Re: Do these cellular amplifiers work for all cellphones?

On 10/04/2022 18:15, RJH wrote:
> he 2022 PC Magazine vehicle cellular boosters review specifically describes
> the "uplink" as the "connection that goes first" when you are at "the edges
> of cell coverage" which they defined as somewhere around below -110dBm.

I'd consider mobile to fixed to be the uplink, but the -110dBm will me 
measured at the mobile end of the fixed to mobile direction.

> 
> Even the cheapest vehicle cell signal booster which is an on-the-dash device
> has 23dB of gain, which should theoretically boost that weak -110dBm signal
> into a respectable range in the mid eighties for that uplink (assuming they
> were honest in their FCC certification, which we have to believe is true).

The limit on signal quality will be set by signal to noise ratio, and 
only indirectly by power level.  -110dBm represents the power level at 
which the signal to noise level gets to be unacceptable for an antenna 
that is in the open.  Boosting it by 23dB isn't going to improve SNR, 
except to the extent that the booster receiver has lower noise front 
end, and, even then, there is probably going to be very little benefit 
beyond about 5dB of gain, even for an ideal receiver.

The technical spec of the first product on the web page was silent about 
noise figures, so it may well have no better a front end than the mobile 
itself, in which case the SNR will be worse.

The main purpose seems to be to compensate for the losses caused by the 
car body, reducing the signal, but that is somewhat equivalent to the 
old way of feeding an external aerial to a docking unit, allowing the 
phone to directly use the external aerial.  To some extent this is going 
to be an expensive way of compensating for the lack of an antenna socket 
on modern phones.

The external antenna will be better than the internal one in the phone, 
so that should be a benefit.

A 23dB boost, on the same frequency risks the retransmission being 
received on the external antenna, so I can't really see why you would 
want to uses so much gain, except as a numbers game.

23dB mobile to fixed would introduce safety problems in terms of jamming 
car electronics and exposure to pedestrians (if used when parked).