[App_rpt-users] USB Sucks Yay! The Sequel!

Doug Bade kd8b at thebades.net
Thu Jan 12 10:49:08 EST 2012


I would have to say that the issue discussed with USB drops/pops/clicks  is
NOT an issue that "has to be".  I use USB sound interfaces (CM108) for my
D-Star repeater(s) running dstarrepeatercontroller software. One of my
system production tests is to generate a dtmf character from my dstar
portable and listen to the recovered dtmf on the far end. If you are
familiar with AMBE and dtmf issues, the AMBE codec handles dtmf as a command
string and sends it through as a command sequence to be regenerated on the
far end. If there is *any* breaks in the data stream encoded through the usb
sound fob, it will be manifested in a break in the dtmf recovered
presentation on the far end. In many setups along the way, this was a
problem, however it *CAN* be tweaked and time slicing corrected to allow no
drops. I have a production system that does not have drops for sustained
PTT's up to/in excess of 3 minutes of a sustained dtmf character that are
clean for that time frame. The data rate of Dstar would seem to exceed any
analog presentation that Allstar may build.

 

                So. It CAN work, it may be that some tweaking of Allstar
and/or the linux code may need to happen, but to say with certainty that
sound fob repeaters are not production quality is unfair at least in my
world. As I can demonstrate otherwise.. uptimes in excess of months are
typical and no USB hangs or dropson both of my dstar GMSK repeaters 

 

                I would also suggest that certain issues may be present in
USB sound fob systems of Allstar that have a problem I/We detected in the
dstar world of implementation that may have to do with some issues in usb
sound implementation. All CM1xx chipsets were designed for telephony and as
such have a sidetone function built in. There is an internal audio loop from
the mic side to the headset side. It is designed to provide comfort audio to
your ear while you are talking but in our repeater world provides a direct,
low level direct analog loop between rx audio and the transmitter. Depending
on series resistance vales and coupling, these levels can become an issue,
it definitely is to GMSK modem data of our dstar implementations.. What
happens is you have 2 loops out of time, one direct and one through the
computer dsp. This is problematical in things that are sensitive to phase
shift and can result in cancelleation etc. A quick and dirty solution is to
use 2 sound fobs for repeating. as one for tx and one for rx. The circuits
are isolated and no dual audio path.. Using 2 DMK URI's might be cost
prohibitive for the most part. but sound fobs can replace maybe one end or
the other on TX or RX. I am not sure how the Allstar implementation would
handle that but it could be done,as  my USB URI implementations for Allstar
are working quite well. 

 

                Where I am going with all this is "glitchiness" of the
systems may be resolvable issues as we HAVE resolutions in dstar. so flat
out bad rapping sound fobs is  maybe not really appropriate..

A significant issue and problem using FXO/FXS cards is you need to deal with
line supervision issues and ptt/cor which are not part of the FXO FXS
"normal" implementation. It can be done but I did some work on a system for
work where we tried to use a pair of Multitech FXO/FXS units to link 2
radios and it was a lot more cumbersome than was worth.. We ended up opting
for Multitech's  E&M versions as audio and signaling are not directly linked
and E&M signaling translates to PTT and COR a lot easier. CTCSS is still
going to be an issue as that would be out-of-band audio for Telco class
FXO/FXS/E&M hardware.

 

E&M is used for microwave analog radio linking because it foots the bill
very well.. but it does not carry CTCSS either way directly. 

 

Doug

KD8B

 

 

 

From: app_rpt-users-bounces at ohnosec.org
[mailto:app_rpt-users-bounces at ohnosec.org] On Behalf Of Steve Gladden
Sent: Thursday, January 12, 2012 10:05 AM
To: app_rpt-users at ohnosec.org
Subject: [App_rpt-users] USB Sucks Yay! The Sequel!

 

 My understanding is that you can use *any* digium FXO/FXS (and possibly a
less expensive clone) card it will work well and skrew the piece of crap USB
interfaces.
I further understand/think that it *MUST* be a two port card with both FXO
and FXS present is this true?
Or can you somehow get away with a single port FXO or FXS card?

Single port cards are cost comparative to a ready made DRI USB which is
--->>>>>*NOT*<<<<<--- production remote repeater site quality/capable and
good only for testing experimenting etc.
Even if such a card is TWICE the price of a DMK URI..  This is the way to go
for a production system..
Which is *ALL* that I would ever run at a site..
And home I'll still maybe d*** around with USB interfaces which truly suck
with app_rpt in ALL of my testing I've done in 3 years.

Am I clear in this understanding?

 

Any suggestions on cards/Interfaces that work well?

Any that don't?? stick with Digium?

I should have asked this bundle of questions 2 years ago *sigh*

 

I realize newer boards will not have PCI slots..  
"USB sucks + is unrealiable"

-->as I have been assured both through my own testing and the developers of
app_rpt.

If you tell me you have a perfectly working sytem I'll have you do *my test*
sit & listen locally at the system to the TX on continuously with PL encode
and you *will* hear the audio pops & interruptions in the trasnmitted audio
that I am confident are present in ALL usb installed systems :-).. but has
been proven liveable for most.

If you absolutely have to go with USB for whatever reason beagleboard etc..
small low power controller
then it's time for a different controller if you require production/site
performance & reliability.

 

 

 


Michigan Broadband Systems
Connecting Your Business!
 


+1 734.527.7150 Direct
+1 248.327.4389 Fax
steve at michiganbroadband.com
www.michiganbroadband.com
 

  _____  

From: app_rpt-users-bounces at ohnosec.org [app_rpt-users-bounces at ohnosec.org]
On Behalf Of Bradley Haney [kc9gqr at gmail.com]
Sent: Tuesday, January 10, 2012 2:24 PM
To: app_rpt-users at ohnosec.org
Subject: Re: [App_rpt-users] App_rpt-users Digest, Vol 35, Issue 20

I thought i would get the server set up and then get the USB to radio
interface.. what is the best and cheap one to buy.  I don't want to roll my
own  as if everything works out well we will move the unit to the repeater
site in the Spring. But for now  i was going to put it on a simplex node.
I just didn't want to buy the adapter then stuck with it with no way to
configure the server..    for the time being i will hook it to the ft2600
yaesu ..

 

any thoughts on usb to radio interface?

On Tue, Jan 10, 2012 at 11:00 AM, <app_rpt-users-request at ohnosec.org> wrote:

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Today's Topics:

  1. Registartion failure -To those who assisted.... (DougH)


----------------------------------------------------------------------

Message: 1
Date: Tue, 10 Jan 2012 12:00:58 -0000
From: "DougH" <specialq.que at ntlworld.com>
To: <App_rpt-users at ohnosec.org>
Subject: [App_rpt-users] Registartion failure -To those who
       assisted....
Message-ID: <A4EDABEE3C824FBEB8F9CDFAE083E47C at DougLaptop2>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
       reply-type=original

....in my 'Registration Failure' question. Thank you.....situation has been
resolved due to a combination of your inputs.

Help much appreciated,

Regards,
Doug - MM0BJA



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