[time-nuts] FMT

[John Ackermann N8UR]

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
> 
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