Hi Paul,

Good info (and similar to my own line of thinking in the response I just sent 
on ALC Overshoot) but I’d recommend one minor change: 

Your statement “The best way to avoid spikes in any rig using FT8...” - I’d be 
cautious with the “any rig” generalization.  Some of the popular radios on the 
market with a closed loop power system like the Elecraft K-line and KX-line 
will actually “power hunt” if the ALC meter is not showing 3-4 bars of activity 
on the ALC meter.  The first 4 bars of the ALC meter on the K/KX-line radios 
function like a vu meter and not necessarily indicate ALC action.  The radio 
itself may actually overmodulate the signal in order to get the power output 
set by the power output control and cause a transmitted signal to be quite 
poor.  I was able to test this using my K3 and KX3 into a dummy load and 
viewing the signal output with a spectrum analyzer and the term for the signal 
produced with “0” bars of “ALC” showing was “icky” at best (very technical, I 
know :) ).  

Just a word of caution for anyone following this thread.  

73,

Jim S. 
N2ADV 

> On Apr 12, 2019, at 2:06 PM, Paul Randall <paulfrand...@hotmail.com> wrote:
> 
> 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
> 
> Sent from my Samsung Galaxy smartphone.
> 
> 
> -------- Original message --------
> From: Bill Barrett <w2pky...@gmail.com>
> Date: 12/04/2019 18:11 (GMT+00:00)
> To: fr...@fkirschner.net, WSJT software development 
> <wsjt-devel@lists.sourceforge.net>
> Subject: Re: [wsjt-devel] Does the FT8 signal spike at the beginning of each 
> transmission?
> 
> From W8JI.com, maybe 5000 has similar adjustments. If the IF Transmit Gain 
> was too high the 1000 would exhibit huge power spikes on key down or pressing 
> the mike PTT button.
> 
> Transmit Gain Menus
> 
> The FT-1000 MK V  has hidden transmit gain menus. They are accessed by 
> pushing and holding FAST and LOCK while turning the POWER switch on. Both of 
> my MK V's  and every MK V serviced here has had the TX IF gain set too high. 
> This causes first character clicks on CW and spits and splatter on SSB.  Here 
> is how to correct the IF gain to prevent ALC clipping on leading edges of CW 
> and voice:
> 
> Press and hold FAST and LOCK before and during initial POWER on.
> 
> Press FAST and ENT at the same time. You are now in the MENU's and the 
> display should say "0-1 GrPI-cH".
> 
> Turn the VRF/MEM CH counter-clockwise to 9-2. The display should say "t iF - 
> GA in" This is the transmit IF gain menu.
> 
> Turn the SUB VFO knob clockwise one position to  " t iF - 018". This is the 
> 1.8MHz transmit IF gain.
> 
> Press the ALC/COMP meter selector until the bar graph says "ALC".  Set RF PWR 
> knob to full power.
> 
> With the radio on CW and a 50 ohm dummy load connected, close the key and 
> adjust the MAIN VFO-A knob until the ALC display is about 75-85% of full 
> scale on the illuminated bar marked "ALC".
> 
> Press the next band button (3.5), make sure the radio is still  on CW, and 
> turn the SUB VFO-B knob clockwise one band to "t iF - 035".
> 
> Again adjust MAIN VFO-A until ALC is at 75-85% of full scale.
> 
> Repeat this process through all bands.
> 
> Most radios I have tested require a setting of 2 to 4 on TX IF gain, with 3 
> being the most common setting.
> 
> This change will reduce SSB bandwidth and distortion. It will also reduce 
> keyclicks and annoying thumps on the leading edge of each Morse character.
> 
>  Hope this helps;
> 
> Bill W2PKY
> 
> 
>> On Fri, Apr 12, 2019 at 12:38 PM Frank Kirschner <frank.kirsch...@gmail.com> 
>> wrote:
>> 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
>> _______________________________________________
>> wsjt-devel mailing list
>> wsjt-devel@lists.sourceforge.net
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