After a long break from projects like these I decided to setup a cellphone network, the Personal PHone System (PPHS). Basically a long range cellphone network where base stations are very far away and using analog technology the signal can reach further. Bases and handsets transmit with massive amounts of power, 5, 7, 10 and 15 watts for the bases and 3 and 5 watts for the handsets. The system also uses Low VHF 6 Meter band which lets the signal penetrate walls and buildings with ease. Works without running cables between stations and 1 station's signal can be repeated by RRs infinitely, so low cost deployment.

System diagram:


Cell structure:


Range Rings:


Because the bases transmit with higher power it is possible to have a condition where the base can reach the handset but the handset can't return a signal to base, the system switches to pager mode then where the handset simply gets notified of incoming calls.

The Radio Modulator unit converts the buttons on the handset to Pulse Dialing digits, do you know of any way to convert pulse dial digits to DTMF tones externally? This means without modifying the Radio Modulator but something that goes between the PSTN Phone Line and Radio Modulator?

There will also be multi frequency transmission where the base and handset transmit the voice on 2 frequencies at same time and the voices are superimposed on eachother to even out static and switches to single frequency if 1 frequency goes out. Example 49Mhz and 150mhz at same time.

And this is not just a research project, it is an actual attempt to compete with wireless telcos!

I think this is really cool! I have some questions that will hopefully help me fully understand aspects I don't:



I assume this isn't recursive. Only 1 station can power a subset but that subset can't power the next?



I'm curious how this works, how does the tower know the phone is in range but that the phone can't communicate back to the tower? Maybe I'm missing something but would it make more sense for the tower to always broadcast in pager mode, if it get's a return signal then the two devices establish a connection and the phone call comes through.

Anyways, I really look forward to updates!

1st question: Yes repeaters can infinitely power more repeaters as the repeat delay is near zero because its all analog (nothing is digital at all in the entire system) and radio waves travel at light speed.

2nd question: You are right, the tower always broadcasts in pager mode because it can't know if the phone is out of range so it assumes it is but the handset switches to pager mode (because it knowns) in order to flash the NoSvc indicator and check for the Δ triangle roaming indicator.

If the phone is completely out of range the NoSvc indicator O with a slash through it stays always light.

Thats pretty cool looking. Now I do have a question. From experience 15w ( I work as an RF test technician) is a pretty large amount of RF power. Personally I would be worried about it interfering with other things as well as my personal being. Is there anything in consideration regarding that in your system? or is this hypothetical.

So far I have been operating it and have not received any complaints. I have payed money for the channels so its not like I care. The other users on the band are non paying users so they have to yield to me.

What's the power like then? Surely the receiving towers must take some power to function, by which iteration is there not enough power for the next tower?

Oh the towers all have their own power source, it can be either grid power or 1 of them uses green electricity with photovoltaic To help save the environment!

Oh, sorry. I meant repeaters. Surely the receiving repeaters must take some power to function, by which iteration is there not enough power for the next repeater?

RF power or electric?

Not sure, you said

So I was just curious how many times that can happen before there isn't enough power to reach the last station, or as you later said a repeater.



Or is it truly infinite?

I have only tried it with 2 repeaters chained because the base covers 20km and my city isn't that big and my friends (that are willing to let me setup a repeater at their house) all live close and the repeaters must be spaces 30km from eachother so they don't interfere with eachother so I don't have enough places in athens to test it out, currently ive setup a base in psychiko and a repeater in glyfada and another one on ymitos mountain and connected the handset in pallini.

So right now I've got a cordless telephone that works all over the entire city of athens xD

From a quick Googling of "Psychiko" and "Glyfada" (although I could have just read to the end of the post and seen "Athens"), I see that you're in Greece. The spectrum licensing in Greece must be a lot different than the United States: here, the spectrum is very tightly regulated, and you have to have a great deal of money to buy rights to spectrum bands from our government agency in charge of such things, the FCC. How does it work in Greece?

comic (and please correct me if I'm wrong, Tom): I believe he's saying that signal-wise, repeaters can repeat ad infinitum. I'm sure he's not saying that the repeaters don't need to be plugged into a socket to get electricity to rebroadcast the signal.

Tom: How do you avoid infinite loops of feedback between repeaters?

Question 1: Yes you do have to have a great deal of money to buy the bands here in Greece too but I know someone that works for the ESR (something like the FCC) and cause were buddies he pulled some strings so I could buy at reduced price and we labeled it as "Scientific and Medical Experiments" when its actually telco band.

Question 2: Infinite loops are avoided using the Yagis to point exactly where you want to get your source signal from and the bases are spaced far apart so the main base and never see the field of a repeater and RX and TX have different frequency.

If you mean how do I prevent the repeater from repeating itself, I use a frequency shifter and shift up on the previous station and shift down on this station

I was a bit depressed with the pulse dialing problem but I finally found this: http://www.dialgizmo.com/

I ordered one and this is supposed to convert pulse to tone with * and # support!

I did the first test operation on Friday and managed to get it working around my entire house. Signal faded outside house but I don't think I have the correct antennas on the transmitter, anyone know where to get a high quality omnidirectional transmitter antenna?

Does anyone know how I can get the signal to travel further because right now its just barely getting around the neighborhood with 7 watts of RF power, this doesn't seem right, I heard that people can go for a mile with just 1 W of power...

7 Watts of RF should be enough for a nice long distance, but 49 MHz is low enough that the antennas are pretty big. Do you have an SWR meter? That would allow you to see how the output of your PA is matched to the Antenna.

I don't have a SWR meter. Ill look around at electronics stores to see if I can find something, is there a way to figure this out without using a SWR meter?
Currently my antennas are 2 wires acting as each pole of the di pole

Also how long would 7 watts get me from 18 meters high from ground?

No, you really need to be able to measure the amount of power that's being reflected from your antenna, so you can tune it. If there's any amateur radio clubs around, they may be able to help.

A starting point would be to make sure your Dipole antenna is the right length, and connected appropriately to the coax connecting it to the back of the PA.


As far as how far 7 Watts will get you, it's difficult to answer. The answer lies in something called a "Link Budget", which is a calculation to determine the distance you can communicate. One key item in a link budget is the sensitivity of the receiver, which you may not have. This determines the signal level that the receiver requires in order to successfully demodulate the signal.

Due to a change in law stuff, we lost our license for the 70 MHz frequencies.
Now the system uses 43.7 to 50MHz which I think might help since I know lower frequencies travel further and penetrate obstacles better. The antennas on the base were made longer however with the new RX/TX hardware the base outputs very low power, around 250mW which is too little and we want to boost it somehow, know any way we can hook an amplifier onto the base?
Right now it reaches 200 meters around the base which is way too little considering the antenna is 18 meters from the ground.