Turn key parts for point-to-point link?

Hi everyone.

I am thinking about linking two farmsteads via a wireless point-to-point
link. Using Splat! (an RF path analysis tool for Linux written by John,
KD2BD), I have determined that with antennas at 30 and 25 feet, I have a
path clearance of 20 feet and a Longley-Rice path loss of 109 dB @ 2400
MHz. Assuming an RX sensitivity of -95 dBm (are they that good?), a TX
power of +20 dBm, antenna gain of 17 dBi,throw in 2 dB for cable/connector
loss (approximately 0 dB for an integrated unit) and I figure the signal
at the far end would be about -74 to -76 dBm which should give about 20 dB
of fade margin. We might have to trim a tree or two at one end. :-)

I've used Google to try and find some off the shelf equipment and I either
wind up finding low grade consumer items meant to link rooms or high end
commercial stuff intended for backbone use. So, what is out there, either
integrated units or something I can put together, for about $500 or less
for this link?

Thanks!

- Nate >>

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

Nate Bargmann wrote:
> Hi everyone.
>
> I am thinking about linking two farmsteads via a wireless point-to-point
> link.
>
> I've used Google to try and find some off the shelf equipment and I either
> wind up finding low grade consumer items meant to link rooms or high end
> commercial stuff intended for backbone use. So, what is out there, either
> integrated units or something I can put together, for about $500 or less
> for this link?

www.inscapedate.com for their wireless gear.

Nate Bargmann <n0nb.DO.NOT.SPAM@ME.networksplus.net> hath wroth:

>I am thinking about linking two farmsteads via a wireless point-to-point
>link. Using Splat! (an RF path analysis tool for Linux written by John,
>KD2BD), I have determined that with antennas at 30 and 25 feet, I have a
>path clearance of 20 feet and a Longley-Rice path loss of 109 dB @ 2400
>MHz. Assuming an RX sensitivity of -95 dBm (are they that good?), a TX
>power of +20 dBm, antenna gain of 17 dBi,throw in 2 dB for cable/connector
>loss (approximately 0 dB for an integrated unit) and I figure the signal
>at the far end would be about -74 to -76 dBm which should give about 20 dB
>of fade margin. We might have to trim a tree or two at one end. :-)

Nicely done. However, methinks you missed on some assumptions and
didn't supply the parameters you used to generate your numbers.

See the FAQ at:
| http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations
for a sample link calculations. The receiver sensitivity should be at
whatever connection rate you're expecting. My guess(tm) is that
you're sharing a cable or DSL line and would like to see at least
6Mbit/sec thruput. That means you'll need at least a 12Mbit/sec
wireless connection. Methinks some safety factor would be helpful, so
I'll use 18Mbits/sec. The corresponding sensitivity for a Dlink
DI-624 is -82dBm. Other hardware may be different, but this is in the
ballpark. Also, everyone lies about rx sensitivity because it's so
expensive and difficult to measure.

You didn't bother to mention the point to point distance. Reverse
engineering your -109dB path loss, I'll guess it's 9500 ft (about 1.8
miles). Is this correct?

You also neglected coax cable losses. Unless you buy an integrated
antenna and radio device, there will be some coax connector and cable
loss. I'll assume you have an external radio, a short piece of coax,
and a pair of dish antennas.

20dB of fade margin is a good target value. Anything less than about
15dB will be flakey.

+20dBm tx power is optimistic. There are some 100mw radios out there
that claim this power level. Most commodity devices are rated at
+17dBm and actually deliver about +15dBm xmit power.

Now, we have enough to run the numbers. I'll do a template and you
change the value to resemble your reality.

TX power = +17dBm
TX coax loss = 2 dB (3 ft LMR-240 plus connectors)
TX ant gain = 17dBi
Distance = 1.8 miles
RX ant gain = 17dBi
RX coax loss = 2 dB (3 ft LMR-240 plus connectors)
RX sens = -82dBm
Fade margin = unknown

Plugging into:
| http://www.terabeam.com/support/calculations/som.php
I get a fade margin of 19.7dB. Close enough. It will work.

Please note that this is the BEST case calculation. It always gets
worse. You didn't mention if you were impacting the Fresnel Zone on
your path. There may also be interference and reflection issues. Of
course much of the hardware isn't up to specifications.

>I've used Google to try and find some off the shelf equipment and I either
>wind up finding low grade consumer items meant to link rooms or high end
>commercial stuff intended for backbone use. So, what is out there, either
>integrated units or something I can put together, for about $500 or less
>for this link?

Sure. I'll assume a symmetrical transparent bridge. Just look for
any of the access points that have a "bridge" mode. For example,
Linksys WAP11, DLink DWL-2100AP, etc. Most access points will also
play bridge. Check the feature list of web setup:
http://www.linksysdata.com/ui/
http://support.dlink.com/emulators/
Figure on about $100 per radio. You'll probably need a PoE adapter
and some kind of weatherproof package. Add about $50 per radio.
Antennas, coax cables, connectors, and mounts will probably cost about
$50. Yeah, it can be done.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 11 Nov 2006 10:15:01 -0800, Jeff Liebermann wrote:

> Nicely done. However, methinks you missed on some assumptions and
> didn't supply the parameters you used to generate your numbers.
>
> See the FAQ at:
> | http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations
> for a sample link calculations. The receiver sensitivity should be at
> whatever connection rate you're expecting. My guess(tm) is that
> you're sharing a cable or DSL line and would like to see at least
> 6Mbit/sec thruput. That means you'll need at least a 12Mbit/sec
> wireless connection. Methinks some safety factor would be helpful, so
> I'll use 18Mbits/sec. The corresponding sensitivity for a Dlink
> DI-624 is -82dBm. Other hardware may be different, but this is in the
> ballpark. Also, everyone lies about rx sensitivity because it's so
> expensive and difficult to measure.

I would probably be sharing a 384 kbps connection from a wireless ISP
which is the only choice other than satellite out there. So, if the link
does no poorer than 1 Mbs, I think we'll be fine. This is just an idea
I'm working on if my brother would like something a bit faster than his
26.4 kbs dialup and I could tie the folks place in too. There will only
be one PC at either end of the link and rarely will both be in operation
at the same time.

> You didn't bother to mention the point to point distance. Reverse
> engineering your -109dB path loss, I'll guess it's 9500 ft (about 1.8
> miles). Is this correct?

I did neglect that. Per the coordinates, Splat! says it's 1.54 miles.

> You also neglected coax cable losses. Unless you buy an integrated
> antenna and radio device, there will be some coax connector and cable
> loss. I'll assume you have an external radio, a short piece of coax,
> and a pair of dish antennas.

I did toss in 2 dB unless I had an integrated unit. I did forget to
subtract 2dB at the far end and add in the 17 dBi antenna gain. OOPS!

> 20dB of fade margin is a good target value. Anything less than about
> 15dB will be flakey.
>
> +20dBm tx power is optimistic. There are some 100mw radios out there
> that claim this power level. Most commodity devices are rated at +17dBm
> and actually deliver about +15dBm xmit power.
>
> Now, we have enough to run the numbers. I'll do a template and you
> change the value to resemble your reality.
>
> TX power = +17dBm
> TX coax loss = 2 dB (3 ft LMR-240 plus connectors) TX ant gain =
> 17dBi
> Distance = 1.8 miles
> RX ant gain = 17dBi
> RX coax loss = 2 dB (3 ft LMR-240 plus connectors) RX sens =
> -82dBm
> Fade margin = unknown
>
> Plugging into:
> | http://www.terabeam.com/support/calculations/som.php I get a fade
> margin of 19.7dB. Close enough. It will work.
>
> Please note that this is the BEST case calculation. It always gets
> worse. You didn't mention if you were impacting the Fresnel Zone on
> your path. There may also be interference and reflection issues. Of
> course much of the hardware isn't up to specifications.

There is one other farmstead in the path, but I think we have pretty good
clearance. Of course, one won't know until it's tried. Like I said, a
tree or two may need to be trimmed.

> Sure. I'll assume a symmetrical transparent bridge. Just look for any
> of the access points that have a "bridge" mode. For example, Linksys
> WAP11, DLink DWL-2100AP, etc. Most access points will also play bridge.
> Check the feature list of web setup:
> http://www.linksysdata.com/ui/
> http://support.dlink.com/emulators/
> Figure on about $100 per radio. You'll probably need a PoE adapter and
> some kind of weatherproof package. Add about $50 per radio. Antennas,
> coax cables, connectors, and mounts will probably cost about $50. Yeah,
> it can be done.

I do appreciate that, Jeff. It helps to get a bit of direction and a bit
of refinement of my rough numbers. I spent about 10 minutes this morning
guessing all of that up. :-)

- Nate >>

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

On Sat, 11 Nov 2006 17:35:24 +0000, decaturtxcowboy wrote:

> www.inscapedate.com for their wireless gear.

Is that link spelled correctly? I get a not found error.

Thanks!

- Nate >>

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

Nate Bargmann wrote:
> On Sat, 11 Nov 2006 17:35:24 +0000, decaturtxcowboy wrote:
>
>> www.inscapedate.com for their wireless gear.
>
> Is that link spelled correctly? I get a not found error.
>
> Thanks!
>
> - Nate >>
>
I think he meant
http://www.inscapedata.com/

Nate Bargmann wrote:
> Hi everyone.
>
> I am thinking about linking two farmsteads via a wireless point-to-point
> link. Using Splat! (an RF path analysis tool for Linux written by John,
> KD2BD), I have determined that with antennas at 30 and 25 feet, I have a
> path clearance of 20 feet and a Longley-Rice path loss of 109 dB @ 2400
> MHz. Assuming an RX sensitivity of -95 dBm (are they that good?), a TX
> power of +20 dBm, antenna gain of 17 dBi,throw in 2 dB for cable/connector
> loss (approximately 0 dB for an integrated unit) and I figure the signal
> at the far end would be about -74 to -76 dBm which should give about 20 dB
> of fade margin. We might have to trim a tree or two at one end. :-)
>
> I've used Google to try and find some off the shelf equipment and I either
> wind up finding low grade consumer items meant to link rooms or high end
> commercial stuff intended for backbone use. So, what is out there, either
> integrated units or something I can put together, for about $500 or less
> for this link?
>
> Thanks!
>
> - Nate >>
>
> --
>
> "The optimist proclaims that we live in the best of all possible worlds,
> the pessimist fears this is true."

Pen wrote:
> Nate Bargmann wrote:
>> On Sat, 11 Nov 2006 17:35:24 +0000, decaturtxcowboy wrote:
>>
>>> www.inscapedate.com for their wireless gear.
>>
>> Is that link spelled correctly? I get a not found error.
>>
>> Thanks!
>>
>> - Nate >>
>>
> I think he meant
> http://www.inscapedata.com/

Sorry about that.......

They discontinued all their 802.11b stuff and have 802.11b/g
that has really come down in price, especially the access points.

The prices on their web page are for retail and I can't
disclose my dealer pricing. You can purchase them through
http://connectronics.com <-- yes, THAT link works :)

On Sun, 12 Nov 2006 16:47:27 +0000, decaturtxcowboy wrote:

> The prices on their web page are for retail and I can't
> disclose my dealer pricing. You can purchase them through
> http://connectronics.com <-- yes, THAT link works :)

Thanks!

That link is very helpful.

- Nate >>

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

Thanks to a post elsewhere, I found the 2.4GHz 19dBi RooTennaTM Compartment
Antenna with CB3 Client Bridge Option at:

http://www.wlanparts.com/product/ZZ-CB3-RT24-18

for about $177 each. This looks like it would fit my situation very well
as a pair can be configured for a point-to-point bridge link (they claim
one is in operation covering a five mile link and I have just over 1.5
miles to cover).

- Nate >>

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."