Hi,

I have been playing with my QMX+ over the last month
or so since I built it, and it has been behaving quite
nicely. Mostly, I have been listening in on W1AW's
high speed CW, hoping to one day have enough confidence
to actually do my first CW QSO since being licensed a
half century ago. W1AW rolls in here very strong.

Anyway, the Canadians were having their RAC contest
over the weekend, so I thought that I would listen in,
and brush up on my experience with contest exchanges.

In the beginning, all was well, but as the contest
built up steam, and there was a forest of CW signals on
the air, I noticed a peculiar thing: The low level
signals all had a raspy random noise signature riding
on top of their CW tones. If a signal was strong
enough to activate the AGC, the noise went away, but for
any signal below the AGC threshold, the noise was there,
no matter where I was tuned relative to the carrier.

At first, I thought the contestants were using poor
quality rigs with bad CW signals... but after the number
of such noisy CW signals reached the dozens, I had to
turn my pointy finger back in my direction.

It has to be my QMX+.

So, this morning, I investigated the QMX+'s low level
signal behavior using a signal generator, to see if I
could duplicate the issue. I couldn't.

The tone was sweet and pure all the way from S9++ down
until it became inaudible.

It would seem that it has something to do with large
numbers of middling strength signals within the
receiver's band.

Note that the noisy signals weren't on the threshold of
disappearing gracefully into the noise. The signals were
all head and shoulders above the background noise. Their
tone sounded like it was being clipped, like a guitar run
through fuzzbox. They would be easy copy if the tone was
clean.

So, to capsulize,

Only a few strong, or weak signals: clean and pure tone.
Lots of middling signals, crackly/clipping noise on top of
the CW tones.

Ideas?

-Chuck Harris - WA3UQV

Chuck,
A crowed contest environment can challenge any transceiver’s receiver. The transceivers that are designed to perform well in contests can cost many thousand of dollars. The QMX+ is an outstanding bang-for-the-buck rig but it does have it’s limitations.
Ed
AB8DF

Hi Ed,

Indeed, contests can be trying, but there wasn't a hot signal
on the band using my little tossed out the window wire antenna.

My little Oak Hills Research QRP 40M rig, with a DBM, was similarly
priced to the QMX+. I didn't try it that night, but in the past
it has been unfazed by much heavier contesting activity, such as
Field Day...

Are others finding the QMX+ receiver to be that weak?

-Chuck Harris - WA3UQV


On Sun, 29 Dec 2024 11:05:30 -0500 "Ed Kwik via groups.io"
<ekwik@...> wrote:

Chuck,
A crowed contest environment can challenge any transceiver’s
receiver. The transceivers that are designed to perform well in
contests can cost many thousand of dollars. The QMX+ is an
outstanding bang-for-the-buck rig but it does have it’s limitations.
Ed AB8DF

On Dec 29, 2024, at 10:46 AM, Chuck Harris via groups.io
<cfharris@...> wrote:

Hi,

I have been playing with my QMX+ over the last month
or so since I built it, and it has been behaving quite
nicely. Mostly, I have been listening in on W1AW's
high speed CW, hoping to one day have enough confidence
to actually do my first CW QSO since being licensed a
half century ago. W1AW rolls in here very strong.

Anyway, the Canadians were having their RAC contest
over the weekend, so I thought that I would listen in,
and brush up on my experience with contest exchanges.

In the beginning, all was well, but as the contest
built up steam, and there was a forest of CW signals on
the air, I noticed a peculiar thing: The low level
signals all had a raspy random noise signature riding
on top of their CW tones. If a signal was strong
enough to activate the AGC, the noise went away, but for
any signal below the AGC threshold, the noise was there,
no matter where I was tuned relative to the carrier.

At first, I thought the contestants were using poor
quality rigs with bad CW signals... but after the number
of such noisy CW signals reached the dozens, I had to
turn my pointy finger back in my direction.

It has to be my QMX+.

So, this morning, I investigated the QMX+'s low level
signal behavior using a signal generator, to see if I
could duplicate the issue. I couldn't.

The tone was sweet and pure all the way from S9++ down
until it became inaudible.

It would seem that it has something to do with large
numbers of middling strength signals within the
receiver's band.

Note that the noisy signals weren't on the threshold of
disappearing gracefully into the noise. The signals were
all head and shoulders above the background noise. Their
tone sounded like it was being clipped, like a guitar run
through fuzzbox. They would be easy copy if the tone was
clean.

So, to capsulize,

Only a few strong, or weak signals: clean and pure tone.
Lots of middling signals, crackly/clipping noise on top of
the CW tones.

Ideas?

-Chuck Harris - WA3UQV

Hi Dan,

That sounds more likely to me than that the receiver was being
crunched by all the signals.

If I switch to the digi mode, the clipping sounds on the CW
signals go away entirely... but the amplitude also drops to a
small fraction of when CW mode.

The AGC settings are currently the factory default settings.

Being a DSP rig, I presume that the AGC is purely an audio
function?

-Chuck Harris - WA3UQV



On Sun, 29 Dec 2024 09:19:58 -0800 "Daniel Conklin via groups.io"
<danconklin2@...> wrote:

Chuck,
It's likely the combination of the filter you were using and your AGC
settings was causing the middle amplitude ro be pulled in two or more
directions. You might play with the AGC settings under busy
conditions to start with, and work from there. I often just turn the
AGC off. -- 73, Dan - W2DLC

Hi George,

As a life long ham, and a retired EE, I am well aware of
such things, and I don't believe I generalized, or in any
way impuned the QMX+'s performance. I just recognized that
the QMX seemed to be the common denominator.

It turns out the the AGC has some characteristics that can
cause it to coat the signal with clicky noise, which could
be another way of describing the phenomenon.

I think the major influence is the relatively high level of
background noise that day. I think it probably was causing
the AGC to cut in and out with the noise, and every time it
cuts in or out, it can make a little click... Which is essentially
modulating the CW tone each time.

The difference between the usual response to noise, and the
response this time, is usually, the signal just blends in with
the noise until it is indistinguishable from the noise.

In this case, the signal was head and shoulders above the
noise, and should have had a pure tone, being so far above the
noise, and yet, the tone was buzzed up with a clipped sounding
noise... Which is exactly what is described in the manual when
it discusses AGC operation, and adjustments.

It would have been nice if the manual went into strategies for
arriving at the best settings, but it wouldn't be the first time
that the features preceded an intuitive understanding of their effect.

-Chuck Harris - WA3UQV


On Sun, 29 Dec 2024 19:34:13 -0800 "George Korper via groups.io"
<georgekorper@...> wrote:

Hi Chuck,

Due to the nature and complexity of radio noise,
which is different every hour and every day,
it is not a good idea to generalize about a radio's performance.
There are thousands of factors, which you yourself are
encountering like a dingy on an
ocean, that can make any radio react differently at any moment.
I don't have any suggestions to make because even radios that
are very expensive have to float on the same sea, and take time to
adjust. A variable CW filter with its own encoder would be nice, to
speed up adjustment. In the meantime you can buy after market DSP
filters like Wolfwave, but they cost more than the QMX+ !

73, George
K3GK