5.8 Ghz Cordless Phone Question

You are right. It doesn't make sense. But the fact is at any frequency signals still travel close to the speed of light and if there is any difference between 900Mhz and 5.8Ghz it is very small to make any difference in the sound quality or data transmission capacity. For all intents and purposes, it doesn't make any difference whatsoever whether you have 900Mhz or 5.8Ghz as long as you have strong reception. Now, if you have interference in one band, then that's not the band's fault. If you have interference you will have problems with reception quality regardless of which band you use. The only significant differences between these bands is the antenna size and the propagation pattern of the signals. At higher frequencies physical objects start becoming an obstacle for signal penetration. Another thing is that digital audio sounds the same whether you transmit it at 5Mhz or 5000Mhz. The carrier used to transmit a digital signal makes absolutely no difference to digital audio as they are totally independent.

 

Yes, it seems that even Cordless phone Marketing Reps arent Tech savvy, & some of them think "more Mhz = more range".
One thing to remember when choosing a cordless phone is that 2.4Ghz can be a potential problem if you have a wireless router, which also operates at 2.4, & microwave ovens cook near 2.4, so 900 or 5.8 may be a better choice for these reasons. (My microwave makes my PC / internet unuseable when it is on, but my PC is on a desk in the Kitchen only a few feet away from it!...)

 

Now, why would anyone have their PC in the kitchen? I can imagine your computer chips are frying in cooking oil.

Don't forget about Bluetooth. It is 2.4Ghz too! I've always heard of those problems at 2.4Ghz, but I have yet to experience any. I have three 2.4Ghz cordless phones in my house, one whose base is parked right next to my computer. I also have a 2.4Ghz D-Link wireless router which is on the floor below me and that's how I connect my computer to the Internet and even though the PC is right next to the cordless phone base, my computer never has a problem with it. I guess it depends on what brand of equipment you have. I have a friend whose Internet WiFi connection always dies when his cordless phone rings and changing the channel on either the Access Point or the cordless phone doesn't help.

Actually, my cordless phone seems to have more problems with my cell phone than anything else! I can hear some buzzing in my cell phone (not the GSM buzz) if the cordless phone is being used and I am near the base. Granted, my cordless phone also picks up the GSM buzz from my cell phone too.

 

Well, I bought a 5.8GHz phone when I bought my first wireless router that operates in the 2.4GHz band. I didn't want to take a chance on interference. Then I switched my router to the 802.11a standard which you all know operates in the 5GHz band. My 5.8GHz phone says it is wireless networking friendly and from watching the two operate, there has not been any intereference with my wireless networking or phone calls at all.

Another thing with my 5.8GHz phone. I noticed the range I have. At my old house, I was able to walk a little over half of my street before I started to here static on my calls. Now I live in an apartment and I could walk what still would be considered "half way up the street" without any problem. I can even go to my brother's apartment which would be across the way without any issues also. 5.8GHz phones kick ***. LOL

 

I'm glad to see this question brought up. I delayed for some time using a wireless router because my own survey showed a 50/50 split from those that had no interference (between 2.4Ghz phone and router) and those that did. The main problem is the router goes down when the phone is used.

I finally got a 2.4/5.8 Ghz router system, and had no problems. I finally turned off the 5.8 Ghz router part. Phone's base in the kitchen, next to microwave, router is only 12 feet away. The 2.4 Ghz satellite phones are sometimes next to the router or next to the laptop upstairs. Never any problems with the microwave either.

I think, without proof, the difference is in the phone. I have an Vtech 2.4 Ghz digital spread spectrum expandable phone (4 phones total). New, a few years ago the base alone was $ 140. I bet if I had a cheap analog 2.4 Ghz phone I would have problems (radio shack $29.).

So far the guys that have no problems, all have high end digital 2.4 ghz phones.

In terms of distance, I didn't notice any improvement from 900Mhz to 2.4 ghz.

 

The key is the potential higher data capacity and not the speed.

 

Recipes, Bobo, recipes. I would love to have a recipe computer in my kitchen and have access to Food Network's website, too. It would be way more organized than my recipe folder and cook books with loose recipes just stuck in the pages all willy nilly.

Also, my mother-in-law's computer is in her kitchen because she has a cool built-in desk there.

 

I have one of those V-tech phones too. They are nice. But we also have a Motorola cordless phone and none of them cause any problems with our router and we are all running at 2.4Ghz. I think you just have to try them out and see if it causes problems in your case. I don't think anyone can predict whether you will have problems or not with your specific combination of router and cordless phone because there are too many variables.

 

My linksys 802.11b will make my Jabra 250 Blue Tooth headset very hard to hear on. My wifi is getting several years old, I imagine I would not have this problem with newer equipment...

 

When someone calls on our phone, our fax machine in our study will interfere with our wireless router by me loosing my wireless connection for a split second when someone calls our landline.

 

I don't think I mentioned before in my post that my phone is a VTech 5.8GHz phone.

 

"The key is the higher data capacity(and data rate), not the speed of transmission".

Engineers use data rate rather than speed, but speed (as in "Why isn't my Web page getting here faster?") seems more meaningful for the less technically inclined. Many of us tend to think that the number of bits getting somewhere over a period of time is their speed of travel. That is not really the case.

At a frequency of 100Hertz, you cannot transmit a 1 MegaHertz signal. At 2.4 GigaHertz you can transmit a 1 Megahertz signal, and, transmit many channels of them. This is why light in a fiber optic cable has such high phone call capacity. Light in fiber is around 100 TeraHertz.

Relative to data transmission, a related term, bandwidth or "capacity," means how wide the pipe is and how quickly the bits can be sent down the channels in the pipe. (The analogy of multiple lanes on a superhighway with cars at the same speed may help).

The actual speed of tranmission of either the 100Hz or 2.4 GHz signal is the same.

Google around for more information.

 

Well yes that would be right. However the reality is limited by lots of things,technical and non technical: FCC rules and channel allocation,business decisions,equipment installed,and real need.

Among the carriers in the US there isn't any real difference in practice, I believe, at the data rates we use for voice and data. I wouldn't spend any time worrying whether the provider in my area is mostly 850 or 1900. There are more important considerations like good coverage and service.

There is a difference between analog and digital however. Using digital it is possible to get higher data rates on the same freq. than analog. Basically digital can convert the multilane highway into a equivalent single lane! Digital combined with 'multilanes' is the best by far, and is what is used in telecommunications today.

 

Well a good theory down the drain. The Motorola is an analog phone and works ok? The kid at circuit city told me that above 1/2 of the routers are returned due to problems with cordless phones...but I think it was a fish story. Most of the verifiable stories seem to be successes, but again people use phones like Vtech or other digital 2.4Ghz.

I just think that the analog versions must splash out a lot of power and bandwidth and possibly corrupts the router equipment. Not certain on that. Maybe I'll but a analog one, try it out , and return it to the 'Shack'.

 

Ahh. Sometimes a simple example for illustration can cause confusion for an inquiring mind.

No, separate internal antennas are not used. The 'channels' are freq. channels around the 2.4 Ghz band. For example (not exact), you may have 2.4 Ghz, and two channels +/- 30kiloHz around 2.4Ghz, or maybe a few hundred channels each spaced 30kiloHz from each other, but around the 2.4Ghz main frequency. For a channel up 30 kiloHz that is 2,800,030 KiloHz, a pretty small variant from 2.4Ghz, but huge and really not possible at 100hz.

Cell phones use hundreds of such channels, each about 30 to 50 kiloHz wide in bandwidth to get the voice quality we have today. The point is more data capacity or bandwidth is available when the higher frequencies are used. The example between 100hz and GigHz is extreme. Between 2.4 or 5.8 Ghz (or 850/1900) is less extreme and may not be used in practice for final products or commerical services.

Again, I am simplifying alot and not covering different techniques used in TDMA, CDMA or GSM. A good starting point for you may be a place like Howstuffworks.com at how cell phones work . There is a lot more info there than I can type into these forums and it has some good references and links.

 

One thing I'd like to point out is that wireless networks today don't use the full physical potential of the band they transmit on. Not even close. Therefore, you won't see any difference in data speed (transfer rate) from data services operating at 850Mhz versus 1900Mhz because both bands have potential for much higher speeds than they use today.

Digital TV operates in the lower UHF and high VHF bands and they currently use several megabits-per-second transfer rate to deliver digital HDTV. This is a much higher rate than cell phones are using today even though the band they broadcast on is lower than that of cell phones. Granted each TV station has a much wider channel bandwidth (6Mhz) than cell phones, but the point is that for various reasons existing wireless cell phone networks are not taking advantage of all their band can possibly do. Therefore, customers won't see any difference in data rates at 850Mhz or 1900Mhz. Only UMTS has a bandwidth that can come close to digital TV standards by using 5Mhz channels, and even then, it has to be shared between many people which hurts individual data rate for each user.

 

This correctly reflects the current situation, and I agree not to spend time worrying about the two frequency bands. In almost any RF band the full capacity is not taken advantage of a variety of reasons, some non technical. But the principal is true, and why light in fiber optics can carry so much data

Bobolito's example is a good one and has come up before in these forums. Old fashion TV can send great live video using only a frequency carrier around 50Mhz (CBS, channel 2 ), but the FCC allows it to use Mhz of bandwidth per channel. In cell phones, at 850 Mhz, they are assigned only a merger ~30Kilohertz per channel. The system was designed and allowed for voice, not video. Wireless carriers now are applying all sorts of games and techniques to squeeze video into those small allotments and hence we get no video or choppy video. The legal bandwidth allotment is the controlling force, not the frequency of the carrier.

 

Actually the FCC gives cell phone carriers spectrum in Mhz, except for Nextel which is licensed per channel. Carriers using 850Mhz are given 25Mhz which they can use any way they want to split it. However, since cellular networks are bi-directional, that splits the 25Mhz into two, so that limits the usable bandwidth to 12.5Mhz for each path (Mobile to Network and Network to Mobile). PCS carriers can get anywhere from 10Mhz to about 40Mhz of bandwidth (not necessarily continuous). Although it is possible to get more than 40Mhz in the PCS band, I haven't seen any carrier being allowed to have more than that.

The FCC does not impose limits of 30Khz for voice. That's only how IS-136 (old TDMA network) separates channels. GSM uses 200Khz per channel and CDMA carriers use 1.25Mhz per channel which is much wider. And now, we have UMTS with an even wider 5Mhz channel! Therefore, carriers can use any amount of bandwidth for voice channels as long as they stay within the limits of their licensed spectrum. It all depends on the kind of network the carrier uses. Now, for obvious reasons every carrier wants to squeeze as many customers as they can within the spectrum they have, so they have to limit as much as possible the amount of bandwidth used per customer. But the carrier can use 5Mhz for just one phone call if they wish to do so.

 

Yes, & 1900Mhz can actually be thought of as worse than 800, in terms of bandwidth/capacity, if trhe carrier has, say, only 10Mhz of spectrum at 1900 vs. 25Mhz of spectrum down at 800.
You can fit more "stuff" into 25Mhz than you can into 10Mhz.
The main reason people think of 1900 as having more "capacity", is because the older 800 networks are already "filled" in every market with voice, both digital & analog(still required), so companies are buying up chunks of 1900 to deploy their high speed data, such as VZW is doing with EV-Do.
EV-Do would work fine at 800, & uses the same 1.25Mhz channel size, but there simply aren't any channels "left" down at 800 to deploy EV-DO in most markets. 1.25 Mhz worth of spectrum IS 1.25Mhz, regardless of weather it is at 50 Mhz or 5.8Ghz.

 

True, but the higher the frequency, the more bits of data you can put in that 1.25Mhz channel. Why? Theoretically, the amount of information you can encode in a signal that vibrates at a higher frequency is greater because the signal vibrates quicker. In other words, if a you could put 1 bit of information per cycle, that means that at 1900Mhz you can put 1900 bits of data per second while at 800Mhz you can only put 800 bits per second. To compensate for this, you'd need a wider channel at 800Mhz than you would at 1900Mhz to achieve the same potential data rate. Therefore, the lower the frequency, the wider the channel needed to achieve the same potential data rate.

One more thing about 850Mhz. While most carriers got 25Mhz, Cingular was the exception when it bought AT&T Wireless. They are actually the only carrier with 50Mhz of bandwidth at 850Mhz in some markets, like Orlando, FL.

 

Which is really the point. They can use all the bandwidth if they want per phone call, but they don't. The 12, 25 or whatever Mhz allotment is subdivided into much smaller bandwidth channels.

 

Right, but I was pointing out this is not an FCC restriction.

Now, don't confuse bandwidth with data rate. One single phone call using CDMA will still use the whole 1.25Mhz channel x 2 which is 2.5Mhz worth of spectrum when you add up the paired channel. This means that 2.5Mhz is the bare minimum necessary to carry a single conversation over CDMA. However, because of multiplexing techniques (spread spectrum encoding, etc.) you can add more users to that same channel without using more bandwidth. So you can probably have anywhere from 1 to 15 or maybe 20 users and still use 2.5Mhz total! The point is that each user is not using just a small chunk of the 2.5Mhz paired channel. Each user is using the whole channel even if most of it is empty. The same thing goes for GSM. You use 200Khz + 200Khz regardless if you use 1 time slot or all 8 time slots. In digital networks, RF bandwidth doesn't vary depending on the number of users. It depends on the number of channels used.

With UMTS, you'll see some carriers in some areas deploy just one channel at 1900Mhz because all they have is a single 10Mhz PCS license. UMTS requires 5Mhz channels which paired adds up to 10Mhz, so that takes up the whole license. If a user wants to make a call, they'll be using the entire 10Mhz, but that doesn't prevent many other users from simultaneously use the same channel because of the CDMA nature of UMTS. In this case, regardless of the number of users, the same amount of bandwidth is used (10Mhz). However, the data rate going through the UMTS channel will vary depending on how many users are attached to it and what they are doing (downloading a file, sending SMS, or talking on the phone).

 

Yes, I know this. I was trying my best to answer the original poster question (the 'speed of data' vs freq) in the least complicated and detailed way without going into all the protocals and methods used in wireless. Just the basic physics of data capacity and carrier frequency, without going off topic too much and adding confusion. A hard thing to do, and maybe could have be done better.

And yes, I should have been more clear on what is FCC, protocal standards, and business decisions. I just use 30khz as an example for the point, not wanting to detail the differences between the systems. Using 200khz, or 1.25 mhz or 6 Mhz at 50Mhz (as you mentioned for TV) would make the same point.