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PA2AGA > HDDIG 17.07.00 16:39l 171 Lines 6777 Bytes #-9389 (0) @ EU
BID : HD_2000_191C
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Subj: HamDigitalDigest 2000/191C
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Sent: 000717/0136Z @:PI8HGL.#ZH1.NLD.EU #:61855 [Den Haag] FBB $:HD_2000_191C
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Mon, 17 Jul 00 01:31:00 MET
Message-Id: <hd_2000_191C>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
measure its impulse response. Then generate a transmit filter that
has the time reversed impulse response of the receiver filter. This
is especially useful when dealing with digital modulation because many
times the transmit filter can be realized in a ROM that can be
addressed by relatively few bits.
An interesting case in point is the IS-95 CDMA cellular system. Here,
the modulation is QPSK at the pseudo-noise chip level. The receiver
matched filter is mechanized at IF using a surface acoustic wave
filter with essentially flat top and very steep skirts, but yet quite
realizeable, repeatable and cheap. We characterized the impulse
response of this filter and generated the time reverse of this in the
transmitter using an oversampled read only memory. I.e., the filter's
response at many samples per baud are precomputed and stored in a
memory. The memory is addressed by a shift register containing a
number of sequential bits and by a counter that indicates whether you
are on the 1st, 2nd, or .... the Nth sample of that chip. The ROM
outputs an 8 bit (e.g.) word and this is converted to analog in a DAC.
Oh, I should mention that the rest of the matched filter in the spread
spectrum receiver is simply an accumulator that adds up all the
sampled SAW filter outputs that occur during the time of one data
symbol.
Sometimes bassackwards thinking works pretty well.
As for whether CW is binary or ternary (or whateverary), I'll just say
that it is what it is and what we call it is only useful in how it
helps us design better systems. For my way of thinking about it, I
find that the binary definition leads me to an optimum receiver a
little quicker. Maybe ternary works better for you.
Klein, WT6G
------------------------------
Date: Sat, 15 Jul 2000 17:52:28 GMT
From: Brian Kelly <kelly@dvol.com>
Subject: Forget HF & CW - Think Digital
On Thu, 13 Jul 2000 07:08:50 -0500, "Steve Sampson"
<ssampson@usa-site.net> wrote:
>"Brian Kelly" <kelly@dvol.com> wrote
>>
>> If it's that simple why haven't you or TAPR or some other digigeek(s)
>> DONE it??
>
>TAPR hasn't done it because they tried to build their own radio
>and failed (I understand Dewayne is going to try and salvage it,
>but his company has never built anything before). Many others
>(Spread Spectrum is really big out here in the real world) are
>deploying networks every day. Almost every University now has
>a wireless LAN, and long range point to point links (long range
>being 12 kilometres). I have put one up myself to see what all
>they hype is about. My home is wireless from the ISDN modem
>on, and a 8 km point to point link is working great. This stuff is
>as cheap as ethernet was in the beginning days, and I suspect that
>10base networks are cost prohibitive (labor plus parts) today.
>
>I see the use of gigabit fiber backbones, and wireless (roam-able)
>LANS as the future for medium and large companies. Laptops seem
>to be the norm, and not many desk computers can be found anymore
>in executive offices.
>
>They want to roam. ("Oh give me a home...").
>
I have a brother/CEO who is one of those who is never home and he
seems to be able to dial into Compuserve from anywhere on the planet.
Last week it was e-mail from Beijing and Hong Kong, no sweat. What's
any of it have to do with Ham Radio??
>
>> We had exactly that 15-20 years ago. Almost the entire East Coast was
>> blanketed with a readily-accesible ham vhf/uhf digital network and it
>> worked like a champ.
>
>Not true. "Worked like a champ" is completely false advertising. It was
>a nightmare.
>
That's absolute nonsense. I was there, I saw it, I used it, and I'm
gonna use it.
>
>The whole system died when it reached saturation.
>
Clue: During the last dx contest season it had constipation again here
and there. As in enough current Y2K users to do that once more.
Distinctly NOT dead. But screaming for 9600.
>
>Hams ran out of money to go to the next level, and nodes started
>coming down.
>
Most quit doing radio swaps, chat and e-mail on the radio and popped
for home computers and landline connections which obviously do those
far better. And in the process those transient users got the hell
outta OUR way.
>
>They won't be back. Learn to love APRS, because that
>*is* packet radio today.
>
I don't see the point to APRS myself but to each their own. You're
*completely* out in left field wrt to APRS being the only surviving 2m
Packet game. We have a helluva lot of packet in these parts carrying
the dx spots, being a bunch more packet traffic than whizzy new-wave
APRS runs, not even close. There are enough spots nodes up & running
via the HF contesting and dxing crowd to cover around ten states.
Right now.
>
>Wideband analog schemes are obsolete, and the FCC is giving big
>hints that Hams need to adopt something more substantial. If all we
>are going to do is CW, SSB, and FSK in the microwave bands, then
>they have a surprise for us, and it's called an auction.
>
Ya missed FM and they couldn't pawn twenty meters off on anybody for
free if they tried so I'm not horribly upset by the latest FCC
grumblings.
>
>But the FCC hints with one hand, and fails to enable with the other.
>There have been many proposals for rule changes to allow more
>technical modulation schemes, but the FCC has blocked them at
>every opportunity. Only recently have they begun to change their
>tune.
>
>I think the cheap vocoder is going to revolutionize Ham radio. We
>will have reason to leave analog methods for completely digital
>solutions, using modern (available) modulation methods.
>
. . . beep beep . . ?
>
w3rv
------------------------------
Date: Sat, 15 Jul 2000 13:42:29 -0500
From: "Steve Sampson" <ssampson@usa-site.net>
Subject: Forget HF & CW - Think Digital
"Brian Kelly" wrote
>
> I have a brother/CEO who is one of those who is never home and he
> seems to be able to dial into Compuserve from anywhere on the planet.
> Last week it was e-mail from Beijing and Hong Kong, no sweat. What's
> any of it have to do with Ham Radio??
I don't know?? Why do you bring it up?
> Clue: During the last dx contest season it had constipation again here
> and there. As in enough current Y2K users to do that once more.
> Distinctly NOT dead. But screaming for 9600.
Oh goody, DX cluster! Yum Yum...
> Most quit doing radio swaps, chat and e-mail on the radio and popped
> for home computers and landline connections which obviously do those
> far better. And in the process those transient users got the hell
To be continued in digest: hd_2000_191D
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