On Sun, 19 Feb 2017 20:44:18 +0000 (UTC), Stijn De Jong
wrote:

On Sat, 18 Feb 2017 23:13:31 -0800, Jeff Liebermann wrote:
Back of the envelope calculation:
+27dBm Estimated transmit power from the cell site
+10dB My guess of the panel antenna gain
-53dBm Receive signal level from your test.

Path loss = 27 + 10 + 53 = 90dB
Calculating the distance where the path loss would be -90dB at 700MHz:
http://www.proxim.com/products/knowledge-center/calculations/calculations-free-space-loss
is about 0.7 miles or about 4,000 ft. The cell tower would need to be
rather close to your location for that to work. Like I said, I'm
suspicious of what you're measuring.

Thanks for showing me how to do the math to approximate the distance to the
antenna based on the received signal strength indication.

Well, I screwed up a little. I left out the antenna gain of your cell
phone, which I assumed to be 0dB at 700MHz. That's probably
optimistic and -3dB would be more reasonable. So, the calcs should be
something like:

+27dBm Estimated transmit power from the cell site
+10dB My guess of the tower panel antenna gain
??dB Calculated path loss
-3dB My guess of the cell phone antenna gain
-53dBm Receive signal level from your test.

Path loss = 27 + 10 - (-3) - (-53) = 93dB
Calculating the distance where the path loss would be -93dB at 700MHz:
http://www.proxim.com/products/knowledge-center/calculations/calculations-free-space-loss
is about 0.94 miles or about 5,000 ft. The cell tower would need to
be rather close to your location or you're getting your signal from
the neighbors.

I must not have stated clearly which is that the only time I get minus
sixty decibels is when the femtotower is in place, where it's only a few
feet from my phone.

The +27dBm (500mw) and +10dBm antenna gain are based on my guess(tm)
of the power per carrier for a real cell tower and a typical panel
antenna and with some reduction in power thanks to transmit power
control. Power levels and antenna gains for DAS (distributed antenna
system), small cell, microcell, picocell, analog repeaters, etc are
much lower.
http://www.rfwireless-world.com/Tutorials/femtocell-vs-picocell-vs-microcell.html
I can build you a table for the various device that will produce more
accurate results.

There *are* antennas two miles away (and sometimes I connect to them); so
the math isn't as bad as I thought. I also connect to antennas ten and
fifteen miles away, but that's driving distance, so I'd have to look at the
distance as the crow flies, which could be in the less-than-five-mile
range.

Also look at the antenna gains on both ends, any RF obstructions
including Fresnel zone blocking, and the accuracy of the signal level
meter in the cell phone. Remember, in RF real RF power, sensitivity,
antenna gains, and path loss, are always worse than calculated.

I don't want to comment on the T-Mobile signal booster due to lack of
experience with the device and general lack of info on what's inside.
If you can supply an FCC ID number, I might be able to excavate
something useful from the FCC ID data dumpster.

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