[ale] OT cellular protocol versions

[Michael H. Warfield]

On Fri, 2015-01-23 at 08:34 -0500, Phil Turmel wrote:
> On 01/22/2015 09:45 PM, Michael H. Warfield wrote:
> > On Thu, 2015-01-22 at 19:29 -0500, Phil Turmel wrote:
> >> On 01/22/2015 06:32 PM, Alex Carver wrote:
> >>> Sounds like a Sidekick.
> >>>
> >>> What network is he on?  That affects the communication channel.  Not
> >>> everything is LTE just yet, lots of things are still using various
> >>> modulations and channel types (2G GSM, 3G EDGE, CMDA, 4G LTE or WiMax).
> >>>
> >>> It might be his phone, it might not be. Tower sharing can cause
> >>> interference and vegetation can cause other issues.  If the phone gets
> >>> dropped a lot then the tiny SAW filters used in some phones can be
> >>> damaged causing poor reception.
> > 
> >> OMG!  Industry is using SAW filters?  (I'm presuming that's "Surface
> >> Acoustic Wave").  My college department head was an early researcher on
> >> these, and I played (briefly) with them as a sophomore EE.  Talk about a
> >> blast from the past.
> > 
> > You're kidding, right?  SAW filters have been used by industry for
> > decades.

> No, actually.  I saw the research he was doing (playing with selectively
> absorptive coatings for dangerous gas & medical sensing) and thought
> "that's an interesting niche".  Didn't occur to me that they'd work well
> at high radio freqs.  My EE focus has largely been industrial control
> systems and plant floor data collection., so no significant exposure to
> the state of the art in RF.

I had an EE prof back at MSU sometime around 1974 wanted to take me out
to lunch just to talk about the kind of RF work I did in the broadcast
business at channel 10.  The concept of 8' tall rigid copper triaxial
shorted stubs (the outer of which was 10" in diameter) handling 100KW of
RF for tetrode finals (operating at a plate voltage of 6KVDC fed from 6
phase mercury vacuum rectifiers) and transmission line tuning just
amazed him (that was the OLD GE beast we replaced).  Plumbing nightmare.
The Harris transmitter we installed was an incredibly improvement.
 
> > Back in the early 70's I helped install a Harris Corporation High
> > Channel (channel 10) broadcast transmitter that used a little tiny SAW
> > filter (about the size of the ceramic oscillators found on most computer
> > mother boards) for it's vestigial sideband filtering at the modulator
> > signal level as opposed to the massive reflection cavities and hybrid
> > ring duplexers operating at 200KW with the old transmitter.

Well, one detail I left out what that the modulator in that Harris High
Channel VHF transmitter operated on a much lower fixed IF frequency
(obviously matching the SAW filter) and was then mixed up to the final
target channel in a linear upvertor after VSB filtering.  So you didn't
have a channel specific SAW filter operating at, say ~200MHz (VHF
channel 10).  I forget the specific modulator / IF frequency but it was
well below VHF channel 2 at 54MHz and the HAM 6M band but high enough
for the required 4.5MHz VSB filtering, which requires at least double
(so somewhere well above 10MHz to avoid frequency ghosting in the
modulators and upverters).  That's not quite as bad for the SAW filters
of the day as what those final frequencies might imply.

> Fascinating.
> 
> Phil

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 978-7061 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
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