[App_rpt-users] usbfobs

David McGough kb4fxc at inttek.net
Wed Jul 6 19:21:33 EDT 2016


My experiences with USB are different than yours. USB works very well, is
very cost effective, reliable and adapters are available from multiple
sources, including building your own, if you want to. There -really- is 
not going to be any shortage of this hardware anytime soon.

There are LOTS of concerns with using on-board GPIO, I2S, etc. That list
has been hashed and rehashed, no need to repeat it.  One thing I will
mention is that the closer you get to the computer (e.g. a RPi2/3 in this
case), the more you've got to worry with RF and ESD causing crashes or
destroying hardware: been there and done that!  With USB, you can use
off-the-shelf accessories to minimize RF and ESD woes. Here are USB
isolators I use regularly:


As a simple, REAL example, here is an APRS system I installed in 2011. It
lives 280 meters up a tower. The same hardware still runs today, 24/7, for
more than 5 years. It uses a DMK URI and the computer is a pcengines ALIX
board. The DSP MODEM software was upgraded to direwolf a couple years ago.


And, the system current "uptime:"

root at WWAY890:~# uptime
19:18:56 up 423 days,  4:48, load average: 0.15, 0.14, 0.14

Here it is on aprs.fi:


It doesn't get much simpler or more reliable than that. And, yes, there is
yet another severe thunderstorm hovering over that tower site as I type

....Just dig in a get something on-the-air and have fun TODAY. Don't worry 
about tomorrow, this hardware is so cheap it's not like you're making a 
long term amortized investment.

73, David KB4FXC

On Thu, 7 Jul 2016, Steve Wright wrote:

> On 07/07/16 09:13, Kevin Custer wrote:
> > [...]  We have spent thousands of dollars on equipment - a lot of it 
> > very high end for reliability.  Take the Dell servers for Node 2135 
> > and other major hubs for instance.  These were built prior to the 
> > Raspberry Pi 2 and 3. [...]  This used to cost thousands of dollars 
> > per location, now it's hundreds.  I have several ACC controllers and 
> > link stacks now excess to my needs, so believe me, I know. [....]   
> > I've personally deployed dozens of $200 - 300 computers and $75 radio 
> > adapters.  It's a hell of a lot cheaper than the alternatives, and 
> > what it used to cost.
>   Stings a bit doesn't it - looking back at obsolete installed gear, but 
> that is the price of being an early adopter/constructor.  :) I've got 
> shed-loads of WISP stuff I give away to clubs..
> >   Building repeaters and maintaining them is a responsibility that 
> > costs money.  app_rpt has cut those costs drastically.  Get over 
> > spending money on deploying a system - it's not going to be cheap if 
> > you want reliability.  I speak from experience - this isn't just some 
> > wild guess. 
>   You have done well to form a progressive group and do that, but you 
> wouldn't do it with a $4k Andrew 23GHz link, you do it with some $89 
> Ubiq link.  Sure you have to babysit the Ubiq, and the Andrews lives 
> forever, but that's what it is.  Script up some monitoring for the Ubiq, 
> bond some critical links for failover..
>   The problem is - the signalling I/O is built into the audio driver, 
> mandating and vendor-locking both.  That has never been 
> ham-radio-suitable and was the whole reason for an open-source approach 
> to begin with.  It was a clever trick to modify the CM119, and 
> economical too, but in view of the new hardware(RPI3 etc), it is 
> unreliable(USB), difficult(soldering), and slow(3 devices max).
>   The I2S bus is demonstrably reliable in consumer gear - unproven in an 
> RF environment.  USB is demonstrably UNreliable, in consumer gear AND in 
> an RF environment.  I run high-horsepower digimodes, and any USB device 
> will reset at least daily.
>   If I was in a position to write a voting DSP channel driver (or hack 
> the XIPAR driver) for six I2S audio devices on an RPI3 with separate 
> signalling, I would go and do that. One box, six channels, voting, site 
> I/O - under US$100 - I'd put my name on that..
> S
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