The higher IF frequency (1.7MHz) means better image rejection on the higher frequency bands (image frequency = signal frequency + 2*IF) Eg: (1) If the IF is 1.7Mhz and the signal frequency is say 25MHz the oscillator frequency would normally be 26.7MHz which would mean the image frequency would be at 28.4MHz, in other words the image frequency is 3.4Mhz (twice the IF (2*IF))above the signal frequency.
Eg: (2) If the IF was lower such as 450kHz then for the same signal frequency (25MHz)as in example 1 then the oscillator frequency would normally be 25.450MHz which by the same reasoning as above would mean the image frequency would be at 25.9MHz which is only 0.9MHz above the signal frequency and therefore would be more difficult to filter out from the signal frequency, the amount of filtering in practice is governed by the bandwidth of the RF tuned circuit(s)
The xtal in the IF will be for the filter, the filter usually has positions for different selectivity settings and quite often a phasing control for single signal reception on CW such as in the Hallicrafters SX28, manual pages 7&8 give a brief outline of the xtal filter/single signal reception etc:
http://www.vmarsmanuals.co.uk/archive/16...X-28-A.pdf
Cold cathode regulators were not uncommon in comms receivers, usually to stabilize the oscillators HT line, the RCA AR88 being just one example.
Lawrence.
Eg: (2) If the IF was lower such as 450kHz then for the same signal frequency (25MHz)as in example 1 then the oscillator frequency would normally be 25.450MHz which by the same reasoning as above would mean the image frequency would be at 25.9MHz which is only 0.9MHz above the signal frequency and therefore would be more difficult to filter out from the signal frequency, the amount of filtering in practice is governed by the bandwidth of the RF tuned circuit(s)
The xtal in the IF will be for the filter, the filter usually has positions for different selectivity settings and quite often a phasing control for single signal reception on CW such as in the Hallicrafters SX28, manual pages 7&8 give a brief outline of the xtal filter/single signal reception etc:
http://www.vmarsmanuals.co.uk/archive/16...X-28-A.pdf
Cold cathode regulators were not uncommon in comms receivers, usually to stabilize the oscillators HT line, the RCA AR88 being just one example.
Lawrence.
