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'[EE]: Passive Cell Phone Repeater'
2002\05\14@164517 by M. Adam Davis

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I get terrible cell phone reception in my basement where my workshop is.
My solution so far is to stand in a particular spot during calls of any
great length - in this position I get pretty decent reception, but it's
out of the reach of my computer and other resources I'd like easy access
to during those calls.

Due to various billing and customer relations issues I cannot use the
landline (or even a second line if I had one) to receive these calls.

My understanding of radio and antenna theory is limited so I had hoped
to find a cheap cell phone repeater (passive) which would have an
antenna in the basement, and coax to the attic to another antenna.  My
searches come up with all the car repeaters or the snake oil cell phone
boosters.

Having waved a dead fish over the problem a few times I've determined at
last to ask if anyone here can help.  I've got a bit of coax, and I can
fashion non-complex assemblies so if you know of a site which has a
homemade unit or can give me an idea of something to try I'm all up for it.

FWIW, the phone is a samsung and I receive digital service at home.

-Adam

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2002\05\14@165655 by Jim

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This *can* work quite effectively - especially
when you're going to 'route' RF into an
otherwise 'black hole'.

I would use a yagi "donor" antenna pointing
to the "serving" cell site - and either a
Yagi or simple dipole as the "coverage"
antenna close to where you are sitting.

I've engineered many active cell-extender
designs - and several of those were with
amplifiers with as little as 20 dB of
bi-lateral gain and achieved a 50' service
radius with a 20 dB gain "Cell Extender".

A device like a DB Products Prism Plus has
upwards of 60 dB of gain and can serve a
football-sized area.

Jim




{Original Message removed}

2002\05\14@170346 by Anthony Bussan

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The ARRL Antenna Handbook is a great aid for quick design of antennas, that
is where I am getting info for my 802.11 link.
What I am considering doing for a cell phone in a steel building, is just
build a pair of high gain antennas, connect them with coax and put one
outside and one inside.  Of course you will have to match impedances, and I
don't know the wavelength of the carrier freq.  You can even use a
directional outside if you know where the cell tower is.  I can't remember
where I came across this in my searches, probably with some 802.11 stuff.

Tony

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2002\05\14@174409 by Jim

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  "You can even use a directional outside if
   you know where the cell tower is."

You had *best* use a directional antenna for what
we call the 'donor' antenna - lest you become
subject to "co-channel" (same-frequency cell sites)
interference in an urban cellular system ...

Uness you *really* want to re-invent the wheel - take
a look at suitable Yagis on eBay.

I even saw a DB Products "Prism Plus" (an "active"
cell extender A/K/A as a bi-directional amplifier
arrangement with suitable band-pass filters integral
to the design) for sale there yesterday.

Jim


{Original Message removed}

2002\05\14@180116 by Peter L. Peres

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Adam, you have two simple possibilities.

The first is to place a large reflector at a strategic place outside the
basement. A meshed wire fence panel about 2 x 3 meters should to. Figure
the cell tower you are slaved to and the angle and put it outside.

The second is to use an antenna with gain (have to - look for 9dBi or more
gain), a very short run of coax, and a re-radiator (antenna) inside. The
latter can be a patch antenna. You have to put a 1.5dB attenuator in the
coax to avoid reflexions between the antennas (you could jam
yourself/someone else or make your best channel unusable). This is 3 SMD
resistors inline on the cable (or at one end).

Put the outdoor antenna as close as possible to the indoor one. Putting it
at the 1st floor level is probably good enough. The shorter the coax the
better.

You need to know what system the phone uses (1.8G, 900M etc).

bye,

Peter

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2002\05\14@192753 by Jim

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Probably a more cost effective set-up than what I pointed
out earlier - and also available in the US 1800 MHz band.

This device seems to connect directly to the phone. I don't
personally know anymore about this device, so, check it out
to your own satisfaction:


Product:- JDTECK  CB920 Cellular Phone Signal Booster

Convenient. The  JDTECK CB920 Cellular Phone Booster is a very
powerful cellular signal amplifier, for persons who have problems
with weak signals in the GSM, TDMA, AMPS, CDMA, DCS, iDEN and PCS
cellular networks, yet it is so small and light that it can fit
in the palm of your hand.

Many mobile phone users who previously had to walk outside to
answer their cellular phone, can now sit in the privacy, and
comfort of their homes or offices and complete a crisp clear
conversation with the help of the JDTECK CB 920 Cellular Phone
Signal Booster connected to their phone via a simple patch lead.
This patch lead can be disconnected in just 1 sec if the need
arises.

http://www.jdteck.com/product/default.htm



Jim


{Original Message removed}

2002\05\15@030300 by Joe Farr

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You can purchase a car installation kit for most phones. These kits
usually suport an external aerial.
I have the same problem. When I go into my workshop, I click my phone
into a car kit cradel fixed next to my work bench. It has an external
aerial that's fixed on the roof (I have to lengthen the cable a bit) and
also has the added benefit that I have hands free facilities and my
phones battery gets charged. I use an old CB power pack to power
everything.

{Original Message removed}

2002\05\15@040636 by Alan B. Pearce

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>build a pair of high gain antennas, connect them
>with coax and put one outside and one inside.
>Of course you will have to match impedances

I would not even worry about high gain antennas.

Working on the assumption that you can get satisfactory reception in the
upper floors of your property, I would make a quarter wave whip with four
radial wires for a ground plane on each end of the coax. With the far end up
on the roof (maybe, or in the attic to keep it out of the weather) and the
other end hanging from the ceiling in the basement I suspect you will get
sufficient signal strength.

If you are using 50 ohm coax try a 5/8 wavelength whip and radials as this
is closer to 50 ohm, although with some reactive impedance.

I would not worry about trying to deal with matching networks unless you are
looking for every last dB of signal transfer, and from your description of
the problem it sounds like you just need to get above marginal signal
levels.

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2002\05\15@062733 by michael brown

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> Working on the assumption that you can get satisfactory reception in the
> upper floors of your property, I would make a quarter wave whip with four
> radial wires for a ground plane on each end of the coax. With the far end
up
> on the roof (maybe, or in the attic to keep it out of the weather) and the
> other end hanging from the ceiling in the basement I suspect you will get
> sufficient signal strength.
>
> If you are using 50 ohm coax try a 5/8 wavelength whip and radials as this
> is closer to 50 ohm, although with some reactive impedance.

You can also bend the "ground" radials down to about a 120° angle with
respect to the radiator.  This should increase impedance to approximately 50
ohms.  It's kinda like folding/unfolding a dipole.  Approx. 35 ohm impedance
at 90° relationship (1/4 wave groundplane) and approx 75 ohm impedance at
180° angle (dipole).

> I would not worry about trying to deal with matching networks unless you
are
> looking for every last dB of signal transfer, and from your description of
> the problem it sounds like you just need to get above marginal signal
> levels.

IMHO, the loss due to any mis-match is outweighed by the loss due to the
coax itself.  At these frequencies, that coax will soak up signal strength
like a sponge.  BTW, the resonant length of the radiator will be 10-30%
shorter than a "calculated" length.  IOW, the formulas will always give you
an antenna that is "cut" too long.  I guess that's better than the
alternative, though.  ;-)

michael brown (sticking my neck out)

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2002\05\15@074411 by go_orlando

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Okay - time for what may be a silly question, but I need to ask it.

So far, all of the solutions presented have been RELATIVELY involved,
especially if someone is not already somewhat experienced with
antennae, repeaters, etc.  They also presume that the user is living
in his own house and has access to the upper part of the building.  In
my case, I am in an apartment on the first floor, and would have no
way to implement what has been presented so far.  In addition, some of
the turnkey solutions have been at least as expensive as just going
out and buying a different phone!  Thus comes my silly question: for
someone who only needs JUST ENOUGH of a boost for his phone to work
(e.g. just a difference of three more feet into my apartment so it
will work when I'm at my computer) will those little "cell phone
boosters" that sell for $5-$20, look like department store anti-theft
tags, and just stick inside the phone's battery compartment actually
be of any help, or are they just snake oil?




----  M. Adam Davis (adampicspamKILLspamUBASICS.COM) wrote:

> I get terrible cell phone reception in my basement where my workshop
is.
>  My solution so far is to stand in a particular spot during calls of
any
> great length - in this position I get pretty decent reception, but
it's
> out of the reach of my computer and other resources I'd like easy
access
> to during those calls.
>
> Due to various billing and customer relations issues I cannot use
the
> landline (or even a second line if I had one) to receive these
calls.
>
> My understanding of radio and antenna theory is limited so I had
hoped
> to find a cheap cell phone repeater (passive) which would have an
> antenna in the basement, and coax to the attic to another antenna.
My
> searches come up with all the car repeaters or the snake oil cell
phone
> boosters.
>
> Having waved a dead fish over the problem a few times I've
determined at
> last to ask if anyone here can help.  I've got a bit of coax, and I
can
> fashion non-complex assemblies so if you know of a site which has a
> homemade unit or can give me an idea of something to try I'm all up
for it.
{Quote hidden}

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2002\05\15@090442 by M. Adam Davis

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This has been discussed at some length on the list before - you can
check the archives for details.

The upshot was that there were a lot of interesting thoughts and
comments about it, but without any real world testing most posters
agreed that it was snake oil.

At the most they may be coupling some internal (normally shielded by the
battery pack) RF to the antenna or edges of the phone.  This may
increase signal strength, but probably also increases noise.
Furthermore most phones already transmit at their maximum allowed power
- if it did increase the power then you are radiating your brain that
much more (for better or worse), not to mention exceeding FCC limits.
The same companies that sell the phone boosters often sell the
radiation blockers that are supposed to save your head from the RF the
phone emits.  All in all they're just trying to make a buck off a little
suspecting public, IMO.

In your situation there isn't much you can do without a preamlifier of
some sort.  If there's a position in your apartment that has good
reception then you could probably go with the coax and whip antennas at
either end (as I will likely be doing when I find my coax) but if you
don't have permission to put an antenna somewhere where you do get good
reception you really can't do anything.  Perhaps the closest you can get
is using a YAGI or other directional antenna (pointing towards a known
tower) and either hooking the phone directly to it or using a whip on
the other end.  Chances are any gains that might give you would be lost
in the buildings and walls between the yagi and the cell tower...

Which gives me a thought - I doubt it would help, but I wonder what the
cable company is putting on the cable system at 800-900MHz?   You
wouldn't want to hook an antenna directly to the cable system, though  :-)

-Adam

Go Orlando wrote:

{Quote hidden}

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