RadioBanter - View Single Post - Yaesu FT-991 AM transmission defective

Fred McKenzie · July 29th 15, 11:14 PM posted to rec.radio.amateur.equipment

In article ,
wrote:

On Friday, February 27, 2015 at 7:09:51 PM UTC-5, Fred McKenzie wrote:
In article ,
wa7kgx wrote:

Yaesu have posted firmware updates to the FT-991 as well as the CAT
codes.

I updated my FT-991 yesterday and spent most of today re-entering
channel data lost in the reset.

There are two separate updates, one called "Main" and one called "DSP".
Each has its own updater program. The Main update went smoothly but the
DSP updater needed some help.

It seems that Yaesu's "enhanced" USB driver installed as COM14 on my
computer, but the DSP updater can only handle COM ports 1 through 10.
It took some research to learn how to change COM14 to COM1. After
making that change, the DSP update went smoothly.

I do not know what all was changed, but did notice that the AM mode is
working differently. Instead of kicking downward during modulation, the
Po meter barely wiggles. It does kick downward slightly with the
microphone gain turned up high. I hear some distortion on a local
receiver, but it may be due to overload. Looking at a PEP wattmeter, I
would guess that modulation percentage might be around 70 or 80 percent.
A scope might tell a different story.

73,
Fred
K4DII

hey dave on am do you know what the power output should be mine only does 20
watts on am

W2MGF and Philip-

The above is either a mis-quote or a mis-statement on my part. I do not
recall posting that the FT-991 AM modulation was that high. I think it
is around 10 percent at most, but my Icom radio has 70 or 80 percent AM
modulation by comparison.

Philip's link to W8JI's AM report seems to describe the FT-991's AM
operation exactly. The problem with his solution is that the FT-991
does not allow you to run the AM power level up beyond about 40 Watts,
so applying a DC level to the ALC terminal would not buy you much. You
could try setting the power level to its maximum and use the ALC to
reduce power to a quarter of that. You might then have a rather low
power but well modulated AM signal!

I recently updated the FT-991 firmware to the July 24, 2015, version.
The update fixed some minor problems, but did not affect AM operation as
far as I can tell.

Fred
K4DII