AM Frequency Measurements

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GregHahn
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Re: AM Frequency Measurements

Post by GregHahn » Mon Mar 19, 2012 10:05 am

Deep Thought wrote:"if your counter agrees substantially with a known standard"

Now, in my world that is what "traceable" means. But what the hell do I know...I've only been doing this for 35 years. 8) When I started this we would routinely check frequency monitors (remember those?) against WWV. Handheld frequency counters were a decade away and accurate ones rarely left the lab. Most of today's modern transmitters are more stable than the measurement equipment was in the 1970s.

You're the one who introduced certificates and lab tests into this.

Good to see you here but you need to know this is not a place for arguing word semantics. As the logo says, it's "a forum for the people who get it done".

That's generally great advice, Mark, though it's hard for me to understand how to avoid semantics on a sub-board specifically devoted to the discussion of written FCC Rules and how to interpret them. Isn't that, by definition, "semantics"?

Congratulations on your 35 years of late night calls and ruined holidays. I will celebrate my 36th year of that this summer myself.

Sounds like we're on the same page. Here's to getting it done.
Greg Hahn
Chief Engineer
WQNU WRKA WVEZ WSFR
Louisville KY USA

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BroadcastDoc
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Re: AM Frequency Measurements

Post by BroadcastDoc » Mon Mar 19, 2012 11:48 am

I do find it interesting how people interpret the rules, however. If there's one thing we can all agree on is that there is often room for interpretation on many of the rules. It reminds me of this past fall at the WBA Broadcaster's Clinic - one of the guest speakers was someone from the FCC field office. He was, not surprisingly, peppered with questions. Most of them he wouldn't answer specifically. It often boiled down to "I can't tell you what's right or wrong, but we'll know it when we see it!".

It kind of reminds me of the joke I like to tell about Broadcast Engineers...

Take three Broadcast Engineers outside on a sunny day, and ask them what color the sky is. One will say "Blue", one will say "Grey" and one will say "Blue, but I would have done it differently!" :)
Christopher "Doc" Tarr CSRE, DRB, AMD, CBNE
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Dave Loudin
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Re: AM Frequency Measurements

Post by Dave Loudin » Mon Mar 19, 2012 4:30 pm

...or "whatever the FCC says on your license."
What's that do....?

kcbooboo
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Re: AM Frequency Measurements

Post by kcbooboo » Wed Mar 21, 2012 6:41 pm

I have read many of the white papers on the NIST site as it mentions using GPS for frequency and time measurements. It's just that they don't come out and say specifically that a GPS-disciplined 10 MHz oscillator can be traced back to WWV. and the way the FCC rules are written, they still call it NBS. I think we all realize that the accuracy of a GPSDO is certainly far better than the +/- 20 Hz frequency tolerance for AM stations, and even zero-beating WWV will get you down to below 1ppm, so a station measured with a counter adjusted against WWV will be within tolerance. In my case, a GPSDO which has been running for several years, is stable and accurate to better than 1ppb, so I'd rather use that than try to pick up WWV when I need it.

Speaking of frequency tolerance, I've checked almost a dozen stations and have found that the ones running IBOC are within 0.01 Hz of their assigned frequency, while the non-IBOC stations are all over the place, but still within the legal limit. I also know of two IBOC stations that are NOT using the GPS receivers in their IBOC exciters (no antenna connected), and they too are within 0.01 Hz. Unfortunately I haven't had the opportunity to measure those two stations when running in stock analog mode, using the oscillators built into the transmitters themselves. I suspect they'll be off frequency a bit, but still be within tolerance. Has anybody else had similar experiences?

Bob M.

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Re: AM Frequency Measurements

Post by BroadcastDoc » Wed Mar 21, 2012 7:57 pm

My Nautel XR6 was always within +/- 5Hz using the built-in oscillator. I now have a GPSr connected to it (I happened to have an extra port free on the receiver) and it's down to better than +/- .02 Hz.

I imagine that most newer gear keeps frequency fairly well.
Christopher "Doc" Tarr CSRE, DRB, AMD, CBNE
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