parabolic antenna and beam width

Hi all,
I purchased two LinkSys WRT54GS wifi routers to set up a wireless bridge
between two houses, the distance is about 340 meters, there are some oak
trees in the line of sight.

I am considering to buy two parabolic antennas from Stella Doradus, but
I am not sure how much gain I need to setup a stable wifi bridge:
<http://www.stelladoradus.com/2.4para.shtml>

I noticed that the antennas with higher gain have smaller beam width, so
I think it is harder to 'point' them in the right direction and they are
less proof to movements (wind, etc.). Is that correct?

I am considering to get the 24 SD19 one, with 19 dBi gain, will it be
enough for my needs?

If I get an antenna with higher gain, just to be on the safe side, will
I have problems to 'point' it in the right direction or will the radio
signal be too 'strong'?
Please excuse my ignorance about this subject ...

What low loss cable do you recommend? Is the LMR400 a good one?

I think the Linksys wifi router has a RP-TNC connection, but I am not
sure about the Stella Doradus antenna, any idea?

Where can I buy a couple of short cables (e.g. 30 cm) already with the
right connectors installed at the ends?

Thanks a lot.

I dont think you can use the wrt54gs as a bridge, it is an Access
point and wont talk to another AP.
You need something like the WAP54g that can function as a bridge, AP,
AP client or repeater.



"meATprivacyDOTnet" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hi all,
> I purchased two LinkSys WRT54GS wifi routers to set up a wireless
bridge
> between two houses, the distance is about 340 meters, there are some
oak
> trees in the line of sight.
>
> I am considering to buy two parabolic antennas from Stella Doradus,
but
> I am not sure how much gain I need to setup a stable wifi bridge:
> <http://www.stelladoradus.com/2.4para.shtml>
>
> I noticed that the antennas with higher gain have smaller beam
width, so
> I think it is harder to 'point' them in the right direction and they
are
> less proof to movements (wind, etc.). Is that correct?
>
> I am considering to get the 24 SD19 one, with 19 dBi gain, will it
be
> enough for my needs?
>
> If I get an antenna with higher gain, just to be on the safe side,
will
> I have problems to 'point' it in the right direction or will the
radio
> signal be too 'strong'?
> Please excuse my ignorance about this subject ...
>
> What low loss cable do you recommend? Is the LMR400 a good one?
>
> I think the Linksys wifi router has a RP-TNC connection, but I am
not
> sure about the Stella Doradus antenna, any idea?
>
> Where can I buy a couple of short cables (e.g. 30 cm) already with
the
> right connectors installed at the ends?
>
> Thanks a lot.

On Thu, 25 Nov 2004 16:42:21 +0100, meATprivacyDOTnet <(E-Mail Removed)>
wrote:

>I purchased two LinkSys WRT54GS wifi routers to set up a wireless bridge
>between two houses,

Send them back and get either a pair of WAP54G bridge radios, or a
single WAP54G to talk to your WRT54GS. Wireless routers don't talk to
each other (unless you're planning to use WDS).

>the distance is about 340 meters, there are some oak
>trees in the line of sight.

Trees are evil.

>I am considering to buy two parabolic antennas from Stella Doradus, but
>I am not sure how much gain I need to setup a stable wifi bridge:
><http://www.stelladoradus.com/2.4para.shtml>
>
>I noticed that the antennas with higher gain have smaller beam width, so
>I think it is harder to 'point' them in the right direction and they are
>less proof to movements (wind, etc.). Is that correct?
>
>I am considering to get the 24 SD19 one, with 19 dBi gain, will it be
>enough for my needs?

Well, I'll be happy to do the math for you, as I've done several times
in this newgroup. However, I need to know coax cable type and length,
and type and length of optional pigtail. See:
http://www.ydi.com/calculation/som.php
for the basic calcs. See:

http://www.google.com/groups?selm=5m...2vnt%404ax.com
for an example of how I grind the numbers.

>If I get an antenna with higher gain, just to be on the safe side, will
>I have problems to 'point' it in the right direction or will the radio
>signal be too 'strong'?

No. There's no such thing as too strong in such a system. The signal
level required to overload the receiver front end is fairly
substantial. I can calculate that if you'd like, but I don't think it
will be an issue at 340 meters.

>What low loss cable do you recommend? Is the LMR400 a good one?

LMR400 is a good choice. However, if the cable run is rediculously
long, heavier cable such as LMR600 may be necessary. By the time you
get to fat cable, methinks it's best to simply mount the radio on the
roof near the antenna.
http://www.sveasoft.com/articles/armored/
(About 6 page. See tiny "next" in lower right corner of page).

>I think the Linksys wifi router has a RP-TNC connection, but I am not
>sure about the Stella Doradus antenna, any idea?

WRT54GS uses R-TNC. The data sheets on the dish at:
http://www.stelladoradus.com/2.4.ghz...c.antennas.php
show a male N connector.

>Where can I buy a couple of short cables (e.g. 30 cm) already with the
>right connectors installed at the ends?

That would depend on what country you were located. In the US, I buy
from:
http://www.fab-corp.com
No experience with international vendors.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

Yes, the gain of antenna comes from squashing the radiated energy into a
smaller beam, so
higher gains go hand in and with smaller beamwidths, and the beamwidth to
the -3dB points
will be approx (1.2 * wavelength / dish diameter) radians (where 2 * 3.142
radians equals 180 degrees).

Link bandwidth will drop with signal strength.
Signal strength will drop with increasing distance - 1/r^2 as the beam
spreads out, and 1/r due to attenuation through
the atmosphere - I've seen a theoretical model somewhere on the net (I can't
find it now); the 1/r term is significant at 2.4GHz as this corresponds to
water absorption.

I'm not sure what attenuation you will get in your environment, but you
could try plotting a graph of signal level against range or log(range), and
extrapolating from that.

I can't comment on the cable - but I'd keep it as short as possible to
minise losses.
Maplin (UK) do various connectors, including TNC (not connected to cable):-

http://www.maplin.co.uk/family.aspx?...id=2&doy=25m11


At a range of about 4 metres I'm getting a signal strength of -34dBm, giving
a
link rate of 54Mbd.I still get a link rate of 54Mbd even if I drop the
received signal
to -55to -60dBm (by badly positioning the antenna - down the back of a
radiator)

At a range of about 50 metres through 2 brick walls and a silver birch I get
around -70dBm,which my Linksys thinks it can manage 1Mbd through.

hope this helps.
Colin


"meATprivacyDOTnet" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hi all,
> I purchased two LinkSys WRT54GS wifi routers to set up a wireless bridge
> between two houses, the distance is about 340 meters, there are some oak
> trees in the line of sight.
>
> I am considering to buy two parabolic antennas from Stella Doradus, but I
> am not sure how much gain I need to setup a stable wifi bridge:
> <http://www.stelladoradus.com/2.4para.shtml>
>
> I noticed that the antennas with higher gain have smaller beam width, so I
> think it is harder to 'point' them in the right direction and they are
> less proof to movements (wind, etc.). Is that correct?
>
> I am considering to get the 24 SD19 one, with 19 dBi gain, will it be
> enough for my needs?
>
> If I get an antenna with higher gain, just to be on the safe side, will I
> have problems to 'point' it in the right direction or will the radio
> signal be too 'strong'?
> Please excuse my ignorance about this subject ...
>
> What low loss cable do you recommend? Is the LMR400 a good one?
>
> I think the Linksys wifi router has a RP-TNC connection, but I am not sure
> about the Stella Doradus antenna, any idea?
>
> Where can I buy a couple of short cables (e.g. 30 cm) already with the
> right connectors installed at the ends?
>
> Thanks a lot.

On Thu, 25 Nov 2004 22:23:41 -0000, "nospam" <(E-Mail Removed)> wrote:

>Yes, the gain of antenna comes from squashing the radiated energy into a
>smaller beam, so
>higher gains go hand in and with smaller beamwidths, and the beamwidth to
>the -3dB points
>will be approx (1.2 * wavelength / dish diameter) radians (where 2 * 3.142
>radians equals 180 degrees).

Let's see how close we get with the antenna in question:
http://www.stelladoradus.com/pdfs/2..../24%20SD27.pdf
It's interesting that the chart at:
http://www.stelladoradus.com/2.4.ghz...c.antennas.php
claims 10 degress for the SD27, while the data sheet says 8 degrees.

wavelength = 3x10^8 meters/sec / 2400x10^6 Hz = 0.125 meters
Dish diameter = 91 cmd
1.2 * 0.125 / 0.91 = 0.164 radians
0.164 radians * 180 / Pi = 9.4 degrees.
Yep, it works.

Argh. I'm late. More later...

>Link bandwidth will drop with signal strength.
>Signal strength will drop with increasing distance - 1/r^2 as the beam
>spreads out, and 1/r due to attenuation through
>the atmosphere - I've seen a theoretical model somewhere on the net (I can't
>find it now); the 1/r term is significant at 2.4GHz as this corresponds to
>water absorption.
>
>I'm not sure what attenuation you will get in your environment, but you
>could try plotting a graph of signal level against range or log(range), and
>extrapolating from that.
>
>I can't comment on the cable - but I'd keep it as short as possible to
>minise losses.
>Maplin (UK) do various connectors, including TNC (not connected to cable):-
>
>http://www.maplin.co.uk/family.aspx?...id=2&doy=25m11
>
>
>At a range of about 4 metres I'm getting a signal strength of -34dBm, giving
>a
> link rate of 54Mbd.I still get a link rate of 54Mbd even if I drop the
>received signal
>to -55to -60dBm (by badly positioning the antenna - down the back of a
>radiator)
>
>At a range of about 50 metres through 2 brick walls and a silver birch I get
>around -70dBm,which my Linksys thinks it can manage 1Mbd through.
>
>hope this helps.
>Colin
>
>
>"meATprivacyDOTnet" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed)...
>> Hi all,
>> I purchased two LinkSys WRT54GS wifi routers to set up a wireless bridge
>> between two houses, the distance is about 340 meters, there are some oak
>> trees in the line of sight.
>>
>> I am considering to buy two parabolic antennas from Stella Doradus, but I
>> am not sure how much gain I need to setup a stable wifi bridge:
>> <http://www.stelladoradus.com/2.4para.shtml>
>>
>> I noticed that the antennas with higher gain have smaller beam width, so I
>> think it is harder to 'point' them in the right direction and they are
>> less proof to movements (wind, etc.). Is that correct?
>>
>> I am considering to get the 24 SD19 one, with 19 dBi gain, will it be
>> enough for my needs?
>>
>> If I get an antenna with higher gain, just to be on the safe side, will I
>> have problems to 'point' it in the right direction or will the radio
>> signal be too 'strong'?
>> Please excuse my ignorance about this subject ...
>>
>> What low loss cable do you recommend? Is the LMR400 a good one?
>>
>> I think the Linksys wifi router has a RP-TNC connection, but I am not sure
>> about the Stella Doradus antenna, any idea?
>>
>> Where can I buy a couple of short cables (e.g. 30 cm) already with the
>> right connectors installed at the ends?
>>
>> Thanks a lot.
>

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

On 11/25/04 5:31 PM, Airhead wrote:
> I dont think you can use the wrt54gs as a bridge, it is an Access
> point and wont talk to another AP.
> You need something like the WAP54g that can function as a bridge, AP,
> AP client or repeater.

Hi,
I am going to use an alternative firmware to get the bridging
functionality for the LinkSys WRT54GS router.

Check this out:
<http://www.sveasoft.com/>

BTW, does anyone know any another (possibly free) alternative firmware
with bridging functionality for that router?

Thanks.

On 11/25/04 10:12 PM, Jeff Liebermann wrote:

> Send them back and get either a pair of WAP54G bridge radios, or a
> single WAP54G to talk to your WRT54GS. Wireless routers don't talk to
> each other (unless you're planning to use WDS).

Actually I am planning to use an alternative firmware (e.g.
<http://www.sveasoft.com/>) to get the bridging feature.

Can I use WDS instead? I don't think so, since I only need to do a
dedicated wifi bridge between the two LinkSys WRT54GS routers. Is that
correct?

> Trees are evil.

Yes, I know that, but they are not a lot. Will higher gain antennas help
with them?

> Well, I'll be happy to do the math for you, as I've done several times
> in this newgroup. However, I need to know coax cable type and length,
> and type and length of optional pigtail. See:
> http://www.ydi.com/calculation/som.php

I found some pigtails in my country (Italy): the length is 30 cm, the
cable type is RG-316. Is it a good one?

> No. There's no such thing as too strong in such a system. The signal
> level required to overload the receiver front end is fairly
> substantial. I can calculate that if you'd like, but I don't think it
> will be an issue at 340 meters.

Great, then I'll get the parabolic antennas with the higher gain I can
find, just to be on the safe side. I should be able to configure the
radio signal power on the LinkSys WRT54GS router.

> LMR400 is a good choice. However, if the cable run is rediculously
> long, heavier cable such as LMR600 may be necessary. By the time you
> get to fat cable, methinks it's best to simply mount the radio on the
> roof near the antenna.
> http://www.sveasoft.com/articles/armored/
> (About 6 page. See tiny "next" in lower right corner of page).

Great article, I think I'll do that, so I only need two pigtails
(probably 30 cm or so), it looks like there are no LMR400 pigtails
around, is it hard to make a pigtail out of that cable type?

> That would depend on what country you were located. In the US, I buy
> from:
> http://www.fab-corp.com

That looks a great online shop, but shipping fees are pretty high.
I found this one at a good price:
<http://cgi.ebay.it/ws/eBayISAPI.dll?ViewItem&item=5733635092>
Does it look good to you?

Thanks a lot.

On 11/25/04 11:57 PM, Jeff Liebermann wrote:

> Let's see how close we get with the antenna in question:
> http://www.stelladoradus.com/pdfs/2..../24%20SD27.pdf
> It's interesting that the chart at:
> http://www.stelladoradus.com/2.4.ghz...c.antennas.php
> claims 10 degress for the SD27, while the data sheet says 8 degrees.
>
> wavelength = 3x10^8 meters/sec / 2400x10^6 Hz = 0.125 meters
> Dish diameter = 91 cmd
> 1.2 * 0.125 / 0.91 = 0.164 radians
> 0.164 radians * 180 / Pi = 9.4 degrees.
> Yep, it works.
>
> Argh. I'm late. More later...

So will this be a good antenna for a 350 meters link?

Don't forget a couple of trees in the LOS ...

Thanks.

"meATprivacyDOTnet" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
| On 11/25/04 10:12 PM, Jeff Liebermann wrote:
|
| > Send them back and get either a pair of WAP54G bridge radios, or a
| > single WAP54G to talk to your WRT54GS. Wireless routers don't talk to
| > each other (unless you're planning to use WDS).
|
| Actually I am planning to use an alternative firmware (e.g.
| <http://www.sveasoft.com/>) to get the bridging feature.
|
| Can I use WDS instead? I don't think so, since I only need to do a
| dedicated wifi bridge between the two LinkSys WRT54GS routers. Is that
| correct?
|
| > Trees are evil.
|
| Yes, I know that, but they are not a lot. Will higher gain antennas help
| with them?
|

To an extent yes but the link budget (path loss) is hard to estimate.
Signal levels can vary by season, if the leaves have dew (ie wet/dry)

| > Well, I'll be happy to do the math for you, as I've done several times
| > in this newgroup. However, I need to know coax cable type and length,
| > and type and length of optional pigtail. See:
| > http://www.ydi.com/calculation/som.php
|
| I found some pigtails in my country (Italy): the length is 30 cm, the
| cable type is RG-316. Is it a good one?

Don;t know much about the RG-316 but I do know that with any coax the
quality can vary considerably.
|

On Sat, 27 Nov 2004 17:25:55 +0100, meATprivacyDOTnet <(E-Mail Removed)>
wrote:

>On 11/25/04 11:57 PM, Jeff Liebermann wrote:
>
>> Let's see how close we get with the antenna in question:
>> http://www.stelladoradus.com/pdfs/2..../24%20SD27.pdf
>> It's interesting that the chart at:
>> http://www.stelladoradus.com/2.4.ghz...c.antennas.php
>> claims 10 degress for the SD27, while the data sheet says 8 degrees.
>>
>> wavelength = 3x10^8 meters/sec / 2400x10^6 Hz = 0.125 meters
>> Dish diameter = 91 cmd
>> 1.2 * 0.125 / 0.91 = 0.164 radians
>> 0.164 radians * 180 / Pi = 9.4 degrees.
>> Yep, it works.
>>
>> Argh. I'm late. More later...

>So will this be a good antenna for a 350 meters link?

Probably. My seat of the pants guess is that 24dBi on both ends is
probably needed to drill through two trees. However I'm a
practitioner of the black art of calculation and always grind the
numbers before passing judgement. You haven't supplied a few key
pieces of missing information, so I can't grind any numbers.

From a previous posting:

Well, I'll be happy to do the math for you, as I've done several
times in this newgroup. However, I need to know coax cable type
and length, and type and length of optional pigtail. See:
http://www.ydi.com/calculation/som.php
for the basic calcs. See:

http://www.google.com/groups?selm=5m...2vnt%404ax.com
for an example of how I grind the numbers.

>Don't forget a couple of trees in the LOS ...

Don't forget the cable lengths (each end). I can usually give a good
guess as to the penetration through trees based on some foliage
attenuation models and personal experience. For that, I need a photo
with the fresnel zone marked on the image, as well as a photo of the
cross section of the intended path. As a general rule of thumb, if
you have soaking wet or frozen broadleaf trees, nothing will work. If
it's needles or very dry (desert) shrubbage, it can be penetrated.
Absolutely nothing goes through a trunk.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558