Tuesday, October 31, 2017

A Little Audio

This is not "high" tech, but finding a solution took a little while.  The AA6E station, for today's purpose, consists of a Windows 10 PC (the Intel NUC), a FlexRadio Flex-6500, and two compact bookshelf loudspeakers.

The usual solution these days for audio setups is to use "powered speakers" for computer audio and possibly for transceiver audio.  But these have problems for me:
  1. For HF Amateur Radio, powered speakers generally are too sensitive to the RF environment and require ferrite suppression.
  2. Powered speakers generally only offer a few feet of cabling between speakers, which is fine for your desktop but not so good if you want to fill a room with audio.
  3. It's awkward to support independent speaker systems for the radio and for the computer.  They take up space, and they make for lots of cabling.
  4. Higher end powered speakers do a fair job with audio fidelity, but not as good as good conventional speaker components.
In my case, I'm starting with these nice inherited speakers (thanks to son Eric!) and I'm working backward.  You need a basic audio amplifier.  These aren't as common as they once were.  There are some interesting very cheap "Class D" switching amplifiers.  I tried one (the Lepy LP-2020A).  It did OK with the audio, but it lacked multiple inputs, and, worse, it produced very strong VHF emissions that wiped out 2 meters for me, even after adding chokes.

I sat on this project for a while, until I ran across a family of simple audio amplifiers by AudioSource.  They offer the AMP100VS, which gives 50 W per stereo channel.  That's more than I need, but you only live once.  Amazon has it for $110.

The system (diagrammed above) provides several unexpected features:
  • Auto On-Off.  The amp can be set to power on whenever an audio input signal appears.  There's about a 3 second delay for turn-on.  Power shuts down after 5 minutes with no input. This feature saves us having to provide switched AC power. In the standby mode, the amp draws 8 W from the line, compared to about 17 W for power on idling. You can argue whether that's a worthwhile saving! (Power can alternatively be controlled by a 12 V DC signal.)
  • Audio Interrupt.  This amp is apparently designed for the commercial public address market, where you might have background music that is occasionally interrupted by "Attention K-Mart Shoppers".  In my case, it is convenient to allow the radio's output to interrupt the computer's output, so I don't need an audio switch or mixer.
This is low tech, as promised, but it sounds fine and solves a knotty little problem.

Monday, October 02, 2017

A little NUC on my desk


When my 8 year old computer, home built with a Core i7-920 processor, began freezing up randomly, a new generation computer was in order.  The only application I normally use that takes significant computing power is FlexRadio's Smart SDR for Windows that needs to control the Flex 6500 SDR transceiver.

Recent SSDR versions are much less demanding than they used to be, so maybe I could make do with a "downgrade" to a Core i5 system.  Intel processors divide broadly between "i3" (dual core), "i5 (dual core, with hypterthreading yielding 4 threads), and "i7" (quad core, 8 threads).  Of course, the later chips ("generations") in each category will be a lot more powerful than the earlier ones.

After some debate, I selected a Intel NUC (next unit of computing) tiny computer configuration in "kit" form.  You need to supply your own SSD (solid state disk) or hard drive and your own DDR4 RAM.  The NUC is available in quite a few versions, but I ended up with the Intel BOXNUC7I5BNH kit, which is a "7th generation" i5 box with room to add a 2.5 in. SSD or HD.

I installed a Samsung 960 EVO Series - 250GB PCIe NVMe internal SSD, which uses the (relatively) new M.2 interface and leaves the 2.5 in. bay free for the future.  Two 4GB DDR4 RAM chips complete the kit.  Assembly is trivial, if you're at all familiar with computer innards. Installing Windows 10 Home from a USB memory stick was quick. Transferring data and software from the old system was simplified by staging files onto an external USB hard drive.

After all that, we have a very fast little computer.  The Passmark benchmark comes out at 3,644, which is roughly 60% of the score of the old i7-920 with GT640 graphics -- but with half the cores and only on-chip graphics.  The NUC is happy to drive my two HDMI displays, although the second display requires a Thunderbolt/USB-C to HDMI adapter cable.  SSD I/O performance is blazing!

But what about Flex SSDR?  That's the primary app for this computer -- when I'm not using the Flex Maestro controller.  Here are some results:

Panadaptors |
window size |
CPU utilization |
Network Mb/s
1
1/4
15%
2.4
1
full
20%
2.7
4
full
33%
6.0
4*
full
44%
9.4
4*
1/4
36%
7.2
(* maximize spectrum frames per second and waterfall rate)

The worst case CPU load (44% across the 4 i5 threads) seems to be a comfortable number.  The Flex 6700, on the other hand, with its maximum 8 panadapters might have trouble, if that's your operating style.

The NUC handles the required load with capacity to spare.  It uses much less power to run and has only about 1/60 the volume of the old system, fitting easily on the desk.

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