ets960 Posted June 9, 2005 Report Share Posted June 9, 2005 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. Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 9, 2005 Report Share Posted June 9, 2005 Hi Ets,Welcome to our forum. ;DSave yourself 500 bucks. If the signal is good outside, put an antenna there and wire it with RG-6 satellite coax cable to another antenna inside. If the antennae are proper for the RF frequencies and the cable isn't too long, I think it will work. ;D Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted June 9, 2005 Report Share Posted June 9, 2005 hi audioguru!are these antennas easily available?at what frequency do they work as i guess mobile phone frequencies in my country may deviate.we generally put signal boosters which are small pin like devices but they certainly pinch on our pocket money ;D Quote Link to comment Share on other sites More sharing options...
ets960 Posted June 9, 2005 Author Report Share Posted June 9, 2005 Audioguru-I like your idea, and I think I will start with it. However, I still like the idea of making a repeater, and I don't think it would be very difficult...I'm gonna need an amplifier (op-amp) that has a very high bandwidth (no attenuation at 850 Mhz). Then I can create a couple active filters to filter out the unwanted frequencies. Any ideas about this?Thanks. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted June 9, 2005 Report Share Posted June 9, 2005 Hi Ets,Welcome to our forum. ;DSave yourself 500 bucks. If the signal is good outside, put an antenna there and wire it with RG-6 satellite coax cable to another antenna inside. If the antennae are proper for the RF frequencies and the cable isn't too long, I think it will work. ;DIt wouldn't cost much to build a simple common emitter amplifier and place it in between the two aerials. However the gain mustn't be too hight and the path loss between the external recieving antenna and internal antenna needs to be high enough to ensure oscilation doesn't occur. Quote Link to comment Share on other sites More sharing options...
ets960 Posted June 9, 2005 Author Report Share Posted June 9, 2005 yeah, I was thinking a common emitter amplifier... I was trying to find a good op-amp that'd have the bandwidth, but I probably don't need that much gain...What about filters? Do you think I need some?Somebody else recommended RF Circulators to me, but that seems really expensive... Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 9, 2005 Report Share Posted June 9, 2005 To avoid oscillation you don't want any gain. Why use an amplifier? Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted June 9, 2005 Report Share Posted June 9, 2005 An audio amplifier has a gain and providing the microphone is kept far enough away from the speaker it won't oscillate.The same principle applies with the RF repeater, providing the path loss is high enough to attenuate the output to a lower level than the original signal before the amplifier oscillation won't occur. Oscillation only occurs when negative feedback is greater than 1, so in other words the attenuation due to the path loss needs to exceed the gain to avoid oscillation.ets960,Have a go with the unamplified option as there's no point in building something when it's not needed. You'll need a pretty good wideband aerial too. I've never seen an op-amp with a high enough gain at this bandwidth for this, the fastest op-amp I've seen has 1GHz unity bandwidth. Quote Link to comment Share on other sites More sharing options...
Shahriar Posted June 10, 2005 Report Share Posted June 10, 2005 HiAs Alun Said, There is no op-Amp in such high frequencies. The FT for 741 is 100Khz and if you are luckymaybe you can find an op-amp which can work at 1.5Mhz. neither CFAs an WTAs can work at these frequecies. this is why you never see an opamp in Transimtters. anyway I am also looking for a transistor working at 1900Mhz,If you find it, please tell me the Part number and where can I buy two or three of them.And at last, can You tell me that how you understood that your phone is working at 850Mhz? Is it written on the back of it?ThanX in advanceShahriar Quote Link to comment Share on other sites More sharing options...
login
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.