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<div class="moz-cite-prefix">On 1/28/2013 6:10 PM, Bill Vodall
wrote:<br>
</div>
<blockquote
cite="mid:CAPSBm52UFULapAM1xcSbN8Tys12o5uK0vmoUHGz0a0D-6Poqtw@mail.gmail.com"
type="cite"><br>
<pre wrap="">
</pre>
<pre wrap="">
Have you seen and/or had a chance to review the ARSrepeaters soundcard
interface.
<a class="moz-txt-link-freetext" href="http://arsrepeaters.com/USB_EchoLink_Adapter.html">http://arsrepeaters.com/USB_EchoLink_Adapter.html</a>
The small form factor and prefabricated interfaces for HT's make it
appear to be a very handy interface for mobile or portable
operations... While marketed for Echolink, they now have an
adjustable transmitter hang time which allows it to work on packet and
other digital modes.
73
Bill, WA7NWP
PS. I'm looking forward to testing this new interface at 2400 baud
and 4800 baud. It might be the missing key that enables stepping
forward with faster packet speeds using all the new soundcard modem
software packages.
</pre>
</blockquote>
<br>
<br>
There's nothing special about this device. It's not really an
"interface" in the usual sense of providing isolated RXA-TXA-PTT-COR
between a radio and a computer. It appears to be just a generic
USB audio dongle, probably based on a C-Media 108 chip or something
similar, with a VOX keyer scheme added. <br>
<br>
The web site is playing up that it "<font style="font-size: 14px;">utilizes
a high-performance 7.1 channel soundcard"</font> A lot of good
that will do on a single-channel audio application. Obviously
such a device with audio response flat out to 15-20K will not be the
limiting factor for 2400 or 4800 baud operation; it's going to be
the audio response of the radio you attach it to. <br>
<br>
The lack of audio isolation transformers is going to be a real
headache in mobile applications. Having common grounds between
radio gear and laptops (especially when powered off of DC-DC
converters) is a disaster. Ground loops yield all kinds of buzzy,
hummy hashy noises from the computers' internal power converters,
mixed with alternator whine from the car's DC 12VDC system. You
gotta have transformer-isolated audio and opto-isolated PTT so there
are no common metallic grounds between the laptop and the radio.
(This is also a glaring deficiency of many models of the much-hyped
"Rig Blaster".)<br>
<br>
Speaking of opto-isolation, there seems to be no CD/COR input for a
squelch line FROM the radio. (The offering of "Plug-N-Play cable
harnesses for hand-helds that connect to the speaker/mic jacks is a
giveaway that there is no squelch/COR input.) Without a positive "RF
channel busy" indication, Echolink operation is very second-rate.
The usual approach of using audio VOX detection within Echolink to
determine when the radio channel is clear (so that the Internet
party can keyup and start talking) is very clumsy. It can't tell
the difference between a closed squelch and quiet pauses in the
mobile radio user's speech, unless you set the VOX detection for an
excessively long wait time. <br>
<br>
This then makes it nearly impossible for an Internet user to break
into an ongoing fast-fire conversation. The turnaround delays in
Echolink are bad enough with the second or two each way Internet
propagation delay. Gratuitously adding another 2-3 seconds of delay
from the VOX system makes fast-break voice operation from the
Internet side virtually impossible. <br>
<br>
[This same issue arises with Echolink on repeaters, if the Echolink
setup is at a user's house rather than bridged across the repeater
TX and TX at the site. Without a hardwired connection to the
repeater receiver's COR line, Echolink's internal VOX gets fooled by
long silent carrier tails on the repeater output channel, unless you
set the VOX for an excessively long delay.]<br>
<br>
<br>
Then don't get me going on how the advertiser is trying to get
people to use crappy handhelds as base stations, when their receiver
front ends typically overload and suffer massive amounts of
intermodulation when attached to base station antennas. <br>
<br>
<br>
Further, how fast-on-the-draw is the transmit VOX keying, and how
fast does it drop out on unkey? Slow on keyup could lead to
horrendously long TXD values on packet., Long hangs on unkey are
essential on Echolink/voice operation so that the TX doesn't pop
on-off-on-off-on-off on every syllable in voice operation. But
long TX->RX turnaround delays on packet will often cause
ACKs/NAKs from the other station to be missed. Any tone keyed
interface needs two unkey delay value settings, one really short for
fast packet/AMTOR turnarounds, and a much longer one (on the order
of 1-2 seconds at least) for voice. <br>
<br>
In my homebrew design, I purposely got the TX-up delay, and the
unkey delay down to less than 5 milliseconds, and then have a switch
to add a much larger capacitor in parallel to lengthen the delay for
voice operation. <br>
<br>
<br>
<hr size="2" width="100%"><br>
--<br>
<br>
Stephen H. Smith wa8lmf (at) aol.com <br>
Skype: WA8LMF<br>
Home Page: <a class="moz-txt-link-freetext" href="http://wa8lmf.net">http://wa8lmf.net</a><br>
<br>
High Performance Sound Systems for Soundcard Apps<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/ham/imic.htm">http://wa8lmf.net/ham/imic.htm</a><br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/ham/uca202.htm">http://wa8lmf.net/ham/uca202.htm</a><br>
<br>
Vista & Win7 Install Issues for UI-View and Precision Mapping<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/aprs/UIview_Notes.htm#VistaWin7">http://wa8lmf.net/aprs/UIview_Notes.htm#VistaWin7</a><br>
<br>
"APRS 101" Explanation of APRS Path Selection & Digipeating <br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/DigiPaths">http://wa8lmf.net/DigiPaths</a> <br>
<br>
<br>
<br>
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