AM TX on FT-857D Lousy. Any suggestions?

[n2jkv]

Hello. I recently got a Yaesu FT-857D ricebox for the car (currently my only shack), and while it is an excellent mobile rig for every mode other than AM, it seems to be even worse than most modern tranceivers when it comes to AM. At its default settings, the 25W carrier swings the meter downward with modulation and gets reports of low audio. Adjusting the carrier level downward via the service menu doesn't help. I can bring the carrier down, but the audio becomes more distorted. This technique may work with an 817, but doesn't work well with the 857 having a pa stage after. Being an obvious back burner afterthought, I believe the way that AM is generated iin the 857 is very inferior than other modern HF radios. Has anybody heard of anyone having any luck with AM tx in this radio? I am wondering if there is any mod floating around out there. Once I set up the base again I'll have other options, but this is all I have now.

[W2VW]

SWR must be 1:1 and no more. The ALC will start to do the transient thing otherwise. A friend was on just last weekend with one of these on AM. They can work. Dunno what other problems might be happening.

[W1QWT]

I have a friend who bought the bigger boxed FT897 but essentially the same radio.
He said he found a switch on the back of the stock mic that switched mic response
between two different tonal qualities. He also said he found a menu setting that changed the
AM mic gain?
Anyway while he didn't sound like a high level modulated and modified AM transmitter would, he was certainly acceptable. At least to my standards.

Seems that all the Japanese rigs have 'downward modulation' but hey, don't let that stop you from
using it on AM.

Regards
Q

[Steve - WB3HUZ]

None of the Japanese rigs I have exhibit downward modulation.

[W1QWT]

None of the Japanese rigs I have exhibit downward modulation.

Hi Steve,
Wonder what vintage rice boxes you have?
I have a TS 690 that does exhibit 'downward modulation' but my TS140 doesn't.
The radio club I hang out at has a TS690 also and a relativily new Yaesu that both
exhibit 'downward modulation'.
Thats why I had the thought that most do these days.

Regards
Q
 

[Steve - WB3HUZ]

Admittedly, mine are a little older, a FT-102 (mid 80's vintage) and FT-101 (70's vintage). The ALC is off in the AM mode in the 101. I've disconnected the ALC in the 102, although, even with it connected, I noticed little negative effects. Seems when the Jap rigs went to solid state finals, the ALC became more of an issue.

Have you noticed the downward modulation at all power levels? For example, even if you back the carrier power level down to say 10 watts versus the usual 20-30 watts, does the ALC cause problems? I'm wondering if it's a headroom problem or an ALC problem.

[WA1GFZ]

How about audio phase, try reversing the mike leads. SSB is positive modulation only.
See if you can disable the alc .

[Ed-VA3ES]

The problem is that the ALC is engaged in the AM mode.  One needs to disengage or disconnect the ALC in the AM Mode, to get proper positive peaks.   Even my FT990 exhibits  downward modulation, when the mic gain is et too high. 

One needs to turn off the ALC in AM.  The positive peaks drives the ALC into action, dynamically reducing the output during audio peaks.

[W2VW]

Turning off ALC isn't an appliance option. One needs a screwdriver, solder iron and some idea what he/she is doing.
Maybe there is a rig which allows this in a menu but it's doubtful.

[Pete, WA2CWA]

We actually talked about this type of thing last year. Bacon called it "reverse carrier control". Using the Search function here, I found the thread:

http://amfone.net/Amforum/index.php?topic=6429.0

[ve6pg]

...I HAVE AN FT847...NICE LITTLE RIG, RECEIVE IS GREAT ON ALL MODES, BUT SUCKS ON AM...I'VE TRIED MANY THINGS FER IT, BUT NO LUCK...BUT I HAVE HERD GUYS WHO SOUND OK, MINE JUST SOUNDS LIKE GARBAGE..I GUESS SOME GUYS MUST BE LUCKY IF THEY GET ONE THAT SOUNDS GUD ON TX...MINE ALSO HAS A VERY QUIET MONITOR CIRCUIT...OTHER GUYS HAVE SET THEIR MONITOR AUDIO TO A LOW LEVEL, WHEREAS MINE IS WIDE OPEN, AND STILL NOT GUD ENUFF...TIM...SK..

[n2jkv]

Hi,
Thanks for all the comments. I restored the default values and then backed down the carrier only slightly. It isn't great but it works and functionally qualifies the radio as an all-mode. It really doesn't sound too terrible other than that, yes, ALC is a bit too restrictive. I may look into loosening it up. A compact radio as the FT-857 doesn't have a dedicated AM tx stage. FYI from the tech liiterature:
"AM Modulator Circuit"
"As in the SSB modulator circuit, a carrier signal appropriate to the transmitting mode (AM) from the CAR-DDS unit and an audio signal from the microphone are applied to the balanced modulator Q1071 (SA602AD). The control signal from the mode switch IC causes a voltage (AM 5V) to be sent from the transistor via D1059 (BAS316), causing the balanced modulator to lose balance. The restored carrier signal and modulated signal are then fed to the TX mixer via the ceramic filter."
That's what I meant in my original post about the "inferior" way the AM is produced.
I'll live with this now and next year the base will have my Kenwood and hopefully I can pick up a nice vintage rig for great AM.
73
N2JKV

[Ed-VA3ES]

On all current model rice-boxes, a high modulation  (mic gain) level will drive the ALC into action. I've found that backing off the mic gain will prevent excessive ALC action, while retaining decent mod %.  Try that.

[w3jn]

"As in the SSB modulator circuit, a carrier signal appropriate to the transmitting mode (AM) from the CAR-DDS unit and an audio signal from the microphone are applied to the balanced modulator Q1071 (SA602AD). The control signal from the mode switch IC causes a voltage (AM 5V) to be sent from the transistor via D1059 (BAS316), causing the balanced modulator to lose balance. The restored carrier signal and modulated signal are then fed to the TX mixer via the ceramic filter."
That's what I meant in my original post about the "inferior" way the AM is produced.

There's nothing at all inferior about that type of modulation.  Done correctly, it can provide absolutely superb audio.  The only hitch in the gitalong here is that the AM signal goes thru the ceramic filter, and the audio circuity prolly shapes the bandpass for 300-3000 hz.

I've modified several junk Heathkit slopbucket rigs for hifi AM using the existing balanced mudulator.  Works FB with a bit of audio work, and bypassing the crapstal filter!

[Steve - WB3HUZ]

Bingo dude!

See here.

http://www.amwindow.org/tech/htm/602mod.htm


and here


http://amfone.net/Amforum/index.php?topic=4888.msg36657#msg36657

[AF9J]

That is very true about the both the FT-857,and the FT-897.  I have an 897 (I'm broker than broke, so I'm stuck with it for now). Both rigs have separate mike gains for each mode.  The gain goes from 0 to 100. The factory default is 50. Every comment I've read about these rigs, and my own experience tells me that the the factory default value of 50 is overkill for SSB, FM, Digital modes (which are SSB based), and more than likely AM.  Yaesu gave these rigs excessive mic gain.  In my experience, a good starting point for the mic gain is around 20-22.  Numerically this seems low, but much more than this, and the audio in every voice mode gets downright nasty.  BTW, the switch on the back of the mic, is basically just for a capacitor.  From what I've been told in on-the-air tests on 2m SSB, Position 2 just adds more bass.  Yaesu has made hand mics with this option for ages.  I used to have an FT-736R in the 90s (good rig - I used it for weak signal stuff on 2, 222, 432, and 1296 - wish I didn't have to sell it), and it's hand mic had the same switch, and it did the same thing.  Now if I could just scare up a QSO or two with my 20-25W of carrier, pee-wee signal (running 100W or more of carrier from an apartment is just asking for trouble with my neighbors).

73,
Ellen - AF9J

On all current model rice-boxes, a high modulation  (mic gain) level will drive the ALC into action. I've found that backing off the mic gain will prevent excessive ALC action, while retaining decent mod %.  Try that.

[W3DBB]

 .

[k4kyv]

I hear a  lot of solid state transceivers with good audio on AM.  Never paid much attention to what brand appliance it was.  The best sounding ones seem to mostly be Icoms, IIRC.  But since the band expansion I have heard a lot of guys try out their stock rigs on AM and answer my CQ's in the Extra class segment, where the congestion is still low. I have heard my share of lousy audio from those rigs, but a few could have told me they were running a converted broadcast transmitter and I would have believed them.

[Rob K2CU]

DG2IAQ has a list of modifications to the FT-897 that may well apply to the '857 as well. IN that list, there is a discussion about audio pumping by the ALC circuit. The suggested correction is to add additional capacitance to the ALC time constant circuit to slightly delay its response to audio peaks.

[kc8ntp]

What I found to help the AM audio on the Yaesu FT-857D: first go to the alignment menu and turn the output power wide open - both AM carrier and and SSB. Next you go through the alignment menu and there is a setting for the ALC - turn it down about half way. Next, turn the power down to 80 by the main menu. I also find that when you use the LPF, and also use the #2 setting on the mic and turn the processor on to about 30, that it really improves the AM audio.

I have been told that it sounded pretty decent when I tried it on 75m AM.
My next step is to get the SSB filter for it, since it can be used on TX, and see what it sounds like after I install it.

John G., KC8NTP, east central Nevada

[KB2WIG]

            "My next step is to get the SSB filter for it, since it can be used on TX, and see what it sounds like after I install it.'

I would venture a guess that any added ssb filter is more likely to reduce the audio quality of the transmitter by reducing the available bandwith.  .......  anyway, "try it, you'll like it "....       klc

[K3ZS]

On my Icom 718, you have to turn the mike compression off, and back down the mike gain until the output power stops dropping on audio peaks.   Its not my regular AM rig, but when I do use it on AM most people comment that the audio sounds good, although never fully modulated.

[W4FCC]

On my Icom 718, you have to turn the mike compression off, and back down the mike gain until the output power stops dropping on audio peaks.   Its not my regular AM rig, but when I do use it on AM most people comment that the audio sounds good, although never fully modulated.

 I take a different approach on my 718-  Mic gain around 10 with the compression on.  Gives the audio much more presence and is not objectionable with a D-104 on which I changed the element with a Radio Shack condenser, and with the Heil ICM.  It's the only rig I have for AM, and seems to be doing very well at 25W carrier, sometimes into the SB-200.
 

  Rick

 W4FCC

[W3SLK]

Nice call Rick

W4FCC

[K3ZS]

Rick-  I'll try using the compressor and backing down the gain more.    Looks like you got the call before Riley had a chance at it.