[TenTec] USING ORION'S RECEIVER

[Sinisa Hristov]

Carl Moreschi wrote:

> Great document about how to adjust the Orion.  Very well done.

Thanks!


> The AGC threshold adjustment on the Orion is
> actually the point where DSP gain is added to a weak signal to bring the
> weak signal up to the same audio level as a strong signal.  Signals below
> this value are not amplified in DSP.

Well, one can say that, starting from the strongest
possible signal downwards, the gain is increased
(or attenuation decreased) to keep the volume constant,
until the threshold is reached, and the gain is then held
constant for signals below the threshold.

Or one can tell this story starting from the weakest
signal upwards - but it's the same story :-)

The transfer function (audio volume vs. input signal level)
looks exactly the same as for any other receiver:
it's a 45-degree rising line clipped to horizontal at the threshold.


> This is opposite all other AGC implementations I have seen. 
> This is why the audio level goes down as you increase AGC threshold.

This is exactly the same as when AGC threshold is increased
by reducing RF gain on usual receivers: volume of weak signals
also goes down, but the volume of strong signals remains unchanged.


> In other receivers, signals below the AGC threshold are heard at full gain
> with no AGC reduction.  This is clearly not the case in the Orion.

This clearly IS the case with Orion too, with "full gain"
determined by AGC THRESHOLD control, just like it's
determined by an overriding RF GAIN control on other receivers.

The only difference is in the direction of rotation:
conventional RF GAIN raises the threshold when rotated
counter-clockwise, but Orion's AGC THRESHOLD control
raises the threshold when, so to say, rotated clockwise.


73,

Sinisa  YT1NT, VA3TTN