Mosaic
Well-Known Member
Hi all , i've been looking @ making an RF spectrum analyzer to hook to a scope , freq range of interest is in the 1Mhz to around 104-112Mhz range.
Questions:
1) For sensing RFI from PCBs etc, what kind of wideband preamp is suggested?
2) Are there combined VCO or (pref. I2C/SPI controlled) oscillators that can cover the freq band of interest? Hopefully they can also produce the IF by difference mixing?
3) By linking the VCO sweep period to the 'scopes trigger I should be able to view the various freq. amplitudes on a single scope channel?
4) By injecting (mixing) known period, small duty, fast square pulses of peak vertical amplitude (based on the VCO cycle period)matching the scopes display I can create horiz. 'scale' markings (vertically) on the CRT of known frequencies to 'calibrate' the CRT freq. display?
eg. If the CRT is displaying the full 112Mhz Bandwidth of the VCO, injecting pulses every 1/8 VCO period should create vertical lines on the CRT @ 14Mhz, 28Mhz , 42Mhz .... 112Mhz; for a 112MHz VCO bandwidth?
5) If #4 is reasonable, can I then create those same calibration pulses alternating at 2 known amplitudes after each VCO period thereby creating an apparent vertical amplitude reference for aligning the vertical deflection of the scope for more accurate amplitude readings?
Eg. Pulse 1 @ 1V, Pulse 2 @ 2v, pulse 3 @ 1V ...etc
6) #5 can be expanded to multiple known amplitudes if a log. output is used to help visualise the signal amplitudes?
Any advice is appreciated.
Questions:
1) For sensing RFI from PCBs etc, what kind of wideband preamp is suggested?
2) Are there combined VCO or (pref. I2C/SPI controlled) oscillators that can cover the freq band of interest? Hopefully they can also produce the IF by difference mixing?
3) By linking the VCO sweep period to the 'scopes trigger I should be able to view the various freq. amplitudes on a single scope channel?
4) By injecting (mixing) known period, small duty, fast square pulses of peak vertical amplitude (based on the VCO cycle period)matching the scopes display I can create horiz. 'scale' markings (vertically) on the CRT of known frequencies to 'calibrate' the CRT freq. display?
eg. If the CRT is displaying the full 112Mhz Bandwidth of the VCO, injecting pulses every 1/8 VCO period should create vertical lines on the CRT @ 14Mhz, 28Mhz , 42Mhz .... 112Mhz; for a 112MHz VCO bandwidth?
5) If #4 is reasonable, can I then create those same calibration pulses alternating at 2 known amplitudes after each VCO period thereby creating an apparent vertical amplitude reference for aligning the vertical deflection of the scope for more accurate amplitude readings?
Eg. Pulse 1 @ 1V, Pulse 2 @ 2v, pulse 3 @ 1V ...etc
6) #5 can be expanded to multiple known amplitudes if a log. output is used to help visualise the signal amplitudes?
Any advice is appreciated.