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

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

Hi Paul,

Thanks to you, too.  Your comment on160m confirms my suspicions.  

’m going to take a careful look at the ALC and see if I’ve got that right.

Does anyone know how to entirely disable ALC on a FT5K?  Or, is this just a dumb idea?

73, Ed
W1KOK	

I am surprised and pleased that this question has generated so much response.  

I’ve been puzzled by this all winter as I struggled with running 5 to 10 watts on Top Band.  

That said, it’s amazing what can be done, including numerous EU, AF, SA and VK/ZL contacts, with so little power on 160m!




> Start-of- transmission power spikes will almost certainly occur on any radio which is using traditional alc to control output power. Spike severity is directly linked to the amount of gain reduction the alc is giving. For example,  a 100w rig with power output reduced to 5w using a power control which operates via the alc system can be almost relied upon to produce 100w spikes at start of transmission. No brainer.
> 
> The best way to avoid spikes in any rig using FT8 is to carefully adjust audio drive level in the software until desired power output is obtained without the rig applying any alc at all. In this way overall system gain is only sufficient to produce desired power and no more - so spikes are eliminated and you get a cleaner transmission.
> 
> That said, I say again that I can exactly  reproduce this problem at will on 160m where my antenna system clearly puts large voltage onto the cable between the pc and the rig. My interface uses industrial quality logic isolators for civ and ptt together with audio isolation transformers and dozens of ferrite rings on tuner - rig - pc cables.  RFI still gets through and kills the usb connection on 160m.  To cure this I will rethink the 160m antenna which I suspect is the easiest way.
> 
> Regards Paul G3NJV
>