The quality of the transmitted signal, using any mode, declines over a period of time - typically within about two days of continuous operation.
For example: a single-tone (JT65-HF) digital mode TX signal will,
immediately after booting the radio, will be sound (on an external
receiver), look on the SmartSDR panadapter and appear on a spectrum
analyzer as expected. The signal will degrade to something
noisier and broader in, at most, two days of continuous operation and much faster when used in a complex (e.g. multiple panadapters) manner.
Receiving seems unaffected.
Rebooting the radio (and restarting SmartSDR as a precaution) restores the system to nominal condition, but eventually degrades again.
Relatively high, as I normally leave radios on for months (collecting spots, etc.) and I will invariably have to reboot the 6700 before attempting transmitting, taking several minutes.
I also normally run my 6700 24 hours per day. I currently operate almost 100% JT65 and JT9 using WSJT-X. I do not listen to my audio and normally have just one panadapter open. A screen shot of a normal JT65 transmission on the panadapter is as follows:
Although it is difficult to see (click on the image to enlarge), the first "artifact" is about 60 dB down from this signal peak. After two or three days of continuous operation, the "artifact" moves up and is only about 20 dB down with a significant broadening as you mentioned. The only way to clear this anomaly up is to re-boot the 6700. I will do a screen capture of the anomaly the next time that it occurs and post both so that a comparison is possible. If I had not monitored the transmitted signal and attempted to operate under these conditions, I probably would have been spewing "garbage" all over the band. This particular screen shot is from 10 meter operation, but I have seen the effect on other bands as well.
Hi Tim - I'm curious if this is the same situation that is shown by Rob Sherwood's spectral purity measurements of a FLEX-6700 and posted in a PDF on the following page link, below his positive remarks about using the 6700 during a 160m contest: http://www.dj0ip.de/transceivers/sherwood-xcvr-tests/flex-6x00/ I know in other fora it has come up as one of the poorer performers in that regard. (not trolling, just concerned.) Thanks!
BTW, Rob's comments were based on very old (as of now) SmartSDR software. It has gotten much better with v1.2.1.
Also his comments about having to use two computers is not a global truth, but is specific to his setup. Using a single quad core or beter PC with twp sufficiently large (> 23") wide screen monitors works just fine for contesting.
Here is a picture of the distorted signal while transmitting a tune signal from WSJT-X:
And the good signal after stopping and starting the DAX channel:
And a wider picture to show the scale (both pictures above are at the same vertical scale):