Carrier Sleuthing, Using IBOC Carrier Accuracy

Using IBOC to Calibrate Receiver Frequency Readout

First Some IBOC History

Here in the U.S. and some areas worldwide, iBiquity acquired the rights to digital HD Radio technology many years ago, making them the monopoly in this business. In 2015, DTS, Inc. announced it had entered into a definitive agreement to acquire iBiquity Digital Corporation. Their product is loosely called "IBOC", or "In Band, On Channel". 

IBOC operates on both the AM and FM bands here, and can operate either in a digital-only mode or in a "hybrid" digital+analog mode. Stations can split the digital bandwidth to carry multiple audio program streams (called HD2 or HD3 multicast channels) as well as show on-screen text data such as song title and artist, traffic, and weather information.

Oh Yes, There Were Problems

Only about 240 stations are authorized to transmit IBOC on the MW band in the US. Many less than that actually use it, and this is true especially at night when skywave interference may be prevalent. Since its inception, inherent interference to adjacent channels was found to be occasionally obnoxious. Little wonder, in that the digital carrier sidebands extend fully 14.72 kHz either side of the carrier frequency. These are easily seen on an SDR receiver's waterfall. The nearly 5 kHz portion overlapping into each adjacent channel is only -16 dBc down from the IBOC station's carrier power.

What's left are upwards of 100 stations using IBOC during the daytime, and perhaps 30 at night. Only two or three use the full digital mode at this writing. The rest use the hybrid mode, which impresses the digital signal over the usual analog AM carrier.

But a Bonus

None-the-less, a bonus is to be found in these remaining IBOC stations for us Carrier Sleuthers wishing to calibrate our receivers to within a cycle (Hz) or so. IBOC being inherently accurate in any case, many if not most IBOC stations are also GPS-synchronized, meaning that they are frequency-accurate to 0.02 cycle (Hz) of the nominal carrier channel assignment.

Let's See What AI Says

I asked Claude AI to give us a little more detail on the accuracy of iBiquity's IBOC system. Here is what it had to say.

My Prompt (you're question is called a PROMPT):

Concerning AM broadcast radio stations which transmit using the IBOC standard, is their carrier frequency dead-on their assigned frequency, within one Hz?

Note: Claude searched 4 separate FCC digital standards documents and 7 separate IBOC standards documents. This is the thorough document search I talked about in my post Interesting Questions Posed To AI, information difficult to obtain sometimes and often outside the reach or missed by the average individual.

Claude's Answer:

Based on the IBOC AM transmission specification document, the total carrier frequency absolute error for a GPS-synchronized (Level I) AM IBOC broadcast system must not exceed ±0.02 Hz maximum, and for non-GPS-synchronized (Level II) systems, the error must not exceed ±2.0 Hz maximum.

So to answer your question: No, the carrier frequency is not necessarily dead-on within one Hz. However, it's quite close:

• Level I stations (GPS-synchronized): Within ±0.02 Hz - essentially dead-on
• Level II stations (non-GPS-synchronized): Within ±2.0 Hz - slightly beyond your one Hz tolerance

Most modern IBOC AM stations operate as Level I facilities to take advantage of advanced system features like fast tuning and synchronization with other stations. These GPS-locked stations maintain carrier frequency accuracy that is far better than 1 Hz - they're accurate to within 2 hundredths of a Hz, which is remarkably precise.

Further, major market commercial stations typically implement GPS synchronization (Level I) for their IBOC systems because:

• It provides better performance and reliability
• It enables advanced features like fast tuning
• It's considered the professional standard for commercial broadcasters

The cost of GPS synchronization equipment is minimal compared to the overall transmitter infrastructure.

According to the IBOC specification document I found, the carrier frequency accuracy requirements are identical for both digital and hybrid modes: GPS-synchronized (Level I) broadcast systems must maintain carrier frequency absolute error of ±0.02 Hz maximum, while non-GPS-synchronized (Level II) systems must maintain ±2.0 Hz maximum.

* * * * *

There you have it. I typically tune to WPHT-1210 in Philadelphia and synchronize my SDR or tabletop receiver to within 1 Hz. This is accurate enough to get you in the ballpark for Carrier Sleuthing. Even if you can't synchronize your receiver, you will at least know its offset from what the real frequency is.

So check out HD hybrid digital stations on the MW band, where you can find them. The FCC's LMS database AM Search or even a Google search will reveal if a station is authorized for digital. If you have an SDR receiver, look for an IBOC station nearby to verify if it is indeed digital. Use its carrier to calibrate your receiver's readout. I offer some tips on calibrating receivers in my series Carrier Sleuthing, part#2. See the section "Receiver Calibration".

Good luck!

Carrier Sleuthing, Using Carrier Offsets

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-

https://mwlist.org/mwoffset.php

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.

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:

Asia & Pacific

Europe, Africa, & Middle East

North America, Central America, Caribbean

South America

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-

https://jaguar-lite.blogspot.com

The download-

https://jaguars.kapsi.fi/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.

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.

810 kHz, 1527-1549 UTC. Receiver tuning offset was 400 Hz.

I.Q.P.T.AI - Interesting Questions Posed To AI

 I.Q.P.T.AI

Definition: Interesting Questions Posed To AI.

This blog, my blog, has not and never will, use AI verbatim in my normal narrative blog posts. However, AI is not inherently evil as many nay-sayers might suggest. In fact it can be quite helpful in understanding and presenting an interesting picture of technology's wonders, and specifically technology's details. It is an expert researcher given the model it has been trained on, and much better than a human in gathering research documents - drawing information from all circles, including academic documents that you have no access to.

But as with any written or verbal discourse, and this includes the thousands of links returned by Google searches when we research a topic in usual ways, one must still use critical thinking skills, one's own lifelong technical sense and common sense, to ferret out truth in information. Welcome to the real world. This we do every day.

That said, I may on occasion post some Interesting Questions Posed To AI, and AI's response to them. I'll always identify what is an AI response and what is not. This is to further the discussion on radio-related matters and present some topical matter which I think you may find interesting.

There are a number of great technical AI sites out there. A simple Google search for "best technical AI sites" will reveal what people are using. The two I use regularly are:

Claude AI -

https://claude.ai

Grok AI -

https://grok.com

Both of these are great at responding to technical questions. I'm also a programmer and I program radio-related software on occasion. Both of these sites have great code generating ability in most computer languages. Give them a try for your next technical question. Why wade through a mountain of links returned by a search engine when you can have AI deliver a nicely formed, deeply-researched narrative answer to your question?

Signing off, but with more to come on this topic.

Modding the MLA-30 Loop

Improvements to the MLA-30 Loop

The MLA-30 single turn loop right out of the box isn't a bad antenna. You could do worse buying unknown loops from eBay or a foreign supplier. I have the DmgicPro branded MLA-30+ bought right off the Amazon site. It was reasonably priced at about $45. They may be even cheaper on sale. Some advertised as plus+ versions are responsive down to about 100 kHz, but not all. Be sure to check the specs before you buy if you need longwave coverage.

As usual, click any image for the bigger picture.

The MLA-30+ with cover removed.

You can spend literally hundreds of dollars on sophisticated, ultra low noise, premium loops. In most cases they will perform wonders. Another step up would be to buy (or build) a premium pre-amplifier module and roll your own. These modules can be had for about $150 and up. To that add the loop itself, bias-T, power supply,  interconnections, and coax.

If you are on a budget, or maybe you're a beginning experimenter, we need to go with what we can afford.

The MLA-30 comes with a nice pre-amp mounted in a sturdy, water resistant ABS plastic box and 30 ft. of coax feedline. A single turn loop, 26 inches in diameter and made of stiff spring steel piano-wire comes with it as well. Rounding off our kit is a bias-T and a short coax jumper feedline for our receiver. The bias-T is the little device that injects DC voltage into the coax feedline which travels up the coax to the pre-amp box, powering it. A capacitor within makes sure this DC voltage doesn't get down the line to our receiver.

I'll use the MLA-30 brand name from here on to generically include the MLA-30+ as well.

Some Defects for Sure

The stock MLA-30 design falls down in two areas.

One, it comes with 30 feet of some sort of cheap, skinny coax, similar to but nothing like the quality of RG-402, RG-316, or RG-174. It is hardwired to the pre-amp output right through a hole in bottom of the pre-amp box. I've skinned this coax and it has only a bare amount of thin spiral-wrapped braided wire trying to be a shield. This has to go.

Second, the bias-T box is overly complicated and uses a buck converter method to convert 5 volts up to 12 volts to power the pre-amp. In and of itself it's a fairly clean converter. But to make matters worse, they provide a micro-USB connector to connect to a 5 volt USB source, itself likely to harbor all kinds of incoming trash because the average consumer will probably plug this into a chopper charger module. This has to go too.

The pre-amp box with modified SMA connector.

People complain about the MLA-30's signal amplifier because it's a VHF TL592B chip. I find that hardly an item to complain about. The noise figure of the pre-amp has been measured by others at about 12 dB - not the best, but not the worst either. At shortwave frequencies, compare that to the published noise figure of these SDR receivers: the SDRPlay RSP1B & RSPdx (~15-20 dB) and the low noise Airspy HF+ Discovery (~7 dB). The MLA-30's pre-amp also seems to show a sharp peak at about 7 MHz, so be aware of that. It does not exhibit linear gain across the shortwave bands, 3-30 MHz, varying between about 10 to 30 dB.

All that said, I don't believe the MLA-30 to be a bad loop, and certainly at $40 to $50 it will get the job done in many cases and you won't be out $200 to $500 dollars for a commercial masterpiece, either. Here at RADIO-TIMETRAVELLER we are all about practicality, so we will go with the MLA-30 and see what we can do with it.

But a Bonus Too

There is a bonus found here, as well. The MLA-30 has a potentiometer gain control on its pre-amp board. This is wonderful news because at its approximately 30 dB gain (full out) the MLA-30 can be a bit over amplified in certain situations. Once we get rid of the 30 ft. of coax and change out the bias-T and supply some well filtered DC, we will have a nice single turn amplified loop for MW and SW.

Let's Start

First we'll get rid of that coax and install a connector at the bottom of the pre-amp box. Consider a panel mount SMA female connector or a panel mount BNC connector, both inexpensively available via Amazon. Open up the pre-amp box by unscrewing the four cover screws. Remove the bead of silicon that holds the coax stationary, coming out of the bottom hole. Slip the coax up through the hole a little farther, then cut it off, leaving about 6 inches of length. Leave enough so that you can strip the end of the coax.

SMA panel mount connectors:

https://www.amazon.com/dp/B078H4F8R6

Next we will drill our new hole, enlarging the existing hole. On mine I've chosen to use the panel mount SMA female connector. The panel mount BNC connector will need a bigger hole. Choosing the properly sized drill bit, drill a newly-sized hole using the existing hole the coax came out of. Be very careful here, as when the drill bit finally punches through the case it will grab and want to pull the drill through suddenly which will destroy the circuit board if it comes into contact with it. Hold on to that drill like your life depends on it.

Mounting the Connector

Mount the SMA or BNC connector in the new hole. Be sure to tighten the nut securely.

Warm up your soldering iron. Strip the coax end back about an inch or a little more, so the center conductor and shield are available, then attach both to the connector and solder. The shield is ground of course. In the image below, the blue control is the potentiometer which controls the pre-amp gain.

Detail of the connector mod.

Replacing the Bias-T

Now to replace the bias-T. I bought a nice, simple bias-T from Amazon, which works clear down into the longwave band. It gives good results down to 200 kHz or a little lower and has only 0.1 dB attenuation in the MW range. It was only $13.

Bias-T:

https://www.amazon.com/dp/B0BR2WCH5D

The new bias-T.

Better Power

Now we need power for the bias-T. In my junk box I had a nice Jameco linear wall adapter, #2328175, which produces 12 volts filtered DC at up to 1500 ma. I connected that to my new bias-T. You must use a linear adapter. A linear one will have some heft to it because it has a big transformer inside. For the total purist, it is possible to power the bias-T with a battery. The MLA-30 runs nicely on a 9 volt battery, and with a little less pre-amp gain too. The square 9 volt battery will supply about 3 days of continuous service. Used a couple of hours a day, it will likely last two or three weeks.

Jameco 12 Volt DC Linear Wall Adapter

Also possible, and perhaps preferable, is to use a common three pin voltage regulator module board to provide 9 volts, regulated DC. It works with either 12 volts AC or 12 volts DC input. Run your Jameco linear transformer, above, into it, and connect the 9 volt output to the bias-T connector. Two wires in and two wires out. Simple.

LM7809, 9 volt regulator:

https://www.amazon.com/dp/B0816B34FR

Be sure to pick the LM7809 module (9 volts). The MLA-30 pre-amp will work very well on 9 volts, and offer slightly less gain as well.

Jameco power supply and 9 volt regulator.

Let's Try it Out

You'll need a short length of good quality patch coax to get from the pre-amp box to the bias-T. Then run some RG58 or even RG6 from the bias-T to your receiver. Be sure to recheck the connections at the bias-T before you power everything up! You don't want to fry your receiver by reversing the connections, sending 9 or 12 volts into the receiver front end!

SMA RG-316 coax patch cables (6 inch):

https://www.amazon.com/dp/B07NCLZWHH

OK, with everything ready, power up the bias-T and your receiver. If you have an SDR, great, you will not only hear, but see the difference immediately.

Adjusting the Warp Drive (apologies to Mr. Scott)

"I'm pushin' 'er as hard as I can, Captain. She can't last much longer!"

Now for the last step, we'll adjust the pre-amp gain control in the pre-amp box. This potentiometer, or "pot", turns oppositely to what you know as a volume control. That is, by rotating the control clockwise you will be decreasing the signal level. Start with the control fully clockwise and we will turn in the opposite direction, counter-clockwise.

On your receiver you're more likely to experience more signal overload on the MW band. I have a big problem here with two close by 5 KW transmitters. Increase the pre-amp level by turning the pot counter-clockwise slowly. Keep increasing gain (counter-clockwise still) until signal overload develops. You may be lucky and encounter none even at full gain. If you do encounter overload, back the pot off in the other direction until the overload stops. Leave the control there and fasten the box's cover back on. You are done with the mods.

Wrap Up

That wasn't so bad. You now have a nicely-modified, workable MLA-30 loop!