True, but 28dbi is a 2' dish at 5hz. Which is what Steve said he has
available. If you're willing to put big enough dishes in you could
probably get a -70 something. It's hard to imagine a scenario where
using a bunch of 3' or 4' dishes makes more sense than burying a 110v
power wire out to the barn. I'm sure it's happened somewhere.
On 2/17/2016 1:38 PM, Rory Conaway wrote:
Good calculation. -87 isn’t that far off though. Get 4-6dBi on the
directional antennas and it works, even with a couple dB loss in the
cable but I’m talking 5GHz, not 2.4GHz.
Rory
*From:*Af [mailto:[email protected]] *On Behalf Of *Adam Moffett
*Sent:* Wednesday, February 17, 2016 11:33 AM
*To:* [email protected]
*Subject:* Re: [AFMUG] passive relay
Exactly. Use an online freespace path loss calculator.
In real life, I've yet to encounter a scenario where the math actually
worked.
Suppose the barn is 5 miles from the tower, and 100 yards from the
customer's office.
Using the calculator at
https://www.pasternack.com/t-calculator-fspl.aspx
<https://www.pasternack.com/t-calculator-fspl.aspx>:
100 yards (customer to barn) = -87db FSPL
5 miles (tower to barn) = -126db FSPL
sector antenna gain (tower) = +16dbi
2' dish gain (barn1) = +28dbi
2' dish gain (barn2) = +28dbi
2' dish gain (customer office) +28dbi
tx power from tower = +26dbm
That adds up to an RSSI of -87dbm assuming everything else is
perfect. So you've got a lot invested to get a signal they won't be
happy with.
If it were 900mhz
100 yards = -71 db
5 miles = -110 db
Let's say yagi antennas x 4 at +15dbi each for a total of +60
Tx power at +21 (to be legal).
That adds up to -100dbm. Doesn't work at all.
So really, you need one path to be short and the other to be
/extremely/ short.
On 2/17/2016 1:11 PM, Ken Hohhof wrote:
When this has been discussed before, it only works if one path is
really short. You add the antenna gains and the free space loss
of both paths. If both legs have FSL on the order of 100 dB, you
are not going to make it up with antenna gain.
The huge billboard style passive reflectors are a different matter.
*From:*That One Guy /sarcasm <mailto:[email protected]>
*Sent:*Wednesday, February 17, 2016 11:40 AM
*To:*[email protected] <mailto:[email protected]>
*Subject:*[AFMUG] passive relay
We have a bunch of old 2' radiowaves dishes laying around.
Im curious what the real world loss would be if we used them on a
midpoint with the feedhorns patched together.
Like for a business buried in trees that has an old tall barn with
no power but line of site to our PoP. this is a really common
occurrence. All we would need to do is get the feedhorns replaced
with dual pol horns.
This is on my list of things I would like to set up here shooting
around the corner of our building out of curiosity, but I never
have time to play with it
--
If you only see yourself as part of the team but you don't see
your team as part of yourself you have already failed as part of
the team.
