2.4 GHz vs. 900 MHz Phone Technology

[mikes6]

I think it is operater error! How are you doing Dean? For anyone reading this, Dean and I are good friends and used to work together. Dean knows more about electronics than I ever will.<p>My 2.4 GHz unit at work has exceptional range, much farther than the 900MHz unit I did use.<p>Anyway, I thought I'd poke a friendly jab at you.<p>Mike

[Dean Huster]

Here's the way Mike and I usually worked: He designed the circuit and I made the circuit board and the cabinet so that it would end up working and looking nice to boot, i.e., he's the one who was all thumbs and all brains, not me.<p>Dean

[perthcom]

I agree with Stephen.
The impression that high frequencies has more to do with marketing hype than the real world.<p>Just think of how far you can hear AM radio stations 540-1600Khz (0.54-1.6Mhz) verses how far you can hear FM radio stations 88-108Mhz.<p>If you have ever been in a small airplane, you will notice that the Communications on the 2-way radio is quite low, but get up in the air a few thousand feet and the radio is chattering away with planes up to several hundred miles away.<p>When you get up to 2.4Ghz even drywall can attenuate the signal quite a bit. Not to mention that when your handset is clipped on your belt, your body will absorb and attenuate the signal drastically. These microwave frequencies are best for wide bandwith Point to Point applications. It takes alot of 802.11 access points to cover the site of a typical facility.<p>I think that 900Mhz would be your best choice. Get a commercial duty Engenious SN920 for the most power and range.

[Dean Huster]

We really have to rule out frequency in general as the guideline for distance, I think, because the low-vs-high equals far-vs-near doesn't wash. In general, the higher in frequency you go, the more line-of-sight the signal will be to the point that microwave signals are lost with the blockage of nearly anything, such as trees, buildings, etc. At the low end of the spectrum, it was the down-into-the audio VLF stuff that the Navy was using to communicate with submerged submarines since the signal penetrated deeply into the earth/oceans. It's the VLF bands that NIST uses for WWVB, although that isn't primarily for the distance as it is the fact that it's all ground wave so that the time signal is less affected by atmospheric propagation -- but it does cover CONUS with a reasonably low power output (as compared to VOA or a television station). The around-the-world stuff is in the HF "shortwave" bands, from 3 to 30 MHz where ionospheric skip lets a signal bounce around to the far side of the earth with just a few watts of power. Typically, VLF doesn't skip like that, killing off the lower-is-farther idea. If lower frequencies were the best, the cordless phones would have stuck with 49 MHz or even better, the 1.8MHz they originally were using that was always eaten up by power line hash.<p>I was always assuming that whether 900MHz or 2.4GHz, the signal was going to be line-of-sight anyway. I thought that maybe there was some fancier stuff built into the signal (or more power at 2.4GHz) that was supposed to make it reach out and touch someone at a longer range.<p>Dean

[toejam]

I think it all boils down to distance vs battery life.

[galois]

I am certainly not a pro on any of the latest S-band technology. But looking at the fundamentals, Radiation acts more like light the higher the frequency (more directional and line-of-sight). Therefore you could be getting lots of RF reflection based on the immediate enviroment (your 10 acres).