[wsjt-devel] Does the FT8 signal spike at the beginning of each transmission?

[Ed S. <w1...@co...>]

Hi Frank,

Many thanks for your input.

For you and for others who may read this thread, here is some additional information.

I think there are several problems working together here.  As you said, I think the FTdx-5000 is doing something nasty.  Even when I limit the power setting of the rig I can see that it is peaking way above what I set for maximum power on the initial spike.

I also agree with you that RFI must be part of the problem because the effect is much more noticeable on the low bands and with the 160m dipole.  I can run full power on 17m with another dipole cut for that band which is even closer to the equipment without any problem.

I am in my winter home in California at the moment and the station in question is being run remotely in Vermont, so until I return home n a month no changes to the setup are possible.  I have about as much ferrite protection installed as can be done (learned from years of experience, HI).  I need to think about the opto-isolators…thanks for that idea.  The Mac Mini doesn’t seem capable of being grounded although I have given some thought over the years to trying to put it inside some kind of Faraday cage.

While it is extremely tedious, I can overcome the problem manually by watching until transmission starts at a low power setting (e.g. -42 dB) on wsjt and then advancing the power slider (to more like -15 dB).  Generally this works but sometimes the audio will still crash, even using this technique.  But, alas, as I said…extremely tedious!

It would be so nice if I could just grab the CAT line from wsjt.  I could write a little routine to wait a few seconds after the start of transmission and then increase the power with my own CAT connection, then drop it back down and give the CAT line back to wsjt.  But I suspect that is impossible.

73, Ed
W1KOK	


> Some rigs, even high-end rigs including the FTdx5000, exhibit a spike on
> initial transmit. I noticed it mostly with the amp. The power would surge
> briefly, and then return to the dial value.
> 
> I suspect the combination of the surge and a bit of RFI is causing the
> problem. I suggest an opto-isolator on both ends of your CAT cable. They
> are available for RS-232 and USB. That, plus some ferrites along the run
> should help with the problem. Also, if you're using a desktop, try running
> several ground straps to the case of the computer. Consumer-grade computers
> aren't very resistant to RFI, and there is no bonding between the pieces of
> sheet metal.
> 
> 73,
> Frank
> KF6E