Re: [VAL] Receiving signals inside Airstream

["Rick Kunath" <k9ao@xxxxxxxxxxx>]

> Watch out !  NONE of the Passive Antennas ever sold worked.. 

Couldn't agree more if you are referring to the gimmicky stick-on 
so-called boosters.

> The only ones that ever worked, and they did not work well, was a 4 X 6 
> X 2 inch amplifier with an input and output cable connection powered by 
> 12 VDC.  You ran coax to an outside antenna from the input connector 
> then a short coax to the inside antenna.  This was only good for about 
> 10 feet on the inside.
> The cost years ago was around $150.  I worked for CellularOne as a tech 
> and eng.

This describes one of the typical consumer-grade BDAs that are quite 
problematical, and as was mentioned, don't often work if at all. This is 
an active device.

External antennas are passive devices, i.e. there is no power consuming 
amplification taking place, but there is definitely reciprocal (transmit 
as well as receive) gain produced, and this is real and usable gain. As 
a rule of thumb, signal strength decreases as the square of the distance 
from a transmitter (move twice as far away and the signal drops to 1/4 
the starting strength), so for example using an external antenna with 10 
dB of gain over your built-in antenna will give you about a 3X increase 
in coverage for a given location. This is a worthwhile and significant 
improvement.

The key to using these is in having a cellphone or other device with an 
accessible external antenna connection so that the device can be 
properly connected to the outside-mounted external antenna.

Again, proper external antenna system design is the key here to good 
performance. Non ground-referenced antennas with very high loss RG-174U 
coaxial cable (this is the small 1/8-inch outside diameter stuff) as a 
feedline are mediocre performers. So called "flat-coax" type cables are 
extremely lossy as the cable impedance is determined by the physical 
cable construction. A flat cable cannot be made reflection-free, and 
appears as an impedance bump to the RF traveling in it. These cable 
impedance mis-match discontinuity caused standing-wave reflections can 
cause pulse jitter and pulse edge rounding on the digital cellular 
signals causing losses in performance above and beyond what the expected 
cable losses alone would predict.

It's easy to throw away good RF performance by a poor choice in hardware 
or installation, and just as easy (and just as cheap) not to.

Rick Kunath