Timeline for Why is superheterodyning better than direct conversion?
Current License: CC BY-SA 4.0
7 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 14, 2019 at 21:49 | comment | added | TimWescott | Headphones require far less power, so far less signal is coupled from the final amplifier onto the power rails -- this reduces the amount of isolation needed between those power rails and the receiver's first audio-frequency amplifier. | |
| Apr 14, 2019 at 21:31 | comment | added | David Cullen | I was asking about why "most direct conversion receivers have headphones". How exactly do headphones help? | |
| Apr 14, 2019 at 21:20 | comment | added | TimWescott | @DavidCullen I think you're asking about sideband suppression in direct-conversion receivers. It's because the sideband you don't want is suppressed by subtracting out a pair of signals that go through separate channels, that must be matched for gain, and which must have phase shifts 90 degrees apart. That is difficult to achieve, and subject to component variations -- so you end up with less suppression than you'd like. | |
| Apr 14, 2019 at 20:58 | comment | added | David Cullen | What's the "reason for this"? | |
| Apr 14, 2019 at 14:24 | comment | added | TimWescott | @ThreePhaseEel yes. I addressed that: "You can mitigate this problem a lot with quadrature downconversion, but while it's enough for digital data reception, it's not good enough for analog". It can be used, and it is, but getting more than 40dB or so of opposite sideband suppression with analog circuitry requires heroic measures. The fact that only a small percentage of commercial receivers ever used it is a strong indication of the cost/benefit tradeoff. | |
| Apr 14, 2019 at 3:55 | comment | added | ThreePhaseEel | Actually, you can do sideband suppression using quadrature techniques, on TX and RX -- there are DC designs in the ham world that do just that | |
| Apr 13, 2019 at 14:58 | history | answered | TimWescott | CC BY-SA 4.0 |