On Mon, 27 Apr 2015 21:28:36 +0100, Jim
wrote:

Firstly sorry if this is OT guys but you do seem the best people to ask.

I'm bored. OT will have to suffice.

The part of London I live in has rubbish ISP speeds (4 mbit) and I have
been offered an old Relish.net router which is a Gemtek WLTFSR-115GN, I
know some of these have external aerial sockets (US ones I think) but
the version I will get does not have any external sockets, so it's a
case of go inside and try to figure out some way of connecting an
external aerial, now the reason I need an external one is I am right on
the edge of their coverage and only get a single bar using just the
router, I do have some images of the inside of the router so I will post
the links for them later, but I was just wondering if anyone has heard
of this being done in the UK?


I once did some experiments with cell phone antenna couplers. Phones
were arriving which did not have a projecting antenna or any easy
method of attaching an external antenna. The trick was to design a
phone base that included some kind of coupler that did not require any
connection or modification to the phone (or the FCC would reject it
for type certification).

The initial design was for 1900 Mhz only, but later mutations covered
both 800 and 1900. In Europe, that would be 1800 and 900 MHz. I
tried patch, loop, resonant loop, slot, cavity backed resonator, along
with various reflectors. All of them were lossy. In the near field,
all acted more like capacitors and xformers than antennas. So, the
executive decision was to use the simplest, easiest, and cheapest,
which was the loop. Second best was a 1/2 dipole, which was
problematic due to its length.

I don't know what frequency your Gemtek WLTFSR-115GN operates on 4G:
http://www.gemtek.com.tw/pro_LTE_WLTFSR.htm
but when you find out, just cut a length of wire 1 wavelength long,
make a loop in almost any shape, and place it as close to the internal
antenna as possible. The impedance will be about 100 ohms, so use 75
ohm CATV coax (RG-6/u) to the antenna. Never mind the mismatch at
both the antenna and the loop. It's not worth the hassle matching it.
You'll need to move the loop around the case to find the best pickup
point. When you find it, tape it in place.

I'm not sure what to recommend for the outside antenna. Much depends
on the frequency of operation. In the US, most of the 4G stuff is
moving to 700 MHz, leaving 800/1900 for voice and 3G data. Therefore,
a single band 700 MHz antenna would be required for the US. No clue
for the UK (and I'm too lazy to look it up). If it is single band, a
simple patch antenna will get you about 8dBi gain. If you want more,
look into yagi, corner reflector, or dish antennas. I'm partial to
AMOS/Franklin antennas, but if your UK 4G system uses polarization
based spatial diversity for MIMO, a single linear polarized antenna
will limit your maximum download speed. This is probably more than
you want to deal with, so I suggest starting with a simple 1/2 wave
dipole and escalate as needed.

Good luck.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558