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Re: Comrex Access Portable 2USB External Antenna
To: CRTech <crtech@crtech.org>
Subject: Re: Comrex Access Portable 2USB External Antenna
From: Sherrod Munday <smunday@ieee.org>
Date: Thu, 2 Nov 2017 12:57:36 -0400
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In-reply-to: <39BDB4B5A083864B9802AFB66985BC07BD6CF4@KSGN-DC.KSGNNET.local>
References: <CAHfB3uPdeB+S_zxKdZx+sRnQWysijrv44tw3SkWVOmxGgNZymw@mail.gmail.com> <39BDB4B5A083864B9802AFB66985BC07BD6CF4@KSGN-DC.KSGNNET.local>
On Wed, Nov 1, 2017 at 1:08 PM, Jon Foreman <Jon@ksgn.com> wrote:
> We are using the Comrex Connect Modem on Verizon. I’m considering connecting
> an external yagi antenna (https://www.cellularsolutions.com/product/SC-230W.html) . I called Comrex
> to see what advice they may have. The tech I talked with had never had the
> topic  come up of using an external antenna.

> I know in theory it should help, but it will make setups a bit more
> complicated as they will need to figure out what direction to point the
> antenna. Where is that tower? How’s the signal strength meter?


I have used almost that exact antenna on a non-proprietary USB
cellular data modem.  (It might be the same one, but I can't tell from
the labeling whether it's the same mfr.)  I used the following:

Here are my observations and notes from several years of experience:

1.  The antenna you linked (and the one I used) is not a standard
single-frequency Yagi-Uda antenna, though its behavior follows the
same basic principles of how a Yagi-Uda antenna works.  The one you
show is a Log-Periodic Dipole Array antenna, commonly known by its
acronym of LPDA.  You can search online to learn more about it (e.g.
https://en.wikipedia.org/wiki/Log-periodic_antenna ), but in short
it's a very broadband antenna with a reasonable amount of directivity
and gain.  A single-frequency (or narrow-band) Yagi-Uda antenna for
the specific frequency band of the cellular modem would produce higher
gain and directivity along with better front-back signal rejection
ratio.  You would need to verify whether you are using an 4G/LTE or 3G
modem and what frequency band Verizon is using.

2.  Use a high-quality low-loss cable (that may be more rigid than
your typical RG-8) because you're going to be sending UHF signals down
that cable, and you'll lose several dB (or many dB, depending on the
frequency) in a typical RG-8 cable.  Don't even think about using
RG-58 or its kin.  Pay the extra money for the cable and you won't
regret it.  I used the following:

3.  The antenna you link will need an appropriate adapter to get from
the N connector to the mini connector likely found on your modem.  Get
the low-loss cable (item #2 above) with an N connector on the antenna
end, and an interim connector on the modem end.  Then use a short
(~6") adapter pigtail and flexible (and higher-loss) cable to get from
the interim connector to the connector type on your modem.  While
you'll need to verify the specific connector for your modem, I used
the following:

4.  When you deploy the system in the field, count on taking a while
to orient the antenna, strap it down, run the cable, and properly
gaffe (tape) it all in place so that the strain doesn't make it to the
cellular modem.  Someone else set up our system once and didn't take
care to do that... and you can guess where this is going ... someone
tripped over the cable, and broke the antenna connector off the
cellular modem's circuit board.  End of story for *that* modem's
external antenna connectivity.

5.  When you do your remotes, ensure that you have access to the
outdoors where you can set up the antenna and run the cable back
inside through a door (e.g. passing through the weatherstripping under
the door), window, etc.  You will get better performance using the
external antenna indoors, but it will be dramatically better outdoors
if at all possible.  The antenna's waterproof when mounted properly,
and ensure that you use weatherproofing (like
) on the antenna connectors that are outdoors.

6.  Look online for tools that identify the cell tower locations.  I
had modems from Sprint, Verizon, and AT&T.  Some of those carriers
provide Google-based maps with overlays that show the actual tower
sites for various transmission types (e.g. 3G vs. LTE).  While you can
find myriad tools online via Google, here are a couple of places to
https://community.verizonwireless.com/thread/766309 (not sure if this
is still current... I haven't used the app so "caveat emptor"!)

Then pull up a current map from your location, and figure out the
cardinal direction for aiming the antenna.

7.  Some tools that carriers provide to use the modem with a PC (e.g.
driver packages that contain software to manage the cellular
connection) will provide you a raw signal strength number (not
"bars").  Lug your laptop to the remote (yeah, I know...) and set it
up with the cellular modem, get into the raw signal meter, and slowly
rotate the antenna around the horizon until you find a strong signal.
Leave the antenna alone, move the modem to your Comrex, and plug it
in.  Done.  (You may need to talk to Comrex to determine if they
provide a Windows/Mac/Linux driver/software package for their modem,
but the specs make it look like any other garden-variety cellular data
modem.  BTW, please don't tell them I said that -- they might get
worked up about me calling it garden-variety when they claim it's
"Pro-Grade" and uniquely suited to professional broadcast use. ;-)
(And, don't get mislead by their claim of the "high-gain (2.1 dB)
antenna that comes with the modem.  Pshaw.  But I digress.)

8.  I guess I should mention -- find a tripod that has a nice wide
base and an extendable pole to get the antenna up in the air a few
feet over your head.  The elevation won't make a real difference, but
it looks cool.  ;-)  Mount the antenna on the pole with appropriate
pipe clamps (that mine came with in the box).  When you're ready to
aim the antenna, loosen the lock on the pole and simply rotate the
entire pole and cable until you find where you want it.  Lock it down
there, and gaffe up the cable.  If you're going to have any chance of
wind (or people around the tripod) then make sure to secure the tripod
with appropriate weights at the bottom and/or tethers (I used
non-conductive standard string) from the top to appropriate anchor
points, ensuring you don't end up with trip hazards or guillotine
cords at neck level.  :-)

Hope this helps!

Sherrod Munday
Follow-Ups: RE: Comrex Access Portable 2USB External Antenna
(Jon Foreman <Jon@ksgn.com>, 2 Nov 2017 18:11:21 -0000)
References: POV
(Tim Swanson <timswanson@kswp.org>, 31 Oct 2017 18:38:12 -0000)
Comrex Access Portable 2USB External Antenna
(Jon Foreman <Jon@ksgn.com>, 1 Nov 2017 17:09:10 -0000)
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