What's going on here then?

Well,

You may remember I've been dabbling with the WSJT modes using meteor scatter and you also might remember that I have a FT-DX5000 with a SCU-17 rig interface.

I tried using the 5000 for 6M MS the other day and found widely swinging power out during transmit. I've done some simple tests today on the set up and with the radio in TX and using a PC based signal generator I see this power output vs. audio frequency:

Now, I would expect this to be reasonably fat across the audio spectrum - this is far from my expectations! This clearly explains why, on TX in JT6M, the power out of the radio varies so much as the tones change.

It's not much better on RX when receiving noise on the band:

Again, I would expect this to be flat.

So, is there something strange going on in the radio itself in the audio circuits or is this the symptom of a spectacularly pants sound card in the SCU-17?

I wonder.....

More on this will follow.

** UPDATE **

I've drawn some conclusions here:

http://g0mgx.blogspot.co.uk/2015/05/whats-going-on-here-then-part-ii.html

Odd, egh?

Left a jumper on the desk today:

Local conditions....