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Author Topic: 146mhz Short Beam vs. 432 long beam - Attic  (Read 820 times)
KM1H
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Posts: 5516




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« Reply #15 on: October 11, 2019, 11:39:21 AM »

Quote
The Friis (please note the correct spelling) equation will predict the free space path loss accurately. Then all other factors must be considered.

- Glenn W9IQ

No matter what you call it the equation is for Free Space only which is fine for the keyboard klackers.

OTOH 432 often exhibits tropo and other openings not always duplicated at 144; 222 is another band that often outperforms 144 when equivalent ERP is used.
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W9IQ
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Posts: 3532




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« Reply #16 on: October 11, 2019, 01:52:28 PM »

Quote
The Friis (please note the correct spelling) equation will predict the free space path loss accurately. Then all other factors must be considered.

- Glenn W9IQ

No matter what you call it the equation is for Free Space only which is fine for the keyboard klackers.

OTOH 432 often exhibits tropo and other openings not always duplicated at 144; 222 is another band that often outperforms 144 when equivalent ERP is used.

Carl,

Not "keyboard klackers" but engineers. You are welcome to follow along if you wish.

When you say "equivalent ERP", you have already included the antenna system gain calculations. So that is simply another way of expressing the prediction of the Friis formula. In the OP's example, the ERP would be equal when the 70 cm antenna system has 9.6 dB gain over the 2 meter antenna system (all other things being equal).

As it relates to tropo, that is a propagation effect, not a free space condition. As has been stated, the Friis equation covers the free space part of the calculation - all others factors, such as propagation, must be additionally considered.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9IQ
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« Reply #17 on: October 11, 2019, 03:46:16 PM »

I should clarify that "equivalent ERP" will not result in the same free space range results for 70 cm vs 2 meters. The 70 cm antenna system will require 9.6 dB additional ERP compared to the 2 meter antenna system in order to achieve the same range (all other things being equal).

- Glenn W9IQ
« Last Edit: October 11, 2019, 03:48:51 PM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KM1H
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Posts: 5516




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« Reply #18 on: October 11, 2019, 05:53:09 PM »

Youre missing the point as usual.

By equivalent ERP that means both bands are radiating the same POWER. maybe you understand equal better.

Many Real hams are also engineers but with Real experience, myself included. Keyboard klackers often lack experience but act as they know everything and are always trying to tell us that.

Propagation comes packaged with daily operating and varies. Free space is dreamland used for only a starting point. Once a Real antenna is used on the air anything is possible.

BTW, your home site seems to be woefully lacking antennas, is that why you spend so much time keyboard klacking?

Allison also made good points which you chose to ignore.

Carry on

Carl

Carl
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W9IQ
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« Reply #19 on: October 11, 2019, 06:03:37 PM »

Antennas radiating the same power and ERP are not necessarily equivalent (or equal if you prefer). ERP is power times gain. You can compare two antennas that are both radiating 100 watts. If the first antenna has a 3 dBi gain and the second antenna has a 0 dBi gain, the EIRP for the first antenna is 200 watts while the EIRP of the second antenna is 100 watts. So both are radiating the same power but with quite different ERP.

The same math applied in 1960.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
G8HQP
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« Reply #20 on: October 12, 2019, 03:12:47 AM »

I am just wondering how a "Real engineer" might calculate path loss for an obstructed path, or one involving a reflection, if he did not know how to calculate a free space path. Friis is the starting point for most path loss calculations (and radar); without it you cannot calculate. Maybe a "Real engineer" would just have to build a system and try it and see if it works? If it works, he won't know how much money he is wasting through overengineering. If it fails, he won't know by how much so he won't know how to modify it. Meanwhile, the "keyboard klackers" are designing military and telecomms systems which actually work.
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KM1H
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« Reply #21 on: October 12, 2019, 05:26:02 PM »

Quote
The same math applied in 1960.

Another good attempt to spin the discussion.

Try to spin this:

 
Quote
Effective radiated power. ... ERP measures the combination of the power emitted by the transmitter and the ability of the antenna to direct that power in a given direction. It is equal to the input power to the antenna multiplied by the gain of the antenna.

If both antennas are radiating the same ERP how it was derived is unimportant. At a local certified antenna range the received signal POWER will be the same.

I wonder how many keyboard klackers here have ever actually been/participated to a ham VHF/UHF antenna measuring contest or worked for a REAL antenna company with a certified antenna range?  I have been to both from VHF to microwave for commercial telecomms and military products.

Tell me who here has denied the Friis calculation? 

Carl



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W9IQ
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« Reply #22 on: October 12, 2019, 06:20:29 PM »

Take an efficient 2 meter antenna and an efficient 70 cm antenna each with the same gain, each with the same transmit power applied and thus each with the same ERP. At some distant, line of sight location (unaffected by reflections, attenuation, diffraction, etc.) place a 1/4 wave ground plane 2 meter and a 1/4 wave ground plane 70 cm antenna (each with the same gain). Orientate the maximum gain direction of the 2 meter and the 70 cm transmit antennas to point to the receive antennas. Measure the received signal power on the respective receive antennas. The 70 cm antenna received power will be about 1/9th that of the 2 meter signal.

The Friis equation predicts this effect. This is in conflict with your assertion:

If both antennas are radiating the same ERP how it was derived is unimportant. At a local certified antenna range the received signal POWER will be the same.

since the received power will not be the same.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KM1H
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Posts: 5516




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« Reply #23 on: October 13, 2019, 08:08:37 AM »

Quote
Take an efficient 2 meter antenna and an efficient 70 cm antenna each with the same gain, each with the same transmit power applied and thus each with the same ERP. At some distant, line of sight location (unaffected by reflections, attenuation, diffraction, etc.) place a 1/4 wave ground plane 2 meter and a 1/4 wave ground plane 70 cm antenna (each with the same gain). Orientate the maximum gain direction of the 2 meter and the 70 cm transmit antennas to point to the receive antennas. Measure the received signal power on the respective receive antennas. The 70 cm antenna received power will be about 1/9th that of the 2 meter signal.

That is a completely useless test and emphasizes your lack of understanding shown by keyboard klackers in general.

Do it with horizontally polarized yagis with the other location much closer such as across a large empty parking lot, large flat field, or other area free of anything that will cause a reflection, diffraction, absorption, or anything else to interfere with the measurement.

The actual distance depends upon the antenna length/gain/pattern. I wont confuse you with phase, Fresnel zones, and other distractions. There are several discussions on how to set up a Real world test range to add to your keyboard klacker data base. This will allow you to maybe convince others later on that you actually have the experience to back up statements.

For the OP's short antennas this might even be done in a driveway.

To add to your klacker database realize that 70cm (and slightly higher commercial signals) are well known to penetrate buildings far better than 2M. Remember that the OP is discussing attic antennas.

Carry On

Carl
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W9IQ
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Posts: 3532




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« Reply #24 on: October 13, 2019, 08:23:47 AM »

Do it with horizontally polarized yagis with the other location much closer such as across a large empty parking lot, large flat field, or other area free of anything that will cause a reflection, diffraction, absorption, or anything else to interfere with the measurement.

I already set the condition of unobstructed, etc. so I am not sure why you are repeating it.

The polarization of the antennas has nothing to do with it. Change all antennas to a horizontal configuration, keep everything else the same and the results will be the same - 70 cm will have 1/9 of the received power.

The actual distance depends upon the antenna length/gain/pattern. I wont confuse you with phase, Fresnel zones, and other distractions.

My examples have not said anything about distance. This entire discussion is about FSPL. Feel free to bring in any other technical terms that you would care to use, I am happy to add them to the discussion. Particularly if it helps you understand or discuss the Friis equation and FSPL.

...realize that 70cm (and slightly higher commercial signals) are well known to penetrate buildings far better than 2M. Remember that the OP is discussing attic antennas.

As I and others on this thread have now said several times, the Friis equation calculates the FSPL. Issues such as penetration are neutral or additive (not subtractive) to FSPL.

- Glenn W9IQ

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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
K0UA
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Posts: 4801




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« Reply #25 on: October 13, 2019, 08:38:50 AM »

What is this "keyboard klackers" Bravo Sierra Carl?  Who are the keyboard klackers? What are you trying to say?  Am I a "keyboard klacker?" Are you one?  Why don't you say what you mean? Why do you use some sort of derogatory name to denigrate people?  Why don't you speak plainly?
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73  James K0UA
ARRL Missouri Technical Specialist
KM1H
Member

Posts: 5516




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« Reply #26 on: October 13, 2019, 04:23:28 PM »

Quote
As I and others on this thread have now said several times, the Friis equation calculates the FSPL. Issues such as penetration are neutral or additive (not subtractive) to FSPL.

Why do you continue to blabber on about Friss and continue to ignore the OP's real world question?

You must simply enjoy trying to make others believe you are superior....not.
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W9IQ
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Posts: 3532




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« Reply #27 on: October 13, 2019, 04:29:47 PM »

If you have run out of technical bandwidth, we can end the discussion.

My hope was that you would learn how to apply the Friis equation. I can see that is not going to happen.

- Glenn W9IQ
« Last Edit: October 13, 2019, 04:44:17 PM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
G8HQP
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Posts: 971




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« Reply #28 on: October 14, 2019, 04:47:30 AM »

Quote from: KM1H
To add to your klacker database realize that 70cm (and slightly higher commercial signals) are well known to penetrate buildings far better than 2M.
I always thought that VHF penetrates most building materials better than UHF, but once inside the UHF bounces around better.

Quote from: KM1H
I wonder how many keyboard klackers here have ever actually been/participated to a ham VHF/UHF antenna measuring contest or worked for a REAL antenna company with a certified antenna range?  I have been to both from VHF to microwave for commercial telecomms and military products.
Sadly, antennas turn out to be one of those topics where both academics and professionals can sometimes get the basics wrong so claims of experience do not carry much weight.
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KM1H
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Posts: 5516




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« Reply #29 on: October 14, 2019, 08:33:57 AM »

Quote
I always thought that VHF penetrates most building materials better than UHF, but once inside the UHF bounces around better.

Either think again or at least supply frequencies as anyone with experience realizes varies over those wide ranges.

Quote
Sadly, antennas turn out to be one of those topics where both academics and professionals can sometimes get the basics wrong so claims of experience do not carry much weight.

Sadly, over educated, egocentric, and inexperienced keyboard klackers cant contain themselves from obsessive replies......must be an academic as true professionals have both the knowledge plus experience.
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