30-06-2020, 12:30 PM
(This post was last modified: 30-06-2020, 12:37 PM by Mike Watterson.)
Here is the wikipedia article on the ring diode mixer.
https://en.wikipedia.org/wiki/Ring_modulation
Often the IF connections are shown where Wiki has "Carrier" (= Local Oscillator), and then the input or output port would be Local Oscillator.
It's used for superhet RF to IF, baseband Audio to Transmit IF, Transmitter IF and synthesiser to RF out, for 10.7 to 455 KHz IF conversion, or 68MHz IF to 6MHz IF , for BFO mixing, for 455 kHz to 12.5 KHz for sound card SDR. It's been used in the 1930s with copper oxide diodes for Telephone multicarrier systems on a coax cable. Largely replaced by ICs, but CBs often still use them for 10.7 MHz IF <> RF conversion. The better the centre tap windings and diodes are matched, the better the suppression of the un-mixed signals between ports, such as LO or RF in on the IF port (receive), or LO on RF in (receive) or IF and LO on RF out (transmit). The 1j42a or 1j37b circuit does give good LO to input rejection, but not as much rejection of unwanted products on the anode. It will however have a better rejection of RF in on the output than a simple mixer using a non-linear device or amplifier as only common mode signals have decent gain on the g1a and g1b and differential signals have poor gain on the g1a and g1b, this is the opposite performance to a differential amplifier like a long tailed pair, two triodes with one cathode resistor, or an opamp.
This is why the RF in has to feed a differential signal to the 1j42a (or 1j37b), it means out of band and signals in or near the IF bandpass are poorly amplified. The LO is amplified, but that's a single known clean signal well outside the IF.
Your LO should on ANY radio design be noise free, have low phase noise and no FM or harmonics, for best performance. This is why early PLL synthesised radios are noisier than types with multiple crystals for the bands and a very stable 5MHz to 5.5MHz or similar mechanical variable oscillators.
https://en.wikipedia.org/wiki/Ring_modulation
Often the IF connections are shown where Wiki has "Carrier" (= Local Oscillator), and then the input or output port would be Local Oscillator.
It's used for superhet RF to IF, baseband Audio to Transmit IF, Transmitter IF and synthesiser to RF out, for 10.7 to 455 KHz IF conversion, or 68MHz IF to 6MHz IF , for BFO mixing, for 455 kHz to 12.5 KHz for sound card SDR. It's been used in the 1930s with copper oxide diodes for Telephone multicarrier systems on a coax cable. Largely replaced by ICs, but CBs often still use them for 10.7 MHz IF <> RF conversion. The better the centre tap windings and diodes are matched, the better the suppression of the un-mixed signals between ports, such as LO or RF in on the IF port (receive), or LO on RF in (receive) or IF and LO on RF out (transmit). The 1j42a or 1j37b circuit does give good LO to input rejection, but not as much rejection of unwanted products on the anode. It will however have a better rejection of RF in on the output than a simple mixer using a non-linear device or amplifier as only common mode signals have decent gain on the g1a and g1b and differential signals have poor gain on the g1a and g1b, this is the opposite performance to a differential amplifier like a long tailed pair, two triodes with one cathode resistor, or an opamp.
This is why the RF in has to feed a differential signal to the 1j42a (or 1j37b), it means out of band and signals in or near the IF bandpass are poorly amplified. The LO is amplified, but that's a single known clean signal well outside the IF.
Your LO should on ANY radio design be noise free, have low phase noise and no FM or harmonics, for best performance. This is why early PLL synthesised radios are noisier than types with multiple crystals for the bands and a very stable 5MHz to 5.5MHz or similar mechanical variable oscillators.
