 26.05.18 07.40, Randy Yates wrote:
>> I was miffed initially by this statement since, as far as I know,
>> there is nothing inherent in wavelength that impacts how RF waves
>> travel through space.
> 
> If you are talking about vacuum then yes. In all other media the 
> velocity of propagation depends on the frequency. E.g. water
> molecules in the air interact frequency dependent.
> 
>> But I guess this was just a way (a confusing one, IMO) of referring
>> to the wavelength dependency of antenna aperture, as explained
>> nicely in this article on the Friis equation?
> 
> The coupling of the antenna to the free space also introduces a 
> frequency dependent group delay. 

All necessary apologies in advance.

All group delay is inherently frequency dependent:

" Group delay is the actual transit time of a signal through a device 
under test as a function of frequency."

http://na.support.keysight.com/pna/help/latest/Tutorials/Group_Delay6_5.htm

A reasonable definition.

I have the conceit that I'm not picking nits here so much as heading
off one potentially confusing interpretation of that
sentence :) The  "quantifiers" for "a group delay" sort of leaves
the phrase "for all group delay" dangling.


> And last but not least a short
> distance link has some frequencies with poor performance due to
> eigenvalues of the overall geometry.
> 

Aka comb filtering/multipath/cosite interference?

> 
> Marcel

-- 
Les Cargill

Randy Yates  <yates@digitalsignallabs.com> wrote:

>In an article in a recent issue of Microwaves & RF magazine, Jack
>Browne makes the following statement:

>  Frequency plays a part in any link budget, especially for longer links,
>  since long-distance links require the LONGER PROPAGATION DISTANCES of
>  larger-wave-length, lower-frequency signals rather than
>  smaller-wavelength, higher-frequency signals.
>
>(emphasis mine). 
>
>I was miffed initially by this statement since, as far as I know, there
>is nothing inherent in wavelength that impacts how RF waves travel
>through space.
>
>But I guess this was just a way (a confusing one, IMO) of referring to
>the wavelength dependency of antenna aperture, as explained nicely
>in this article on the Friis equation? 

It's a pretty sloppy statement at best.

The Friis pathloss assumes 0 dBi antennas, and the aperture of
a 0 dBi antenna is about 0.05 times the wavelength squared.
(Some sources say 0.07.)  The aperture of a parabolic dish is
roughly the area of the dish, so a given size dish has more
gain (in dBi) at shorter wavelengths.  This is why space communications 
uses short wavelengths.  

The (perfectly executed) New Horizon mission to Pluto operated at 6 GHz.  

I'm betting Jack Bronwe never worked on a space datalink?  That
or they just slipped up when they wrote this.

Steve

On Sat, 26 May 2018 01:40:39 -0400, Randy Yates
<yates@digitalsignallabs.com> wrote:

>In an article in a recent issue of Microwaves & RF magazine, Jack
>Browne makes the following statement:
>
>  Frequency plays a part in any link budget, especially for longer links,
>  since long-distance links require the LONGER PROPAGATION DISTANCES of
>  larger-wave-length, lower-frequency signals rather than
>  smaller-wavelength, higher-frequency signals.
>
>(emphasis mine). 
>
>I was miffed initially by this statement since, as far as I know, there
>is nothing inherent in wavelength that impacts how RF waves travel
>through space.
>
>But I guess this was just a way (a confusing one, IMO) of referring to
>the wavelength dependency of antenna aperture, as explained nicely
>in this article on the Friis equation? 
>
>  http://www.antenna-theory.com/basics/friis.php
>

For the most part you're right, the frequency effects are
predominantly associated with antenna characteristics.   I wrote and
article about it about a decade ago:

https://www.dsprelated.com/showarticle/62.php

There are some atmospheric effects, etc., that are frequency
dependent, and materials penetration/reflection is frequency
dependent, but for the most part free space propagation is independent
of frequency.

Hi Marcel,

Thank you for responding and discussing.

Marcel Mueller <news.5.maazl@spamgourmet.org> writes:

> On 26.05.18 07.40, Randy Yates wrote:
>> I was miffed initially by this statement since, as far as I know, there
>> is nothing inherent in wavelength that impacts how RF waves travel
>> through space.
>
> If you are talking about vacuum then yes. In all other media the
> velocity of propagation depends on the frequency. E.g. water molecules
> in the air interact frequency dependent.

Does the velocity of propagation affect path loss/attenuation? 

>> But I guess this was just a way (a confusing one, IMO) of referring to
>> the wavelength dependency of antenna aperture, as explained nicely
>> in this article on the Friis equation?
>
> The coupling of the antenna to the free space also introduces a
> frequency dependent group delay.

I didn't know that. I can certainly see that group delay impacts the
overall response (namely, the phase response), but it doesn't cause 
attenuatation. 

I was mainly interested in attenutation.

> And last but not least a short distance link has some frequencies with
> poor performance due to eigenvalues of the overall geometry.

I love it! Applying linear algebra to wave propagation! Do you have
a reference (hopefully easy to read)?
-- 
Randy Yates, DSP/Embedded Firmware Developer
Digital Signal Labs
http://www.digitalsignallabs.com

On Sat, 26 May 2018 01:40:39 -0400, Randy Yates
<yates@digitalsignallabs.com> wrote:

>In an article in a recent issue of Microwaves & RF magazine, Jack
>Browne makes the following statement:
>
>  Frequency plays a part in any link budget, especially for longer links,
>  since long-distance links require the LONGER PROPAGATION DISTANCES of
>  larger-wave-length, lower-frequency signals rather than
>  smaller-wavelength, higher-frequency signals.
>
>(emphasis mine). 
>
>I was miffed initially by this statement since, as far as I know, there
>is nothing inherent in wavelength that impacts how RF waves travel
>through space.
>
>But I guess this was just a way (a confusing one, IMO) of referring to
>the wavelength dependency of antenna aperture, as explained nicely
>in this article on the Friis equation? 
>
>  http://www.antenna-theory.com/basics/friis.php
>
>@article{microwaves-and-rf-difference-between-long-and-short-haul-links,
>  title = "What's the Difference Between Long- and Short-Haul Links?",
>  author = "Jack Browne",
>  journal = "Microwaves \& RF Magazine",
>  month = "April",
>  year = "2018"}


I don't suppose he could have been referring to ground wave or
ionospheric propagation associated with low frequency transmissions
?.....   Or, how higher frequencies have more of a line of site
characteristic ?

boB