Do you need a 4647? Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y les...@veenstras.com
452 Stable Ln (HC84 RFD USPS Mail) Keyser WV 26726 GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 Jamaica cell: +1-876-456-8898 -----Original Message----- From: ed breya [mailto:e...@telight.com] Sent: Wednesday, May 11, 2022 1:57 AM To: time-nuts@lists.febo.com Subject: [time-nuts] Noise down-converter project The noise converter project based on the Scientific Atlanta 4647 is moving along nicely. Still no luck in finding any more info about this unit, but I did quite a bit of digging in the guts, and figured out enough to make progress. The noise generator, to my surprise, is not a typical noise-diode-based type, but an all-amplifier deal, and apparently the fundamental noise source is a 75 ohm resistor in conjunction with the input noise of a 2N5179 amplifier front end. The first few stages are broadband, followed by maybe eight bandpass stages, to craft the power level and shape, resulting in the 50-90 MHz noise signal, which gets passed to the noise amplifier box. The noise amplifier is broadband again, then feeding a CATV type hybrid power amp for final output, which goes through a ferrite part, which is either a splitter or directional coupler, for leveling, then on to a decade step attenuator using Teledyne TO-5 style relays. The leveling signal from the local detector is sent back to the noise generator box where it somehow does the gain control. Altogether, a couple dozen or so transistors are used in the gain stages. The step attenuator output is sent to the last box, the "C+N amplifier," where the external carrier input is attenuated with a step attenuator, then amplified up and leveled in similar fashion (including another CATV hybrid PA), then through its own step attenuator, and added to the noise through a reactive power combiner. So, the noise and carrier signals are each at least 3 dB bigger than the spec output levels, to accommodate the adding process. I added a small board into the noise amp module, with an RF relay to pass the signal as normal, or route it to the new converter. The maximum PSD of the noise available there is about -70 dBm/Hz, versus the -73 dBm/Hz at the normal C+N output. The rest of the action is all built into the 70 MHz oscillator/agc amp module now. I sacrificed the agc amp function, and utilized the space for the mixer and LPF, and added yet another CATV type PA in the oscillator section, for the LO. More on this in the next installment. Ed _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com