Hello,
a little code reading before my question on value of frequencies
Code UBITX V4.3
The uBITX is an upconnversion transceiver. The first IF is at 45 MHz.
? ?The first IF frequency is not exactly at 45 Mhz but about 5 khz lower,
? ?this shift is due to the loading on the 45 Mhz crystal filter by the matching
? ?L-network used on it's either sides.
? ?The first oscillator works between 48 Mhz and 75 MHz. The signal is subtracted
? ?from the first oscillator to arriive at 45 Mhz IF. Thus, it is inverted : LSB becomes USB
? ?and USB becomes LSB.
? ?The second IF of 12 Mhz has a ladder crystal filter. If a second oscillator is used at
? ?57 Mhz, the signal is subtracted FROM the oscillator, inverting a second time, and arrives
? ?at the 12 Mhz ladder filter thus doouble inversion, keeps the sidebands as they originally were.
? ?If the second oscillator is at 33 Mhz, the oscilaltor is subtracated from the signal,
? ?thus keeping the signal's sidebands inverted. The USB will become LSB.
? ?We use this technique to switch sidebands. This is to avoid placing the lsbCarrier close to
? ?12 MHz where its fifth harmonic beats with the arduino's 16 Mhz oscillator's fourth harmonic
*/
// the second oscillator should ideally be at 57 MHz, however, the crystal filter's center frequency
// is shifted down a little due to the loading from the impedance matching L-networks on either sides
#define SECOND_OSC_USB (56995000l)
#define SECOND_OSC_LSB (32995000l)
?
?
//these are the two default USB and LSB frequencies. The best frequencies depend upon your individual taste and filter shape
#define INIT_USB_FREQ? ?(11998370l)-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Code KD8CEC.....
?#define SECOND_OSC_USB (57003400l)
? #define SECOND_OSC_LSB (33010400l)?
? //these are the two default USB and LSB frequencies. The best frequencies depend upon your individual taste and filter shape
? //Not used, Just comment (Default)
? #define INIT_USB_FREQ? ?(11996500l)
....
MY TESTS:
I made a model to test my 45MHZ filter with a nanovna (So i change the value of inductance and capacitors for maching (1.5 ?h and 8pf) on my homebrew assembly))
this gives:
Central frequency: 45.004280 MHZ
Low frequency at -3DB: 44.997900 MHZ approximately
High frequency at -3DB: 45.010480 MHZ approximately
My question:
function of the values (which are different) in the code v4.3 of the Ubitx and KD8CEC? and my filter frequencies description , what would be the 3 best values for USB freq, OSC USB and OSC LSB knowing that a priori they take into account matching ?
I would like to amend the code to that effect
cdt
Gerard