--- In Repeater-Builder@yahoogroups.com, [EMAIL PROTECTED] wrote:
>
> Hello all from Adam Kb2Jpd
>
> One point some may be missing is that we should not continue to tie up
> precious spectrum just so we can continue to use old repeater
> technology.
>
> We have a mandate for expiermentation.
>
> in the past, we went from AM to widebabd FM to narrowband FM and
spacing.
>
> We need to set aside frequency pairs to try out real-world
> implementations of digital radio. We should set aside several pairs
> for expiermental use for a limited time frame. should the
> implementation be popular among ham radio operators, they should apply
> for a conventional pair or moved to a digital repeater segment.
>
Well, there is a problem with mixing analog and digital modes in a
coverage area.
I'm retired from Western Union, and then I worked in Mobile Radio
Conmmunications, as age 50 was really too early to retire without
Social Security!
While the digital people will normally see putting more signals in the
space normally used by a analog signal, the spectrum noise created by
the digital signals will raise the RF noise floor by quite a bit, say
20db, causing too much noise to operate some analog repeater receivers,
leaving the analog repeaters virtually useless!!
With digital alternating square waves the leading and trailing edges
of the pulses have lots of high frequency harmonic content that is
not needed, and the tops and bottoms carry low frequency elements of
bandwidth. This is the kind of wideband alternating DC signals that
are used to test wideband amplifiers.
When these signals are sent down a line as DC pulses, the capacitance,
inductance and resistance charectoristics of the line cause bad
sawtooth like distortion, as in the signals used in early transmitter
/ printer circuits. Because of this, the printers had to be
adjustable as to where on the wave to operate, or use a Polar Relay
at the Printer end! Then they "modernized" and converted to Analog
(audio) / DC conversion, as in "Modems"!!!
You probably will never find such a textbook, but check "integrated"
and "differentiated" Digital DC pulse waveforms and see what kind of
noise is created!! I had to take courses in this stuff to do some of
the work I did!! I also worked in Terrestrial Microwave, and
customers putting some of this over Microwave circuits sure caused
problems!!
With the currant move to Digital TV, this has had drastic effect on
area Analog repeaters!!
Dick, W7TIO
