# Phone antennas

Science 10 Mar '08 17:53
1. 10 Mar '08 17:53
How the hell can someone make mobile phone antennas so small, when they work at around 2 Ghz frequencies?
2. sonhouse
Fast and Curious
10 Mar '08 21:32
How the hell can someone make mobile phone antennas so small, when they work at around 2 Ghz frequencies?
They have resonators that cut down the size. I am a ham operator, so I can give you an analogy to a low frequency dipole: At about 7 Mhz, the "40 meter" ham band, a dipole is about 67 feet long, cut in the center where the feedline goes. If you want to shorten it, you add inductance say, about halfway, depending on how much you shorten it, you might get away with something like 30-35 feet long. The problem with that scheme is the transmit efficiency goes down, you pay for it with a somewhat smaller transmitted signal, even though you might have a decent VSWR (Voltage Standing Wave Ration).
You strive for a 1:1 ratio, where the final amp output goes to the antenna and nothing gets bounced back. How it gets bounced back is with an impedence mismatch, so the typical impedence is 50 ohms, and if the transmitter is 50 ohms and the transmitter looks into a 50 ohm antenna, all is good, all the energy leaving the transmitter goes out the antenna and none comes back, a mismatch, say an antenna impedence of 25 ohms means a VSWR of 2:1 and a certain percentage comes right back down the feedline. Now that is not the whole story. The transmitter can think its 50 ohms alright and the antenna can say, Hey, I'm 50 ohms too, so the RF checks out and does not check back in (bad for the transmitter, it gets heated twice that way). The kicker is the antenna transmit efficiency. If you have a pure dipole, you have a certain transmit efficiency, forget the exact # but it is charactoristic of most all dipole antennae. Now if you do like I said in the case of the shortened antenna, some of the energy that would have been transmitted in a high effiency system now goes into heat at the antenna
3. menace71
Can't win a game of
11 Mar '08 04:35
My Dad was a Ham radio operator. I remember he had to match his transmitter to his antenna when he turned his Unit on. One time he forgot to do just that and smoked his transmitter. I don't much about it all but I remember that much. I remember him saying that antennas were a science unto themselves. He made the antenna in our backyard. WA6ANR was his call sign.

Manny
4. sonhouse
Fast and Curious
11 Mar '08 23:22
Originally posted by menace71
My Dad was a Ham radio operator. I remember he had to match his transmitter to his antenna when he turned his Unit on. One time he forgot to do just that and smoked his transmitter. I don't much about it all but I remember that much. I remember him saying that antennas were a science unto themselves. He made the antenna in our backyard. WA6ANR was his call sign.

Manny
A California dude. Same as me, I started out as KN6QDT then K6QDT when I advanced out of novice. What part of Calif. was he from?
I talked about that in my post, the antenna impedence wants to match the transmitter impedence to get the most power out and the least reflected energy back to the transmitter. Why your dad's transmitter smoked is when the impedence mismatch becomes great enough, it doubles the heat load on the transmitter, say it puts out 1000 watts and then goes to a poor antenna and that 1000 watts gets reflected back, its like being heated with 2000 watts which will burn it out if it goes on like that too long. Its not really free energy but it acts like it in the transmitter. BTW, my call is now AI3N. See if you can figure out what state I live inπ
5. nmdavidb
11 Mar '08 23:38
Guys...since I have been working on my degree to quit doing stand up in clubs and get on the radio I have always been fascinated with messing around with the whole HAM radio deal.

Can anyone tell me what would be a good set up and the price range?

Oh and trust me I know all about the FCC and all...i do a clean act...which is why most of my gigs lately have been all corporate.

Dave
6. sonhouse
Fast and Curious
12 Mar '08 00:26
Originally posted by nmdavidb
Guys...since I have been working on my degree to quit doing stand up in clubs and get on the radio I have always been fascinated with messing around with the whole HAM radio deal.

Can anyone tell me what would be a good set up and the price range?

Oh and trust me I know all about the FCC and all...i do a clean act...which is why most of my gigs lately have been all corporate.

Dave
That depends on how you want to play the game. There are several varieties of amateur radio, entry level to the top level called Amateur extra. The entry level of novice allows you to talk on some bands while more advanced licenses give you more places on the radio dial to talk and other forms like digital mods. Here is a link to the bands allowed and the level of license it takes to get those bands.
http://www.arrl.org/FandES/field/regulations/allocate.html
It is a bit daunting to go through I know. But you can talk on some bands with the novice license and the tech license allows talking on some high frequency bands like 2 meters, which is 144 to 148 megahertz, a pretty big band, 4 megs wide. You can also learn morse code and do what is called CW or the dots and dashes like dit dit dit dah is V, and so forth. So the cheapest way to get into it would probably be at a hamfest where you have dozens and maybe hundreds of hams with the back of the van full of gear for sale cheap.
7. nmdavidb
12 Mar '08 02:32
Wow! that was alot of info.

Maybe pm some links and all and I will check out the local Ham club here in Denver.

Thanks!

Dave
8. sonhouse
Fast and Curious
12 Mar '08 16:29