Earth Ground / Oscillators and Transmitters.

[killivolt]

Can these 2 Circuits work without Earth Grounds?


If not, can I simulate one?

 

[JimB]

In the case of the 434Mhz *radio, yes no problem.
Ideally for a radio transmitter antenna system, there are two conductors (this is turning into a horrid generalisation).
A dipole has two wires, a monopole works against a ground plane where the antenna is one wire and the ground plane is the other.
In the case of your little transmitter, the rest of the circuit wiring forms the groundplane. Not an ideal situation, but good enough for most practical applications.

In the case of the touch switch, it works by the capacitance of the body to ground altering the waveform entering the D input of the flipflop and causing a delay, that is why there is an earth connection. If there is enough capacitance from the body to the circuit itself, it will work OK.


* As you are in the USA, 434Mhz radio modules are not "approved" by the FCC.
However if you buy such a module from a supplier in the US, they will (or should) supply ones for the appropriate frequency, which I cant remember at the moment, but it is not 434Mhz.

JimB

 

[MikeMl]

Yes, they do not need an earth ground. However, most of the makers of these devices give really bad advice about how to build an antenna. They usually suggest a 1/4λ monopole without a counter poise or ground plane. A proper dipole which is 1/2λ in length will give ~20db better far-field signal strength than a 1/4λ with the mickey-mouse ground consisting of only the PC trace.

This applies equally to the receiver as well as the transmitter. Also, remember that both antennas need to be polarized vertically, or horizontally. Crossing their polarizations creates a 25db loss.

 

[killivolt]

Yes, they do not need an earth ground. A proper dipole which is 1/2λ in length will give ~20db better far-field signal strength than a 1/4λ with the mickey-mouse ground consisting of only the PC trace.

I'm only planning to go 5 to 10ft. So, my antenna should be based on that.

This applies equally to the receiver as well as the transmitter. Also, remember that both antennas need to be polarized vertically, or horizontally. Crossing their polarizations creates a 25db loss.

Ok.

In my area I found that 447mhz is were most broadcast will be in the ham bands. I have 5mhz plus or minus from that so, I shouldn't interfere with other frequency's.

kv

Edit: Of course you should know that because you and I are not that far away from each other.

 

[MikeMl]

I'm only planning to go 5 to 10ft. So, my antenna should be based on that.

...

Ok, then use a wet noodle

 

[killivolt]

Ok, then use a wet noodle

Exactly. lol

Edit: It's actually weird in some ways, for so long you see posts that need a longer range, then my application requires no data and short range.

I think I got pretty lucky with this one.

 

[mneary]

We discussed the rules for 310 and 433 MHz in this thread: https://www.electro-tech-online.com/threads/where-are-310mhz-and-433mhz-rules.101312/

 

[Hero999]

Disclaimer: I'm no RF expert.

The lower the frequency the higher capacitance the ground plane needs to be, meaning it needs to be larger. At UHF I would've thought a PCB ground plane or even a battery would be fine. You only need a real earth connection at low frequencies.

 

[JimB]

We discussed the rules for 310 and 433 MHz in this thread: https://www.electro-tech-online.com/threads/where-are-310mhz-and-433mhz-rules.101312/

Yes, I remember that thread, I just could not remember the context and how long ago it was.

JimB

 

[JimB]

Disclaimer: I'm no RF expert.

RF can be funny stuff!
I will modestly claim that I know "quite a bit about it".

The lower the frequency the higher capacitance the ground plane needs to be, meaning it needs to be larger.

To get an idea of what works well, think in terms of wavelength.
To work efficiently the elements of an antenna system need to be one quarter of a wavelength long.
434 Mhz has a wavelength of approximately 70cm, so, the two legs of a dipole should be 17.5cm long, or for a monopole antenna, a 17.5cm rod vertically mounted on a 17.5cm diameter conductive ground plane.
These are ideal conditions.
For most practical applications, the antenna is a piece of wire just flopping around and the groundplane is the rest of the circuit, whatever it is. Not great in terms of getting the maximum range from the device, but adequate for most purposes.

At UHF I would've thought a PCB ground plane or even a battery would be fine.

Exactly!
Consider the "plipper" you use to lock/unlock your car, that probably operates around 434Mhz, mine do.
There is nothing 17.5cm long about that.
The antenna for the receiver in the car is just a short wire dangling out of the box with the electronics (at least in one of my cars, I dont know about the other one), and dont forget that this is inside a steel box, something which is half way to being a Faraday Cage.
Yet it works OK, I can lock/unlock the doors from 5 or 6 metres away, I dont need any more range. In fact a longer range could be a disadvantage.
Using the same RF modules with dipole antennas mounted in the clear could have a much greater range (several hundred metres if not a km).

You only need a real earth connection at low frequencies.

At much lower frequencies, such as longwave, mediumwave and shortwave frequencies the usual "earth" connection is a mat of buried wires radiating radially from the base of the antenna mast.
There may be a hundred or more radial wires up to one quarter wavelength long. A LOT of buried copper.

As the frequency gets lower it becomes most impractical to have a quarter wavelength vertical element for the radiating part of the antenna system, in which case there is often a lot of horizontal wire at the top of the vertical element to provide top loading capacitance.

JimB