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Was FM... then 900MHz, and 2.4GHz is getting popluar

J

Jerboy

Banned
Thats the frequencies of cordless phones in use today. I understand that each type use different radio frequency and different type of modulation such as analong, digital, digital spreadspectrum and such..

What difference does it make in reality? higher frequency and lower wavelength is better because?

 
A higher frequency, typically means a higher bandwidth - the old 27 MHz band allocated to cordless telephones, had a 500 kHz bandwidth, meaning that there were roughly 8 channels or so.

The newest DECT specification uses 1.88 GHz - 1.90 GHz (a bandwidth of 20 MHz) - providing over 100 channels - more channels mean less interference between neighbouring users. More channels also give more flexibility - I find using multiple DECT handsets as intercoms very useful.

The high bandwidth of DECT also means that there is the possibility of higher data rates - multimedia devices using the DECT band are already well into development.

The other advantage of higher frequencies, is the shorter wavelength - shorter wavelengths mean that aerials can be much smaller - no need for the 5 yard long aerial wires dangling from the base station, and foot long telescopic rods on the handsets. at 1.89 Ghz, the aerials can be less than 1 inch long (and indeed should be for optimum performance).
 
Yeah...

You can tell the diff btw them all side by side, the ones with the lower frequency will have more static and interference(because of less channels and longer wavelengths), while the higher freq. ones will be much better.... on side note, anyone else think telephone quality sucks? So there is a point at which adding more ghz to the freq. won't matter for phone conversation, but for other things... like wireless communication devices......



zs

 
Simplest explanation is that there is much less 'traffic' at higher frequencies.... hence, less interference, and hence, better signal quality, and hence again, longer distance functionality. Sorry... kinda buzzed right now 🙂
 
One further thing you will notice about the cordless phones being in a higher frequency is that they are intercommunicating with the baseunit digitally, ie no analog voice information is transmitted. 27MHz is perfect for analog voice communication but you need much more bandwidth to transmit digital sampled audio.

I also know many of the 900MHz phones get almost a mile (some more) of line-of-sight useable range from the baseunit.

I'm not an expert on radio transmission and why what particular frequencies are chosen, is anybody on here able to answer that?

Cheers!
 


<< One further thing you will notice about the cordless phones being in a higher frequency is that they are intercommunicating with the baseunit digitally, ie no analog voice information is transmitted. 27MHz is perfect for analog voice communication but you need much more bandwidth to transmit digital sampled audio.

I also know many of the 900MHz phones get almost a mile (some more) of line-of-sight useable range from the baseunit.

I'm not an expert on radio transmission and why what particular frequencies are chosen, is anybody on here able to answer that?

Cheers! >>




Ok here's the story..

MY POS GE 2-6920 40ch 900MHz died. My testing shows RF in the handset went bad. Even though they sell handset as a replacement part, it costs $34.95, more than what I paid for the whole thing. I think I'll pass and get a new one.

Today, I bought another GE. I know... I'm not too fond of them, but I do have to say that GE makes phone that is most comfortable for me physically when I have it between my head and shoulder. I would have avoided GE, but comfort should be on higher priority than technical superiority.

My new phone is a 2.4GHz GE, also a 40ch.

It isn't any better than my 900MHz, if not worse at static, clicking and interference. Unfortunately, I wasn't able to find anything that feels as good as this phone, so I guess I'll buy yet another GE in a year or two unless someone else comes up with a comfy phone.



I don't like those Vtechs that have earpiece pooching out since they tend to be painful for my ears.
 
For telephones, the frequency should not matter nearly as much as the quality of other components. One of the big reasons is eliminating interference with other devices; since there are very few unlicensed RF bands (read: free to use), this is a big problem. In fact, I would not buy a 2.4Ghz portable phone because many other wireless devices (i.e. bluetooth, IEEE 802.11) are ripe for interference.
 
Go all-digital! Get a cable modem/DSL for internet access and use Sprint/Verizon/ATT/whoever for mobile/home phone.

Landline w/dialup internet:
~$30/mo for landline with caller id, call waiting, etc
Long distance bill varies
~$20/mo for internet
$20 phone + $10 modem = $30 initial cash outlay
bad phone quality + slow internet access


Sprint mobile phone w/ATT broadband
~$40/mo for mobile phone with caller id, call waiting, etc, 250 anytime + 2250 night/weekend mins
No extra long distance charges
~$40/mo for ATT broadband
$0 phone + $120 modem = $120 initial cash outlay
good phone quality + fast internet access

Plus, most people already have a land line and a mobile phone, so they might actually save money from this scheme. And of course you get better phone quality + much faster internet access. So for $30 or less (depending on your long distance bill) extra per month you get many fewer hassles. And Sprint's pretty lenient with their phone exchange policy, ie if a cool new phone comes out you can usually haggle your way into it for little or no cost.
 
2.4ghz definately can be better for sound quality and range
we have a 2.4 and a 900... the 2.4 can go 4 to 5 times as far from the base as the 900mhz...the 900mhz gets interference from halogen lamps and stuff
we have a cheap 2.4 that cuts out whenever we turn on the microwave, however....
 
Jerboy is right.... the Vtechs are painful! haha... anyone know the FCC's specified frequency band for public telecommunications?
 


<< 2.4ghz definately can be better for sound quality and range
we have a 2.4 and a 900... the 2.4 can go 4 to 5 times as far from the base as the 900mhz...the 900mhz gets interference from halogen lamps and stuff
we have a cheap 2.4 that cuts out whenever we turn on the microwave, however.... >>




Yeah so says the sales department of every manufactures and some customers, but there has to be a technical theory for it to have a meaning full proof.
 
Today, I bought another GE. I know... I'm not too fond of them, but I do have to say that GE makes phone that is most comfortable for me physically when I have it between my head and shoulder. I would have avoided GE, but comfort should be on higher priority than technical superiority.

thats what headsets are for silly🙂 i leave a headset connected to each and every handset🙂 ppl have died crunching their necks to hold phones hehe

i still use 900mhz phones, recently got 2 more for 14bux each. came with caller id, phonebook feature,headset etc, equiv features in a 2.4ghz costs 100+.. not worth the premium😛
 
I picked up a few 2.4 GHZ's from home Depot for $57 with caller ID, phone book, ect. Did not come with a headset, that was 0.99 from newegg 🙂
 
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