Frequency and timing errors

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G8JNJ
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Joined: 2008/05/19 - 12:32
Frequency and timing errors

Hi All,

I've been WSPRing for a few weeks now and have noticed a couple of common problems, as a result of comparing my logged signal aginst that of others nearby.

Sometimes I find that I'm not hearing (or being heard by other stations) when I should be. This is generally due to cumulative TX / RX frequency errors putting stations outside the 200Hz or so 'window' for WSPR operation. As an example I've been running on 20m for the past few days. I've had a few reports during the evenings but not much during daytime, when different stations are operating. As an experiment I tried varying my tranceiver frequency by -100Hz and then for a further session by +100Hz above my normal operating frequency. By doing this I started spotting and getting spotted by others.

I'm not saying that my frequency accuracy is any better than anyone else, I'm simply pointing out that frequency errors cause problems. This situation becomes worse if you tend to set your transmit frequency at the upper or lower limits of the window.

So please take some time to see if your average transmit frequency as logged by others is close to your WSPR transmit frequency, if not try making some corrections.

The second problem I find is PC clock drift and timing errors. Once the PC clock is more than a few seconds out, WSPR does not work.

I use Dimension 4 software to sync my PC clock to an internet time server every 15 minutes. During the day it is not unusual to find corrections of 2 or more seconds occuring. If the internet link is down then errors of 20 to 30 seconds during 24 hr period are possible. I use this software on three different PC's and they all exhibit similar errors.

Take a look at any compensation you may be adding for timing errors. Can you see the edges of other peoples transmissions starting or ending either side of the 2 minute slot boundries on the WSPR display ? If so you may have a problem.