Low budget in-house cellular repeater project questions
 

Howdy,
I would like to get rid of my land phone line. The only thing keeping me
from doing this is the relatively poor indoor reception on my cell phone
(outdoors is just fine). I can't justify spending $700 for a powered
repeater set-up, but since I get good outdoor reception, would it be
possible to couple a dual frequency (800 & 1900 MHz) high gain (36 dbi)
directional antenna directly to an indoor multi directional unit (both 50
Ohm impedance)? This would only cost a couple hundred bucks, but will it
work in theory? Any advice or
other suggestions would be greatly appreciated.

Mark

I would like to get rid of my land phone line. The only thing keeping me
from doing this is the relatively poor indoor reception on my cell phone
(outdoors is just fine). I can't justify spending $700 for a powered
repeater set-up, but since I get good outdoor reception, would it be
possible to couple a dual frequency (800 & 1900 MHz) high gain (36 dbi)
directional antenna directly to an indoor multi directional unit (both 50
Ohm impedance)? This would only cost a couple hundred bucks, but will it
work in theory? Any advice or
other suggestions would be greatly appreciated.

While passive repeaters are often used, what kind of antennas are you going
to use to get 36 dbi ?

The trick to passive repeaters:
The inside antenna that re-radiates the signal from the cell tower
will have 22dB path loss for the first wavelength of distance, and 6dB
for each doubling of distance past that. Ferinstance, say the
re-radiating antenna needs to be able to cover a distance of 30'.
That's 30 wavelengths (more or less) at 800MHz. So the loss from the
reradiating antenna is 22 (first foot)+6(second foot)+6(to 4')+6(to
8')+6(to 16')+6(to 32') or 52dB. If the outside signal is, say,
-80dBm (which would be ok), then inside you're -132dBm, or useless.

Gain on the "outside" antenna needs to make up at least the 52dB loss
in this scenario, or you're still worse off outside than in. You
won't find a 52dB antenna at 800MHz. Nor a 36 probably. Note that
the "usual" 4-5' panel antennas used at 800MHz are about 14dBi gain.

The situation isn't any better at 1900. Although you can get more
gain from the "outside" antenna, the 30' of coverage is more
wavelengths (nearly twice as many) for 6dB or so more free space loss.


On Sun, 4 Jan 2004 11:51:57 -0700, "Mark Atanovich"
wrote:

Howdy,
I would like to get rid of my land phone line. The only thing keeping me
from doing this is the relatively poor indoor reception on my cell phone
(outdoors is just fine). I can't justify spending $700 for a powered
repeater set-up, but since I get good outdoor reception, would it be
possible to couple a dual frequency (800 & 1900 MHz) high gain (36 dbi)
directional antenna directly to an indoor multi directional unit (both 50
Ohm impedance)? This would only cost a couple hundred bucks, but will it
work in theory? Any advice or
other suggestions would be greatly appreciated.

Mark

Big Yagi:

http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=41 298

Is this BS or is this kind of gain at least theoretically possible?

"Ralph Mowery" wrote in message
...
I would like to get rid of my land phone line. The only thing keeping
me
from doing this is the relatively poor indoor reception on my cell phone
(outdoors is just fine). I can't justify spending $700 for a powered
repeater set-up, but since I get good outdoor reception, would it be
possible to couple a dual frequency (800 & 1900 MHz) high gain (36 dbi)
directional antenna directly to an indoor multi directional unit (both
50
Ohm impedance)? This would only cost a couple hundred bucks, but will
it
work in theory? Any advice or
other suggestions would be greatly appreciated.

While passive repeaters are often used, what kind of antennas are you
going
to use to get 36 dbi ?

Well, I guess that answers that! Thanks. Would you have any
recommendations for an affordable BDA I could use for this project?

Regards,
Mark

"Scott Townley" wrote in message
...
The trick to passive repeaters:
The inside antenna that re-radiates the signal from the cell tower
will have 22dB path loss for the first wavelength of distance, and 6dB
for each doubling of distance past that. Ferinstance, say the
re-radiating antenna needs to be able to cover a distance of 30'.
That's 30 wavelengths (more or less) at 800MHz. So the loss from the
reradiating antenna is 22 (first foot)+6(second foot)+6(to 4')+6(to
8')+6(to 16')+6(to 32') or 52dB. If the outside signal is, say,
-80dBm (which would be ok), then inside you're -132dBm, or useless.

Gain on the "outside" antenna needs to make up at least the 52dB loss
in this scenario, or you're still worse off outside than in. You
won't find a 52dB antenna at 800MHz. Nor a 36 probably. Note that
the "usual" 4-5' panel antennas used at 800MHz are about 14dBi gain.

The situation isn't any better at 1900. Although you can get more
gain from the "outside" antenna, the 30' of coverage is more
wavelengths (nearly twice as many) for 6dB or so more free space loss.


On Sun, 4 Jan 2004 11:51:57 -0700, "Mark Atanovich"
wrote:

Howdy,
I would like to get rid of my land phone line. The only thing keeping me
from doing this is the relatively poor indoor reception on my cell phone
(outdoors is just fine). I can't justify spending $700 for a powered
repeater set-up, but since I get good outdoor reception, would it be
possible to couple a dual frequency (800 & 1900 MHz) high gain (36 dbi)
directional antenna directly to an indoor multi directional unit (both 50
Ohm impedance)? This would only cost a couple hundred bucks, but will it
work in theory? Any advice or
other suggestions would be greatly appreciated.

Mark

Mark Atanovich wrote:
Big Yagi:

http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=41 298

Is this BS or is this kind of gain at least theoretically possible?

Probably more BS than truth!

dB is a ratio. To simply quote 35 dB gain is 100% useless. It has to be
gain compared to what?

The images at the web site show a 13 element Yagi. Thirteen elements
typically produce about 15.8 dBi or about 13.7 dBd.

The higher gains quoted, 35 dB, can be achieved in BIG DISH antennas
[100 foot diameter at 2 GHZ or 300 foot diameter at 800 MHz].

I suspect there is more marketing than science in the 36 dB gain figure.
It may be, I say again may be, based on signal inside a house compared
with a signal from an outside antenna at altitude. But 36 dB is an
increase of 4000 times. That sounds like a stretch.

"Mark Atanovich" wrote in message
news:k7eKb.26608$i55.6640@fed1read06...
Big Yagi:


http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=41 298

Is this BS or is this kind of gain at least theoretically possible?


Most likely big BS . I did not see what the db was related to. The
biggest Yagi I could find in a quick search of my material at home that I
have any faith in is 40 elements and 20.8 dbi is all that it has. That is
almost 3 times as many elements as the ebay antenna. Assuming almost a
perfect antenna it would hav to have a boom of over 30 wavelengths to get to
24 dbi.

The antenna may well have 36 db of gain over the internal antenna of the
cell phone. If you cup your hand around a cell phone you may loose the 20
or more db of gain. That and about 15 dbi of gain that a 15 element beam
will have may be close to the 36 db of antenna gain.

Any antenna that gives much over 10 to 15 db of gain is not to be trusted.
Some will do that but not many that are on the market and you have to know
the physical size (boom lenght) to get a good estiment.

Ralph Mowery wrote:
"Most likely big BS."

Also:
"---40 elements and 20.8 dbi is all that has. That is almost 3 times as
many elements as the ebay antenna."

Ralph is on the mark.

John Kraus in "Antennas", page 705, demonstrates how the gain of a
curtain antenna adds up:

"The gain of a single 1/2-wave dipole is 2.15 dBi and of 2 collinear
in-phase 1/2-wave dipoles is 3.8 dBi. The array of 8 such collinear
dipoles adds 3+3+3 =9dB. The reflectoer screen adds 3 dB more and the
ground bounce another 6 dB for a grand total of 3.8+9+3+6=21.8 dBi or a
directivity of 151 approx."

36 db is the sort of gain that one can get from a dish that is very
large in terms of wavelength and that has extremely small imperfections
in its surface. As Kraus shows, you only hope to gain 3 db more when you
double the number of elements in an array.

Best regards, Richard Harrison, KB5WZI