Orion Hi Cut / Low Cut Explained

From the Ten-Tec Reflector January 5, 2004

I'll try to explain Hi Cut / Lo Cut succinctly:

We (Ten-Tec) had a long discussion about whether HI CUT / LO CUT is a bandwidth value or a passband tuning value when deciding how to update the display on the Orion - it's actually some of both.

For an example of why LO CUT (and HI CUT) are both a PBT and a BW value, try this:

Tune in a CW signal. Put your CW offset (using SPOT) at 600 to 700 Hz. Tune the CW signal to match the SPOT tone. Put the BW value at 1000 Hz, PBT at 0, select LO CUT.

As you rotate the LO CUT control clockwise, the PBT value increases as one side of the filter is moved towards the center of the passband. Because this also has the effect of narrowing the total filter bandwidth, the BW value is also updated to reflect the total BW available. As the CUT is narrowed, however, it is also possible to move past the center frequency of the filter until the CW signal you are listening to eventually disappears. The BW will still show a value of maybe 450 Hz or so, as that is now the BW of the available "distorted" filter after moving one side in towards or past the original center frequency.

If only the BW was adjusted, not the HI CUT or LO CUT or the PBT, when the filter was narrowed to 450 Hz you'd still hear the CW signal in the center of the filter. As opposed to PBT, where the filter BW is constant and the filter is then moved back and forth across the center frequency. HI or LO CUT moves one side of the filter or the other towards or past center frequency.

The PBT and BW values are supposed to update on screen graphics and text - unfortunately compounding the confusion is a bug that is present when HI CUT is adjusted. LO CUT shows the adjustment of PBT and BW values simultaneously, while HI CUT only shows the BW update, not the PBT value. This needs to be corrected.

Scott Robbins, W4PA