Minimizing antenna lead loss

Hi,

I am setting up a couple of antennas to connect 2 buildings about 300 feet
apart. I have discussed this with several people and a subject that came up
was antenna lead loss. One person said it was a big issue, and another says
it is nothing to worry about. Can anyone give me the straight scoop? BTW,
my antennas will be on roof tops, so I need enough lead length to get inside
to the access points.

Thanks,

Jerry

Real Big Losses per foot
what cable are you using - somebody will tell you loss per ft quickly

I ordered a Cisco 15db Yaggi and part of the package included pre-made 50'
belden RG8u which takes away 10db right off the bat not counting connectors
surely wont do much good. Good thing I got a deal otherwise I would
have been upset if I knowingly paid for that cable.

"JerryK" <(E-Mail Removed)> wrote in message
news:41802fa5$1_1@127.0.0.1...
> Hi,
>
> I am setting up a couple of antennas to connect 2 buildings about 300 feet
> apart. I have discussed this with several people and a subject that came
up
> was antenna lead loss. One person said it was a big issue, and another
says
> it is nothing to worry about. Can anyone give me the straight scoop?
BTW,
> my antennas will be on roof tops, so I need enough lead length to get
inside
> to the access points.
>
> Thanks,
>
> Jerry
>
>

On Wed, 27 Oct 2004 16:40:02 -0700, "JerryK"
<(E-Mail Removed)> wrote:

>I am setting up a couple of antennas to connect 2 buildings about 300 feet
>apart. I have discussed this with several people and a subject that came up
>was antenna lead loss. One person said it was a big issue, and another says
>it is nothing to worry about. Can anyone give me the straight scoop? BTW,
>my antennas will be on roof tops, so I need enough lead length to get inside
>to the access points.

It's a BIG issue. At 300ft, you can probably afford quite a bit of
loss. However, it's considered good form to calculate rather than
guess. See:
http://www.ydi.com/calculation/som.php
use 300/5280 = 0.057 for the range in miles. Minimum fade margin is
about 10dB. For an 802.11g link, running at 25Mbits/sec, you should
aim for 30dB fade margin. Use 1.0dB for every connector pair.

For cable loss, see:
http://www.ocarc.ca/coax.htm
You'll probably be using LMR-400 which eats 0.067dB/ft.

If the numbers look bad, then I strongly suggest at least one end of
the link uses a roof top radio, with no coax cable.

If you want me to do the numbers for you, kindly disclose some
hardware details (radios, coax type, coax length, antennas, antenna
gain, range, 802.11a/b/g, etc).

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# 831.421.6491 digital_pager (E-Mail Removed) AE6KS

And dont forget to add in the lightning arrestors!


"JerryK" <(E-Mail Removed)> wrote in message
news:41802fa5$1_1@127.0.0.1...
> Hi,
>
> I am setting up a couple of antennas to connect 2 buildings about 300 feet
> apart. I have discussed this with several people and a subject that came
up
> was antenna lead loss. One person said it was a big issue, and another
says
> it is nothing to worry about. Can anyone give me the straight scoop?
BTW,
> my antennas will be on roof tops, so I need enough lead length to get
inside
> to the access points.
>
> Thanks,
>
> Jerry
>
>

Jeff,

What do you mean by a "Roof top radio with no coax"?

On both sides, I am planning on hooking directly from the Access Point (ex.
Dlink DWL-G700AP) to a directional panel antenna (claimed 16db gain). The
cable length should be under 20 feet.

jerry

"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Wed, 27 Oct 2004 16:40:02 -0700, "JerryK"
> <(E-Mail Removed)> wrote:
>
>>I am setting up a couple of antennas to connect 2 buildings about 300 feet
>>apart. I have discussed this with several people and a subject that came
>>up
>>was antenna lead loss. One person said it was a big issue, and another
>>says
>>it is nothing to worry about. Can anyone give me the straight scoop?
>>BTW,
>>my antennas will be on roof tops, so I need enough lead length to get
>>inside
>>to the access points.
>
> It's a BIG issue. At 300ft, you can probably afford quite a bit of
> loss. However, it's considered good form to calculate rather than
> guess. See:
> http://www.ydi.com/calculation/som.php
> use 300/5280 = 0.057 for the range in miles. Minimum fade margin is
> about 10dB. For an 802.11g link, running at 25Mbits/sec, you should
> aim for 30dB fade margin. Use 1.0dB for every connector pair.
>
> For cable loss, see:
> http://www.ocarc.ca/coax.htm
> You'll probably be using LMR-400 which eats 0.067dB/ft.
>
> If the numbers look bad, then I strongly suggest at least one end of
> the link uses a roof top radio, with no coax cable.
>
> If you want me to do the numbers for you, kindly disclose some
> hardware details (radios, coax type, coax length, antennas, antenna
> gain, range, 802.11a/b/g, etc).
>
> --
> # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
> # 831.336.2558 voice http://www.LearnByDestroying.com
> # (E-Mail Removed)
> # 831.421.6491 digital_pager (E-Mail Removed) AE6KS

"JerryK" <(E-Mail Removed)> wrote:
>What do you mean by a "Roof top radio with no coax"?

An outdoor access point. Something like
http://d-link.com/products/?sec=0&pid=303 where the feedline loss is
approximately zero. You can use something like
http://d-link.com/products/?model=DWL-1750 if you want an external
antenna, and then you can keep your feedline short (though you've
still got connector losses). N-Type connectors (and feedline and
antennas) will keep your losses low...

JerryK wrote:
> Hi,
>
> I am setting up a couple of antennas to connect 2 buildings about 300 feet
> apart. I have discussed this with several people and a subject that came up
> was antenna lead loss. One person said it was a big issue, and another says
> it is nothing to worry about. Can anyone give me the straight scoop? BTW,
> my antennas will be on roof tops, so I need enough lead length to get inside
> to the access points.
>
> Thanks,
>
> Jerry
>
>
Loss IS a big deal. You want to keep coax runs as short as possible. I'm
sure someone on this group (Mr Leibermann?) can advise on figures. If
you cannot get your AP close enough to the antenna, you should consider
getting an AP that supports power over ethernet and put everything in a
weatherproof box and mount it outside.
Peter

Consider something like a Senao outdoor bridge CB-3 in an outdoor enclosure
such as the rootenna which has an integral panel antenna.
http://shop.defactowireless.com/s.nl...it.A/id.118/.f
$170. {If you look real hard these can be had for about $150}. Some of the
wireless mesh operators in NE Texas and Louisiana are using these for the
final connection of community wireless to individual homes or business. The
Senao device provides for power over Ethernet so all you need is an Ethernet
cable to the box with power injected onto the Ethernet cable.

The Senao card is a high powered 200 mW output with a +14 dBi panel antenna.
802.11b only

--
Bob Alston

bobalston9 AT aol DOT com
"Sandy Baby" <(E-Mail Removed)> wrote in message
news:clrjd1$hfa$(E-Mail Removed)...
> JerryK wrote:
>> Hi,
>>
>> I am setting up a couple of antennas to connect 2 buildings about 300
>> feet apart. I have discussed this with several people and a subject that
>> came up was antenna lead loss. One person said it was a big issue, and
>> another says it is nothing to worry about. Can anyone give me the
>> straight scoop? BTW, my antennas will be on roof tops, so I need enough
>> lead length to get inside to the access points.
>>
>> Thanks,
>>
>> Jerry
>>
>>
> Loss IS a big deal. You want to keep coax runs as short as possible. I'm
> sure someone on this group (Mr Leibermann?) can advise on figures. If you
> cannot get your AP close enough to the antenna, you should consider
> getting an AP that supports power over ethernet and put everything in a
> weatherproof box and mount it outside.
> Peter
>
>


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On Thu, 28 Oct 2004 11:22:31 -0700, "JerryK"
<(E-Mail Removed)> wrote:

>What do you mean by a "Roof top radio with no coax"?

That's where the access point is mounted in a waterproof box or is
imbedded in the antenna. Power is supplied with either an independent
cable run, or through the ethernet cable using PoE (power over
ethernet). The big advantage is that it eliminates the coax cable
loss problem and allows substantial flexibility in installation, that
isn't possible with a big fat lossy coax cable run.

It's fairly messy to repackage an indoor router/AP but possible.
http://www.sveasoft.com/articles/armored/

>On both sides, I am planning on hooking directly from the Access Point (ex.
>Dlink DWL-G700AP) to a directional panel antenna (claimed 16db gain). The
>cable length should be under 20 feet.

I didn't realize that you already owned the hardware.
http://www.dlink.com/products/?pid=326
16dBi panel (patch) antennas are just fine. Probably too much gain,
but with the added benifit of not hearing junk to the sides of the
antenna pattern. You should have more than enough fade margin. If
you're only using 20ft of unspecified coax cable, you should have
enough fade margin for getting maximum speed from your bridge.

I can work out the numbers, but you may have a bigger problem. I
don't think the DWL-G700AP will act as a transparent bridge (also
known as a "wireless bridge" or "bridge mode"). I'm looking through
the data sheets and find nothing about bridging. This is strictly an
access point used to connect from individual wireless clients and
cannot be used to glue two networks together.

Is there anything else you didn't mention? (type of coax, line of
sight, fresnel zone clearance, interference potential, number of MAC
addresses bridged (32 max for the cheapo bridges), traffic expected,
etc.)

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

Hi Jeff,

I own the antennas, but not access points. I am open to suggestions on
brands and models. I like the idea of the roof top antenna with no coax,
but the cost may be prohibited. I am not doing a "commercial" installation.
A friend and I are just trying to share a connection between two hangars at
an airport. My hangar has access to a wired DSL connection. His hangar is
300 feet away and we want to hook him to my connection. We are mounting the
antennas on the roofs and plan on placing the access points inside the
hangars. We are trying to do this as cheaply as possible.

Regarding your questions:
"(type of coax, line of
> sight, fresnel zone clearance, interference potential, number of MAC
> addresses bridged (32 max for the cheapo bridges), traffic expected,
> etc.)"

Whatever coax I can get that will work is fine, but price is a
consideration. I would love to be able to run 40 feet on each end, since
that would mounting the access points much easier.

There should be no interference. The roofs are approximately 25 feet and
there are no interviening buildings.

He will only have 2 or 3 system on his end, so we can go with the cheapo
bridge.

Traffic. On my end I will only use the connection once or twice a day. On
his end maybe 5 or 6 times a day. The typical activity will be web browsing
and email. No media players, streaming video, etc. So the load should be
pretty light.

Other factors. All systems will be PCs. I may also have a wireless router
in hangar for my tablet.

Thanks for your help,

jerry

"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Thu, 28 Oct 2004 11:22:31 -0700, "JerryK"
> <(E-Mail Removed)> wrote:
>
>>What do you mean by a "Roof top radio with no coax"?
>
> That's where the access point is mounted in a waterproof box or is
> imbedded in the antenna. Power is supplied with either an independent
> cable run, or through the ethernet cable using PoE (power over
> ethernet). The big advantage is that it eliminates the coax cable
> loss problem and allows substantial flexibility in installation, that
> isn't possible with a big fat lossy coax cable run.
>
> It's fairly messy to repackage an indoor router/AP but possible.
> http://www.sveasoft.com/articles/armored/
>
>>On both sides, I am planning on hooking directly from the Access Point
>>(ex.
>>Dlink DWL-G700AP) to a directional panel antenna (claimed 16db gain). The
>>cable length should be under 20 feet.
>
> I didn't realize that you already owned the hardware.
> http://www.dlink.com/products/?pid=326
> 16dBi panel (patch) antennas are just fine. Probably too much gain,
> but with the added benifit of not hearing junk to the sides of the
> antenna pattern. You should have more than enough fade margin. If
> you're only using 20ft of unspecified coax cable, you should have
> enough fade margin for getting maximum speed from your bridge.
>
> I can work out the numbers, but you may have a bigger problem. I
> don't think the DWL-G700AP will act as a transparent bridge (also
> known as a "wireless bridge" or "bridge mode"). I'm looking through
> the data sheets and find nothing about bridging. This is strictly an
> access point used to connect from individual wireless clients and
> cannot be used to glue two networks together.
>
> Is there anything else you didn't mention? (type of coax, line of
> sight, fresnel zone clearance, interference potential, number of MAC
> addresses bridged (32 max for the cheapo bridges), traffic expected,
> etc.)
>
> --
> Jeff Liebermann (E-Mail Removed)
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 AE6KS 831-336-2558