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Old Yesterday, 08:11 AM
hifinsword is offline
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United States, VA, Williamsburg
Joined May 2012
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Quote:
Originally Posted by Tsheets View Post
Radio antennas 101 (I'm really rusty) the receiver antenna has minimal effect in the reception. The transmitter antenna is critical. Too long or too short tx antenna will cause signal reflection back to the transmitter which turns to wasted heat. If you remember old CBs etc had SWR meters built in. That's "standing wave ratio" and is the ratio of reflected signal vs transmitted signal.

High freq is very omnidirectional and passes through objects well, but I'm sure there are optimal relationships, but none would be as critical as antenna length.
That's what I remember from almost 30 years ago when I was in school and could run the calcs
Keep in mind 2.4ghz is cellphone range. How much antenna do you see on your phone?
...cell tower?
I'm rusty too. My experience with radios and radar comes from my time in the USN operating in the HF, VHF & UHF ranges ending about 2 decades ago. The Tx antenna length actually determines the frequency of the transmitted signal. That's why you see smaller & smaller blade antennas sticking out airplanes as the frequencey gets higher and higher (VHF to UHF). Those long fishing pole-like antennas you see on ships, and wires strung from wing tips to tail on planes are the HF (2.0-29.9MHz) antennas. The antenna lengths for the LF range can be quite long. That's when you see NOTAMS around planes using them extending out for miles. You won't see that around subs cause you aren't supposed to know where they are.

The 2.4GHz is in the UHF range and is line of sight (LOS). Signals start becoming LOS in the middle of the VHF (30.0MHz-299.9MHz) range at around 225MHz.

The 2.4GHz (2,400-2,483.5MHz) band we operate in is called the ISM (Independent, Scientific, Medical) band. Cell phones, microwaves, bluetooth, internet routers, RC and almost anyone can use it (in the USA) if they comply with the FCC's Part 15 rules, or ETSI in Europe. To receive a signal both antennas need to be able to see each other. Our UHF signals can bounce off objects to some degree, but a direct signal is preferable.

The older VHF (27-72MHz) equipment with the 1M long antennas can bounce around or thru things. But our 2.4G signals cannot go thru or around things like metal frames or batteries or CF material. Some cell phones and some of our PCBs have an antenna traced on the board, so an antenna length outside the board isn't always required, depending on the board. And if it is there, it may be as a backup for the traced antenna. Often the antenna protrudes thru a hole in the PCB. So the solder and the antenna material going thru the hole in the board add to the required 31.25mm required. That's why oftentimes the antenna sticking outside the board is less than 31.25mm. The closer the antennas are to the optimum length, and the clearer the path is between them, the better the signal is at either end.
Don
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Old Yesterday, 02:55 PM
Tsheets is online now
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United States, NV, Gardnerville
Joined Feb 2015
117 Posts
Quote:
Originally Posted by hifinsword View Post
I'm rusty too. My experience with radios and radar comes from my time in the USN operating in the HF, VHF & UHF ranges ending about 2 decades ago. The Tx antenna length actually determines the frequency of the transmitted signal. That's why you see smaller & smaller blade antennas sticking out airplanes as the frequencey gets higher and higher (VHF to UHF). Those long fishing pole-like antennas you see on ships, and wires strung from wing tips to tail on planes are the HF (2.0-29.9MHz) antennas. The antenna lengths for the LF range can be quite long. That's when you see NOTAMS around planes using them extending out for miles. You won't see that around subs cause you aren't supposed to know where they are.

The 2.4GHz is in the UHF range and is line of sight (LOS). Signals start becoming LOS in the middle of the VHF (30.0MHz-299.9MHz) range at around 225MHz.

The 2.4GHz (2,400-2,483.5MHz) band we operate in is called the ISM (Independent, Scientific, Medical) band. Cell phones, microwaves, bluetooth, internet routers, RC and almost anyone can use it (in the USA) if they comply with the FCC's Part 15 rules, or ETSI in Europe. To receive a signal both antennas need to be able to see each other. Our UHF signals can bounce off objects to some degree, but a direct signal is preferable.

The older VHF (27-72MHz) equipment with the 1M long antennas can bounce around or thru things. But our 2.4G signals cannot go thru or around things like metal frames or batteries or CF material. Some cell phones and some of our PCBs have an antenna traced on the board, so an antenna length outside the board isn't always required, depending on the board. And if it is there, it may be as a backup for the traced antenna. Often the antenna protrudes thru a hole in the PCB. So the solder and the antenna material going thru the hole in the board add to the required 31.25mm required. That's why oftentimes the antenna sticking outside the board is less than 31.25mm. The closer the antennas are to the optimum length, and the clearer the path is between them, the better the signal is at either end.
Don
Yep, I used to be able to calculate half wave or quarter wave antenna lengths given frequency, but now I can barely count my toes

I miss that stuff. I actually used it once. Before the modern 2.4 ghz stuff I had to build a control system on UHF. I had to design quarter wave antennas for each station (they were all the same). Once I built it on paper I used an SWR meter to fine tune the real ones. I think I was less than a half inch from optimum.

I also built a home TDR (Time Domian Reflectometer). That was fun and it worked. Saved the company $$ by not having to excavate a bunch of cable. I found a break in a half mile of buried control cable by 6 inches

Nobody teaches electronics like the Navy
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Last edited by Tsheets; Yesterday at 03:19 PM.
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