[Replicant] The (!)Baseband/Public Cellular Telephony Network Path

Tj replicant at iam.tj
Fri Aug 11 19:53:21 UTC 2017


On 11/08/17 19:29, Josh Branning wrote:
> Hi,
> 
> Recently I attempted a 9km communication via 4W CB radios and a homemade
> 1/2 wave dipole, from a rural village, to a town. I figured with more
> power and a low frequency, they might fare for unlicensed
> communication. (I am based in the UK.) Unfortunately, I didn't manage a
> voice signal over that distance. Someone other, who is into amateur
> radio told me it may be to do with being at the peak of a solar cycle.




In the distant past I regularly managed 15-25km local regular
conversations on 27MHz with 4 watt transmitters and 1/2 wave dipole.
Further with a 3/4 wave Sigma 4.

The critical issue is to ensure the standing wave ratio (SWR) is really
low (lower than 1.5:1 and preferably 1.2:1) and that the antenna has a
good ground plane, otherwise the signal footprint for the vertical
elevation, instead of being flat along the ground like a a baguette,
will be elliptical or even circular, meaning that the signal close to
the ground will get weak quickly the further out the receiver is. I know
some people that would top-feed the antenna rather than bottom-feed it
to avoid needing to add a ground plane.

> I am pretty surprised that the unlicensed link you used in the talk went
> 39km. I would be interested to know the make and model of the USB
> transceiver you used. Other people always seem to be able to go real far
> on little power [7][8], I myself am jealous and have had little success.

Using a pair of TP-Link CPE510 5.8GHz WiFi units I am able to link 2
farms 13km apart. The antennas are internal planar 2 x 2 MIMO and have a
very directional footprint.


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