Update on NAA. The tracor d-msk-r was completed last night and tried it out.
Someone on this thread said I would find that the lm3900 was acting as a half wave rectifier and he was right. The whole thing is a frequency doubler. But the last stage removes the higher frequency. Its a bandpass filter. The magic goes like this. NAA is at 24,000Hz and the LO is at 23,900 Hz. Result a 100 Hz baseband signal modulates + and - 50 Hz MSK. The doubler multiplies 50 Hz to 100 Hz. the 150 is multiplied and rejected by the bandpass filter. Result, a 100 hz signal only for one of the MSK carriers. The one at 23950 Hz. (Because of the low side LO injection that may be flipped. But no real effect.) I barely looked at the stability of that 100 Hz. The fact is I have no 100 Hz locked reference. There is a bit of humor everyday. Never thought I would need one. Easy enough to make and I will dig in further tonight. Regards Paul WB8TSL On Tue, Sep 9, 2014 at 8:50 PM, paul swed <paulsw...@gmail.com> wrote: > A short update on NAA as some sort of reference. > Have completed a simple direct conversion circuit using a NE612. A few > minor changes because the system only needs 100 Hz or less. It is > essentially this circuit. > http://www.qsl.net/ik2pii/lf/dcrx136.htm > > Its receiving NAA just fine with about 1 Vpp out and the official MSK is > there. No attempt to use the tracor 900 circuit yet. Also the LO is a HP > 3335a locked to the station RB. Somewhat a massive system connected to a > small board. A start none the less. > > Will not be hard to build the tracor d-msk-r to see what happens. > Regards > Paul > WB8TSL > > On Wed, Aug 20, 2014 at 9:01 AM, Bill Riches <bill.ric...@verizon.net> > wrote: > >> NAA -50 dbm (1 MV) using a mini-whip. -60 dbm on the k9ay loop. >> Mini-whip >> is full of surprises. >> >> 73, >> >> Bill, WA2DVU >> Cape May, NJ >> >> -----Original Message----- >> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >> Behalf Of paul swed >> Sent: Tuesday, August 19, 2014 9:51 PM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] Cutler NAA on 24.0kHz.... >> >> Did measure NAA near Boston 8000uv using a dipole for 80 meters. >> Looking at various vlf receivers it looks like a LPF or maybe a BPF filter >> to a ne602 mixer followed by a tl081opamp LPF makes a direct conversion >> receiver. Then hit the tracor d-msk-r. >> Regards >> Paul >> WB8TSL >> >> >> On Mon, Aug 18, 2014 at 2:34 PM, Charles Steinmetz <csteinm...@yandex.com >> > >> wrote: >> >> > Paul wrote: >> > >> > Nat Semi App Note 72 page 18, par. 6.4 shows the configuration for >> >> bandpass active filter. This matches the last LM3900 stage, so you >> >> would seem to be correct. The shift in filter frequency for 200bps >> >> is because the higher modulation rate results in a greater frequency >> >> shift. It's like 50hz instead of the 25hz of the 100bps rate. >> >> >> >> Robert wrote: >> >> >> >> It's simple, but not obvious. The LM3900 is a Norton amplifier, and >> >>> while it has differential inputs they are current driven. * * * >> Both >> >>> the upper amplifier and the second lower amplifier have 1M feedback >> >>> resistors, and + inputs fed 10V by 1M bias resistors. That would >> >>> bias the output at near the supply rail, turning these stages into >> >>> something like half-wave rectifiers. Since the first lower stage has a >> 2M bias resistor it >> >>> idles at about half supply, and behaves as a simple inverter. * * >> * >> >>> combining the two outputs produces a negative going full wave >> >>> rectification of the signal. The fourth LM3900 stage looks like an >> >>> inverting bandpass filter, but I'd have to dig out some reference >> >>> books to determine its behavior in more detail. As f or the 100-200 >> >>> switch I'm confused, why would the bandpass frequency be lowered for >> the >> higher modulation rate? >> >>> >> >> >> > The circuit as a whole operates as a frequency doubler using full-wave >> > rectification and filtering. The rx LO is 100Hz below the nominal >> > carrier frequency, so in "normal" (non-MSK) mode, the IF frequency is >> 100Hz. >> > Referring to the MSK addendum, a received 200 baud MSK signal is 50Hz >> > below nominal, and a 100 baud MSK signal is 25Hz below nominal. With >> > the LO 100 Hz below nominal, this makes the IF frequency 50Hz when >> > receiving a 200 baud MSK signal, and 75 Hz when receiving a 100 baud >> > MSK signal. After doubling, these become 100 Hz (200 baud) and 150 Hz >> > (100 baud), so the BPF is switchable between 100Hz and 150Hz. They >> > used a FET to chop the 150Hz >> > (100 baud) signal with a 50Hz square wave. >> > >> > I can't say I'm impressed with the design, even for the era. The >> > whole instrument is built mostly with LM3900s, which makes it >> > thousands (maybe even millions) of times noisier than it would be if >> > it had been properly designed with standard op-amps. It may work more >> > or less, but it's a fugly way to get there. There are other >> > questionable choices (like the FET chopper, an overall design that >> > depends on lots of one-shots, etc.). The designers knew about the >> > LM301 (there is one in the unit), so there was really no excuse for >> > using LM3900s. Yeah, the 301 was more expensive -- but this was >> > supposed to be a state-of-the-art measuring device for characterizing >> good >> OCXOs down to PPB or below. >> > >> > I simulated the MSK board in LTspice. Let me know (OFFLIST ONLY, >> > please) if you would like the files to play with (662kB ZIP file). >> > (Note that these won't do you any good if you're not an LTspice user.) >> > Again, please do not clutter the list with requests for files -- >> > OFFLIST ONLY, please (check your headers carefully before you hit >> "Send"). >> > >> > Best regards, >> > >> > Charles >> > >> > >> > >> > >> > _______________________________________________ >> > 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. >> >> >> --- >> This email is free from viruses and malware because avast! 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