Brian, Was there any particular reason to go from 5MHz to 20MHz in two steps ? couldn't be just one x4 stage followed by the filter (preferably xtal) ?
Luis Cupido. ct1dmk. wa1...@att.net wrote: > John- > > The BPFs in the 5 to 20MHz chain are just 7-pole LC > filters with the goal of trying to keep any other > harmonics other than the desired at least -50dBc. > Xtal filters would be the better choice, no doubt. > > The -50dBc level is clearly not the best > that one could get, but was enough for an earlier > 240GHz project. I just used the same OCXOs and early > stages of multipliers to get the latest system running > on 630GHz. > > In the 241GHz system, I ended up building a direct > frequency synthesizer to get 110MHz from a 10MHz > drive signal. At the time, the Freq West PLL > blocks I used wanted a VHF signal to drive > the sampling detector to phase lock the L-band > cavity VCO. The original Freq West units used 5th OT > xtals for the commercial applications. > > By later experimentation, I found that > the same sampling detector would also work with a > much lower frequency reference and still lock the > loop. The risk however is that the PLL might lock > on the wrong harmonic of the reference (i.e.: value of N) > or can have higher reference spur levels since the > PLL was designed assuming a VHF reference and not an > HF reference frequency. But this is not a commercial > design project, and I can live with a difficult alignment > procedure or initial power-up PLL lock troubles. > > But all this aside, my efforts are currently aimed at > best close-in noise within the first 1KHz of BW around > the carrier. > > The PLL bricks all seem to have several kHz of loop BW, > so my close-in noise going from 20MHz to 1320MHz should > be only slightly worse than 20Log(n), with n=66 in my case. > But I'm not ruling out the chance of 1/f noise (or similar) > showing up from the sampling detector or some other yet-to-be > determined source. > > However my focus is currently on the 5MHz to 20MHz portion > of the LO chain and to be sure the gain stages are not > running near compression. I do still agree with your > earlier comment about getting the most from that portion > of the chain. > > -Brian, WA1ZMS > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on > Behalf Of John Miles > Sent: Tuesday, December 16, 2008 7:53 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Close-in phase noise question...more info... > > >> More info on the LO chain: >> >> 1) 5MHz Wenzel OCXO <--Custom Osc for me. >> 2) MSA-1105 buffer MMIC and lumped LPF >> 3) 5MHz to 10MHz 1N5711 diode based doubler >> 4) MSA-1105 buffer and lumped LPF >> 5) 10MHz to 20MHz 1N5711 diode based doubler >> 6) 20MHz BPF > > What kind of BPF? A really narrow crystal filter would be nice here. (You > have basically reproduced the 8568A/B's 20 MHz reference section.) > >> 7) 20MHz drives sampling detector inside surplus Frequency >> West PLL block to lock 1320MHz cavity oscillator. > > Sounds OK as long as the sampler loop's noise floor doesn't limit you. I > haven't measured the in-band residual floor of any bricks but I'd be > surprised if an SRD multiplier wouldn't be quieter. > >> 8) 1320MHz drives Frequency West SRD multiplier to 6.6GHz. > > If I wanted to get to several GHz with what's in my junk box right now, I > would do what you did to get to 20 MHz, BPF it with a multipole crystal > filter, and then use a few more multiplier stages to get somewhere between > 100 MHz and 1 GHz, a la the 8662A reference section, depending on the choice > of the next stage. > > That VHF drive signal would go into either an HP 33002A or 33004A SRD > multiplier, or one of the Picosecond NLTL multipliers (e.g., > http://www.picosecond.com/product/product.asp?prod_id=109 ) I picked up in > their fire sale when they shut down their fab. > >> 9) 6.6GHz to 39.6GHz Milliwave diode multiplier/amp/filter >> 10) 39.6GHz to 79.2GHz in varactor doubler >> 11) 79.2GHz to 158.4GHz in varactor doubler >> 12) 158.4GHz into x4 sub-harmonic mixer > > AFAIK the rest of the chain is fine. I'd focus on getting rid of the brick > PLL, or at least taking pains to make sure that it's not the problem, before > worrying about the MMICs in your early stages. > > Remember that there's no point in optimizing the PN of any one stage much > below the input-referred residual noise of the following stage. MMICs, in > saturation or not, are pretty quiet. Quieter than sampler loops anyway. > > -- john, KE5FX > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.