VO-52 has been a very loud and easy to work satellite since the recovery and change to the Dutch Transponder. The CW beacon is very loud and you can usually find an image of it elsewhere in the transponder passband.
If you are running full doppler control, you have probably noticed that your settings (uplink calibration) have to be changed from pass to pass. The beacon frequency is not constant either so I suspect that the frequency source is not very stable. Stability is usually a function of temperature so it would appear that the temperature inside the satellite is changing due to internal electronics and/or effects from the sun. This would be something that the control team would be aware of. Any feedback from them would be appreciated.
I do not recall that the India Transponder had a similar problem but maybe someone else could comment on that. If it did drift, it was only one or two hundred Hz. Initially the difference between the India and Dutch Transponder was about 2KHz. Now it seems to vary plus or minus 500 Hz or so. Maybe some others can comment on this.
73, John K8YSE