Subject: [NEXTEL-1] Question about use of digital

From: [email-masked]
Date: Thu, 29 May 2003 12:04:46 -0400

-------- Original Message --------
From: "Keith Gilbertson" <[email-masked]>
Subject: Re: Question about use of digital.

Sorry Dave but I have to agree with most of the point raised by Mr.
Tong.
I can't agree that digital is the answer for anyone who is looking for
the
most economical means of point to point communication with the highest
performance (sensitivity, selectivity, intermodulation etc.)  today.

Digital works when it works.  I've not seen any results of performance
in
the fringe of P25 systems compared to analog.  Not sure how much useable
range is lost in digital vs analog.  If anyone has any data here I'd
love to
see it.

As a matter or economics, from my exposure to high end VHF radios, the
digital counterparts of the analog incumbents are 1.5 - 2 times more
expensive.  The cost of the digital radios is not that much higher but
no
one is willing to give away the technology at the same margin as analog
radios.  I think those leaders in the technology want (or need) to keep
the
price up to pay back their investments.  Analog technology is very
inexpensive to build.  My company quit making our own RF modules and we
now
purchase modules from a major land mobile manufacturer (Not the Blue Bat
Wing either).  These modules are integrated into my radio design with my
controller, Interface circuits and user panel.

Just to vent a little here.  I looked into the basics of P25 radios
around 5
years ago.  At that point the technology was several years old.  AS a
supplier, this "free" technology was going to require signing licenses
with
three companies of which one was going to cost $125K.  The latter of
which I
speak is the vocoder technology implemented in P25 radios.  For that
measly
sum you get software to implement the voice to digital conversion in
several
popular DSP engines.   Funny the vocoder company later came out with a
slightly different vocoder technology which might even be superior and
is
available in silicon (integrated circuit).  To my knowledge the P25
vocoder
technology is only implemented in DSP's.  This may be keeping  the cost
of
digital radios up.  Most inexpensive radios do not typically need the
processing speed of a DSP engine.  With the high speed comes more
expensive
high speed RAM, Flash and what have you.  In time this too may pass.

At the price of cheap ceramic filters at the 455Khz 2nd IF, DSP's are
much
more expensive to implement the required filtering to achieve the same
performance.  However IF you are stuck using a DSP then one would need
to
evaluate how much it could do to replace analog circuitry and equivalent
costs.

I am currently trying to determine if I need to develop a digital
solution
for my customers or continue to market our current dual mode analog
radio.
If my customers decide to go digital then I guess I will have no choice.
Currently price/performance is tending to keep the market in the analog
technology as they migrate to narrowband.  Again the primary need is
mobile
to base communications with ability to go mobile to mobile as well. 
Current
analog technology does all they need it to do.

As a supplier I guess the latest FCC mandate forcing all non-safety
license
holders to migrate to Narrowband (12.5KHz) by 2013 (amoung other
stipulations) would be a good thing.  I must protest in principle the
forcing of an industry to spend millions to replace good equipment with
new
equipment at faster than current attrition rates.  One only need look
behind
the mandate to see who benefits from such a ruling and it ain't the
radio
users.

WE may all experience the same situation when HD TV is the only allowed
standard and we haven't replaced our old analog sets.  However, I can
find
other means of entertainment.  If my business depended on it, I'd take a
little different view.

----- Original Message -----
From: "Jeff Tong" <[email-masked]>
Sent: Tuesday, May 27, 2003 3:25 PM
Subject: Re:  Question about use of digital.

> Dave;
> With all respect I'd like to pose some questions to you that have
concerned
> me for some time.
>
> ----- Original Message -----
> From: "Maples, Dave" <[email-masked]>
>
> All: It's a matter of economics, IMHO, as I have tried to say before:
>
> >1. It's easier and cheaper to manufacture a digital radio.
>
> Aren't all electronic components similar physically and won't most current
> pick and place pc board manufacturing equipments install analog I.C.'s and
> components  as well as digital I.C.'s and components.
>
> >>a. Beyond the points of conversion of the baseband signals, there are no
> longer an infinite number of levels to deal with, but rather only a
discrete
> set of states (a state can be a given amplitude, frequency, phase, etc.).
>
> Whats the difference between digitizing the 455Khz I.F. of an analog radio
> and what you are talking about? By that level of conversion in a reciever
> chain, the demod's alc's have pretty much leveled the signals. All the
> dynamic range variation is before A-D conversion anyway.   Don't you still
> have to provide a tuned front end with down conversion and filtering to
> obtain the desired baseband product without interferers and unwanted
signals
> to digitize?
>
> >The receiver components and software algorithm therefore only have to be
> able to distinguish that discrete set of states.  This reduces the need
for
> high-accuracy components in the receiver, thus reducing costs.
>
> I t seems to me that in order to recieve and successfully demodulate the
> current digital standards such as P25, which are sent and recieved
> asynchronously, that the demodulation meathematics have to be more
concerned
> with compensating for multipath, fading , and doppler  (amongst other
> things) than conventional analog transmission and reception. Doesn't this
> need to do more signal processing result in a requirement for more
> computational power within the radio itself?
> Isn't that why asynchronous digital radios need higher signal to noise
ratio
> signals  in order to successfully render a usable audio output, than
analog
> radios?
> >  It also reduces the need for manual adjustment of receiver stages after
> assembly.
> Current analog radios don't require manual tuning.
>   But I think the conversion to baseband is the real question.
>
> b. Item (a) also allows the parts count for a receiver to be reduced.
With
> IF-level DSP, there will be very little to NO need for discrete components
> in the radio (other than perhaps a first IF bandpass filter, audio output
> stage, speaker, microphone, PTT switch, and antenna cable / connector).
>
> > The actual "parts count" may actually be less in an analog radio given
the
> amount of components required to do the computational manipulation of a
> digital signal. It's just the packaging that is changed.
>
>
>  It's just not possible to do that level of construction in the analog
world
> AND have little or nothing to adjust when finished building.
>
> > Most newer analog radios do all their adjustment within the CPU and
> adjustment would be easier and cheaper using some sort of automated test
> equipment rather than techs and communications analyzers.  ( Sorry guys,
but
> thats how it is,)
>
> > Most of the high end analog radios I deal with digitize the signal after
> demodulation and handle all the audio on transmit and recieve digitally
now.
> There's just a lot less mathematics involved in the process verses a
> completely digital  system  from conversion of baseband I.F. through  to
> demodulation and audio amplification or modulation and upconversion to a
> baseband for transmit.
>
> 2. It's easier to have a family of radios with different feature sets in
the
> digital realm than in the analog realm, because adding features becomes a
> FLASH upgrade to memory.  I don't, for example, think we have even
scratched
> the surface of possibillities in the DSP world to date.
>
> > This
> 3. It's easier to transport signals from the mountaintops using digitized
> voice than it is to continue to construct special analog circuits for
this.
> The native transport method is digital today, and we convert to analog at
> both ends.  Why keep adding costs this way?  How hard is it today to get
> competent maintenance on an analog special circuit?  What do you think
that
> will look like in the future?
>
> These things (plus the ability to sell new features and rake in good
> margins) are the things that are going to drive the transition to digital
> modulation.  I don't think the train can be stopped or turned aside,
either.
>
> Just my opinions, of course.  All replies welcome.
>
> Dave Maples
>

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