How common is 8.33 kHz channel spacing on the US?

[KC0QNB]

A couple of weeks ago I bought a RTL-SDR dongle, I figured cheap enough why not try it. I paired it with SDR# then added what I had for channels I saved on my old RS scanner. I like the setup and for the most part it works for me. Since I started using this setup I have found more 8.33 kHz spacing being used. Just curious.

 

[andy51edge]

A couple of weeks ago I bought a RTL-SDR dongle, I figured cheap enough why not try it. I paired it with SDR# then added what I had for channels I saved on my old RS scanner. I like the setup and for the most part it works for me. Since I started using this setup I have found more 8.33 kHz spacing being used. Just curious.

US ATC does not use 8.333 spacing. It is theoretically possible in the aviation support band between 128.825 thru 132.0 plus 136.5 thru 137.0. I have never seen it used (from Texas) and my air carrier doesn't even have 8.333 installed.

Is your SDR correction set correctly?

 

[KC0QNB]

US ATC does not use 8.333 spacing. It is theoretically possible in the aviation support band between 128.825 thru 132.0 plus 136.5 thru 137.0. I have never seen it used (from Texas) and my air carrier doesn't even have 8.333 installed.

Is your SDR correction set correctly?

I started with 25kHz spacing but as of right now I temporarily set it for 8.33 I was listening to 126.325 with a 12.5 kHz spacing and it wasn't really readable, I clicked the 8.33 step spacing and it sounded better. I think I will reset all of the channels to 25 kHz , just to see. it is easy enough to do so.

 

[nd5y]

State of Air Band and 8.33 KHz Channel Spacing in the US

The radio Reference article on the Air Band refers to the lack of use of 8.33 KHz channel spacing in 2012. Has it changed much over the past 12 years. Any need to bother to search with the 8.33 KHz step?

forums.radioreference.com

8.33 spacing questions

I was wondering if anyone here has an xls file with the 8.33 spacing from 108.000 to 137.000 that I can compare to what I did. I tried using something I found online but I am not sure its correct. It did say that with the 8.33 spacing I should get 2280 channels and I did get 2280 channels with...

forums.radioreference.com

 

[buddrousa]

As common as a screen door on a submarine.

 

[spanky15805]

Ryan, I'd say the transmitter is not tuned correctly.

 

[dave3825]

I started with 25kHz spacing but as of right now I temporarily set it for 8.33 I was listening to 126.325 with a 12.5 kHz spacing and it wasn't really readable, I clicked the 8.33 step spacing and it sounded better. I think I will reset all of the channels to 25 kHz , just to see. it is easy enough to do so.

Is your ppm set properly? If not it can sound that way.

 

[Ubbe]

A 4KHz error, the difference between 8.33 and 12.5, at 126MHz are 30ppm. My two old RTL-SDR's had 1,5ppm error and two new RTL-SDR have 4ppm error.

/Ubbe

 

[KC0QNB]

Ryan, I'd say the transmitter is not tuned correctly.

Well you may be correct. I heard several United flights on 126.325 last night that were, as it appears using the 8.33 channels, how do I know? The voices were "fuzzy" until I changed from the 25 kHz to 8.33 kHz spacing. Then they were clear as a bell. Southwestern and American were clear on the 25 kHz spacing. I even recorded a video illustrating the difference. I live about 100 miles from the Ogallala RCAG site, of course I can't hear it here. It's one of the Denver sector sites.

 

[dave3825]

The voices were "fuzzy" until I changed from the 25 kHz to 8.33 kHz spacing. Then they were clear as a bell.

Is your ppm set properly? When it’s off on my dongle voices are fuzzy and when set, pretty clear. This is on a step size of 25

 

[KC0QNB]

Is your ppm set properly? When it’s off on my dongle voices are fuzzy and when set, pretty clear. This is on a step size of 25

Well if it wasn't set right then everything would be fuzzy, FM broadcast, 2 meter ham etc. right?

 

[KC0QNB]

You tell me what you think, is the ppm set right or is it the channel spacing?

 

[Ubbe]

Tune in to a digital transmitter, preferable in the 700-900MHz range, as most are GPS controlled and look at the spectrum and adjust ppm until you get the data signal exactly centered. Then you'll have the ppm set correctly for that specific dongle.

/Ubbe

 

[KC0QNB]

Tune in to a digital transmitter, preferable in the 700-900MHz range, as most are GPS controlled and look at the spectrum and adjust ppm until you get the data signal exactly centered. Then you'll have the ppm set correctly for that specific dongle.

/Ubbe

Not sure if there are any of those around here, how would I find out?

 

[dem1]

Check your band plan. To my ear it sounds like your receive is switching to NFM in 25 KHz steps, even though the radio button still indicates AM.

The spectral display shows the signal squarely centered in the passband when tuned to 126.325 MHz. That would not be the case if the ppm were way off.

 

[n3obl]

Not sure if there are any of those around here, how would I find out?

you dont have a trunking system nearby? thats what they meant. The control channel and all voice channels are GPS controlled for time sync.

 

[KC0QNB]

When I switch between the AM and NFM there is a huge difference between the sound. It's AM for sure.

 

[dave3825]

To my ear it sounds like your receive is switching to NFM in 25 KHz steps, even though the radio button still indicates AM.

That what I was kind of leaning towards towards. Going to view the video on my 60 inch when I get home.

 

[dave3825]

Do you get the same results if you use sdr# ?

 

[KC0QNB]

you dont have a trunking system nearby? thats what they meant. The control channel and all voice channels are GPS controlled for time sync.

There is a countywide and statewide system but I haven't figured out how make it work yet.