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 >> https://lists.sourceforge.net/lists/listinfo/wsjt-devel > _______________________________________________ > wsjt-devel mailing list > wsjt-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wsjt-devel
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