RX and TX distortion with 5000A and iMac
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RX and TX distortion with 5000A and iMac Expand / Collapse
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Posted Friday, May 27, 2011 4:34 PM
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I just returned home two days ago from Dayton, where I had a new Flex 5000A delivered to my hotel. This afternoon was spent meticulously hooking everything up correctly as per the manual, following the instructions to the letter. (I am a first time Flex user). I used it with a recent Apple iMac 4GB core duo, under bootcamp running on Vista.

I then switched on, and everything fired up just fine, however....

With good Kenwood headphones plugged in, I hear horrible distortion/artifacts/pops/hash on receive.....sounds like sand being poured into my headphones. This noise can be viewed on the waterfall - bright yellow and orange right across the band, solid. However, this noise comes and goes. It seems to last several minutes, and then goes away leaving a nice quite band (how it should be)

When I get this noise, if I try to transmit, then this distortion is also very evident and is mirrored on my transmit audio. Sounds really horrible if I monitor myself through headphones. But after several minutes, when the RX noise clears away, and I quickly transmit - then I transmit a lovely clear signal. This also happens on CW.

My first reasoning was that I had set everything up in a temporary location, and that I was getting all this noise because I had not grounded the flex or the iMac computer. So, I moved everything into the shack, and hooked a good earth to the Flex, and also to the body of the computer. I also thought I would change my power supply, and hooked up the Flex to a car battery. Result ? the noise/hash is still there making it very unpleasant to listen to, and impossible to transmit.

Anyone have ideas ? it is not hash from a switch mode power supply, as I tried with a deep cycle battery, and it is not an earthing/RFI problem as I secured the earthing on my second attempt to both the Flex and the computer.

Oh.....when the noise is there, I tried changing the buffer size, and immediately the noise goes away, only to return again after about 10 or 15 seconds

Thanks and 73

John, ZS5J
Post #4365
Posted Saturday, May 28, 2011 11:01 AM
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Your last sentence tells it all.  You probably have long Deferred Procedure Calls (DPC) from some lousy driver on your computer.  It could be a WiFi, Bluetooth, 1394, USB, etc.  What happens is that all the drivers in your PC ask Windows for execution time.  Windows lines them all up, and executes them according to their priority.  In the meantime, Windows defers all of the other requests.  This works just fine, unless some of the drivers are waiting for something to happen before they release Windows to do the next procedure call.  Bluetooth and Wifi are notorious, but there are others.   While Windows is deferring procedure calls, anything with a continuous data stream like PowerSDR or live audio, will get interrupted.  When PSDR gets interrupted, it gets unsynchronized with itself.

Download a DPC checker.  DPC Latency Checker (free) from www.THESYSCON.de  is commonly used, and  LatencyMon from Respendence gives a lot of details on which driver or process is getting hung up.  If DPCLat shows DPC spikes over about 1000us, you have to track down the errant driver, and either disable it or update it.  A well-behaved system will have DPC latency under 300us.  One of Neal Campbell's super-tuned systems will get less than 30us.  (Neal can also tune your system remotely, if you're not interested).

In the meantime, there are workarounds that will let you use the Flex, at the cost of increased audio latency.  Safemode 1,2, or 3 in the Flex driver panel lets the Flex buffer more input data, to bridge over those pesky DPC's.  Lower Sample Rates and higher Audio buffers in the (Setup |Audio) tab, and  longer DSP buffers in the Setup | DSP tab do the same thing.  

Read the Flex Wiki for more info.  The Flex Yahoo group is another good source. 

Post #4368
Posted Saturday, May 28, 2011 1:51 PM
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James, many, many thanks for your informative and comprehensive reply. Your confidence in the source of the distortion, and your solution to the problem has given me renewed hope.

Yes, this distortion of ALL signals across the band is immediately cleared up, when I change the buffer size - regardless of what buffer size I change it to, the severe distortion clears up completely.....only to return between 10 and 30 seconds later. It really has become irritating, and signals become unreadable when this distortion happens.

I will follow your advice and get those pesky drivers updated or muted.

Many thanks again

73
John, ZS5J
Post #4369
Posted Saturday, May 28, 2011 1:58 PM
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John,

Yes check your DPCs, first turn off the wireless, the security to access points can cause everything to stop waiting for a response, this usually clears most of the errors up..









ZS5J (5/28/2011)
James, many, many thanks for your informative and comprehensive reply. Your confidence in the source of the distortion, and your solution to the problem has given me renewed hope.

Yes, this distortion of ALL signals across the band is immediately cleared up, when I change the buffer size - regardless of what buffer size I change it to, the severe distortion clears up completely.....only to return between 10 and 30 seconds later. It really has become irritating, and signals become unreadable when this distortion happens.

I will follow your advice and get those pesky drivers updated or muted.

Many thanks again

73
John, ZS5J


73,

Dudley

WA5QPZ
Post #4371
Posted Saturday, May 28, 2011 2:46 PM
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FEEDBACK:

James and Dudley

You were right on the money !!!! I downloaded and ran that app (thesyscon) that you told me about. When I ran the app, I saw on the graph that every 15 seconds or so, I would get a spike going up into the red - sometimes higher than 15000 us !!!

I disabled several of the drivers, and observed the graph again - no more spikes. I have now been listening to my Flex 5000A for around 20 minutes, with absolutely no distortion anymore. Fantastic !!!!

Many thanks again for the help. I am now a happy Flexer.

73

John, ZS5J
Post #4372
Posted Saturday, May 28, 2011 4:46 PM
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Glad it helped.  The good news is that there is a large body of Flex PSDR's out there, and a lot of support is available.  If you think that PSDR is touchy on DPC's, you should see what the live audio guys go through.  It's not the speed of the processor, it's the smoothness (low latency) of the data streams. 

Windows Indexing service is another one that constantly trips Flexers up.  It starts reading and writing to the disks, and all heck breaks loose.   

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