dual band RF amplifier

[kdm3170]

was wondering if it is possible to build an amplifier for cell phones, preferably dual-band, but single band will work. i've seen the ones online for sale n they go for about 300 bucks atleast and thats just for the amp doesnt include antennas. so was wondering if its possible to build 1 with out being an expert and for relatively cheap money. ive looked online for diagrams and kits but i havent come across anything for the cell phone frequencies.

 

[davenn]

hi welcome to the forums

yes it is possible, but $300 for a commercial unit is the much cheaper way of doing so with garanteed success. Working with RF electronics at UHF and SHF (ultra hi frequency and super hi frequency) is not a trivial task. It requires lots of expensive test equipment to ensure that your transmitter is putting out a clean signal, much experience ... I have been working on frequencies through that range and beyond for some 30+ years and I still dont know it all

Cuz you would be transmitting on a commercial frequency, your transmitter would have to be inspected and type approved by the authorities of your country... eg
USA = FCC, Australia = ACMA, UK = OFCOM. And there would be licence fees to pay for its operation.

now depending on the output power of those "$300" units you have referred to, they may be below the output level where a licence is required

cheers
Dave

 

[kdm3170]

well what about a passive repeater, high gain outdoor antenna hooked to an antenna inside my house, wont b as good as an active one but would at least get me a stronger signal. whats the best way to make one? id assume as high gain as you can get for outside and directional since the tower wont b moving, but what about for the inside antenna would i want to get another high gain or a low gain antenna? and does the cable impedance matter since its not connecting to anything other than the antennas?

 

[davenn]

Back to back antennas will work, there are significant loosses involved. It would be worth trying out.
yes the impedance of the cable matters. It must be the same impedance of the antennas with will probably be 50 Ohms
Hi gain antennas are significant size and tho looking good on the outside of your home, wouldnt look very pretty hanging on your living room wall

just as an example one that is mid-range gain for the 1.7-1.9 GHz cell band
14dB, 1800MHz antenna

you wouldwant the indoor and out door antennas as close as possible to each other to minimise losses in the coax cable

Dave

 

[kdm3170]

what would have more signal loss, a high gain connected to a passive to stick on the back of my phone, or a high gain (preferably yagi) to a panel antenna inside? and would having a high gain antenna on the inside increase "coverage area" as opposed to a low gain antenna?

 

[davenn]

the higher the gain the narrower the signal beamwidth from the antenna
therefore the less coverage. But in the situation of a house the coverage area is relatively small anyway, so not the big deal as trying to cover a wide area outside.
Its kinda a catch-22, trying to get high gain and wide coverage dont go hand in hand

a high gain connected to a passive to stick on the back of my phone

that comment wasnt really clear ... you wanted to put an antenna on the back of your phone ? very few mobile phones these days have external antenna connections

Dave

 

[kdm3170]

i was wondering if theres less loss involved using 2 professionally tuned antennas or using 1 high gain antenna with a passive adapter, 1 of those things u just velcro to the back of your phone and it emits the signal towards the internal antenna. its made for phones that dont have an external antenna connector. http://www.wpsantennas.com/359914-passiveantennaadapter.aspx

 

[davenn]

i was wondering if theres less loss involved using 2 professionally tuned antennas or using 1 high gain antenna with a passive adapter, 1 of those things u just velcro to the back of your phone and it emits the signal towards the internal antenna. its made for phones that dont have an external antenna connector. http://www.wpsantennas.com/359914-passiveantennaadapter.aspx

ok I didnt know those things existed
the problem is you are still going to be connected to a gain antenna that wont be exactly portable

I see on another page that company have quite a range of cell repeater units varying in price and power output
that is probably a much better and efficient way to go. I dont it would take too long before you got sick of other other system dangling off the back of your phone

cheers
Dave

 

[davenn]

how far are you from the closest cell site ?
do you get a lot of signal dropout when inside your home ?

Dave

 

[kdm3170]

verizon says i have 3 towers within 3 miles, closest 1 being less than 1 mile, but every time i wanna use the data on my phone i cant because the signal is so low. and i only need it while in the house, so having the passive/inductive thing on the back of my phone isn't a problem since it will b sitting on my desk. the repeaters on their website are out of my price range. im not looking for miracle improvements, i'm just looking to be able to actually use the data plan i'm paying for. but what method would have the best results, 2 antennas spreading the signal in the house or 1 antenna with that inductive thing that focuses the signal to just my phone?

 

[davenn]

the answer to that will probably be the result of a bit of experimenting.
for the cheapest option try the inductive arrangement connected to a gain antenna pointed at the closest cell tower see if thats enough it mite give that extra bar of signal that you are looking for.
if not then go to the next costlier step of the back to back antennas

Dave

 

[kdm3170]

ok thanks for the help