Uhf/vhf/fm coax connectors for home made hd antenna

Ylli

Joined Nov 13, 2015
1,053
Because best power transfer occurs when source impedance is same as antenna, and free space impedance is 377 Ohms so 75 Ohm antenna would give very poor results.
I know this is an antique thread, but that statement bugs me. A properly tuned and matched antenna acts as a transformer in that it matches the impedance of free space to the impedance of the transmission line. The impedance of the antennas output port has no bearing on the antennas efficiency.
 

SamR

Joined Mar 19, 2019
3,607
Several factors involved, impedance and frequency being the most important. Actually the impedance is, of course, dependant on the frequency. Typically a Balun is used between the feed coax and the antenna to match the impedance and the antenna tuned to resonate at the transmit frequency. To put it in a nutshell.
 

Janis59

Joined Aug 21, 2017
1,356
RE:<<can you step dowt the ohms by adding a resister and by passing it all together and just solder it?>>
No, You cannot.

If want to know better then read anything starting with "Smith chart". The only knewn method have name "to tune".
 
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nsaspook

Joined Aug 27, 2009
8,901
I know this is an antique thread, but that statement bugs me. A properly tuned and matched antenna acts as a transformer in that it matches the impedance of free space to the impedance of the transmission line. The impedance of the antennas output port has no bearing on the antennas efficiency.
Actually it does. https://en.wikipedia.org/wiki/Radiation_resistance

You properly tune and match the transmission line to the feed point of the antenna. The impedance of free space and the antenna Radiation resistance might be widely separated.
 

Papabravo

Joined Feb 24, 2006
17,247
Impedance matching is more critical in a transmitter than in a receiver. Most communications receivers will adequately receive a signal from a random length wire tacked up on a wall or strung out of a window. A typical "weak" signal at the antenna might be -120 dBm or about a femto-watt. A good receiver can turn that minuscule amount of power into a usable signal without even breaking a sweat. for a receiver, impedance matching is a complete waste of time. For a transmitter, it's a completely different story.
 
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nsaspook

Joined Aug 27, 2009
8,901
Impedance matching is more critical in a transmitter than in a receiver. Most communications receivers will adequately receive a signal from a random length wire tacked up on a wall or strung out of a window.
True for casual communications.
It's important for signal integrity when you have 100's of receivers connected to a receiver antenna farm the size of a football field.
 

Papabravo

Joined Feb 24, 2006
17,247
True for casual communications.
It's important for signal integrity when you have 100's of receivers connected to a receiver antenna farm the size of a football field.
Is that hundreds of receivers connected to a single antenna, or hundreds of receiver/antenna pairs with the antennas in close proximity (within 1-2 wavelengths)?
 

nsaspook

Joined Aug 27, 2009
8,901
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