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This is a sweet mod!
Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
Owner - Operator
Big Signal Ranch – K9ZC
Owner – Operator
Villa Grand Piton - J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
On Jan 8, 2018, at 8:52 AM, Alex Buurlage <pa1fox@...
Next to my chain of 12 MHz crystals SSB chain, I have placed a similar chain of 5 MHz crystals to create a narrow CW filter. I added the necessary firmware modifications. Pressing the function button and hitting the CW key just after will switch the CW mode from wide to narrow and vice versa. Very convenient. The BFO is switched to 5MHz instead of 12Mhz where it needs similar LSB and USB carrier sets as the SSB BFO.
The results are already very good, but there are some issues which I would like to share:
Don't use 5MHz for the CW crystals. Your BFO will be oscillating close to 5MHz and the result will be that the 9th harmonic will appear in your IF at 45MHz. Better is to use 4MHz crystals where the harmonics will not interfere with your IF.
There are no additional hardware switches necessary for the SSB and CW intermediate frequencies. Just switching the 2nd oscillator from 57 to 50 MHz is enough. SO:
SSB: 57 - 45 = 12 (LO-1st IF = 2nd IF)
CW: 50 - 45 = 5 (LO-1st IF = 2nd IF)
Using 470pF capacitors between the 5MHz crystals gives a bandwidth of under 200Hz. This is very narrow, gives amazing selectivity, but can be too narrow for practical use. With the 4MHz crystals, which will automatically make things even more narrow, 220pF or 150pF should be better. Will try out what the optimal values will be.
The combined use of the function button together with a short hit of the CW key works flawlessly. Since you are only switching CW bandwidth when doing CW you will have a key connected anyway. My function button now has 4 major functions:
Short press - enter menu: RIT, Calibration, LSB carrier, USB carrier, CW carrier (currently only USB mode)
Long press - frequency lock. I still use the original potmeter tuning from Ashhars first uBitx video since I like that tuning method.
Press and tune - band select
Press and CW key - CW narrow/wide
The more I work on this rig, the more I love it.