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ZL3AI > APRDIG 03.11.06 02:47l 277 Lines 10758 Bytes #999 (0) @ WW
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To : APRDIG@WW
Message: 7
Date: Tue, 31 Oct 2006 11:49:41 -0800
From: "Stephen H. Smith" <wa8lmf2_at_aol.com>
Subject: Re: [aprssig] desirable laptop computer features?
rodpadmore_at_ns.sympatico.ca wrote:
>What are the most important features found in an APRS
>friendly computer available in today's market place? Does anyone have
>other suggestions such as brand and model?
>Thanks to anyone that has an informed opinion on these questions. 73
>de Rod.
1) Real serial ports!!! This is critical to avoid the hassle with
USB-to-serial converter "dongles". which have endless compatibility
problems with some programs and operating systems.
This is even more of an issue when using soundcard-based programs that use
the handshaking lines of the serial port independently of the data flow in
unorthodox ways, to key transmitter PTT lines, send CW and RTTY-FSK at odd
rates like 45.45 baud, take in receiver squelch status, etc.
Unfortunately, virtually NO consumer mass-market laptops have serial ports
anymore. You will have to go to higher-priced business and specialty-market
machines to get real ports. (This is why I just paid USD $1500 for a new
Panasonic Toughbook CF-51 15" CoreDuo laptop through a specialty reseller,
instead of buying a similar consumer market machine for under $1000.)
[Actually the Toughbook has other attributes that make it desirable for
APRS. It's designed to work reliably at high temps and to withstand dust,
shock and vibration such as in a car or at field day. Large numbers of
Toughbooks are used as mobile terminals in police cars, delivery trucks,
etc. ]
An alternative to the messy USB-to-serial devices is to buy (rather pricy)
PCMCIA cards with real serial ports on them. (Assuming the laptop still
has "classic" PCMCIA card slots!) On many machines these are being dropped
in favor of multiple types of slots for flash memory cards.)
2) Decent sound system if you intend to use soundcard-based soft TNCs like
the AGW Packet Engine or MixW. Most laptops now lack a stereo line-level
audio input. They only have a monophonic mic input. This has two real
disadvantages. First the mic input is almost always far too sensitive for
the audio levels coming out of a radio speaker or packet/aux jack, forcing
you to kluge resistor attenuator networks in the cable to keep the mic
input from overloading. Second, you throw away the ability of programs
like the AGW Packet Engine to create a dual-port TNC that can support TWO
radios at once. ( With a STEREO input, you can actually connect one radio
and soundcard interface to the left channel, and a second one to the right
channel at the same time.)
3) Other things being equal, a machine whose chassis power input from it's
supplied "power brick" is 12-14VDC rather than the 19-20 VDC that is most
common. This gives you the option to operate directly from 12 VDC power
setups in cars, at field day, etc without DC-DC upconverters or worse
12DC-to-110VAC inverters with their attendent inefficiencies. This was
an unexpected pleasant surprise and bonus when I got the Toughbook.
4) PS/2 keyboard/mouse port. These are beginning to disappear also in
the face of the everything-USB juggernaut. Even if you don't use it for an
external keyboard, the PS/2 port has traditionally been a handy source of
+5 VDC for powering serial GPS devices, powering TinyTraks while being
programmed, charging cellphones, etc.
--
Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: 14400 [Think bottom of the 2M band]
Home Page: http://wa8lmf.com --OR-- http://wa8lmf.net
------------------------------
Message: 8
Date: Tue, 31 Oct 2006 11:53:45 -0800
From: <scott_at_opentrac.org>
Subject: RE: [aprssig] Re: *** TNC Test CD Update - Mirror Server Now
Available***
>As I explained on the web site (and in the readme file), I used CD audio
>tracks rather than regular CD-ROM data.WAV audio tracks to avoid the
>timing errors present in many motherboard-based sound systems on
>low-cost PCs.
But if the files were posted in .wav or .aiff format, people could burn
them to audio CD tracks using whatever they have available.
Scott
N1VG
------------------------------
Message: 9
Date: Tue, 31 Oct 2006 14:01:06 -0600
From: Gregg Wonderly <gregg_at_wonderly.org>
Subject: Re: [aprssig] *** TNC Test CD Update - Mirror Server Now
Available ***
Steve Huston wrote:
>On 10/31/2006 12:20 PM, Gregg Wonderly wrote:
>
>>>Might be easier to have the .wav or .aiff files posted separately for
>>>download.
>>
>>I missed the dual mode part of the image discussion. I was thinking
>>that there would be mp3s on the disk to play as files.
>
>I don't remember enough about the MP3 algorithm, except that it's
>definitely a lossy compression - I don't know how that would work for an
>audio data stream, might mess things up enough to skew the results.
>
>Though, FLAC is lossless, but even less things can play that.
Yes, man my mind is numb or something, I should go sit in a corner. Okay,
a lossless audio recording would be necessary, not MP3. There are several
to select from. The files could be on there in a lossless format as audio
files to click on, in addition to the disk being multi-mode.
Gregg Wonderly
W5GGW
------------------------------
Message: 10
Date: Tue, 31 Oct 2006 14:04:39 -0600
From: Gregg Wonderly <gregg_at_wonderly.org>
Subject: Re: [aprssig] Re: *** TNC Test CD Update - Mirror Server Now
Available ***
Stephen H. Smith wrote:
>As I explained on the web site (and in the readme file), I used CD audio
>tracks rather than regular CD-ROM data.WAV audio tracks to avoid the
>timing errors present in many motherboard-based sound systems on
>low-cost PCs.
Stephen, I'm sorry that I so hurriedly tried to "fix" a problem that wasn't
really a problem. It's now clear to me why you made all the choices. You
did good, and again I'm sorry for being so thick headed.
Gregg Wonderly
W5GGW
------------------------------
Message: 11
Date: Tue, 31 Oct 2006 15:11:03 -0500
From: KA8VIT <ka8vit_at_ka8vit.com>
Subject: Re: [aprssig] *** TNC Test CD Update - Mirror Server Now
Available ***
I have used MP3 recordings of packet, SSTV, PSK31 and Hellschrieber and
they decode just fine...
They were recorded at 8000 Hz, 8-bit, mono.
73
Bill KA8VIT
------------------------------
Message: 12
Date: Tue, 31 Oct 2006 12:12:00 -0800
From: Dale Blanchard <wa7ixk_at_earthlink.net>
Subject: Re: [aprssig] desirable laptop computer features?
Stephen H. Smith wrote:
>etc.
>
>Unfortunately, virtually NO consumer mass-market laptops have serial
>ports anymore. You will have to go to higher-priced business and
>specialty-market machines to get real ports. (This is why I just paid
>USD $1500 for a new Panasonic Toughbook CF-51 15" CoreDuo laptop through
>a specialty reseller, instead of buying a similar consumer market
>machine for under $1000.)
Fry's still sells some with serial ports.
It is there own brand ( Great Quality )
They had some for $300.00 that I missed out on.
I have one I got for $500.00, been on sale for less since.
It has 4 usb ports, one serial port, one Parrelel port.
CD writer. 40 gb drive.
No A drive tho.
When Fry's open a new store they have specials in all stores.
I use two of the 99 dollar special linux loaded tower type in my shack
along with the laptop.
The lap top is used for controlling my radios.
Dale
------------------------------
Message: 13
Date: Tue, 31 Oct 2006 14:44:30 -0600
From: Gregg Wonderly <gregg_at_wonderly.org>
Subject: Re: [aprssig] desirable laptop computer features?
Dale Blanchard wrote:
>Stephen H. Smith wrote:
>
>>etc.
>>Unfortunately, virtually NO consumer mass-market laptops have serial
>>ports anymore. You will have to go to higher-priced business and
>>specialty-market machines to get real ports. (This is why I just paid
>>USD $1500 for a new Panasonic Toughbook CF-51 15" CoreDuo laptop
>>through a specialty reseller, instead of buying a similar consumer
>>market machine for under $1000.)
>
>Fry's still sells some with serial ports.
I don't really think this is as big of an issue as some make it out to be.
It really depends on the software that you are using, which USB->Serial
adapter you get, and then how you can configure that adapter based on the
manufactures software support for "setting" the comm port. The keyspan
devices, as has been mentioned here before, seem to be the best choice.
Stephen, I think you've discussed using the keyspan devices before. Can
you share more about your need for a real port?
Gregg Wonderly
W5GGW
------------------------------
Message: 14
Date: Tue, 31 Oct 2006 12:45:59 -0800
From: "Stephen H. Smith" <wa8lmf2_at_aol.com>
Subject: Re: [aprssig] *** TNC Test CD Update - Mirror Server Now
Available ***
ka8vit_at_ka8vit.com wrote:
>I have used MP3 recordings of packet, SSTV, PSK31 and Hellschrieber
>and they decode just fine...
>
>They were recorded at 8000 Hz, 8-bit, mono.
>
>73
>
>Bill KA8VIT
They may worked "just fine" on your particular setup.
However, an 8 Khz sample rate on a waveform running as high as 2200 Hz
means under 4 samples of the waveform per cycle. This makes the
zero-crossing time (i.e. phase) of the waveform highly ambiguous. Further
the MP3 coding process further "mangles" the original phase integrity.
(Human hearing is quite insensitive to phase errors in signals but many
electronic devices are VERY sensitive to phase!) For demodulators that
use zero-crossing detectors or pulse counters (rather than analog PLL
systems or tuned audio filter channels) the exact time of zero crossing of
the waveform is critical.
I was striving to create a high-quality standard reference signal set for
critically comparing the performance of various TNC designs. A crude
waveform re-constructed from less than 4 points per cycle represents
considerable phase jitter that might bias test results for some types of
TNCs. I recorded the original signals at the high quality sampling rate of
44.1KHz. This had the added advantage that no re-sampling or sample rate
conversion (with it's phase integrity issues) was required to make the
audio CD since commercial audio CDs are ALWAYS done at 44.1KHz.
I then choose to release the signal set as CD audio tracks rather than as
.WAV or .AIFF files to discourage their playback through crappy unstable PC
motherboard sound systems (see my other post on this issue) that would make
the findings by various parties running tests less than consistent.
--
Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: 14400 [Think bottom of the 2M band]
Home Page: http://wa8lmf.com --OR-- http://wa8lmf.net
------------------------------
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