What is minimum frequency that can transmit live video?

MrSalts

Joined Apr 2, 2020
2,767
Both transmitter and receiver are lying on the ground.
Is the ground moist or dry? If moist, is the ground water salty or pure water? Is there a limit to the length of the antennas on the ground? How do we design this ground mounted antenna of 0-height as omnidirectional (a previous requirement).
 

Thread Starter

Man10

Joined Jul 31, 2018
163
Is the ground moist or dry? If moist, is the ground water salty or pure water? Is there a limit to the length of the antennas on the ground? How do we design this ground mounted antenna of 0-height as omnidirectional (a previous requirement).
Does dry ground absorb radio waves more than moist ground? Or does moist ground absorb radio waves more than dry ground? Does the ground absorb radio waves at all?
 

drjohsmith

Joined Dec 13, 2021
852
Does dry ground absorb radio waves more than moist ground? Or does moist ground absorb radio waves more than dry ground? Does the ground absorb radio waves at all?
Hi

you seem to have been asking a few questions here

May be a summary ,
I hope your not just writing an esay

Video bandwidth.
as a minimum black and white, and you have the video as lines, made into a frame
a line with alternate black / white pixels will produce the max frequency
qed. The max frequency of the video in Hz is
is ( number of pixel per line / 2) * number of lines per frame * number of frames per second
timing info can add to this ,

Video bandwidth (2)
If you have more levels to give grey scale, the bandwidth increases
If you have colour, you have three times the number of pixels

Video bandwidth ( 3 )
Encoding, can reduce the real bandwidth needed, examples being PAL / NTSC / DVB

Radio waves
Antennas can give gain, by being selective in one direction over another

Radio waves (2)
Antennas of the same gain are smaller for higher frequencies.

Radio wave (3)
For a first approximation, ( yes there are singe side band, suppressed carrier, FM et all but )
If you modulate a high frequency Fc, with a lower frequency signal of bandwidth Fb, then you transmit Fc - Fb to Fc + Fb
e.g. 2 MHz on a 100 MHz carrier, covers 98 to 102 MHz of bandwidth,

Radio wave (4)
again for a first approximation,
Its much simpler / efficient to make a high gain amplifier of AC than DC,
qed, we tend to not transmit a DC signal , but modulate the base band video to a higher frequency

Radio wave (5)
The ground is your enemy and your friend at the same time !
Radio waves bounce off the ground
ground blocks radio waves (think large buildings for your car radio / gps )
Your antenna might well rely upon the ground plane reflection to work !
Damp air can attenuate radio waves , look at atmosphere atteruation plots

https://en.wikipedia.org/wiki/Compu...uation,absorption of its different components.

Way to design a link is typically, first power / sensitivity

look at distance,
look at attenuation at the frequency you want to use.
This gives you the amount of dB you need, from antenna gain, receiver gain and transmit power.

Bandwidth.
You have the basic equation above for raw bandwidth
you then need to think how much "effort" you want to use to change this
 

drjohsmith

Joined Dec 13, 2021
852
You are missing the curvature of the earth, line of sight, and height of antenna.
Thank you @MrChips

I did say at various points in the text words to the effect that these were to a first approximation
I tried to aim the review at the level I had picked up the original poster was at

By all means if you think I have missed something, add to the list,
Im ceetain the OP will appreciate your expertise in the effect of earth curvature, line of sight and antenna eight.

Have a good new year
 

MrChips

Joined Oct 2, 2009
30,714
TS began in post #1 by asking for the minimum frequency to transmit video.

Analog TV has a bandwidth of 4.5MHz. Thus in theory the minimum frequency is 4.5MHz.

Broadcast TV has a bandwidth of 6MHz with the audio added. TV channels begin at around 40MHz with 6MHz spacing per channel. AM RF would require a bandwidth of twice the modulating frequency, i.e. 12MHz. Broadcast TV uses SSB (single side band) in order to limit the required bandwidth.

On further questioning, TS adds the 100-mile requirement which is a conundrum without realizing it. The curvature of the Earth's surface puts a limit of 50 miles for high frequency RF communication. For 100-mile line-of-sight the transmitting and receiving antennas would have to be positioned 5000 ft above ground.

MrSalts in post #41 brings up a relevant point about the electrical conductivity of the ground. While this goes beyond the original question it does bring up an important point. The ground effect is highly dependent on wavelength. At lower frequencies, a ground wave image is present which alters how the RF signal propagates along the surface of the earth. At higher frequencies, the ground becomes a reflective surface that alters the direction of the transmitted wave depending on the polarization of the wave.
 

ronsimpson

Joined Oct 7, 2019
2,989
Is the point to find the lowest frequency or to send video 100 miles?

I can see video of my back yard from 100 miles away. There are no 5000 foot towers or large transmitters. When the FedEx truck arrives, a camera notifies me. If I gave you my IP address and passwords, you could see also.
 

drjohsmith

Joined Dec 13, 2021
852
TS began in post #1 by asking for the minimum frequency to transmit video.

Analog TV has a bandwidth of 4.5MHz. Thus in theory the minimum frequency is 4.5MHz.

Broadcast TV has a bandwidth of 6MHz with the audio added. TV channels begin at around 40MHz with 6MHz spacing per channel. AM RF would require a bandwidth of twice the modulating frequency, i.e. 12MHz. Broadcast TV uses SSB (single side band) in order to limit the required bandwidth.

On further questioning, TS adds the 100-mile requirement which is a conundrum without realizing it. The curvature of the Earth's surface puts a limit of 50 miles for high frequency RF communication. For 100-mile line-of-sight the transmitting and receiving antennas would have to be positioned 5000 ft above ground.

MrSalts in post #41 brings up a relevant point about the electrical conductivity of the ground. While this goes beyond the original question it does bring up an important point. The ground effect is highly dependent on wavelength. At lower frequencies, a ground wave image is present which alters how the RF signal propagates along the surface of the earth. At higher frequencies, the ground becomes a reflective surface that alters the direction of the transmitted wave depending on the polarization of the wave.
Hi @MrChips
I think your limiting your thought to "terrestrial" US analog TV when you say 4.5 MHz

for instance, 500 KHz seems to have done a fairly good job from the moon
https://en.wikipedia.org/wiki/Apollo_TV_camera

And if the OP wanted to look at digital compression ( a big step I realise)
it could be a lot less as you and I know,
all I was trying to do was put correlate and into one place the wonderful information that has been hinted at already

I assume you font have a problem with that
your comments on antenna , height , curvature, Im certain the OP could do with some more details on the pros and cons
don't forget to add things like line of site is not a absolute requirement, sky bounce, wave guide effect , wave curvature et all , depends what the OP wants,
I decided not to go into that, but please feel free to add

Re your comments about ground effect, ground effect,
I covered that in the comments about the ground is your friend and your enemy
Im working on the basis nothing I have said is controversial, or detailed,
but it might point the OP at the problems in one place and let them ask more directed questions,
 

drjohsmith

Joined Dec 13, 2021
852
Is the point to find the lowest frequency or to send video 100 miles?

I can see video of my back yard from 100 miles away. There are no 5000 foot towers or large transmitters. When the FedEx truck arrives, a camera notifies me. If I gave you my IP address and passwords, you could see also.
I receive TV from 42 million meters away !
but hay, 100m terestiral TV, that must be out in the US,
nothing in the UK is that far apart !

You have a great new year
 

ronsimpson

Joined Oct 7, 2019
2,989
About 50 years ago, we were sending Slow Scan TV over armature radio. We used low frequencies that bend around the world. I remember using 50 watts. I cannot remember but I think we sent a picture every 2 seconds. By reducing the resolution and frame rate the data was reduced to the audio range. 3khz bandwidth!
At Sony years ago we worked on video over the phone lines. Same thing where we reduced the data until the data could be sent over normal phone lines. (we had some really tricky software that increased the data rate, ask me if you want more details)
slow scan
I believe photos were sent over telegraph line by 1913.
1672515345182.png
 

MrSalts

Joined Apr 2, 2020
2,767
TS is asking for "live video".
Is 2 seconds per frame considered "live video"?
In my area the "live traffic camera" on the interstate is photos updated every 2- to 5-seconds. So, I'd say yes but the OP has been asked several times without a response. Also, he said he was done placing constraints on the problem so we can interpret video frame rate any way we want.
 

WBahn

Joined Mar 31, 2012
29,979
TS is asking for "live video".
Is 2 seconds per frame considered "live video"?
It might. Depends on what the purpose of the feed is.

Which just underscores that the TS has not done a good enough job of defining the problem and everyone else, myself included, is just whistling in the wind.

At first, it seemed like he was trying to get at a pretty simple concept which might be phrased something like this:

I have a signal that has a particular bandwidth, let's use 10 MHz as an example. Is it possible, in theory, to transmit that signal using an arbitrarily low carrier frequency? Let's use 1 MHz in this example? If so, how? If not, what is the minimum carrier frequency that can possibly be used?

In trying to get at what the TS is really asking for, they tried to clarify it with a specific case -- transmit it 100 miles with no repeaters in between. We have no idea where that came from and it's possible that it is just a value pulled out of thin air just to have a number. Or it might be a number that has particular interest to what the TS is actually trying to do. We simply don't know because the TS hasn't told us.

It all comes down to what knowledge the TS is actually trying to gain, which we simply don't know.
 

MrChips

Joined Oct 2, 2009
30,714
Fair enough. I believe that we can have a guess at what the TS wants. TS is just pulling numbers out of a hat without realizing and understanding the implications. TS needs to learn more about RF terrestrial communications.
 

drjohsmith

Joined Dec 13, 2021
852
Fair enough. I believe that we can have a guess at what the TS wants. TS is just pulling numbers out of a hat without realizing and understanding the implications. TS needs to learn more about RF terrestrial communications.
As the OP had asked a few general questions,
I thought I'd do a general round up for them,

lest see if they reply
 
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