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<mailto: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<mailto:wsjt-devel@lists.sourceforge.net> https://lists.sourceforge.net/lists/listinfo/wsjt-devel
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