[Icom] 756ProII CW "Buzz"

[George, W5YR]

Jeffrey, what you are hearing is 99% the result of using too low a CW PITCH
offset frequency combined with twoo wide a filter setting. The capability
of setting up this operating conditon so readily is one reason some folks
have a problem using the PRO and why others comdemn it as inferior.

As you have noticed, you get this problem with a fairly wide filter
bandwidth and a very low offset frequency, but going to a higher offset
and/or reducing filter width makes the problem go away. 

Remember that with that bandwidth, you do not have the narrow bandpass
filter bandwidth even with a PRO and you are enhancing the problem by using
the soft filter setting. You have the same passband shape as you do on SSB
except that instead of being centered on 1500 Hz, the filter is centered on
your offset of  300-350 Hz.

You may not have noticed since you are a new PRO user, but what this
combination does is allow you to hear a 1400 Hz passband centered on 350
Hz, for example. This setup allows you to tune an incoming signal all the
way through true, actual zero beat and "up on the other side." What this
means is that when you have tuned in a signal to your desired 350 Hz
beatnote, you are also hearing anything that is present, QRM and band noise
if nothing else, in the filter passband which now passes from 350 Hz BELOW
zero beat to 1050 Hz ABOVE zero beat. This is not a workable or productive
setup.

On my PRO, this setup does not greatly distort any signal I tune in within
the large passband, but signals tuned for a 350 Hz beatnote do not sound at
all "good" to my ear. I don't know if you are hearing what I am and
describing it as a "raspy buzz" but it clearly it not a signal that I want
to copy. And there is no need to have to copy such a signal unless you have
a serious hearing deficiency, in which case the solution is to correct that
with hearing aids and not to maladjust the radio - it just doesn't work as
you have discovered.

Others have run into this problem in an effort to use (a) a low pitch to
compensate for hearing problems and (b) a wide bandwidth in order to hear
more of the band at once. With the PRO and now your PRO II this is not a
workable scheme. I use a 700 Hz offset and even with a 1000 Hz filter, the
CW notes are clean. Going to 500 Hz bandwidth or even lower does not change
anything except remove QRM and increase S/N.

So, my recommendation is that you first put the CW PITCH back up around
600-800 Hz and then use a 500 Hz BPF setting on CW and then evaluate the
sound of CW signals. I doubt very much that Icom would find anything at all
wrong with your new radio.

Hearing a noise while rotating the CW PITCH knob is normal. Find a pitch
you like and remain with it. I never touch my CW PITCH knob aftr finding
that 700 Hz works best with my ears and headphones. Tune the radio, not the
PITCH knob to select the beatnote frequency you want to copy.

Try all this out and let me know what you find!

72/73/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
Icom IC-756PRO #02121  Kachina #91900556  IC-765 #02437

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Jeffrey Steinman wrote:
> 
> Hi All,
> 
> I am a brand new 756ProII owner. Love the radio, but noticing some strange
> behavior on CW.
> I hear a "buzz" during RX on CW notes under certain radio settings (outlined
> below). It's a pretty raspy buzz, at that. If I add in some attenuation (say
> 6 dB) it tends to take the rasp out. I don't notice any such buzz/distortion
> on SSB. I thought it might be some type of mixing in the front end but ruled
> that out when I heard the buzz on a lonely VK on 10M CW late at night.
> 
> ICOM is being very helpful, saying to send the radio in for them to inspect.
> Before I do that I thought I might see if anyone else has noticed this
> problem.
> 
> 73,
> 
> Jeff Steinman, N5TJ
> 
> ***********
> The radio is set as follows:
> Mode: CW
> Filter BW: most noticeable from ~ 900 Hz to 1400 Hz
> Filter shape: Soft
> Sidetone: Very low pitch, 300-350 Hz (if I turn to a higher pitch the rasp
> is less noticeable/gone. Interesting that when rotating the pitch control I
> hear a similar type of noise/distortion)
> Band: Any
> Signal Strength: Most noticeable above S5
> Preamp: Irrelevant (hear it off/on)
> Audio: Heard through headphone jack and/or speaker jack. Seems more
> prevalent at lower volume (or could just be harder to detect at higher
> volume).
> Noise Blanker: OFF