[aprssig] New APRS HF/VHF Igate/Webserver Now In Service At WA8LMF

Mon Jan 28 23:36:57 EST 2013

 From the looks of it the sound card is likely one of these or their 
variants, soldered in place as a daughter board

http://www.ebay.ca/itm/External-USB-2-0-to-3D-Audio-Sound-Card-Adapter-7-1-ch-/110419668623?pt=US_Sound_Card_External&hash=item19b5866e8f

p

On 1/28/2013 11:20 PM, Stephen H. Smith wrote:
> On 1/28/2013 6:10 PM, Bill Vodall wrote:
>>
>> Have you seen and/or had a chance to review the ARSrepeaters soundcard
>> interface.
>>
>>    http://arsrepeaters.com/USB_EchoLink_Adapter.html
>>
>> 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.
>>
>
>
> 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.
>
> The web site is playing up that it "utilizes a high-performance 
> 7.1 channel soundcard"   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.
>
> 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".)
>
> 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.
>
> 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.
>
> [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.]
>
>
> 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.
>
>
> 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.
>
> 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.
>
>
> ------------------------------------------------------------------------
>
> --
>
> Stephen H. Smith    wa8lmf (at) aol.com
> Skype:        WA8LMF
> Home Page: http://wa8lmf.net
>
> High Performance Sound Systems for Soundcard Apps
> http://wa8lmf.net/ham/imic.htm
> http://wa8lmf.net/ham/uca202.htm
>
> Vista & Win7 Install Issues for UI-View and Precision Mapping
> http://wa8lmf.net/aprs/UIview_Notes.htm#VistaWin7
>
> "APRS 101"  Explanation of APRS Path Selection & Digipeating
> http://wa8lmf.net/DigiPaths
>
>
>
>
>
> _______________________________________________
> aprssig mailing list
> aprssig at tapr.org
> http://www.tapr.org/mailman/listinfo/aprssig

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.tapr.org/pipermail/aprssig_lists.tapr.org/attachments/20130128/725d1565/attachment.html>