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PA2AGA > HDDIG 16.02.00 03:10l 196 Lines 7636 Bytes #-9578 (0) @ EU
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Subj: HamDigitalDigest 2000/46C
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From: pa2aga
To: hd_broadcast@pa2aga
Subject: HamDigitalDigest 2000/46C
X-BBS-Msg-Type: B
someday, but for now...) I am investigating the possibility of setting up
some sort of link over amateur radio. While I initially thought of something
similar to Kenwood's Sky Command, I realize that I don't need to transmit HF
from the remote site. I've a good enough transmit setup here (Force 12 C4S
at 56 feet). I was thinking about just installing a computer controlled
receiver at the remote site and then transmitting the audio back to my QTH
over UHF. One possibility would be to use two UHF links - one over slow
speed (1200 baud) packet to provide control of the receiver and another to
transmit the analog audio (with appropriate ID insertion, etc). Another
option would be to use a single high speed packet link that digitizes the
receive audio and transmits that over packet. What kind of data rate would I
need for usable audio, especially with a weak HF signal (remember if the
audio is real strong / clear to begin with I can probably copy it from my
home QTH)? Would 19.2K baud do it? Assuming 19.2K baud would do it, what
kind of TNC and UHF radios are required? Is 19.2K packet equipment
available? Where? How much? How can I get started? Would an analog audio
link and 1200 baud control packet be less expensive?
I planning on developing my own software for this project. I've got a pretty
good handle on the receiver control / packet communications stuff, but
haven't much experience digitizing (should be easy), and compressing (the
tricky part) the audio. I know it's doable (i.e. RealAudio and MP3); is
there a good resource for rolling my own?
If I go with a digitzed audio approach, some of the newer radios use DSP
processing. Is it possible to get the digital output of these radios before
it is converted to analog and use that?
I haven't checked out the link, but it would be about 16 miles over
relatively flat terrain with no major obstacles. I have a 56 ft tower at
this end and will have something similar at the remote site. I pretty sure
440 would make it. If I go with two UHF links, I'd have to use another band
for the other link. Would 902 MHz or 1.2 GHz make it with small fixed
antennas up 40 -50 feet at each end.
I'm pretty sure that I shouldn't use 2 meters for the control link (even
though the remote site isn't transmitting HF, it would be transmitting the
received audio), but could I use legally use 2 meters to transmit the analog
audio from the HF receiver?
Is there any merit to this idea? It intrigues me as a fun project.
73,
Mark
>.
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Date: Mon, 14 Feb 2000 16:26:10 -0500
From: "Mark Erbaugh" <mark@nospam.microenh.com>
Subject: remote HF radio control over packet
Gary Coffman <ke4zv@bellsouth.net> wrote in message
news:uDWoOALRB8TyGBprQc5rl96QaAVC@4ax.com...
> Last question first, undoubtedly analog audio would be cheaper because
> you can use nearly any off the shelf pair of FM radios to do it. Higher
speed
> digital requires a purpose designed RFmodem. That'll run you about $600
> for each end (modem, transverter, and antenna) for a 56 kb system (WA4DSY
> RF modem available from Paccomm). But a pair of $50 surplus Micor or Exec
II
> FM radios could handle the analog audio.
Thanks for the info on the 56kb stuff. Cheap is definitely better.
> Now if you decide that you *want* to use a digital link anyway, there are
> number of codecs you might consider. There are codecs which can produce
> decent sounding speech with only a 4800 baud link. That could be carried
over
> an ordinary FM radio like those mentioned above using HAPN modems. There
> are other codecs which offer higher fidelity at the cost of greater bps,
ie there
> are voice codecs which operate at 9.6 kb, 19.2 kb, etc. One thing you
should
> keep in mind, however, is that these codecs depend on a clean voice signal
> input for their compression algorithms to work correctly. A weak noisy
signal
> won't work very well because it doesn't fit the model of the human voice
that
> the codec compression schemes use.
Good point. I hadn't considered that compression depends on clean signals.
> To properly reproduce the weak noisy signals you want to convey, you need
> something that is more on the order of straight CD quality sampling.
That's
> going to require about 22 kilo*bytes* a second, or 172 kb. You can use a
> compression scheme to crunch that down so it should fit a 56 kb bitstream.
> (8 kilobytes per second sampling might be sufficient for "communications
> quality" audio, and that'll fit a 64 kb bit stream without compression.)
> There's no reason to packetize this data for a simple point to point link.
The
> packet overhead doesn't buy you anything because you don't need packet
> routing, and you don't want packets with a few errors to be discarded and
> retried because that'll leave gaps in the realtime audio stream. Better to
> just accept a few bit errors, which will slightly add to the noise of the
original
> signal. So you just drive the RF modem directly with the bitstream
generated
> by the A/D sampler and compression engine you choose. A sound card works
> as the digitizer. You'll want to use a compression scheme that's tolerant
of
> a few bit errors. Some compression techniques fall apart if they encounter
> bit errors. You don't want that.
More good points.
73,
Mark
>.
------------------------------
Date: Mon, 14 Feb 2000 17:25:30 +0100
From: "Thomas Weiland" <thomas_weiland@yahoo.de>
Subject: suche für meine icom blackbox
Hallo,
> ich hab den pcr1000 von icom gibts da auch andere soft um den zu betreiben
> oder kann mir jemand seine mch -files schicken?
ja, es gibt andere Software. Ich habe mich damit nämlich schon mal befasst.
Leider habe ich den Link nicht mehr. Aber in einer Suchmaschine solltest Du
mit den Suchworten "Icom +PCR1000 +Software" schon was finden.
Gruß
Thomas
>.
------------------------------
Date: Mon, 14 Feb 2000 19:01:36 GMT
From: ko4qc@mindspring.com (Joel)
Subject: Ten-Tec Pegasus
Any comments,pro or con,concerning the Ten-Tec Pegasus PC radio are
requested.
>.
------------------------------
Date: Mon, 14 Feb 2000 13:04:14 -0800
From: Rob Dover <rdover@bclc.stamp.out.spam.com>
Subject: X1J4 question
Greetings.
I have a number of X1J4 nodes that I look after which all exhibit the
same intermittant problem. Periodically the radio port will lock in
transmit. The hardware watchdog timer kicks in and shuts the transmitter
down but the TNC is still locked up. This isn't critical as long as
there is another TNC in the node stack which allows me access through
the serial side so I can send a reset. If the TNC is standalone, a site
visit is required. Does anyone else see this or know if there is a fix?
And before you comment UZI, yes I have tried to get Flexnode but they do
not seem to want to respond to the e-mail listed on their web site! If
there is another way to get an evaluation copy please let me know.
Thanks 73 -Rob-
Reply to: is spamblocked. Remove the obvious to reply by e-mail
>.
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End of Ham-Digital Digest V2000 #46
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