On 3/27/2016 5:12 PM, Jeff Liebermann wrote:
On Sat, 26 Mar 2016 14:08:12 -0400, rickman wrote:

The datasheet for the NanoStationlocoM9 which seems to be the newer
version of what I have has a return loss graph for the internal antenna.
This seems to show a range centered on about 917 MHz and not too wide.
It says the frequencies used are 902 to 928 MHz.

Unless Ubiquiti is doing something odd, if they use FHSS (frequency
hopping spread spectrum), the radio must hop all 83 channels (in 1 MHz
increments) within some interval that I'm too lazy to excavate from
FCC Part 15. In effect, you'll see it hop the entire allocated
frequency range.

One source of confusion is whether an antenna has to TUNE over a
frequency range, or whether it has to OPERATE over a frequency range.
It's possible to find a narrow band FM 900 MHz antenna that will tune
the desired range, but once tuned, has a much smaller operating
bandwidth. High gain Yagi and big gain patch/panel antennas are
potential problems.

I'm talking about the antenna built into a working unit. You seem to be
discussing the state of the art in general.


I looked at the highest gain antennas from each of these two and neither
supplies VSWR graphs. The Laird PC9013N has 13 elements and says freq
range is 902 to 928 MHz which seems to roughly match the internal antenna.

The L-com model HG914YE with 14 elements says it works from 824 to 960
MHz. It claims a 1.5:1 VSWR "average" which I guess means something,
but I'm not sure what.

Average is not the usual term. I would have no problem with 1.5:1
maximum VSWR, but average sounds like they're hiding a problem.

This unit has 14 dBi of gain while the Laird is
13 dBi.

Many of the gain plots are simulations and are not the result of field
tests or anechoic chamber tests. It's fairly easy to recognize the
difference. The real tests show lower numbers and look far from idea.
The simulations look too good.

I'm thinking 1 dB is not so much. The Laird seems to be well
over $100 and the L-com around $50 with free shipping. I'll also need
an N to SMA pigtail. First I need to ask my provider. He may have to
twiddle something in the box to enable the antenna input.

Ask your WISP what kind of antenna he recommends. I doubt that this
is the first higher gain antenna that he's installed.

Bet it *is*! In fact, I bet the only high gain antenna he has installed
was the point to point link to connect his antennas. He likely doesn't
do the work himself since that requires climbing towers and likely a
crane. Do they carry the components up by hand? I can't imagine they
would.

He said something about adding a tower in a few months which will add
bandwidth to the system. But he has always said my air link was
marginal when compared to my neighbors, at this point some 6 dB worse.
I'd like to fix that. I know none of my nearest neighbors who get his
service are even in the area. It is on a lake and one guy is only here
on weekends in the summer and the other guy is only here a *few*
weekends in the summer. He does have cameras that are accessed over the
Internet, so they might use bandwidth all the time, don't know, maybe
only when someone wants to look. He uses some third party service to
make the connection. They might be recording all the time.


I still recommend using a panel antenna. I have a few in the office,
but they're circular polarization for near field devices and probably
won't work for you. Start he
https://www.google.com/#q=900+mhz+panel+antenna
Anything over about 10dBi gain should be sufficient.

The existing internal antenna is 7 dBi. I can't see going to the
trouble of using an external antenna to get another 3 dB. I did find a
couple of panel antennas that give 12.5 dB. They might be cheaper than
the Yagi I found at $70. One panel was $40, but out of stock.


BTW, one of these antennas says the directors are welded to the boom.

Yes. Good idea if you want it to survive. All of the Laird (Antenex)
Yagi's that I've used were welded and had rounded ends to improve the
bandwidth. They're more expensive than bolt together Yagi's but I
think it's worth it for mountain top use, where I have to pay an
expensive certified tower climber to deal with any damage. However,
for the average consumer, it's probably overkill.

I always thought the elements were insulated from each other and the boom.
I recall seeing insulation on old TV antennas, was that just to
prevent corrosion or something?

No. It makes the TV antenna easy to ship in a smaller box. If TV
antennas were welded and shipped ready to install, they would be huge,
and the shipping would be seriously expensive.

Making them collapsible doesn't require insulators. Each folding
element had a piece of what looked like card stock between the element
and the mounting point on the boom. Was that to prevent corrosion maybe?

I assume the active element is insulated, right?


The elements of a Yagi do not need to insulated from the boom.
However, the length of the elements is affected by the boom. The RF
path goes around the boom in the welded design requiring 1/2 the
circumference of the boom to be added to the element length
calculation.



--

Rick