Transmit Latency
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Posted Friday, January 1, 2010 11:24 AM
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I understand the concept of latency when applied to receiving. However, I know there is a certain amount of latency while transmitting in CW as when I use the MON function the short latency makes it impossible to key so I use the monitor in the keyer. However, I intend to use a linear amplifier in the near future and the latency can be an advantage by allowing the changeover relays to completely operate before the RF appears. This prevents hot switching of the relays and makes them last much longer and does not present a transient high SWR to the transceiver. The changeover time is only on the order of 20 ms or so. How much is the latency time from pressing the key to when RF appears? Can it be changed by changing sample rates and buffer sizes without screwing up the receive function?
Post #2127
Posted Wednesday, March 10, 2010 7:16 AM
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I began to experience problems such as yours and also delays when changing frequency using the mouse in 50 Hz steps.  Using CW above 30 WPM became difficult also.  I remember reading a post where it said to trim down your PC by uninstalling all programs not used by Flex radio.  In my case I uninstalled the HP update feature which I found out would search frequently and now use the manual means to do so.  Microsoft updates were put on manual along with my AVG antivirus by using manual scans.  Since the QUAD 4 computer is only used for Flex operations, the Microsoft Office features, media programs for photos and videos among many more useless software programs were taken off.  I do need the internet however which is used when logging since I enjoy seeing the stations photo he may have on QRZ by subscribing.  The HP computer is now very fast with never a glitch and my settings are 512 buffer, 96,000 bandwidth and in safe mode 1.  A separatre computer is used for general bill paying, e-mail and browsing.  Ooops, have to run since I hear a VK station on 20 metres.

We suffer from kleptomania and sometimes have to take something for it.
Post #2331
Posted Friday, March 19, 2010 12:48 AM
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If you look back to the SDR-1000 archives, you'll find a lot of discussion of the latency. The simple explanation is there is a lot of math churning in powersdr. It's not really necessary to strip your PC down to steering wheel and tires. <img src="http://forums.flex-radio.com/Skins/Classic/Images/EmotIcons/Wink.gif" width=20 height=20> I'm running a Xeon 3.0 GHz, 2Gigs of RAM, SDR-1000, & FA-66. I'm not sure that you can even buy anything that slow today. I can run the Kitchen sink and it works fine. For starters is XP Pro SP3, PowerSDR, Ham Radio Deluxe, DM-780, Internet Explorer, Google Earth, and some pieces of MS Office or Open Office. I use two 19" Monitors split vertically, and bunches of windows.

The latency doesn't really change that much. If the PC can't keep up, you'll hear blank spots. Latency is reduced by reducing the amount data churning, ie sample rate and buffer sizes. There's another benefit to smaller: The narrowest bandwidths can't be attained at 192K. I usually run 48K sample rate and 2k buffer. That reduces the latency, but I don't use the MON for CW anyway. In something like CQWW CW running 30-40 WPM, you can crank the bandwidth down to 25-100, and work 150 stations in one pass from 7.0 to 7.050 ish. You sure can't do that with any other transceiver. Even the spurs you learn ignore or use SR. When you hear more, you discover that you're being heard more. I've worked the planet on 60W CW and 20W Digi. Needless to say, my SDR-1000 will follow me to the grave.

After 55 years as a ham, I have a couple of rooms full of gear. The only thing that gets used regularly on HF is the SDR-1000. The other stuff is for nostaligia.

Cheers!<img src="http://forums.flex-radio.com/Skins/Classic/Images/EmotIcons/Smile.gif" width=20 height=20>

Byron L. Armstrong

www.e-therapist.net or w8syd.com

w8syd@e-therapist.net

Post #2401
Posted Monday, May 9, 2011 7:06 AM
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Yes, I did go somewhat overboard by uninstalling a few programs but our regular household PC takes care of video/photo operations and bill payments.  You are correct about never going back to regular transceivers after using Flex Radio.  I also have a Flex 1000SDR besides my Flex 5000A-V/U which am keeping just for nostalgic reasons but it works fine with an older PC and XP.  My ICOM756, Yaesu FT847 and Kenwood rigs are boxed up, either for selling or a donataion to a worthy school or club in the area.  Never dreamed I would have a station that is a pleasure to sit down to and work CW on 20 Metres while listening at the same time for openings on another band with the RX2 built-in receiver.  There are still things with the V/U unit that needs software fixes but it functions OK to run an amplifier on 144 MHz and once a week have a schedule 110 miles distant on 144.210000 Mhz and am accurate within 2 Hz.

We suffer from kleptomania and sometimes have to take something for it.
Post #4305
Posted Monday, May 9, 2011 8:59 AM
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I suggest that youi don't rely on the latency of the audio to determine if your transmit relays are hot-switching or not.  If you are concerned about hot switching, go to the Antenna tab, and set the "Switch Relay with TR" delay setting to the delay your amp needs, like 20-35 milliesconds. 

You can also reduce or virtually eliminate the audio latency by changing the buffer sizes and sample rate.  The tradeoff is latency versus sharp filter skirts. 

Post #4306
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