Hi Normand -- Your method is similar to mine, except that I use a much closer beat note (usually less than 100 Hz) and use spectrum analyzer software and a sound card to measure the beat note (in the form of the delta between two traces on the waterfall display).
I think one of the reasons this method works so well is that the FFT effectively averages the signal over some time, and I use a tool in the software to derive an average across all the FFT results. That smooths out the instantaneous variations that make real-time measurement such a challenge. John ---- Normand Martel wrote: > Personnaly, i use a self-developed technique to > remotely measure a station's frequency: > > I use a precision OXCO controlled RF signal generator > to inject an unmodulated (CW) signal (via a > directional coupler) signal 1000 Hz below the actual > station's frequency (example, to monitor CHU at 7335 > kHz, i inject a 7334 kHz signal into the coupler). I > then adjust the generator's level to obtain a > comfortable 1000 Hz from my receiver (in AM mode > preferably, but it even works in FM... do not use SSB > or CW modes, since the receiver's BFO will interfere). > Finally, i measure the 1 kHz beat's frequency with > precision (for that, i use an synthesized audio > generator with a ramp (sawtooth) output on an o'scope > in a X-Y function (X = ramp, Y = beat). > > I prefer to use a ramp rather than a sine signal, > since the ramp closely resembles a classic temporal > sweep in a scope. This way, it becomes very easy to > see if the generator's frequency is above or below the > beat's frequency, which is much harder with a sine X > input. > > One other way is to use the scope in classic mode with > the audio synthetizer (preferably in square wave, but > sine would also do the job) feeding the scope's > external trigger. > > However, on distant HF signals, it becomes very hard > to precisely measure the station's frequency due to > the signal's fading which has important effects on the > signal's phase. This phase unstability originates from > the constantly changing RF signal's path due to the > naturally unstable ionosphere's condition. > > The receiver does NOT need to be a precision unit (you > could even use a VFO controlled radio), since the beat > comes from the heterodyning between the station's and > the generator's signals. > > 73 de Normand Martel VE2UM > Montreal, Qc. Canada. > > --- John Ackermann N8UR <[EMAIL PROTECTED]> wrote: > >> Hi Colin -- >> >> Actually, the transmitters used for the FMT seem to >> be very stable and >> as far as I've been able to observe (during each of >> the 4 FMTs since >> they restarted the event) don't drift by a >> noticeable amount during the >> test. >> >> I'm actually more concerned about the ARRL's >> measurement setup than I am >> about the transmitter stability. At least through >> last year, they >> measured the frequency off-air by hooking the >> counter to an outside >> antenna through a bandpass filter, rather than >> tapping off the output of >> the transmitters. With multiple KW signals floating >> around the >> vicinity, there's lots of opportunity for counter >> confusion. Some of us >> believe that ARRL's frequency measurement of the >> 160M signal last year >> was about 0.4 Hz off, and I suspect the measurement >> setup caused that. >> >> John >> ---- >> >> Colin Bradley wrote: >>> I just finished several email exchanges with Joe >> Carcia, station manager for W1AW, about the >> operation of the station. I had hoped that the >> regular daily bulletins broadcast by W1AW would be >> tightly controlled in frequency, which would allow >> me to get some practice measuring them. He informed >> me that they use two IC-756Pro II¢s and one Orion I >> for the transmissions. These radios do not permit >> the use of external standards for frequency control. >> Neither do the Harris 3200¢s. All of these radios >> use TCXO¢s for frequency control. This setup will be >> the same used for the FMT on the 15th. They will >> monitor frequency with a counter hooked to their >> Z3801. >>> >>> It¢s hard to believe, with a 100-watt amplifier in >> the same case, that these radios don¢t drift several >> cycles during a long transmission. For that reason I >> would encourage persons making measurements to do so >> during the specified time for each frequency in >> question. I think it would be very hard to measure >> the frequency to 1 cycle or less with the frequency >> control they use. The West Coast station that will >> broadcast a 40-meter test signal which will, most >> likely, be more accurate. That station will be using >> a Heathkit DX-60 into a 400-watt amp. Frequency >> control is from a HP-107BR into a HP-5100 >> synthesizer. While old, this equipment will probably >> be up to the job. The oscillator is set against GPS >> and the whole setup will be independently monitored >> by another station a mile away with a Cesium >> standard. >>> Colin Bradley >>> >>> _______________________________________________ >>> time-nuts mailing list >>> [email protected] >>> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> >> _______________________________________________ >> time-nuts mailing list >> [email protected] >> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > > ____________________________________________________________________________________ > Do you Yahoo!? > Everyone is raving about the all-new Yahoo! Mail beta. > http://new.mail.yahoo.com > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
