Frequencies with 5 numbers right of decimal place

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BCasto

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In Raleigh NC we have a new trunking systems with frequencies like 769.20625 with 5 digits to the right of the decimal place. My 996XT and my ProScan software use 4 digits, essentially rounding off the last digit.

There are a lot of smart people in the forum and I am sure one or more can help me with this.

Is that last digit significant? Do I need to program it in the scanner? If so, how? My 996XT as configured only takes 4 digits right of the decimal point.

Thanks for your help
 

captclint

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Is that last digit significant? Do I need to program it in the scanner? If so, how? My 996XT as configured only takes 4 digits right of the decimal point.Thanks for your help
No. It will round up to nearest 4-digit. You will not notice any difference.
 

jeatock

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... or round to 3 digits on an older scanner. Look at it this way: If my neighbor's kid aims his BB gun at the exact center of my window but hits it one inch off-center the window will still break.

Don't sweat it.
 

Voyager

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No. It will round up to nearest 4-digit.
That is absolutely not true. It will not round off anything. It is merely masking (not showing) the last digit, but the unit is on the exact frequency you want it to be on (excepting VCO tolerances).

This goes back to the 70s where the BC210 series would not show the last digit for frequencies like 453.3125 (it showed 453.312).

It is correct that it will not affect reception since it's on the correct frequency. (not like 50 Hz would matter anyway)
 

garys

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I was selling scanners back in those pre internet days and fielded lots of questions about the "missing" 4th digit. Deja vu all over again.:D

That is absolutely not true. It will not round off anything. It is merely masking (not showing) the last digit, but the unit is on the exact frequency you want it to be on (excepting VCO tolerances).

This goes back to the 70s where the BC210 series would not show the last digit for frequencies like 453.3125 (it showed 453.312).

It is correct that it will not affect reception since it's on the correct frequency. (not like 50 Hz would matter anyway)
 

Minus1

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As I like to point out, frequencies are not phone numbers.

There is insignificant difference between 769.20625 and 769.20620 because the bandwidth of the transmission and characteristics of the receiver will likely pick up the signal anyway.
 

buddrousa

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Is that why Motorola Allows all 5 or 6 digits past the . as in 769.206250. That might be one reason Motorola radios work better. If it did not matter then the FCC would not have mandated narrow banding. If a glass has a hole in it and you drink real fast you will not lose all the water but you will still lose some of it. Myself I believe it does matter that the receiver has all the numbers in it.
 

ecps92

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You are confussing the use of a Scanner vs the programming of a Commercial Two-Way Radio
The FCC does care about a Radio that Transmits

As for a Scanner being a few khz or hz Off Frequency, Nope

Apples and Squash

Is that why Motorola Allows all 5 or 6 digits past the . as in 769.206250. That might be one reason Motorola radios work better. If it did not matter then the FCC would not have mandated narrow banding. If a glass has a hole in it and you drink real fast you will not lose all the water but you will still lose some of it. Myself I believe it does matter that the receiver has all the numbers in it.
 

jeatock

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In simplified terms any FM receiver, including scanners, will track any RF energy that appears within its defined bandwidth window and AFC settings. The frequency change value of a tracked carrier's center frequency is what sends both analog voice and digital data.

There is always a pucker-factor built in; if the transmitter's carrier center frequency is off (within limits) it will still work, If the center moves outside the receiver's defined window the receiver will consider it adjacent-channel interference and ignore it. If the 2.5KHz or 1.25KHz total frequency shift span of the carrier stays anywhere in a 15 or 6 KHz defined window, it doesn't matter if it is left, right or in the middle. All receivers do that differently, and some are better than others. Scanners are generally more forgiving than land mobile radios, and most were originally designed for a big, fat 5 KHz wide carrier wideband shift in a 20 KHz window.

The hard reality is that no receiver or transmitter has any idea what a channel's center frequency is, only where the tech sets it in relation to a (hopefully accurate) arbitrary and external analog standard. That's why there is a wide pucker-factor. The same goes for the distance the transmitted carrier shifts from relative center to send a signal. The radio's frequency reference can be anything from an old-fashioned crystal in most radios to an external GPS for base transmitters. Poking numbers into a keypad is all relative to the radio's aligned reference point, and bad alignment can send that off 0.05 MHz or more.

Errors, weakening signal strength and RF noise spikes will all cause poor audio. In analog that shows up as static which worsens starting the second you begin to move away from the source and continues until you exceed the receiver's front end ability to track a carrier relative to the background noise. The user's ear usually gives up first, and old ears seem to be better at it than young ones. Digital converts the analog carrier's frequency shift-stop-shift-stop into 0's and 1's, then a codec program extracts and simulates the voice. Data and voice information are sent at the same time, occupying different parts of the digital sentence's string of 0's and 1's. Audio quality and data work exactly the same over distance, up to the point the receiver has more noise than signal and abruptly stops doing anything.

In analog, the further the wandering offset the louder the voice, which is why wide-band scanners will still receive narrow band analog, albeit at a lower volume. In digital, the offset points are defined as distance from perceived center, and AFC with error correction can gloss over a lot. (Yes, digital is really sent via an analog carrier that shift-stop-shift-stops at predefined offset points for a defined period of time vs. the less defined wandering analog carrier that directly emulates the audio waveform.)

In the real world, no transmitter ever made by anyone is exactly on frequency, either as they age, as internal heat from transmitting changes the values of the components or as the frequency gets further from the aligned VXO lock point. Its all a shade of gray and generally transparent to a scanner's front end.

Is that why Motorola Allows all 5 or 6 digits past the . as in 769.206250. That might be one reason Motorola radios work better.
Vertex, Icom and others also do 6 decimals. Kenwood allows 5 or 6 decimal places depending on the model. No matter who made it the radio will reject any frequency data entry that does not fit into its defined channel spacing mask. Radio software allows a multi-decimal input for human interfacing, but many write a hex channel slot number instead of the frequency when it clones the radio.

As far as 'better' I have aligned M products that were at best scratchy at the 'industry standard' 0.25mV signal input. Many other brands will be full quieted at 0.25 and open with a usable signal at 0.18mV, and remain within 10 Hz after two minutes in transmit. The old GM300's are notorious for talking a long time to shift to the right frequency when first put into transmit, and for drifting south the longer they stayed in transmit. Even today M gave up tracking or sending the 1.25 KHz carrier shift (6.25 KHz super-narrow) that others do with their low end models, hence M's push to 2.5 Mhz shift TDMA and P25 Phase II (12.5 KHZ narrowband). 'Better' is a highly subjective perception.

But I digress; that's for land mobile radios and the radios that scanners listen to.
 
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Voyager

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Is that why Motorola Allows all 5 or 6 digits past the . as in 769.206250. That might be one reason Motorola radios work better.
You're not understanding the issue of masking.

The Motorola will show 769.206250 and be on 769.206250 MHz.

The Uniden will show 769.2062 and be on 769.206250 MHz.

Just because the last one or two digits are MASKED doesn't mean they won't both be tuned to the exact same frequency. So, that's not why the Motorola may work better. The reason it may work better lies in the hardware (filtering and other aspects).

Again, Uniden doesn't round the frequency off - it merely masks (doesn't show) the last X digits. The synthesizers won't round off.
 

buddrousa

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Voyager why be LAZY and mask anything. Just display the proper numbers then.
 

Jay911

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Voyager why be LAZY and mask anything. Just display the proper numbers then.
It would certainly be nice, but the truth of it is, it doesn't harm anything. The biggest issues with this are RRDB submissions where the db admin gets a sub like "769.2062" and/or the confusion which arises in threads exactly like this one.

The part that really confuses me is that the display code for the HP1 (and presumably the HP2, though I don't have one) actually displays out to 5 digits, and Sentinel will let you store frequencies to 6 digits, but the code that stores the frequency data in the radio strips off the fifth digit. So you can program in 769.20625, and in Sentinel (until you read it back out from the radio, at least) you will see 769.206250, but the radio will display it as 769.206200. You'd think, with the code built up to handle display of the frequency, that the code for storage of the frequency would have been upgraded to match.
 

mattimac

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Im undigging it. Is it possible to program a frequency from the scanner itself with lastest firmware with 6 digits after the dot (needed for some very narrow nxdn systems)
 
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