It [still] Buggers Other Channels - FM Edition

I recently wrote an article about how IBOC (known by its commercial name of "HDRadio") causes interference to other broadcasters. That article was based on the AM/MW band but you'll be interested to hear that it is also the case on the FM band too.

I live in the greater Philadelphia area. A scan of my local FM band reveals some 23 radio stations broadcasting both an FM signal and an IBOC signal.

IBOC in "wrapper" mode

In the screenshot to the left we can see how the digital radio transmission is wrapped around the main analog (FM) carrier.  The IBOC signal (properly known as "In Band On Channel") is seen here in its "wrapper" mode. This is where the data carrier is split into 2 segments and sent out on different frequencies separated by the analog FM signal.

The IBOC system uses a COFDM type transmission method and so the data is in fact on lots of frequencies all at the same time. That there is a gap in the middle of it does not matter. The decoder simply skips over the gap looking for more data carriers. 

The maximum data throughput for this mode is 120kbps. If there were no analogue FM carrier in the middle and the gap was filled with more data the throughput increases dramatically to several Megabits. At that speed we are able to transfer TV images! This is only available on the FM band due the the wider bandwidth of the signals. The AM band is limited to a total of 20kbps.

Similar to our discussion in my previous article, here in the USA radio stations are given a fixed set of 100 KHz wide frequencies spaced out every 300KHz for every radio "market". This allows markets that butt up against each other to coexist interference free. Well, that's the theory at least.

Among my many (too many?) radio receivers is an RTL-SDR. This is a USB stick that is capable of receiving radio signals from about 30MHz up to 2GHz. By computer sampling a received radio signal and then pushing that sample through some software we are able to decode the information it carriers. This is known as Software Defined Radio. 

For this article I connected my RTL-SDR to one of my many (too many?) outdoor antennas and performed a scan of the FM radio band. As noted above I received 23 stations transmitting IBOC data. I used a combination of "GQRX" (Linux) and "RTL-SDR FM-Radio" (Android) as well as the RTL-SDR driver software for the USB device itself. These are all open source applications and are freely available. 

GQRX SDR software showing a few Megahertz of spectrum including some FM/IBOC stations

In the below picture we can see just how offensive IBOC is. We are looking at 3 FM/IBOC stations side by side. As you can see there is no room in between the stations. There should be a gap here. In this gap should be a stations from the adjacent radio markets of NYC, Wilmington, Scranton, and Lancaster.

IBOC shuts out its neighbours.

So, what is this data carrying anyway? Well, obviously its a digital version of the analogue output. But its so much more than that. Many broadcasters operate more than one media stream. Some of them relay their AM broadcasts, others a partner station from somewhere else on the band. Others yet carry special interest media stream such as Russian language or LGBTQ+ tailored music.

WIOQ 102.1 has 3 media streams

Here we see WIOQ on 102.1MHz. You can see that the stations transmit not only the audio stream but often pictures too. Pictures of the artists, album covers. Often head shots of the DJ too.

And that's not all. Radio stations are the traditional source of news, weather and travel information. Every 10 minutes during drive time you can hear them announce the traffic jams on the Schuylkill Expressway. But instead of just hearing about it how would you like to see a map?

Traffic map

Of course, I'm using an application on my computer to display all this information. But most people will be receiving this in their cars, So this map would pop up on the radio's display. Weather maps too. talk about distracted driving!!

Adventures in WeFAX

One of my "go to" frequencies for testing my HF equipment is 6338.6KHz USB. There I will usually find the US Coast Guard's WeFAX service pushing out weather information in FAX format. This is a time tested way to send weather maps and printed statements to ships at sea. And yes, FAX machines are still a thing.

My local WeFAX transmitter (callsign NMF) is up in Boston and so presents an approximate 300 mile distance between me and the transmitter. This would be about the same if I were a ship at sea. 

NMF transmits on a handful of frequencies depending upon the radio conditions and the time of day.  Today I decided to try their 12750KHz frequency (a first for me) to see if it would yield better pictures than I have been able to receive lately. With the rise in solar activity and the local electrical noise around here 6338.6KHz (dial) has been a tough catch.

A broadcast schedule received from NMF

As if by magic I am receiving an interference free (if a little blurry) FAX message. As the day goes by one can receive all sorts of written weather statements and pictures. They even send out satellite pictures too. A schedule of all the world wide FAX transmissions can be found here.

I am using my FT-710AESS HF transceiver and the FLDigi software. But "hold on" I hear you say. "The radio is tuned 1.9KHz lower than the frequency published by the USCG". Why yes it is. It's a USB signal with its tone pair centered on 800hz. In order to receive both the mark and space tones (it is data after all) one has to tune down in frequency so that the tones fit into the pass band of the radio. The accepted tuning offset is 1.9KHz giving a tone pair frequency of 1500/2300hz.

FLDigi software

FT-710 receiver

Follow this link for an explanation of how to receive these pictures. It's pretty easy.

Digital Radio Mondiale

 This is a re-post of an old web page from my now defunct g7ltt.com site.

DRM reception reports

It had to happen sooner or later. QSLing has finally come of age. In the world of DRM you can not only send your reception report to your favourite broadcaster but you can also email them screen shots of your reception!

Below are a collection of screen shots from the various DRM stations that I've received. They have all been received here at G7LTT in Randolph, NJ. 

CVC is a religious broadcaster from Australia. This broadcast was caught on a Saturday afternoon during the Rugby world Cup. It came from Moosbrunn in Austria and was aimed at the UK.

RCI's Sackville transmitter is my local DRM site. They sublet their airtime every day to other broadcasters such as Radio Sweden, Vatican etc.

I got this from DW's Sines transmitter in Portugal. Note that they are sending a Journaline text broadcast too.

This is DW's Journaline broadcast. The blue coloured headlines are actually web links which will open up the story in DReaM's mini web browser.

I got this one from Moosbrunn in Austria. Notice that there is no Journaline with this broadcast. this is unusual for DW.

This broadcast starts with the Call to Prayer. It comes direct from Kuwait and does very well here on the East Coast of the US.

In the DRM world these guys rock!! Not because they have lots of flashy stuff embedded in their data stream or because their programming is excellent (which it is!) but rather because they are a low power station running a mere 4KW. Yet despite their low power they are able to reach their target audience with a 100% decodeable signal. This broadcast was bagged whilst they were aiming their antenna towards Europe.

Unfortunately many SW stations don't seem to respect the fact that they share the bands with other broadcasters. In this picture we see an AM carrier right in the middle of the DRM carrier. The AM station clearly thought that the DRM noise was just that; noise. So they popped up their carrier thus trashing the DRM signal I was listening to. Click the picture to hear the result. The rushing noise is actually the data that would be the HCJB broadcast.

China Radio International comes from Radio Canada's Sackville site.  It's an English language service aimed at North America.

Radio Sweden is another Sackville client. Indeed they even mention during their sign-on that they are being broadcast from Radio Canada International's Sackville transmitter. I really like their magazine programme "60 Degrees North".

This is RFI's offering from Montsinery in the Caribbean. It was a special broadcast to the NAB show in Las Vegas which is held every April. It was actually aimed at the West Coast of the US but was very well received here in NJ. Despite the English speaking target audience it was in fact a French and Spanish language output.

RNW has a number of DRM outputs that reach us here in the US. This one was on 9800KHz from Sackville. They also have one from their Bonnaire station in the Caribbean. On good propagation days we can also get their 5865KHz output from Luxembourg.

Radio New Zealand International is a bit of a stretch for me. They must the the absolute farthest DRM station from my location. I can usually hear their carrier but can rarely decode their data. However, over on the West Coast they come crashing in.

Just like it says! I bagged this one directly from Italy on 11630KHz. Vatican radio are a major player in the DRM world. They have outputs on SW and MW all over the world. They are also a lessee on Radio Canada's Sackville transmitter.

This is another tough one for me. This is RFI's 1KW station on 3695KHz from Issodoun in France. It's a local French broadcast that seems to get out here to the East Coast very well at night. The tough part is that it's in the middle of the US 75 meter ham band. Both RFI and DW have an output in this band. I've heard many a comment from an ignorant ham operator complaining about the 10K wide "noise". They just ignore it an park their conversation on the top thus killing the DRM transmission stone dead.

Again, another tough one. This is Bayern RundFunk's news headlines output "B5 Aktuel" (B5 Notices). It's a 100W local output on 6085KHz. It's really only available when the band conditions are favourable. Note that they are sending some multi media as well as the audio stream. I was not able to get any better signal that this so couldn't decode the audio or multi media.

Another European capture. This one is from Radio Romania International (30KW Kvitsoy, Norway). Local broadcasters were to blame for me not getting the audio on this one also (3 green lights = full decode).

Damn those God bothering religious shortwave broadcasters! I had an S9+40db signal from Radio Prague (100KW Wofferton, UK) but couldn't decode much of it. Just 5kHz below them was one of my local God bothers prattling on about the book of Galations and he was spilling over his channel allotment something awful! So much for "love thy neighbour".  

Sometimes getting up early in the morning pays off. I bagged this Spanish broadcaster at 3:45 in the morning on 9730kHz. It appeared to be a current affairs programme but I'm not sure as my Spanish is about as good as my American.

I snagged this one totally at random. It's a 100kW signal from Woofferton in the UK. VT are one of the big players behind DRM and act as an airtime wholesaler. They own/manage a bunch of transmitters in the UK. This particular broadcast was on 9850kHz at 1230UTC. It was a relay of a Radio Taiwan Intl programme.

Satellite Exploits

 This is a reprint of a few pages from my old g7ltt.com website originally posted in 2002 ...

Firstly lets look at my station. I own the ubiquitous Yaesu FT-847 transceiver. This radio is very commonly found in the stations of many a satellite enthusiast. I have beam antennas for 2mtrs, 70cms and an MMDS down-converter with dish for 13cms (2.4GHz) all of these antennas are mounted on a cheap azimuth and elevation rotator arrangement by Satelectronics.

I have owned this radio for about a year with the intention of getting active on the satellite bands and was finally able to install my antenna system onto my new house in the early summer of 2002. All was not well. I bought one of the first Sat-El rotor systems that were made and it came with a few surprises. Firstly, the software was severely lacking. So much so that I took to developing my own program so that I could make my satellite prediction software control the antennas. QA was also a serious issue. One of the 2 rotators wouldn't work. After several trips to the roof and almost 6 weeks in waiting I finally got a replacement rotor. Having proved that the new one worked I took it apart to compare it with the broken one. The broken one was missing a very large capacitor! It never worked so how could it have passed the manufacturers QA process?

Aligning the antennas was another pain. The antennas must be accurately mounted onto the rotator so that when the rotators think they are looking at the Pole Star the antennas are too. In this way whenever the software controlling the rotators wants to look at a given point in the sky the antennas will correctly look there. This was not an easy task. It took me almost 6 months to complete this stage of the alignment. I couldn't seem to get the rotators to line up with anything.

A few nights ago I was watching "The Dish" on video. Its the story of the Parkes Radio Telescope in Australia. This was the dish that brought the TV pictures of Neil Armstrong's Apollo 11 moon walk back to the world. The story told in the movie is apparently true and it chronicles the goings on during the 2 weeks around the moon walk. Parkes was the only dish in that part of the world capable of receiving the pictures as the moon was only visible from Australia at the time. Well Parkes computer had a problem just a few hours before the big event and they lost contact with the space craft. After an hour of bluffing NASA about land line problems they finally found the space craft by randomly pointing the dish at the moon and waving it around a bit. This gave me an idea!!

So picture the scene. Its 10:30PM. Its dark. Its DAMN cold. The moon is out. Mark is on the roof trying to work out why his antennas are not pointing at the moon when he tells them too. I figured that I could align the antennas with the moon as my point of reference rather than the Pole Star. I can see the moon. I don't know what the Pole Star looks like. I start by guestimating the amount of error between my antennas and the moon's location. I guess 20 degrees. I go down to the basement where I control them from and fiddle with the settings. I go back up onto the roof. I reckon I made it worse. I go back down to the basement. And so on for about half an hour.

I'm getting cold and annoyed. It's getting late and the neighbors dog keeps barking at me up on the roof. I retire to the bedroom to spend some time with my wife before she forgets what I look like. On the way I fall over my laptop computer. A light goes on! I have a wireless network card in my laptop and some remote control software on my computer in the basement. Quick as a flash I'm back on the roof with my laptop. Now I can see what I'm doing!! Within about 5 minutes I was able to align the antennas so that they pointed at the moon. As the antennas are only about 6 feet above the roof of my house I was able to look from the back of them up to the moon and see that they were perfectly lined up. Back down the ladder and off to bed.

Sunday morning and I'm up early and down in the shack. I run up Nova (satellite tracking program) on my computer and find that I'm just in time for a PacSat pass. I instruct my antennas to point to it. A quick check of  Amsat's Operational Satellites page tells me what frequency I need to listen on. Sure enough, there's a whole bunch of data being transmitted. Result! My antennas are looking at a satellite. I don't have anything set up do receive the data so I just listen to it. Not quiet 10 minutes of data was heard here at KC2ENI QTH.

Next up was a crack at AO-40. This is what I started building my satellite system for. I have an MMDS down converter and a 3 foot BBQ grill dish (more about this here) which allows me to listen to the 2401MHz band. This is where all the activity is now as AO-40 has had some sort of unexplained accident which killed off all its other facilities. Sure enough when the satellite came around later that day I was hearing some hams sending each other SSTV pictures. I tried to decode the pictures but I wasn't able to get a good enough signal from the satellite. I was able to decode the telemetry beacon with some success as you can see from the screen capture above.

You can see I was only getting about 40% of the data packets from the telemetry beacon. I'm not sure quite why that is but I suspect that it has something to do with interference from all the 2.4GHz (2401MHz) gizmos we have around the house like our wireless network and some CCTV cameras.

On the next pass I'll turn all the 2.4GHz stuff off and see of it makes an improvement on the telemetry. If so it looks like I'll be spending a lot of time hard wiring the network devices to the main switch here in my shack.

It [still] Buggers Other Channels

 A few years back I presented an essay at the SWLFest titled "Whatever Happened to Digital Radio?" The gist of it was that Digital Radio was already on the decline in the US having failed to gain any market traction. The story is the same worldwide on shortwave too. 

Unlike other markets around the globe the US uses a product from Ibiquity called In Band On Channel. Ibiquity has been bought and sold a few times since the release of IBOC. Its product name was made a little more friendly by the phrase "HD Radio" giving the illusion that the audio quality was superior to the existing traditional AM and FM systems

Over time the IBOC system gained the nickname "It Buggers Other Channels". It's easy to see why. Take a look at the below screenshot taken from my SDR software. I have an Afedri SDR-Net connected to a MLB-30 active loop antenna. I spotted this signal while looking for something else.

It's 30KHz wide!!  AM stations in the US are normally placed into a 10KHz slot. There is a vacant 10KHz slot either side of them (called "guard channels") which are usually reserved for stations in other markets thus allowing a kind of jigsaw puzzle whereby the various markets fit into each other without interference. 

So a signal 30KHz wide would invade both the guard channels on either side of the allotted frequency. The IBOC signal is injected in "wrapper" mode whereby the digital data is sent in 2 carriers either side of the main AM signal. In the above picture an AM carrier can clearly be seen in the right hand data bundle (the square thing to the right of the red line). Listeners to the station on buried by the data signal will hear a rushing noise along with their normal station.

Perhaps this interference is why IBOC is on the decline? Its the same story on the FM band too. A scan of my local AM band (15 miles NW of Philly) reveals just 3 stations using IBOC down from 15 just a few years ago.

NinoTNC to Yaesu VX-6R wiring

Some folks have asked me to document the wiring/pinout for my  NinoTNC/Yaesu VX-6R cable. See the below drawing. It is based on a pre-terminated cable I got from Amazon .

Upgrade your old TNC to a USB interface

With the current resurgence of Packet Radio I decided to dust off my old Packet Radio Terminal Node Controller (TNC). There were untold thousands of these made in the late 80's and early 90's and to this day can be found at junk sales and hamfests for very modest prices.

One of the issues facing us today is that these modems typicaly used an RS232 serial port to communicate with the host computer. Take a look at your computer. Do you have an RS232 port? Most likely not. They have gone the way of the printer port and the dinosaur. Everything has moved over to USB.

The upgrade is very easy requiring only a USB-TTL interface commonly used to program the Arduino and other like microprocessors. The interface connects to the TTL facilities on the rear of the TNC.

The wiring is trivial. Using some female DuPont connector wires connect the 2 devices together as follows...

USB                             TNC

GND -------------------- GND

TX   -------------------- TX

RX  --------------------  RX

Set up your terminal program to reflect the port and speed settings reqired by your TNC then turn it on.