[TenTec] One complicated radio!

[Bill Tippett <btippett@alum.mit.edu>]

KC9CDT wrote:
>Are these issues (the interaction of RF gain, AGC threshold and decay, and
BW) design issues, meaning does the ORION design / implementation have some
problems? OR... are these issues necessary to get a better performing RX 
function.

        Great questions Lee!  The simple answer is probably YES to BOTH.
To me, one of the most striking differences about Orion has to do
with the action of its Digital AGC (not the Analog AGC which only operates 
to prevent over-driving the ADC with S9+30 signals).  I
certainly don't fully understand it even though I have read KF6DX's
article carefully several times:

http://www.doug-smith.net/digitalagc.htm

Although the IC-756PRO2 is also a DSP radio, and probably also has a
version of digital AGC, its AGC action apparently doesn't have the same
unique characteristics as Orion.  I've never used one, but I don't believe 
it has the same degree of AGC adjustment (i.e. Threshold and
Hang...Decay is probably included in the Fast/Medium/Slow setting).  I
also don't know if the PRO2's AGC works as well as Orion's does.  Orion
was truly amazing in the CQ WW SSB. I was able to run DX stations
from the noise floor up to S9++ while seldom needing to adjust AF
or RF Gain.  With my previous MP, I would continually need to adjust both 
controls.

        Orion's AGC may be one of the BEST features of the radio, but it
may also be one of the WORST under certain conditions.  I believe these
conditions are for very specific noise (impulse, but not galactic or
"white" noise) when it becomes very critical to adjust the AGC for
signals right AT the noise floor.  This is why it takes some learning to
use it on the low bands which have impulse-type noise (lightning QRN).

        So yes, you probably get the best truly "Automatic Gain Control"
I've ever seen in any radio, but for certain specific noise conditions,
Orion may require more work than we are accustomed to make it work
well.  The good news is that the Digital AGC is completely contained
within the DSP, so as TT develops improvements, AGC improvements should
be available in future firmware updates.

        I'm personally willing to live with the AGC issues awhile because:

1.  Orion's front-end performance is far better than any other radio,
which is very important to me for contests and low-band DX-ing.

2.  I have confidence Ten-Tec will continue to refine Orion based on our
inputs, including the AGC action and ease-of-use, in future updates.

                                        73,  Bill  W4ZV

P.S.  Regarding your second post about Orion's noise level, just learn
to adjust Threshold upwards until the noise floor drops to a reasonable
level.  This level is different on every band depending on conditions,
time of day, etc.  Think of it as adjusting RF Gain in a traditional
radio.  

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