Let's dive into Carrier Offsets. Carrier offset lists are helpful tools which we can use in our carrier sleuthing. Be sure to check out my series on Carrier Sleuthing.
Carrier offsets are an interesting topic. They are the offset a station is from its assigned frequency. This can vary by single digit "cycles" (Hz), or sometimes much more. Offsets are like fingerprints and can be used to identify one station from another on a common channel.
For example, let's tune to a frequency like 810 kHz at 1530 local time, here in western New York. I see evidence of 13 transmitter carriers of various strengths on the Spectrum Lab waterfall. Looking at the FCC list of stations on 810 kHz, there are 25 total in the entire US. Half of the stations in the entire country are detectable and visible at this time. That, my friend, is amazing. If I listen on the headphones I hear only one, and it is weak even, barely audible. That would be WGY-810 in Schenectady, NY, at 50 KW over near Albany, 181 miles from here. It's running about 1.5 Hz high in frequency by my measurement, only a hair's breadth above 810 kHz. There is no evidence of any other station in the 'phones. But there on the waterfall I see 13 carriers fading in and out over a 22 minute observing period. Be aware that daytime skywave enters the picture here for some of these carrier traces, especially at this time of year. See the image at the bottom of this post.
When Carrier Sleuthing, it's helpful and sometimes imperative to know carrier offset in order to properly identify a station. This is especially true on the Medium Wave band, where stations can be mere tenths of a cycle off the band's channel step. Think fingerprint again.
There are a couple of offset lists, one which covers basically all frequencies from 0 - 30000 kHz, and one covering Longwave and the AM broadcast band, 530 - 1700 kHz. Popular stations on these lists are updated "somewhat" frequently, but beware, many offset observations on these (perhaps 80% ??) can be a year, two, or more out of date. Thankfully, transmitters, unless serviced or adjusted, can remain rock stable at a certain offset for a year or two or even more. So, quite possibly, a station's published offset may still be fairly accurate a year or more out. Some stations are also known to drift a cycle or two, or many, one way or another. These drifts are often published in the same lists.
The two lists produced which I know of are by (1) the MWLIST organization's, "MW Offsets", and (2) the Jaguar software package, the "Turtle" list.
MWLIST
The MW Offsets List by MWLIST is constantly being updated, little by little, likely several items each day. One advantage of this list is that it also documents the date of the offset observation. From this we can tell whether we should rely on the posted offset or question it. It also has drift ranges on some stations, some hourly schedule information, and occasional anecdotal information.
The MWLIST's offsets file can be viewed online or even downloaded. It can be converted to a simple text file right from the website.
To view online, see-
Using this link, the entire file is presented as one big list. A small search box at the top of the page allows you to search on a particular frequency. You can search on the "nominal" frequency, like 1017 kHz, by typing 1017 in the box. All stations documented for that nominal frequency will be shown. The list covers the entire frequency range from 0 - 30000 kHz. There are many shortwave entries too.
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| Asia & Pacific carrier offsets for 1017 kHz |
If you'd like to save it, simply "Save As" a text file using your browser's menu, or select the entire page, copy, and paste into a text editor program like Notepad. Going further, try using AI to convert this resulting text file to a spreadsheet. This is another great use of AI.
Additionally, MWLIST in the links below provide us detailed lists of stations on each mediumwave channel, worldwide. The following links take us to different regions of the world:
Each channel page will also have a link taking you directly to the offsets for that channel.
TURTLE
The Turtle list from Jaguar is published monthly, but only seems to be available from within the Jaguar program. It covers the LW and MW bands. Jaguar software is written for the original Perseus SDR receiver (~2007, still greatly used) and is used by many to determine frequency resolution down to 0.1 Hz, both for receiving and playback of SDR recordings. Great news, you don't need a Perseus SDR to try Jaguar. The Pro version is payware, but not to worry, there is a Jaguar Lite version which can be installed to get this file. Jaguar is Windows only, unfortunately. For our interests here, we'll install the Jaguar Lite version and use it to download their latest Turtle offset file. It's a simple text file which you can peruse, just like the MWLIST offsets file.
The Turtle file is based off of the MWLIST offsets file. Besides showing nominal frequency, offset frequency, country, and station name, it also shows station day/night power figures which are handy for estimating possibility of reception. Within you will also find anecdotal information like station slogans and transmitter latitude and longitude. Missing, unfortunately, is the critical offset observation date.
A little info-
The download-
Get the latest version. The install is simple, and non-invasive to your Windows installation. Unzip the downloaded file into a folder of your making. Click on the JAGUAR.exe file within. Once started, on the main window you'll see a line allowing you to download the latest Turtle file. Click it, then click the "Download Latest" option. Within your Jaguar install folder will be a folder named Turtle. Look inside this folder and you'll see some Turtle text files. The new one will be in there, and you can tell its date from its file name. Open it and have a look. Copy it somewhere handy. And bonus, you'll also see some separate Turtle TIS text files which document the Traveler's Information Stations in the US, handy if you DX these stations.
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| Jaguar Lite main window. Turtle file access. |
These files are your entry into the Carrier Sleuthing world, especially on the MW band. Take the steps necessary to ensure the accuracy of your receiver. Some of these steps are documented in my recent series, Carrier Sleuthing, part#2. Try to get your receiver frequency calibration (readout) to within 1 Hz, or at most 2 Hz. In the medium wave band, stations broadcasting IBOC HD are notoriously accurate to within 1 or 2 Hz, or within 0.02 Hz if they are GPS synchronized. Many are.
Use carrier offsets in your DXing and especially in your Carrier Sleuthing. Fun stuff!
The following reception of 810 kHz was done with a tabletop ICOM IC-718 ham transceiver coupled to a passive 1 meter diameter loop, fed through 20 ft. of RG-58 and a 1:1 balun at the loop feedpoint.
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| 810 kHz, 1527-1549 UTC. Receiver tuning offset was 400 Hz. |
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