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Hello,

My "old" non D FT857 exhibits an ALC problem:
The output power is unstable and the ALC bars
follows this variation.
This behavior is present on all bands, including VHF and UHF.
I've tested with external audio modulation in SSB and FM modes.
I've also tested with internal 1750Hz (repeater opening tone).
I've not tested, for the moment, in CW mode.
At all RF output level, between 5 and 100W, these variations
are present.

Have somebody an idea where to search to correct this instability ?

Thank you for any proposal.

My best 73,
Rudi, HB9ARI

Rudi,
I have a feeling the we got two threads "tightly coupled " - so this is about the ALC.

I recently had same problem while testing a new antenna. Got some woo-do suggestions ( even from reliable source ) and nice private tech discussion with one OM.
My conclusion , and your mileage may vary, if the rig does not like the antenna the SWR indicator will go wild and after few minutes of testing the rig cooling fans will not keep up with the abuse.
Keep in mind that SWR is independent of power , at lest in theory. ( You have indicated that this is independent of power applied)
When the SWR goes OVER some high value , the ALC will also compensate for it - higher ALC = less modulation.
My ALC followed my SSB modulation pretty nicely!
Just check you SWR, MOD and PWR during your test.
The bottom line – high SWR = high ALC, at least in my case.
73 Vaclav AA7EJ

Vaclav,

Thank you for your reply.
I've omit to say that i get the same problem
when using a dummy load (Cantenna filled with PCB free oil)
and a ~ 1.05:1 to 1.3:1 SWR depending HF/VHF/UHF bands.

73, Rudi, HB9ARI

Rudi,
Just for clarification.
Your SWR reads OK, but the ALC is full scale without modulation?
And MOD is doing opposite as ALC.
This is a long shot – how is your MIC SSB gain set?
The ALC should still work even on 100 setting, but I do not recall what mine did when I had the problem.

Are you aware that in CW ALC will follow the code - full scale.

Per Yaesu that is normal, in my opinion useless and weird.

I suppose if you get on the air you will get complains that your audio is cutting out, right?
73 Vaclav

Hello Vaclav,

Thank you one more time to help me to solve my problem!


On 15.01.2013 21:04, vaclav_sal wrote:

Rudi,
Just for clarification.
Your SWR reads OK, but the ALC is full scale without modulation?

- Yes, SWR is always well under the FT857 "limit" (1.5:1 if i'm correct)
When the power is stable at the correct level, corresponding
to the selected RF power level (measured with LP-100 up to 50MHz),
no or one ALC bar on the FT857; when instability begin, the power
varies between 1/4 and full power, and the ALC bars are following
thes variations in a reverse manner, that is to say less power=> more
ALC bars.

And MOD is doing opposite as ALC.

- As i'm using exclusively JT65 mode, it's a quasi constant modulation
level, except at the filter edges, but i don't work frequently in
these conditions, and RF level vary only to minus 10 to 20%,
for me, it's a correct behavior.

This is a long shot -- how is your MIC SSB gain set?

-I adjust my MIC level to get "just" the selected RF out put level,
that is to say if i've adjusted 20W RF level, i go up with the
MIC level until i'm just at the 20W level, with very little lower
level like 17-20W, depending upon the current JT65 tone.

The ALC should still work even on 100 setting, but I do not recall
what mine did when I had the problem.

-If i've selected 100W (only for measurements, too much for JT65 operation),
0 or 1 ALC "flashing" bar, EXCEPT when power, in an erratic manner, is going
down to a value between 20 and 100W; as said before, the ALC "follows"
the current power level.

Are you aware that in CW ALC will follow the code - full scale.

- I don't have a "keyer" connection, i will install a switch during
next week-end to do some testing in "CW" mode.

Per Yaesu that is normal, in my opinion useless and weird.

I suppose if you get on the air you will get complains that your audio
is cutting out, right?

- Never get bad reports and local monitoring show that these 6 to 8dB
less power
should be "corrected" by my correspondent RX AGC. During this problem,
no viewable distortion or spurious appears on my local monitoring (Winradio
G313/180 E with 50 ohms load to avoid to high receiving level)

Sorry for this too long message !

73, Rudi, hb9ari

73 Vaclav

Hello Rudi,
you mentioned MIC level setting to achieve 20 W RF.
So this is pretty stupid to ask , but - when you run JT65 what is the mode setting on the rig? SSB or CW or other? I know nothing about JT65.

Is it audio modulated RF or unmodulated (CW) ?

Could JT65 be called A2 modulation?

In theory ALC is a modulation control and since in CW mode it goes max in CW ( by silly design) this funky behavior may be normal especially at "low" RF setting.
Just a wild guess on my part now.
73 Vaclav

Hello Vaclav,

you mentioned MIC level setting to achieve 20 W RF.
So this is pretty stupid to ask , but - when you run JT65 what is the
mode setting on the rig? SSB or CW or other? I know nothing about JT65.

- The "standard" with JT65 is to use USB mode for all HF/VHF bands

Is it audio modulated RF or unmodulated (CW) ?

- Audio modulated

Could JT65 be called A2 modulation?

- It's like a AFSK, with constant amplitude tones

My best 73, and many thanks !

Rudi, HB9ARI

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