Can someone help me with simple technical info about MHZ? ...

[LGM]

I apologize for posting here, but I didn't know where else to go and searched on the internet for an answer to a simple question about mhz but couldn't find one.

I figured you all might know since my question has to do with frequencies, and you are probably all very well versed in this area.

I am purchasing a little weather station for indoors that has an outdoor remote sensor communicating with the base unit through radio frequencies. There are two models to choose from -- one using 433 mhz and the other using 915 mhz.

Would getting the 915 mhz model offer any advantages over the other model? Does it have a greater communication range than the 433 mhz model? What about interference with existing electronics such as my wireless LAN and cordless phone? My current home cordless phone operates at 900 mhz.

I live in an apartment building and so there is often a lot of interference. But the outdoor temperature sensor will be placed no more than 30 feet from the base station, with basically only a single brick/concrete wall in between.

I would appreciate any advice.

Thanks in advance,
LGM

 

[SAR923]

I have a weather station that transmits on 433 MHz and have never had an interference problem either with my radios or the weather station. It's hard to tell which one might have greater range without knowing the actual transmitter and antenna specs since either frequency could be better depending on those two factors. I would tend to shy away from 915 MHz only because it's getting uncomfortably close to cordless telephone frequencies.

 

[adamsdawson]

yea i would stay away from the 900 Mhz range. plus you said that there is a brick wall so the 433 Mhz range will not bounce off of the wall as much as the other will.

 

[LGM]

I was under the assumption that the bigger number meant the greater range. I'm also surprised to learn that the 900 mhz range is more likely to bounce off a brick wall. My apartment building's exterior is definitely brick plus some other assorted stone and metal materials, so it seems like the 433 mhz model might actually be best for my needs. Plus it's less expensive, though all other features are the same as the 915 mhz version.

Thanks for the replies. You've been a big help.
Pat

 

[boatbod]

I was under the assumption that the bigger number meant the greater range.

Quite the opposite actually! The higher the MHz, the more it is affected by attenuation and reflections (multipath distortion) from surrounding objects. Ever noticed a satellite tv signal drop out when a big storm cloud crosses in front of the dish? HF communications (2-30Mhz) can travel around the world. Try that with 900Mhz!

 

[kb2vxa]

Bod, please don't confuse people by comparing apples to oranges. Under normal conditions HF relies on ionospheric refraction to propagate around the Earth while VHF-UHF is strictly line of sight as it penetrates the ionosphere into space.

"The higher the MHz, the more it is affected by attenuation and reflections (multipath distortion) from surrounding objects."

At least that much rings true, the higher the frequency the more RF behaves as light, just another part of the electromagnetic spectrum.

 

[n8emr]

A number of the wireless weather stations are moving to 900mhz. In the 900mhz part 15 band you get a little more power, have a few more modulation options and have less things to interfere with you. Its great for ham's since the little wx stations didnt work worth crap on 400mhz when there was a UHF ham signal nearby.

For the short distance MOST of these are designed for, if your not a ham or have one living next to you with unit is fine. Otherwise the 900mhz is the way to go.

 

[N8RUS]

I have also looked into weather stationsand will go with the 433mhz. This due to the fact my 900mhz cordless phone interferes with my 900mhz wireless internet connection at times.

 

[roadranger]

ligitimate argument

433 Mhz is good for distance, like tall apt buildings. 900 Mhz devices are for punching through walls, which may be why so many PDs are going trunked, not to mention our phones are going that way, as limited as they seem.

 

[poltergeisty]

900mhz cordless phone interferes with my 900mhz wireless internet connection at times.

You mean 2.4 GHz???

Don't know if a weather station that bursts data will cause interference with a WIFI signal. I do think it may cause problems if you listen to digital systems in the 800 MHz range.



The 400 MHz. range may interfere with the garage door... *sarcastic* :lol:

All in all, I doubt you will have any trouble with both.

 

[pgibbons]

I like the comment about higher frequencies punching through walls.
What would happen if you were underground in a cave or mine. There are no walls to punch through but tunnels. Would the 400MHz range work better than 900?

Also one must keep in mind how well the system, especially the antenna is tuned. It makes a great difference for transmit and receive. A shorter antenna might be easier to work with.