Orion 250 Hz & 500 Hz Filter Center Frequency Adjustment

From the Ten-Tec Reflector January 20, 2005

This is very simple requiring only a steady signal source (i.e. no noise sources, Spectrogram plots, etc.)

  1. Tune and zero beat Orion to a steady signal source.
  2. Set DSP = 1000 or higher to take any DSP filtering out of the adjustment. Enable and select desired filter in Filter Menu. Do NOT leave it in Auto.
  3. With C.F. Adj highlighted and not touching VFO, adjust your Multi knob so that you see equal downward deflection on the S-meter on both sides of the carrier. I would suggest about 1 S-unit or 6 dB deflection, or whatever meter marking is closest to that (i.e. not critical as long as you make it the same deflection on both sides).
  4. Write down the readings for each side of center. For example, you might have something like -60 and +20. Add these two numbers together and divide by 2 ([-60 +20] / 2 = -40/2 = -20). Set C.F. Adj. to that value. Your filter is now properly centered, independent of any passband ripple.
  5. Now check your work by first noting VFO zero beat (A=B is a simple way to keep track), and tune VFO to both sides to the same meter mark you used in 3 above, noting both frequencies. If you've done it correctly, both should be at an equal offset from the zero beat frequency.
BTW, if you install the Inrad 762 in the 1000 Hz position, you don't need either 500 or 250 Hz filters since it exceeds the IMD performance of both. Details below:

http://users.vnet.net/btippett/inrad_.htm

73, Bill W4ZV

Alternate method for adjusting the 250Hz and 500Hz CF Using Spectrogram

  1. A PC with sound card is needed
  2. A copy of Spectrogram.exe and a cable from rig audio out to PC mic input
  3. The registration for the program is optional since the 10 minutes it runs is ample time to do the adjustment
  4. A copy of the pdf titled "Using Spectrogram To Measure Filter Response" by

John Grebenkemper, KI6WX that will help with the initial setting of the program.

  1. Use a noise generator at the antenna input or use an empty spot on a band and use the background noise.
  2. Connect the rig audio out to the computer's sound card.
  3. Start Spectrogram and use the above document and set the initial settings. This is trivial and will take a few minutes.
  4. Place the rig BW just a tad less than 500Hz to engage the 500 filter.
  5. Under the menu item on the rig select 500Hz CF Adj.
  6. In Spectrogram, place the cursor (usually a cross hair) in the center of the bandwidth shown.
  7. Or you can calculate it by subtracting the lower skirt edge from the upper skirt edge, dividing that result by 2, and adding this to the lower edge reading.
  8. Back on the rig, use the Multi knob to center it.
  9. Repeat for the 250Hz by setting the rig's BW to a tad less than 250Hz.

Here is a short Youtube video depicting what I'm trying to describe above http://youtu.be/7Pcp4pU2VwM

73, Fernando N2FQ/6


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