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 > > time-nuts@febo.com > > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > 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 time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
