This is a great write up and I'm grateful to you, Jerry, for taking
the time to generate it.
Now, while I've had my O II for over a year, circumstances have
prevented me from using it as much as I'd like. I've not contested
with it, yet, and so have not experienced it in actual combat, as it
were. I've mainly played DX and bit of rag chewing and all of that
CW, along with a very small amount of digital stuff (just to make
sure everything was connected properly). During all this time, I've
been playing with all sorts of settings, trying to understand how to
optimize the receiver performance, knowing full well that I'm in
unfamiliar territory because all of my previous experience has been
with analog radios. Based on my analog experiences, I've almost
never used the NR or NB; when I tried them, they didn't seem to much
help, though I have noticed they provide some improvement on SSB.
With that preamble, the approach you have outlined seems to distill
down to a "knobology" of: "preamp on, max AF gain, ride RF gain for
proper listening level." Is that right? If so, I think I understand
the rationale underlying this approach. But that leads me to my next
question: is this a general strategy (as in "use it all the time") or
are there times when I want to alter this basic formula? If there
are, what might they be and what alterations should I try.
Kim Elmore, N5OP
At 02:45 PM 1/31/2008, you wrote:
>"OK, I brought this up before, and was specifically told that "low RF
>gain and high AF gain," as is traditional in analog radios, does not
>apply to the O2."
>
>I am going to get some flak here (which is why I read this reflector
>less and less these days) for what I am about to add... but here goes:
>
>
>I must emphatically disagree with the comment quoted above. Why? I
>actually operated with the same thought for nearly two years and in
>that time I learned to hate my Orion a bit more each day.... much
>for the same comment regarding CW readability in a pile up, but also
>to weak signal audio distortion, extreme AGC compression and clicks
>in the speaker and headphones. Regarding this particular reflector
>thread....There is just too much AGC compression taking place in the
>Orion if the RF Gain is at maximum. However like most hams I had
>gotten use to not touching that control. Fact many transceivers
>don't even have an RF Gain control (and generally sorely missed).
>
>About three months ago I was talking (complaining) to one of my
>engineering friends at Ten-Tec regarding 'clicks' in the audio when
>I key. It was one of many things that continued to annoy me... and
>was really on my mind as I had just completed a CW contest and my
>ears were in pain. Anyway, I was hoping that there might finally be
>a 'fix' for this problem. At one point during our conversation he
>asked me how I set my RF GAIN, PREAMP, and ATTEN during normal
>operation. I explained that I normally didn't adjust down the RF
>Gain control unless maximum attenuation and no RF Preamp still
>resulted in too much signal (i.e. 40 or 80 meters at night with S7
>or above noise floor). I could hear a 'frown' forming itself over
>the phone... and then he (a long time CW operator) explained what my
>engineering background had me consider a bunch of times but
>eventually ignored. Basically he said, to NOT use the attenuator
>unless I was in a genuine overload situation and that I actually would wa
> nt to have the RF Preamp in under most conditions.... and that I
> should advance the audio output as high as possible and use the RF
> Gain to reduce the final audio level to what was pleasant to my
> ears. Sounded a lot like 'pre product detector days' to me. But
> frankly I was just about to give up on my Orion 565 (latest version
> 2.x) at that point.... already doing a lot of K3 research. So I
> decided to listen and maybe learn.
>
>We discussed the A-D converters in the Orion and that it was their
>practical sampling limit.... or max range of ability.... that made
>it important to keep the Preamp IN. The object there is to make sure
>that there is sufficient signal available to the A-D converters so
>that the conversion produced a better sampling overall (think of
>early audio CDs). If the RF energy applied to the A-D converters is
>too weak then the conversion process generates too few samplings...
>resulting in continual sampling errors which many of us experience
>as 'distorted' weak signal audio (I certainly had). Then it was
>explained (rather nicely) how the DSP derived AGC should be
>minimized.... even partially defeated by the Orion's RF GAIN control
>and that leaving the RF Gain MAX would result in extreme AGC
>compression and initial AGC overshoot.... even overdrive the
>following audio stages momentarily (resulting in the clicks and yet
>another situation of discernible audio distortion). The high AGC comp
> ression on the CW signals coming through the same passband
> lessened my ability to sort through CW pile ups and created the
> ever present key clicks (especially in the headphones) as a side
> effect. Think about it.... to discern one CW signal from another
> you need audible 'markers' to help you separate them from each
> other. Since most of today's CW transmitters output essentially
> pure notes (no chirp, drift, hummm, etc.)so what we have left is
> separation in note... differing audio levels... and differing
> keying characteristics (speed, hand key, keyer, keyboard, dot-dash
> ratio, etc.). So eliminating differing audio levels (extreme AGC
> compression) eliminates one normally important factor that helps us
> separate. And if you further consider the eventual conversion back
> from digital to audio you can see the advent of more audio 'error'
> since the digital signal that is being converted is merely the sum
> of all digitized RF signals through the bandpass at any particular
> moment. No mat
> ter how good the digital to audio conversion at this point it will
> generate more apparent error when compared to a well engineered,
> fully analog signal path. This apparent conversion error adds to
> the ear's confusion when working overtime to separate so many
> signals.... so closely spaced... during extreme reception
> conditions... i.e. CW contest.
>
>Finally.... learning to operate with the RF gain used to control the
>audio output (Audio GAIN at or near maximum) produces the best
>signal-to-noise ratio in the Orion's receiver. And isn't that what
>we usually want?
>
>So before you completely dismiss what I have written why not do what
>I did.... I turned off my automatic 'disbelief' button for a few
>weeks and started considering my Orion as a unique receiver that
>simply didn't provide its best performance when driven in a
>conventional manner. I began driving it as recommended and soon
>afterwards I began to develop a new respect for the Orion's
>abilities. And no more audio clicks... no more extreme AGC
>compression... no more weak signal distortion.... and I could more
>easily separate the piles of CW signals during a contest... or
>simply during the hunt for new DX.
>
>73,
>Jerry, KG6TT
>Fairfield, CA
>
>
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