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Reading OTA Transmit Frequency
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I'm not sure if this works on the frequency reading but on the other ones there is the ability to average the gauge. If you highlight the units with the cursor as I recall the was an average key that you may need to hit the blue shift key first to use. Then you set the average to 10 or so. On Thu, Aug 4, 2022, 07:22 lobos305 via <lobos305=[email protected]> wrote: When reading a transmitter's frequency, the last few digits jump around so much it is hard to determine what is real.? Is there a setting to normalize or smooth that so I can warp it onto frequency? |
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If you are reading the frequency of an FM transmitter, this is normal - its frequency changes with modulation.
If you are reading a non-modulated signal, and it's substantially higher than the noise, the analyzer has a problem. There is no smoothing or averaging function for frequency, only for amplitude. |
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Use the Blue shift button and then the AVG botton.? Use the keypad and enter a number such as 10 or 20. The higher the number, the more delay in the updating. To clear the AVG function use the blue shift button, AVE and the button labled OFF.
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If you are on the AVG those letters will be on the screen just below the frequency readout.
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Ralph ku4pt.
On Thursday, August 4, 2022 at 10:22:21 AM EDT, lobos305? wrote:
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When reading a transmitter's frequency, the last few digits jump around so much it is hard to determine what is real.? Is there a setting to normalize or smooth that so I can warp it onto frequency?
Pat _._,_._,_
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Do the reading on an unmodulated FQ signal with no DPL.? Tone PL doesn't seem to be so bad.
AVG should be at 5 to start, more than 10 and I am waiting.? You can also enable the bar graph and set the upper and lower edges of the bar and it will be easier to read from a distance.? It also helps to set your filters so there is less response to noise and modulation. If you read an OTA frequency standard, you shouldn't see rolling digits.? An easy OTA is the Pilot signal from various ATSC TV stations in your area.? Although the FCC specification for accuracy is lenient, many of them are using some kind of frequency standard.? ATSC standard calls for the pilot to be 309.440559 Khz up from the lower channel edge.? Set your filters to ignore the data stream. For example; ATSC signal on RF channel 13 is 210.309440559 Mhz? (but we don't have that many digits). It is useful to keep a few of the strong ones as saved screen setups to verify your instrument. They usually have enough stability to be able to plot the drift of your instrument over time. After plotting mine, the oven was ready enough for my purposes after 20 minutes and was as stable as it could ever be after 1 hour.? I took to keeping an external OCXO warm all the time.? I also toyed with adding an external 9-12v wall wart input and diode isolation keep the internal OCXO warm, but I don't really know if that would shorten it's life or cause me to have to calibrate more often.? rambling... |
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The 8924C keeps the OCXO warmed up as long as it is plugged in. I ignore the last digit, maybe even the last 2. Even reading the output of a GPSDO, which is pretty stable, my 8924C jumps 1 number up and down in the last digit, which is Hz, in my case. I have noticed this kind of behavior in every frequency counter I have ever used. If there is any kind of modulation, even AM, it will cause some wiggle in the displayed frequency.
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On Fri, Aug 5, 2022 at 11:34 AM, wspx472 wrote:
The 8924C keeps the OCXO warmed up as long as it is plugged in. I ignore the last digit, maybe even the last 2. Even reading the output of a GPSDO, which is pretty stable, my 8924C jumps 1 number up and down in the last digit, which is Hz, in my case. I have noticed this kind of behavior in every frequency counter I have ever used. If there is any kind of modulation, even AM, it will cause some wiggle in the displayed frequency.No modulation - It is not uncommon to walk 1 hz at a time as it warms up with averaging off, but flip back and forth then solid.? I normally enter frequency manually so it's in Freq Error mode. If you are just looking OTA on some TX, then you have to wait until NO modulation or just guess. The 8920a does not leave my 08920-61035 module powered up, the On-Off switch is mechanical.? According to the Amtronix website it is also used in the 8935.? I "saw" a 61035 in an 8921.? They also claim an 08920-61835 or 61192, but for 8924c they show a 1813-0644 "McCoy" unit.? My CLIP doesn't tell me what "U22" actually is, and I have never seen a CLIP for any of the others in the family.?? Would hate for the oven to die and have to replace it.? Maybe go with external 12v input with protection to warm it up for trips.? Even so it might want 10 min to stabilize.? Not a big deal to power it up at the bench and do something else for a while. |
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I agree about the 8920 not keeping the OCXO powered. It does come with a down side. The little switcher that does this failed in my 8924C, and I had to pretty much completely disassemble it to repair it. It needed 2 capacitors, and has worked since. A green LED inside the unit indicates it is on. I agree the best use is in frequency error mode, and the carrier can't have any modulation if you want the most accurate results. Getting real accuracy in off air measurements is a challenge.
A local TV transmitter used to have a rubidium standard, and I would often use the video carrier as a quick check. It would bounce around a few Hz, but it was a quick way to tell if the instrument was working properly. |
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