30-11-2023, 12:37 PM
There are some superhets from perhaps 1926. RCA had a patent, though should not have (USPTO broken since 19th C., as 1. it's maths, 2. French did it first. No-one should have had an FM patent either.). So most in USA were sold as kits. The mixer was and issue till pentodes and originally a separate triode oscillator was needed. The IF needed to be low at about 120 KHz, so image rejection was an issue. However they would often have used 6 to 8 valves and a rectifier. They had to have an RF stage to stop LO leakage to the big aerial. The US continued to add an RF stage into the 1950s for that reason on otherwise quite ordinary superhets.
VHF tuners used the 1st valve more to block radiation from the triode mixer osc (or triodised) than gain.
Later with ferrite rod aerials the AM mixer /osc was deemed to not be the issue it was on valve sets with long wire aerials.
VHF tuners used the 1st valve more to block radiation from the triode mixer osc (or triodised) than gain.
Later with ferrite rod aerials the AM mixer /osc was deemed to not be the issue it was on valve sets with long wire aerials.
