⇑TOP ANALYZE FTDX101 TRANSMIT SPECTRUM WITH BUILT IN DISPLAY

Fortunately, ZL3DW explains an undocumented feature in his book on page 187. The native spectrum scope will display the FTDX101D transmit output spectral purity. I used a 20 watt power setting for these tests, because it was about right to drive the linear amp to a reasonable level approaching its output, but not so high it was too much drive. Temporarily set the multifuncton knob to control LEVEL using the MENU. Transmit 20 watts CW and observe the spectrum display; adjust the LEVEL control so that the bright line representing the CW carrier just touches the upper line on the display. This works best with the S meter displays minimized and the spectrum display maximized, with as little waterfall as possible. Do not use MONO or you cannot see the ALC function because the right hand meter disappears. Consult the Yaesu manual which explains the display adjustments. Set the transmit band width to 50-3000. Set the transmitter for LSB on 80 meters. Set the SPAN for a 20 K wide display. That is ±10 KHz from the center carrier frequency. Any products to the right of the center frequency marker are in the UPPER side band and represent distortion products. Any products to the left of 3 KHz from the carrier are distortion products.

Each horizontal line in the grid represents 5 dB down from the peak main signal. Now switch to SSB and observe the spectral output. Any signal that is below the 6th line down is -30 dB from the main signal, considered passable performance on distortion products. That is your goal when adjusting all the various MIC gain, AMC, and PROCessing LEVELS.

Here are screen shots of the large monitor I use to display the FTDX101D small radio display. Note the dual Autek computing wattmeter, which shows 40 watts output, typical of what is used to drive a linear amplifier. (It is annoying that it is necessary to provide an external peak reading wattmeter to be able to monitor that function. The FTDX101D can only display one parameter at a time, using the imitation "analog meter" display, when it could have used the same display space to monitor ALL functions simultaneously using bar graphs with an optional peak hold function.) These display photos show the very best possible performance obtainable using the settings enumerated at the end of this article. Those settings are for ZERO deflection of the ALC meter, 10 dB of the COMP meter (COMP=100), and 10 dB deflection of the AMC meter (AMC=35), and mike gain of 20 or enough to result in the above conditions. EQ is ON, and COMPressor is ON. Using COMPression results in better IMD performance. Power for the photos is set to 40 watts PEP. The best IMD performance is on the order of -30 to -35 dB for a steady state voiced vowel. Note that the left photo (E) the IMD products apppear more than 4 KHz below (left of) the supressed carrier, and smaller spurs appear in the area to the right of the suppressed carrier, in the UPPER side band. Total span for both photo is 20 KHz, or 10 KHz on either side of the carrier. Click on a photo to enlarge it.

 

The photo on the left is steadily voicing "E", which results in more IMD products. The photo on the right is steadily voicing "O" which is more of a sine wave audio signal and results in comparatively less IMD than "E."

Now that you know how to use this function and calibrate it, I invite you to play with your AMC, MIKE gain, and COMPressor settings to evaluate the effects of changes.

⇑TOP IMPORTANCE OF AMC AND ALC WHEN USING FT8 VIA AN EXTERNAL SOUNDCARD INTERFACE

UPDATED 1/24/24 This discussion is not about digital modes, although it is relevant if you use a digital mode interface which enters the FTDX101 via the mike jack. TheFTDX101 has an internal USB sound card which is quite capable and I see no reason to use an external interface. That said, some attention to these settings and keeping the ALC meter at ZERO during ANY mode such as SSB or FT8 on the FTDX101 will result in fewer unwanted products in the transmitter spectrum.

Make sure to use "split mode" and "fake it" to minimize harmonic distortion when using digital modes with the FTDX101. Also, experiment in the proportioning of signal levels in the digital interface. Use the techniques recommended to observe distortion in voice modes presented here to evaluate your settings when using digital modes like FT8, for a clean signal. There is a rear panel jack for RTTY for an external modem which employs true FSK; it is the definitive method for a clean RTTY signal, and skips all the problems of using an audio modulation method (AFSK). I have not yet successfully set up RTTY using the internal USB connection.

Apparently serious issues exist with the internal sound card in the FTDX10, according to the link shown below. Some have given information on setting the level in the menus to a higher value so that the sound card does not run so high that it generates harmonics and distortion. Some have even taken to using an external digi sound card interface to clean up the distortion. People are seeing harmonic distortion of a single tone (tune mode), which suggests there is significant intermodulation distortion (IMD) as well in the FTDX10. This would lead you to believe that the source of the SSB distortion may lie outside the initial audio preamp stages and resides in the transmitter RF or ALC sections. In any event, I would strongly advise FT8 users owning FTDX101, FTDX10, FT710 or any other Yaesu gear employing AMC make certain absolutely no deflection on the ALC meter. Any deflection of ALC results in unacceptable distortion in the RF output. Whether there is anything that can be done to mitigate problems at lower levels remains to be determined by experiment.

https://groups.io/g/ftdx-10/topic/ft8_audio_harmonics/82436261

I have done extensive tests on my FTDX101D and was unable to duplicate the problems shown in the link below relating to the FTDX10. I deliberately selected a transmit spot in the lower 300 Hz region, turned "fake it" off, and even allowed some ALC meter motion. The built in spectrum display did not show significant distortion, under any condition I could devise. That's the good news for FTDX101D users. Here are my settings to get good control from the FT8 computer control screen. This seems to get audio drive for receive in a reasonable range, while also making transmit settings from the FT8 control panel in the computer not so touchy. Remember do not exceed 30 watts on any 100 watt radio to prevent over heating the final ammplifier. This is a continuous duty cycle mode like RTTY or AM.

FTDX101D SETTINGS FOR FT8 USING A USB CONNECTION TO THE INTERNAL SOUND CARD
• SELECT DATA-U AND THEN PRESS PRESET
• ADJUST RECEIVE BANDWIDTH TO 3 KHz IF NECESSARY
• AMC = 60
• POWER = 30 WATTS
• RPORT GAIN = 5
• DATA OUT LVL = 50
• TX BANDWIDTH = 100-2900

⇑TOP FIRST, AN EXPERIMENT

Since the AMC is always on, you must get that setting correct before setting the the mike gain level or COMPression.

Here is an experiment to learn what is going on with the AMC control, with a power setting of 20 watts. Set the displays to show COMP (really AMC because the compression is off) on the left and ALC on the right. Set the AMC level to 100 (as close to OFF as you can get.) Push the mike gain knob to switch off the processing. Slowly advance the MIC LEVEL starting at zero, while you watch the spectral display and ALC meter. At MIC GAIN = 0, you get no power output as observed on the external power meter.

Transmit a constant "aaaahhh" while advancing the MIC GAIN. First you will see the external power meter increase to about 8 watts average at a setting of 10 for MIC gain. No ALC action yet. The spectrum is tightly contained to the 3 KHz area to the left of the carrier marker.

Increasing above MIC gain of 10, note that ALC begins to rise, along with side products; focus on the area to the right of the carrier marker and notice the growth of distortion products. At MIC gain 13, the ALC quickly rises to the maximum suggested level or S9+5 dB. The distortion products also rapidly appear to the right of the carrier marker. They should be just below -35 dB or 4 lines up from the bottom. When stopping and starting the "aaaahhh" you will notice that the ALC meter kicks up to S9+20 dB and quickly falls to the normal range; the left COMP meter indicates AMC and also kicks up and falls to zero. This is a clear demonstration that the AMC and ALC circuits attack time is too slow to control overshoots which produce splatter. This happens even though the AMC is set to 100 or OFF. We have just proven that AMC cannot be defeated; possibly there is circuitry that couples some of the ALC signal into the AMC in an attempt to control the splatter resulting from slow attack time. The average reading power meter on the FTDX101D is about 5 watts for a 20 watt setting.

Advancing the MIC gain to 50 results in ALC reaching S9+30.

ZL3DW claims that even with the ALC driven well beyond its "normal" range, the distortion productes are still below -35 dB on a steady state signal such as a standard two tone test. This is stated on page 17 of the ZL3DW book. This is widely considered acceptable performance. This would not have been possible without the AMC feature. Those statements apply only to steady state inputs from the mike input.

Now stop any voicing and begin speaking normally, with words beginning with p, t, b, d, g, k. "Peter Piper picked a peck of pickled peppers." At a MIC gain of 50 and an AMC of 100, the left COMP meter (really AMC) will go full scale, over 20 dB of attempted compression, but the ALC meter will only peak just above the "normal" range. Observe that the spectral display shows products at about -40 dB spreading to ±8 KHz. While these are still below -30 dB, imagine passing that through an amplifier which has boosted your signal to a received strength of S9+40 dB. Your side products on "plosives" are S9 dB or more on side channels. An audio system with a fast attack time could have controlled this better. So we have to find a work around, to reduce complaints from neighboring channels.

The buckshot on adjacent channels will happen after a pause in speech and a restart, particularly with a speech "plosive" (p, t, k, b, d, g). A fast attack time will help suppress the overshoot resulting from these transients. A slow attack time will allow those transients to clip in the amplifier and result in splatter.

This reveals a fatal flaw in the testing procedures employed in transceiver distortion tests. They are all done using a two tone steady state signal, which allows the ALC, AMC, processing and other circuits to settle back from the uncontrolled peak of the initial audio containing a "plosive." Manufacturers and the ARRL test labs need to devise a test which checks for this very common and ignored transient response problem. It would prevent splatter and amplifier damage. This should be an essential component of the ARRL's "clean signal initiative."

My 1980 vintage Ten Tec Corsair looks great on a remote SDR with a spectral display through the exact same amplifier. But its transmit signal goes through an 8 pole crystal filter on the way to the final amplifer, and the internal ALC is extremely fast attack, with no overshoot. The FTDX101D transmit path is all SDR, no crystal filter on transmit path. Once again, modern SDR technology has to play "catch up" to thorough old school design.

ADJUSTMENT PROCEDURE WITH AMC ONLY: For a maximum punch signal, set the AMC to 100. Increase MIC gain to get an ALC deflection above the "normal" range, S9+20. Adjust AMC level down from 100 to get ALC near S7 with a steady state "aaaahhh" and note that average power has dropped about 10% from 11 watts to 10 watts. The scope shows little change in PEAK power or PEP. It does show reduction in flat topping without substantial loss of average power in the lower peaks. The COMP meter (really AMC) should stay at or below 10 dB for stead state, kicking into 20 dB at "five." My tests show -35 dB or better on the unwanted sideband products. This is with PROC LEVEL set to COMP and AMC RELEASE TIME set to FAST. This adjustment is stable for SSB with the processor OFF. I found a maximum setting of AMC of 55 was the end result. (This is NOT suitable for AM, more later.)

To experiment with better spectral purity at the expense of power output, change the setting of the AMC from 55 to lower numbers and watch the spectral display and ALC. At a setting of AMC=40, the ALC meter stops moving, the distortion products are below -40, and the RF power drops from average of 12 watts to 7 watts (60%). Of course, an amplifier can make up that loss.

BOTTOM LINE: The correct AMC setting lies somewhere between 55 and 40. With a setting of AMC=60, the ALC rides around the middle of its range or S5. This approaches the best compromise between adequate transmitter output and reasonable distortion control. For absolute best spectral purity, keep mic gain and AMC at levels that result in NO ALC deflection at all. Try to use the faster acting PROC level to regain as much of the punch as you can. This also seems to agree with the quoted Yaesu maximum recommended value of AMC=55 in various internet forums. My MIC gain was set to 20 with the XM-8500 mike.

⇑TOP WHAT ABOUT THE AM MODE?

There is little information on AM operation with the FTDX101. QST and other reviewers rarely mention AM performance. Here is a FTDX101 review from a hard core AMer. You may find the FTDX101 serves your purpose for casual AM operation. I personally do not know of any current "knob" transceiver which I would use for my primary AM station. I think such a thing is a mytical creature, like a Unicorn. But the Yaesu FTDX101 is capable of delivering a reasonable signal comparable to other available rigs. I also have a K7DYY Super Senior, a Viking II, and a DX-60 paired with an ICOM R8600, HQ-180, and an SB-303. Some of the SDRs currently available seem to put out good AM signals and have receivers good enough for daily use. The FTDX101 is designed for a purpose; AM is incidental, like all its contemporaries.

AMC definitely gets in the way of AM. Turn AMC=100. Watch the scope for 100% modulation and increase the MIC gain to get a proper amount of audio, higher than the 20-25 for SSB. A spectral display of the spoken letter "A" or like the Fonz used to say it, will show a well contained 6 KHz wide AM signal with acceptable distortion products. I would be very comfortable operating on 7295 on AM with this signal. ALC will kick up to S9+25 but ride around S9+10 dB with no modulation. AMC action as observed on the COMP meter should almost never move the needle. The POWER output will drop from 25 watts to as low as 12-15 watts on the POWER meter in the FTDX101 during modulation. An external true PEP reading power meter may not attain the normal theoretical four times the carrier level power indication, unless properly adjusted. My Autek WM-1 does show almost 4X power on peaks on speech modulation. The scope photos below show that the FTDX101 will attain 100% modulation on a steady tone or speech. Hammering the AMC circuit with more mike gain drive will only cause more carrier reduction, and may result in distortion, because the modulation can exceed 100% negative peaks. This type of modulation is the exact opposite of that employed in the DX-60 peak carrier control, where the carrier rests at a lower level, and jumps up during modulation, to reduce heating in the final or a subsequent amplifier. This effect is common in modern multimode HF transceivers.

These settings hold at any power level settings. I recommend an AMC setting of 100 for AM on the FTDX101 for fullest possible modulation. Its a fool's errand to attempt to use this obscure AMC circuit as a compressor on AM. If it were possible to connect an external audio processing chain, you would get much better results. I was unable to activate the rear audio input for AM or SSB mode from an external audio chain. I am still working on a possible connection of an external audio chain. If you are able to devise a solution to this problem, please let me know your solution.

If you drive excess audio on AM, the carrier reduces and harmonic distortion products appear at roughly 8 KHz from the carrier as observed on the FTDX101 spectrum scope (when correctly set to display transmit spectrum.) The ALC will also reduce the carrier on modulation peaks if you over drive the audio.

I have not experimented with using a negative DC voltage applied to the FTDX101D ALC input. Be certain that you do not exceed the maximum voltage specified in the Yaesu manual of -4 volts. Do not apply positive voltage. Damage can occur if you ignore these rules. Some other radios respond well to this measure to improve AM operation of a solid state transceiver. Some people use a high value series resistor in series with the feed to ALC, to reduce the current available; this possibly protects against transceiver damage by limiting current flow.

It is important that you experiment with the phasing of the wires from your mike for AM. Use the connection which produces maximum UPWARD peaks; all voices and mikes are different, and require adjustment, even when changing EQ settings. You can do this by inserting a short XLR extender cable. You can experiment with phasing connections by reversing pins 2 and 3 on one end. This way, you do not have to modify the HEIL cable or open the mike up to swap phase wires.

Since the compressor cannot be activated for AM mode, you will be using the EQ settings for PRMTRC, not P PRMTRC. If you wish to use compression or processing on AM, you will have to provide external equipment for that purpose. Adjust those "PRMTRC" EQ settings accordingly for best AM and SSB ragchew sound, and use the "P PRMTRC" EQ settings for a more aggressive sound for poor SSB conditions or contesting. For AM, you want a TX BW of 50-3050 or TTBF. I did not find any useful improvement using TTBF, and abandoned it. See the measured frequency response curves in the final section. Cliff's Notes: TTBF doesn't work; don't use it. The receive band width is controlled by pressing the upper mode selection button and holding it til a menu pops up on screen. Select either AM or AM-N for narrower receive. This has no effect on transmit band width. The width knob on the right hand of the radio has no effect. There is no reason in an SDR that this could not be implemented in a future software update.

The FT-450D has three AM receive band width settings. The new FT710 even has an EQ for RECEIVE audio! I would love to see a receive EQ included in the next round of software updates for the FTdx101. You can use the CONTOUR control for that also, but then it cannot be used for other useful QRM reduction. I have a Visaton speaker installed in a thrift store speaker box which brightens up the high end nicely. Bass response with this system probably will not satisfy hi fi AM aficianodos, but it works well on SSB and CW. See my other article on FTDX101 receive audio and speakers for parts sources and ideas.

I did some audio sweeps of the transmit speech amplifier. They are shown below.

I have done no experiments with FM mode on the FTDX101. I can only speculate that the circuitry and response time for that mode are similar. However, in FM the power level remains relatively constant for voice modulation. The EQ settings may be comparable to those used for AM. If you use a remote SDR to check your FM sound and band width, be sure to use NARROW FM settings in the menu and keep tests very brief at time when the band is not busy. Do not use FM at 100 watts output; it is a continuous mode like RTTY, and power should be reduced to 30 watts or less to prevent overheating the finals. I would be interested in hearing from anyone who has played with the transmit audio and equalization for FM on the FTDX101.

 

⇑TOP SETTING THE PROCESSOR LEVEL

The compression level cannot be properly set until the AMC is set. We begin with MIC gain of 20 - 23 and AMC set to 40-55, as previously determined for SSB. The key is the initial default setting of AMC=40-55, which Yaesu does not give you in its procedures. The processor cannot be used on AM, its disabled. This is an audio processor, not an RF processor.

Press the MIC gain control to cause the PROC light to the left of the mic gain knob to come on, and turn on the Processor. (Note that the feature to use CW while in SSB mode automatically assigns this knob to CW SPEED. Change this menu item if you need to, or you will not be able to perform audio adjustments in voice modes.) The PROC knob now adjusts only the PROC, not the AMC as before. See page 51 of the Yaesu manual, and the software update sheet (which can be downloaded from Yaesu.com.) The LED to the right of the mic gain knob indicates whether the key jack is set to a straight key or an electronic keyer.

Before setting the COMPressor level, set the AMC to 40 for lower distortion or up to 55 for more output. ZERO ALC readings are directly correlated with lower distortion products and splatter. The better controlled ALC action seems to suggest that using compression all the time on SSB might improve your signal purity. This suggests the compressor attack time is faster and controls "plosives" or transients in speech better. Listen to your signal on a remote SDR and/or record it and play it back, to get an idea of what you prefer for processor and EQ settings for transmit audio. The internal Yaesu MONITOR function may or may not be definitive due to whether your mike and headphones are properly in phase with the bone conduction in your head.

The correct setting for COMPression seems to be 100, and you have to increase the MIKE GAIN to adjust the drive higher to get a COMP meter reading of around 10 dB. Otherwise, you will get no deflection of the COMP meter. The distortion products experiments with these audio tests are encouraging. Remember an amplifier is likely to add distortion on the order of -30 dB. It will make you louder but also increase the strength of your exciter distortion products, if you don't get these settings right.

⇑TOP UNDERSTANDING THE PARAMETRIC EQ IN THE FTDX101D

The majority of transceiver manufacturers display their transmit equalizers in a simple graphic EQ sliders or bass and treble format. Yaesu does it differently, but there is a way to display the effect of the parametric EQ controls in a comprehensible format. In the OPERATION SETTINGS/TX AUDIO menu, there are non intuitive parametric EQ settings which are not easily understood by the average operator. The Yaesu audio EQ is the work of Bob Heil, the noted amateur audio expert and microphone manufacturer. The EQ settings can also result in overload and splatter if misadjusted.

In addition to this, we are confounded by the Parametric EQ settings. These are not intuitive. I owned a Yaesu FT-950 which had the same Bob Heil designed system. At that time, Yaesu furnished a very helpful utility to control the FT-950. You do not need to have a FT-950 to profit from the EQ setting utility. Here is what it displays when you adjust Q and levels and frequencies in a parametric EQ, which is equally applicable to the FTDX101D. It shows you the effect of EACH EQ section, and the final composite result.

This software utility assumes that the other elements in the FTDX101 are flat frequency response. That may not be the case. One ham used an audio noise generator injected into the mike input and a spectrum analyzer connected to the RF output to measure how much EQ was needed to actually obtain a flat frequency response over the 50-3050 Hz spectrum. His findings were astonishing to me. I had wondered why the unexpected amounts of low cut and high boost in my final EQ settings were necessary. Watch his youtube video and take note of what his Q and dB levels are. He is using -10 dB cut for lows and 4 dB boost for highs to get a flat response! I plan to try to verify this finding using simpler equipement, a sine wave generator injected into the mike input and a power meter, to do a sweep of the audio response of the speech amplifier. Another ham has done a SPICE analysis of that circuitry, and it shows some other surprising findings. They are discussed near the end of this article in the TTBF section.
https://www.youtube.com/watch?v=_-FT_y8zpe8

For a full discussion of the use of this program see my Yaesu PCC-950 Software Review.

Download the PCC-950 utility program from the Yaesu web site at: https://www.yaesu.com/downloadFile.cfm?FileID=6739&FileCatID=42&FileName=PCC-950_V124.zip&FileContentType=application/x-zip-compressed.

The EQ display at the right is the one I used on my FT-950. Its a pretty mild amount of EQ, because it does not have all the complications of the FTDX101 peaky audio stage in the speech amp.

My EQ settings are summarized in a table at the end of this article.

⇑TOP REAR INPUTS ON FTDX101 FOR SSB AND AM

I had thought I could work around the problems associated with the low level speech amplifier by connecting an audio system to the rear jack normally used for RTTY. This would bypass all the elements associated with the front panel mike input. All the external audio equipment would be easily understood, fully documented, and have a fast enough attack time to be effective in suppressing splatter and increasing talk power. I did this before with my FT-950.

I bought a W2IHY cable for the rear connector and tried it; it was wired correctly per the instruction manual for the FTDX101D and ohm meter checks. The rig did not respond to single ended line level audio at the rear connector, despite my attempts at finding a menu setting. One internet source states that you have to activate the PTT via the rear connector also, otherwise the rear connector audio will not be employed. There was no information from W2IHY on this problem, if used with his processor equipment. I hope a future software update corrects this situation. The menu does not seem to actually choose the input. This is frustrating, because I had good Behringer audio gear I had successfully used with my FT-950, as well as a newly acquired MAX processor (which worked great on my AM gear, a K7DYY transmitter.) I was unable to get this to work correctly without distortion when using the mike jack; I am still working on this, hoping an isolation transformer will cure the problem. If you have success, please let me know.
https://www.internetwork.com/MAX/

I have heard that the rear RTTY input can be used on voice modes IF YOU ACTIVATE THE PTT FROM THAT JACK. I have not tried this. The W2IHY cable does not have a PTT connection. I don't know if the W2IHY system works without the PTT being activated from the rear connector.

Another point you should be aware of is that the front panel mike input is active when using the USB internal FTDX101D sound card rear input for digital modes. This is true regardless of menu setting. I even asked Yaesu about it, and they confirmed it. So when you operate FT8, be sure to disconnect the mike or turn the mike gain down to zero to avoid shack noise from going out over the air when operating FT8. Also turn off the "Windows sounds" on your computer to prevent noises from the computer being transmitted. On FT8, you regularly hear "new country" or "youve got mail" from improperly configured FT8 or windows software.

⇑TOP POSSIBLE PROBLEMS FROM TTBF

I have found that TTBF does not actually increase the band width to 4 KHz because of the response of the audio preamp and filtering. There is also a very peaky audio filter (+7 dB) that might contribute to circuit overload and consequent splatter I observed when using the kind of high frequency boost I employ in the EQ. I observed a bright area in the remote SDR waterfall at around 3.5 KHz from the carrier frequency which made me uncomfortable. I enjoy the radio and the good reports I get with the 50-3050 setting; this choice disappears when TTBF is added. You may choose to experiment further with TTBF; if you find a solution you are confident about, please write me.

For more information, see the K6JRF website, which is very informative about TTBF and FTDX101 audio. He is an ESSB advocate. I include this graphic as encouragement for you to explore that web site for a fuller discussion. It is well worth your while if you want to try out TTBF and ESSB with the FTDX101 or FTDX10. https://www.k6jrf.com/FTdx101_ttbf_Analysis.html

For balance, I offer a different take from W8JI. This is the ham who designed the most popular amplifiers used today, and the antenna analyzers many of us have. He explains how distortion products are generated. He explains why a wide audio spectrum in a transmitter, especially with boosting the bass and treble ends of the spectrum is more prone to generating a wide signal. He explains a 6 db discrepancy in test methods for transmitters. He explains why a three tone test is needed to accurately portray transmitter distortion. Its required reading if you want to understand the FTDX101 distortion products and how to minimize them.
https://www.w8ji.com/transmitter_splatter.htm

On the web, you will find a youtube video that shows someone using a broadband noise generator and looking at the spectral display. He then adjusts the Yaesu FTDX101 EQ settings to get a flat response. My results differ; they are done with simpler brute force methods, using an audio generator and power meter. There is no substitute for actual measurements rather then speculation with a SPICE analysis of a single audio stage. This constitutes a complete end to end test of the entire transmitter system from mike input to antenna output. I used an HP 204 sine wave generator to feed the FTDX101 input. I set AMC=100. EQ was set to OFF. I observed POWER out and ALC on the FTDX101 display. Power readings were converted to dB on a calculator. No ALC action was allowed, so that any gain compression was not a factor in the measurements. These measurements were taken in SSB mode at 100 watts into a Bird Dummy Load with 1.000:1 SWR. Reference zero dB was at 1 KHz. Low end roll off was sooner than anticipated. TTBF high frequency performance offered little improvement over standard 50-3050 TX Bandwidth setting. At higher frequencies, the reduced filtering of possible distortion products in TTBF mode outweighs any minimal advantages. Overload in the region of the SPICE analysis peak region are possible in TTBF mode. My earlier conclusion to avoid TTBF was confirmed for both AM and SSB. I get good reports with 50-3050. But try it for yourself; you may think otherwise.

⇑TOP SUMMARY OF AB2RA TX AUDIO SETTINGS FOR FTDX101

The frequency response curves below are for the FTDX101 in SSB mode under various EQ conditions. In this case, audio from the HP 204 generator is applied via a 20 dB attenuator to the unbalanced input of the FTDX101. The transmit bandwidth is adjusted as stated. In all cases, no ALC, AMC, or COMP action is allowed, by adjusting mike gain drive appropriately. The amount of EQ applied may seem extreme, -10 dB bass cut and +10db treble boost. I have confirmed my settings with another trusted friend with an FTDX10 and others on the air with similar EQ settings. However, the actual amount of EQ is moderated by the AMC, ALC, or COMPression applied AFTER the EQ. Any automatic gain reduction reduces amplitudes and tends to make amplitudes nearly the same for varying frequencies. In other words, compression AFTER the EQ undoes much of what the EQ did. You have to overdo EQ in order to correct for that. Post compression EQ also has down sides, but that is another technical discussion. How the COMPressor comes into play is another speculation. Back in the day, user manuals provided at least a block diagram of functions along with a rudimentary explanation of circuits. Yaesu omitted this, along with other basic information needed to attain acceptable SSB performance with a minimum of splatter.

	NO EQ
	PRMTRC EQ
	P PRMTRC EQ

I tried but abandoned efforts to use external audio gear, due to problems interacing it with the FTDX101. With my old FT-950, the DSP transmit audio compressor did not have fast enough attack time, and introduced grundge on the leading edge; there was no option but outboard solutions. In that case, I got it to work via the mike input. If you are able to get the FTDX101 to work with the rear RTTY input jack, I would like to hear from you.

This is basically an SDR with knobs. This opens up a lot of possibilities. For instance, rather than referring to this chart (which is posted at my operating position), why couldn't Yaesu offer "profiles" like some of the SDRs do? SSB 1 for ragchew, SSB 2 for "space shuttle audio" for contesting, AM for a more mellow sound. And why does the "afterthought" for FT8 require you to select either SSB or a digital mode, then click on "PRESET" to load the parameters for that mode? FT8 is the more popular than all other modes combined. Kludgey, but it works better than nothing at all. I am not being so fussy that they have to duplicate the smell of hot dust on vacuum tubes for me. But with software, you should be able to fix things up in an update better than this.

In my opinion, if you have to have a tower or desktop computer as large as the radio, and the radio has no knobs, you don't have a radio, you have a "PERIPHERAL."

In my opinion, if you need a pile of audio gear next to your transceiver as big as the transceiver, just to get acceptable transmit audio, you may need a new radio.

There is no way to sugar coat this. If you do not adjust the FTDX101 AMC for zero ALC meter deflection, you will have gawdawful splatter.
For Yaesu to not have issued a bulletin to alert users of this problem and how to deal with it by this late date is inexcusable.

OK, curmudgeon mode off. This transceiver has a great receiver, and I am willing to put up with the quirks of the transmitter to keep it around. Is the AMC a part of the ALC circuit with a different threshold setting? I might explore that. Yaesu does not have a block diagram or tell us "what's in the box." Remember when manuals used to have that information?

There is a pervasive problem right now in currently available amateur transceivers. Improper adjustment of an FTDX101D or FTDX101MP absolutely will result in nasty splatter and IMD products for an unnecessarily wide transmit signal. Had the ALC circuit been designed with a lower threshold, to begin limiting drive BEFORE the distortion began, this problem would have been less awful; better time constants should have been chosen as well. ANY ALC action will result in distortion. Make adjustments with the goal of ZERO ALC meter movement. Most all RF designs using FETs or LDMOS devices cannot seem to break the -30 dB IMD barrier. For instance, QST reviewed the fTDX101D and the FTDX101MP. No warning of potential splatter or IMD distortion in the transmitter was published. I did not take a carload of test equipment to the dealer when I evaluated this radio. Subsequently, problems surfaced beyond my control. I did due diligence in researching the AMC feature, which can go a long way in suppressing IMD on the transmit signal. As long as you keep AMC settings more toward 40-45 in SSB, the IMD products will be as low as the inherent Yaesu design permits, on the order of -30 dB. Adaptive predistortion is only offered on some esoteric SDR brands like Anan and FLEX. My KPA1500 has an output port for such a system, but the feature is not implemented in the matching K4 transceiver. None of the current big 3 transceiver manufacturers offer the predistortion feature to reduce IMD.
• https://ieeexplore.ieee.org/document/1411217
• https://westminsterresearch.westminster.ac.uk/item/92x3w/distortion-correction-of-ldmos-rf-power-amplifiers-using-digital-predistortion
• https://groups.io/g/FTDX-101D/topic/76800877
Pay special attention to the comments of K4TK/Tim.
• "Transmit distortion - For SSB, TX IMD performance has not really improved from the 1960's (actually worse)..granted most rigs are poorly used (a shame in itself) - but many TX output stages are adequate at best and some downright dreadful - this is not an insoluble technical problem with proper output stage and ALC design. Apache Labs have brought at least two SDR models that offer a software feedback feature to reduce the 3rd order IMD products on transmit to very low levels. All modern transceivers and linear amplifiers should have a 'pure signal' feedback option to bring super clean signals onto our bands..but they don't. I asked Rob Sherwood about the appalling state of some transmitted signals and why the big manufacturers have no software options for a pure signal capability. He indicated it may be down to the computing power or firmware design in the transceiver architecture." - from G3ZPS http://www.g3zps.com/about.html
•My comment: Or just sloppy design due to software engineers who have limited RF experience.

For the time being, I will continue to operate this radio in as conservative a fashion as I can. But I am optimistic that newer radios will be even better in the future, especially on the transmit side. Unless someone can offer me a transceiver with equivalent receive performance which has improved lower IMD distortion products on transmit, I remain among the aficionados for the FTDX101. Other manufacturers have failed to produce anything that is significantly better on transmit IMD, other than FLEX and ANAN.

It is clear that I have reached the end of the possible adjustments which are limited by the speech amplifier and AMC circuits associated with the front panel mike jack of the FTDX101. It is also clear that in SSB and digital modes, the way to avoid distortion is to have ZERO movement of the ALC meter. Something other than the hand mike will go a long way to improving audio.

I hope you enjoy operating your Yaesu FTDX101 as much as I do.

My other articles about the FTDX101D

Don't let this happen to you....