RF antenna 433MHZ

[MikeMl]

... bit brown round there isn't it?.

Depends on when the aerial photo was taken. We live in the high desert. It gets really green here during monsoon season; July, August, and part of Sept. Most of our yearly rain comes then. Rest of the year it drys out.

Hottest temps in the summer: ~95degF, but low humidity. This time of year, overnight temps ~15degF but it warms up to ~55degF during the day...

 

[ddominguez]

Actually, not the garage doors, but the drive-through swing-gate. The actuator I am using takes about 30sec to move the gate from closed to open, so if I send the command from about 1000ft away, the gate is open by the time I drive up to it...

Seriously though, that's a dope antenna!

For my project I figured that the 433mhz frequency reduces my options for even a short transmission line.

I have some small diameter high quality shielded coaxial cable, but I figured (by the math) that it was probably more sensible to build the antennae right off the the Tx or Rx boards. And then run the dataline and ground with the coax and voltage on a third wire.

Does abandoning the transmission line idea seem sensible given the short wavelength?

 

[Mosaic]

Question:
Is the wavelength size calc. predicated on the speed of light or the speed of electron propagation in the antenna?

 

[ddominguez]

Not sure if that's to me, but I should clarify.

If I want a good transmission line then presumably I would need to take into account impedance matching.

But given that the tx is so small, I could build a dipole directly off the board and thus not have to worry about impedance. I couldn't possibly make the board traces shorter.

If I wanted a transmission line of 2m, I would need to consider impedance for max radiation strength from my constructed antenna.

Given that 433 Mhz is shorter than 2m, it might be easier to just to make the connections to the tx board 2m instead, no?

I'm not clear on how to calculate the impedance of the tx and match it to the 2m coaxial.

 

[davenn]

Question:
Is the wavelength size calc. predicated on the speed of light

speed of light times the velocity factor if the wire is bare ( no insulation) then the Vf is around 0.95 of the speed of light
the Vf drops as more or different types of insulation are used

EG. for standard RG58 ( 1/4 inch dia) coax cable the Vf is around 0.66

so to work out the ELECTRICAL wavelength

300 / freq in MHz x Vf

EG
300 / 100 MHz = 3 metres
3m x .66 = 1.98m

or the speed of electron propagation in the antenna?

no such realistic thing

the electrons oscillate about a point at the freq rate be that 50/60 Hz for AC mains or 100 MHz for some RF signal

EG
in your house wiring and say a light globe, the electrons in the filament of the globe never leave the filament

 

[Mosaic]

the electrons oscillate about a point at the freq rate be that 50/60 Hz for AC mains or 100 MHz for some RF signal

EG
in your house wiring and say a light globe, the electrons in the filament of the globe never leave the filament

Heh, unless we stick it in a vacuum and heat it to a few hundred degrees with an anode in close proximity...

 

[davenn]

Heh, unless we stick it in a vacuum and heat it to a few hundred degrees with an anode in close proximity...

huh ?????

edit....

ohhh
wondered what you were referring to .... I assume the thermo electric emission of electrons

 

[MikeMl]

Seriously though, that's a dope antenna!

I hope that's a compliment.

For my project I figured that the 433mhz frequency reduces my options for even a short transmission line.

I have some small diameter high quality shielded coaxial cable, but I figured (by the math) that it was probably more sensible to build the antennae right off the the Tx or Rx boards. And then run the dataline and ground with the coax and voltage on a third wire.

Does abandoning the transmission line idea seem sensible given the short wavelength?

1. The feed-point impedance of a half-wave dipole is ~70Ω; lower if the dipole is coupled to other nearby conductive material such as the hangar wall in my picture.
2. We can only hope that the transmitter is designed to drive a nominal 50Ω antenna impedance.

If 1. and 2., then you can place a 50Ω feed-line (RG58 or RG174) of almost any length between the transmitter and the antenna feed-point.

A consideration will be loss in the cable (tiny if the feedline is only a few wavelengths long).

If unbalanced coax is used to feed a balanced antenna like a dipole, then common-mode current on the outer part of the coax will distort the antenna pattern a bit, you can ignore this for this simple case. (I did)