[TenTec] ORION II CW pile up readability

[Bob McGraw - K4TAX]

I've been reading this thread with interest.    There's a couple of things 
that I'd like to point out.

First, there is clearly the need to run to audio gain at a level for 
comfortable listening.  However, running the gain "wide open" or at a very 
high setting does leave one exposed to likely ear damage, headphone damage 
or speaker damage in the event of some accidental feedback condition that 
might develop. Be careful, headphones are about the most dangerous device 
one can place over or in our ears.

As to RF gain, keep in mind that the A-D and D-A processing clearly has a 
limit as to the dynamic range it can accurately handle.  Exceed this range 
and the system will produce all sorts of rude sounds and results.  Now to 
keep the A-D and D-A systems within their correct signal handling range 
there is an internal AGC function that is not user accessible.  At the same 
time in order to maintain the highest S/N ratio for reception, some type of 
gain control system is required, thus enter the user AGC system.  That 
system too has its limits of input dynamic range vs. output dynamic range. 
Now to operate within that range comes the "human interface" thus the 
dreaded manual RF Gain control.

The noise floor of these radios is extremely low.  Clearly many dB below the 
atmospheric noise and antenna thermal noise.  This is necessary to "hear the 
weak ones".  At the same time the gain of the radio, input to output is 
quite high.  Again needed to hear the weak ones.  Typically I find that 
after setting the AF gain at a modest level, it is then quite easy to find a 
RF gain setting for the band conditions and signals present.  I really find 
that I don't have to "ride the RF Gain" when tuning the bands.  The internal 
AGC systems handle the signals quite well.  Changing bands or antennas 
systems or even sometimes beam heading changes the noise floor and thus some 
minor RF gain adjustment is needed.

Perhaps we are not being clear in out terminology between AVC and AGC.  In 
case you thought so, they aren't the same.   Today's digital radios don't 
have AVC systems so don't expect the AGC system to do what a AVC system 
does.

I'm still not convinced that the PRE AMP on condition is really needed for 
most HF operation as it provides some 6 to 24 dB of gain.  In most cases on 
HF, again atmospheric noise will be the weak signal limiting factor.  There 
are certain exceptions that apply.  However, adding gain via the PRE AMP 
will raise the signal and will also raise the noise thus reducing the 
dynamic range that can be handled by the receiver AGC systems.  In my case 
the use of a PRE AMP is one that is mounted at the antenna and its purpose 
it to make up for the signal loss in the feedline between the antenna and 
the receiver thus maintaining or improving the NF of the receiver.  I 
believe we must get away from the thinking that more gain will allow us to 
hear weaker signals.  Actually it is more gain and less noise that 
accomplishes this task.  Thus, reduction in RF Gain is the objective.

73
Bob, K4TAX


----- Original Message ----- 
From: "Doug" <douglas.shock at gmail.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Friday, February 01, 2008 9:27 PM
Subject: Re: [TenTec] ORION II CW pile up readability


>I have been playing with the max af, ride the rf, pre-map on idea all
> evening. My "ears" tell me that there is an improvement. The NR actually
> works better than it ever has.
>
> The problem I have with this is that I am not sure the ergonomics's of
> the radio were designed with this setup in mind. So perhaps it is just a
> work around until TenTec blesses us with another release of SW.
>
> Merle Bone wrote:
>> Jerry Volpe (KG6TT) said:
>> ---------------------------------------------------------------------------------------------------------------------------------
>> "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)."
>> ------------------------------------------------------------------------------------------------------------
>>
>> I continue to return to the V1 firmware for my Orion for a number of 
>> causes - always
>> hoping that a new release of V2 will be as good as the V1 firmware. And, 
>> I certainly have no
>> reason to doubt what Jerry heard from one of the Ten-Tec engineers about 
>> the
>> A/D converter issue with the V2 code for the Orion and the Orion II. To 
>> look for that issue
>> in the V1 code, I ran some basic "minimum discernable signal" tests 
>> tonight - similar
>> to those run by the ARRL for their test reports. I started with a 
>> calibrated signal generator,
>> on 20 meters, and use a calibrated attenuator pad to further reduce the 
>> signal. I used
>> Spectrum Lab software, and most importantly my ear, to find the "minimum 
>> discernable
>> signal" and listened carefully to thee beat note from the signal 
>> generator through the Orion.
>> With the preamp off I got to a -121dbm signal that I judged to be the 
>> "minimum discernable signal"
>> from the ARRL procedures - that is about .224 microvolts for those that 
>> think better in those
>> terms. The RF gain of the Orion was set to 86.  The note from the 
>> generator was
>> clear and undistorted.
>>
>> I then turned on the Orion preamp and inserted additional attenuation 
>> looking for the
>> minimum discernable signal. With the preamp on I got to a signal 
>> of -133dbm - or
>> about .047 microvolts. The Orion RF gain was set to 80. The note from the 
>> generator
>> was clear and undistorted.
>>
>> So I think it is safe to say that  the V1 code doesn't appear to have any 
>> issues with A/D
>> errors at the level of signals that we use in communications through the 
>> Orion. Of course
>> the noise level on all but the highest HF bands is much above the levels 
>> of these - and the
>> ARRL's - tests. So, the signal levels passing through the Orion are 
>> significantly above the
>> test levels.
>>
>> -----I stopped writing for a couple of minutes to work EL2DX on 160M - My 
>> QTH, the radio
>> black hole of urban St. Louis Missouri ----- :-)
>>
>> As I just worked the EL2 on 160M, my preamp was off, my RF gain was on 
>> 78, my AGC
>> threshold was on .37 microvolts, AGC Decay was at 45dB/S and my hang was 
>> set to
>> .04. You could not ask for a cleaner signal to work - all be it close to 
>> the noise here in
>> Missouri!
>>
>> Maybe we will hear more from Ten-Tec about this A/D converter error with 
>> the V2
>> code and the "AGC overshoot." And maybe even get a new V2 code release 
>> for the
>> Orion and Orion II with some more of the issues resolved!
>> 73, Merle - W0EWM
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>>
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