Applied physics: range of HD antennas.

[Bushranger]

There are a host of inexpensive HD antennas for sale that seem to promise reception that seems beyond possible.  I have always understood the  broadcast T.V. signals are pretty much line-of-sight or about 35 miles before a tower is needed to get above the curvature of the earth. 

I recently watched a comercial that claimed 100 miles reception with one of those non-elevated, mount indoor, H.D. antennas.

Two questions:  

1) Is that 100 mile claim an outright lie?

2) If not an outright lie, what specific electronic technology would make 100 mile reception possible?

If you choose to answer my questions, please list your qualifications (to weed-out pretenders)...electrical engineer, or some other pertainent qualification?

Edited May 10, 2020 by Bushranger
addendum

[StringJunky]

So, one who lists their qualifications cannot be pretending?

Found this. Have a look:

Quote

In this article I will review what the best long range outdoor HDTV antenna on the market is today. Our list will only look at those antennas that boast at least a 70+ mile range.

Before we get started, I’d like to table is slight disclaimer. While most websites and review sites will be quick to provide you with a list of antennas claiming to reach 100, 150 or even 200 miles. I’m here to tell you that unfortunately you’ll be hard-pressed to reach any of these types of distances.

The truth is that current digital broadcast transmissions will begin to degrade drastically after approximately 60 miles. Any reception received beyond that will be “iffy” at best. The other reality is that in order to receive strong signals from long distances you are best going with a bigger style antenna with multiple sensing elements, mounted at a sufficient height.

https://www.antennajunkies.com/best-long-range-outdoor-hdtv-antenna/

 

[studiot]

1 hour ago, Bushranger said:

There are a host of inexpensive HD antennas for sale that seem to promise reception that seems beyond possible.  I have always understood the  broadcast T.V. signals are pretty much line-of-sight or about 35 miles before a tower is needed to get above the curvature of the earth. 

I recently watched a comercial that claimed 100 miles reception with one of those non-elevated, mount indoor, H.D. antennas.

Two questions:  

1) Is that 100 mile claim an outright lie?

2) If not an outright lie, what specific electronic technology would make 100 mile reception possible?

If you choose to answer my questions, please list your qualifications (to weed-out pretenders)...electrical engineer, or some other pertainent qualification?

Surely this belongs in the enginnering section, you even asked for an electrical engineer.

It is not rocket science after all.

However asking for an engineer is a good idea since there is much engineering commonsense and experience involved.

'Line of sight' is funny thing because it begs the question "who can see what ?"
Height is important, but not all important. It depends what is in the way.
You can (sometimes) achieve the same result moving two feet to the right or left to avoid a nearby chimney stack as 20 feet or more vertical elevation to look over the top of it.

I agree with the underlined words of this extract from StringJunky's link
But Amazon as a first class engineering supplier ??
The linked site seems only to shop at old smiley.

Quote

Don’t cheap out on the coax cabling used! Use a high quality RG6 cable such as the Mediabridge Broadband Coaxial Cable found on Amazon.

 

Some advice if you are doing this yourself.

Only a vey small part of the antenna is actually the receiving or pickup device. Most of the antenna is either focusing/directing/filtering metalwork.
So dimensional and alignment accuracy and stability are vital in assembly. (Most DTV antenna come as self assembly flat packs).
Small errors of twisted or displaced parts can ruin the performance of the best antenna.

 

To answer your two questions directly,

The range depends mostly upon the height of the transmitter, not the receiver.
Which is why these are placed on mountains where possible.
And yes if the transmitter can place a signal 200 miles away, that signal can be received.

As an example, my antenna is about 75 miles form the Bristol Transmitter, which is placed on top of the Mendip range of hills.
It is installed in my attic  (roofspace) simply hanging by two cords.
I get a better signal inside the roof than on top of it because of nearby chimneys.
I get almost zero signal at ground and first floor level, even in the trees in the garden away from the house.
The antenna picks up a better signal from the Mendip transmitter than the nearer Blackdown Hills transmitter, which is only 20 miles away.

Edited May 10, 2020 by studiot

[Strange]

10 minutes ago, studiot said:

Surely this belongs in the enginnering section, you even asked for an electrical engineer.

!

Moderator Note

OK. Moved to Engineering.

 

10 minutes ago, studiot said:

The linked site seems only to shop as old smiley.

What? 

[studiot]

13 minutes ago, Strange said:

What? 

Thanks for pointing out the spelling mistake.

at old smiley (did  i mention Ama _o_ ?)

[Strange]

1 minute ago, studiot said:

Thanks for pointing out the spelling mistake.

at old smiley (did  i mention Ama _o_ ?)

Ah, I see. A reference to their logo? In which case, maybe you should have written "_ma_on" 🙂

[StringJunky]

32 minutes ago, studiot said:

Surely this belongs in the enginnering section, you even asked for an electrical engineer.

It is not rocket science after all.

However asking for an engineer is a good idea since there is much engineering commonsense and experience involved.

'Line of sight' is funny thing because it begs the question "who can see what ?"
Height is important, but not all important. It depends what is in the way.
You can (sometimes) achieve the same result moving two feet to the right or left to avoid a nearby chimney stack as 20 feet or more vertical elevation to look over the top of it.

I agree with the underlined words of this extract from StringJunky's link
But Amazon as a first class engineering supplier ??
The linked site seems only to shop at old smiley.

 

Some advice if you are doing this yourself.

Only a vey small part of the antenna is actually the receiving or pickup device. Most of the antenna is either focusing/directing/filtering metalwork.
So dimensional and alignment accuracy and stability are vital in assembly. (Most DTV antenna come as self assembly flat packs).
Small errors of twisted or displaced parts can ruin the performance of the best antenna.

 

To answer your two questions directly,

The range depends mostly upon the height of the transmitter, not the receiver.
Which is why these are placed on mountains where possible.
And yes if the transmitter can place a signal 200 miles away, that signal can be received.

As an example, my antenna is about 75 miles form the Bristol Transmitter, which is placed on top of the Mendip range of hills.
It is installed in my attic  (roofspace) simply hanging by two cords.
I get a better signal inside the roof than on top of it because of nearby chimneys.
I get almost zero signal at ground and first floor level, even in the trees in the garden away from the house.
The antenna picks up a better signal from the Mendip transmitter than the nearer Blackdown Hills transmitter, which is only 20 miles away.

I have noted the bolded for when I replace mine. Cheers.

[Enthalpy]

Qualifications? Well, I leave you guessing mines. Do you really-really believe that a diploma is a guarantee that someone understands the topic a little bit? And that real experts have an academic background? Especially for radiocomms and antennas, you get better advice and expertise from amateur radio.

Unless a competing antenna is botched (long cable without preamplifier), it can improve only by its height, position, size, sometimes background noise picking. A small indoor antenna better than the others is a scam, as is nearly everything for consumer electronics. And don't forget to test under rain conditions.

Line-of-sight does matter, but even then, ground proximity determines the attenuation of terrestrial communications. This differs radically (40-60dB worse) from free-space transmission, but is rather well modelled just by a conducting ground. The received power varies as h₁²*h₂², where h₁ and h₂ are the heights of the transmitting and receiving antennas. So a mast on the roof for 10m height gains much over an indoor antenna 3m over the ground, as much as an antenna 10 times bigger, provided that a preamplifier at the antenna compensates the big cable losses.

Some antennas, for instance parabolas, are sensitive to the exact shape. Most are disappointingly insensitive to everything. Added elements bring at most 2dB each, a small Uda-Yagi improves only 10dB over a single dipole. Depending on the weather, the mountains... a transmission uses to be 20dB better or worse than necessary, so most times, all refinements can be completely discarded. You may notice a difference when someone moves before the antenna or when it rains, that is, well after you left the shop.