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Cellular Phone Repeater for Home Use - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


sioked (at) gmail.com
Post subject: Cellular Phone Repeater for home use Posted: Thu Jun 09, 2005 2:36 am
So I've been thinking about trying to build a cellular phone repeater to use inside a home (my girlfriend's basement) because she gets good signal outside, but bad signal inside. I'm thinking its as simple as having a couple good antennas (one for outside, one for inside), band pass filters, and a gain stage or two. The frequencies i need are around 850 Mhz, and possibly the 1900 Mhz range. Has anybody tried this? They sell them for around 500 bucks. I think I have the right idea about this, but am I missing something? Let me know what you guys think.


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Ivan
Post subject: Posted: Thu Jun 09, 2005 8:54 am
If you have a good signal outside why don't you try just the 2 antennas?


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sioked (at) gmail.com
Post subject: Posted: Thu Jun 09, 2005 2:39 pm
I probably will, but I just have a feeling that it won't get that great of a signal (The signal outside isn't perfect)... I will try and see how it works, I'll see from there.


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AP
Post subject: Re: Cellular Phone Repeater for home usePosted: Mon Jun 13, 2005 11:10 am
sioked (at) gmail.com wrote:
So I've been thinking about trying to build a cellular phone repeater to use inside a home (my girlfriend's basement) because she gets good signal outside, but bad signal inside. I'm thinking its as simple as having a couple good antennas (one for outside, one for inside), band pass filters, and a gain stage or two. The frequencies i need are around 850 Mhz, and possibly the 1900 Mhz range. Has anybody tried this? They sell them for around 500 bucks. I think I have the right idea about this, but am I missing something? Let me know what you guys think.


I think you'll have to watch out for feedback, since you're transmitting and receiving at the same frequency. Especially for your inside antenna, since the signal will scatter off the walls, you'll probably end up receiving it again.


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Repeater Guy
Post subject: Posted: Mon Jun 13, 2005 5:37 pm
Better make sure your noise is invisible to the network. I don't think the service provider would be too happy if you jammed their basestation. Noise, intermods, possible oscillation could all jam a basestation.
Feedback ocsillation is a big problem with repeaters. This was already mentioned. Is this even legal? You would be transmitting on a licensed frequency band.


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ST
Post subject: Posted: Tue Jun 14, 2005 1:31 pm
[I think you'll have to watch out for feedback, since you're transmitting and receiving at the same frequency. Especially for your inside antenna, since the signal will scatter off the walls, you'll probably end up receiving it again.]

Tx and Rx are not the same frequency. For example 850MHz CDMA cell phone Tx/Rx signals in the US are separated by 45MHz. At 1900MHz they are separated by 80MHz. A good duplexer in the repeater provides the needed Tx/Rx rejection. [/quote]


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Guest
Post subject: Posted: Wed Jun 15, 2005 3:30 pm
ST wrote:
[I think you'll have to watch out for feedback, since you're transmitting and receiving at the same frequency. Especially for your inside antenna, since the signal will scatter off the walls, you'll probably end up receiving it again.]

Tx and Rx are not the same frequency. For example 850MHz CDMA cell phone Tx/Rx signals in the US are separated by 45MHz. At 1900MHz they are separated by 80MHz. A good duplexer in the repeater provides the needed Tx/Rx rejection.
[/quote]

It seems like the original poster just wanted to make a repeater out of a couple of antennas and some amplifiers, in which case the Tx and Rx frequencies would be the same.


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ST
Post subject: Posted: Wed Jun 15, 2005 4:34 pm
Quote:
It seems like the original poster just wanted to make a repeater out of a couple of antennas and some amplifiers, in which case the Tx and Rx frequencies would be the same.


Well in this case he would quickly find the repeater repeating much more than just the TX and Rx frequencies since the repeater would be an oscillator. Briefly anyways, until his amplifiers smoke. Rule-of-thumb: Tx/Rx rejection needs to be at least 10dB more than the repeater gain to keep the repeater from oscillating.


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davidge
Post subject: indoor amplifier for cellularPosted: Wed Jul 13, 2005 1:29 pm
Guys,

Those amplifier aer widely available for sale. So, I assume it is "legal", they may got license for FCC?

example link attached below:

http://www.malcomwireless.com/wireless/ ... ypeid=1121

I was play with it before, and even opened one to see its cofiguration. Here is what their block diagram:

"Port Connected to outside antenna" coneects to a "duplex Common Port", from "duplex RX port" connects to "LNA" etc, then connects to second "duplex RX port", second "dulpex Common Port" coneects to "indoor antenna". On the revise side, is the same expect with TX amplifier module which provide lots of gian and few Watts out.

Any way, for yourself with experiment, you can make low gain, low power model, just enough from your grilfriend's basement to basestation. (As our friend says here, make sure you don't TX garbage). But, basic architure with duplex possible a must.

David


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opjeb0
Post subject: Cell Phone RepeaterPosted: Fri Dec 30, 2005 6:31 am
Any chance that any of you would have a diagram of how this would work? What components to use ect.. I'm new.

thanks


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Guest
Post subject: RepeaterPosted: Fri Dec 30, 2005 1:46 pm
1. Just because a device is for sale doesn't make it legal to use - the FCC periodically has to crack down on "long-range cordless telephones", and users - even innocent users - can get fines. Check for the FCC registration/type certification/type acceptance numbers, unique to the device you're interested in.

2. If you're new, you might not know about FCC type certification and type acceptance. These are not just "nice to have", they're legally required - and both expensive and a major pain to get. Why do they do this? Suppose you build up your repeater, and it oscillates. You now have a jammer which could interfere with emergency communications - not good. The FCC has the authority to level $10,000 a day fines for this kind of interference.

3. It really requires a spectrum analyzer to make sure that you're not sending out spurious signals on other frequencies. I suspect that as a person new to the RF world, you don't have one, or even access to one.

Bottom line - go outside to talk on the cell phone, or change cell systems to one which can reach the basement.

Good Luck!


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guest
Post subject: Posted: Sat Dec 31, 2005 8:30 am
I have used beam benders to extend mobile phone coverage and even used similar beam benders with an outdoor yagi and an indoor omni in a factory for GSM and though it wasn't terrific, it did offer enough of an improvement to make it worth while.

I was also given a device by my work which was an active GSM repeater. Being a telco, there wasn't an issue with it's use in my case. It was just a small metal box with some bandpass filters as diplexers. Provided there was sufficent isolation between the antennas it would work correctly.

In our case yagi antennas were placed on each side of a building on top of a hill to act as a repeater. Again it worked, but for the amount of fiddling and testing, we could have installed a small GSM base station with a G.703 UHF link. The ecconomics of it would be an issue to hobbiests.
Bottom line is that it is possible, but not very practical compared to a beam bender.


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Guest
Post subject: RepeaterPosted: Sat Dec 31, 2005 7:51 pm
Re the previous message:

That's the only easy and legal way to do it. Thanks for the comment.

A reflector for the 800 MHz band should be at least a couple of wavelengths on a side - that would give a square about 1.5 meters on a side.

Good Luck!


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MCarrick
Post subject: LegalityPosted: Sat Mar 04, 2006 12:07 am

Lieutenant

Joined: Sat Mar 04, 2006 12:02 am
Posts: 1
Cellular repeaters are available here for about $260. They are incredibly easy to install (I managed it myself with no difficulty) and I think that they have or are pending FCC approval (this shouldn't be a problem though because there are already similar models with approval). They come with thirty feet of cable and have an external directional antenna and signal booster - so will give you better signal in your basement than you usually get outside it!



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