BETA TESTING
So I started begging to test this marvel and, after a while, got some beta gear. More recently, two production
encoders and several late proto-type radios arrived. Since last winter I have installed and evaluated FMeXtra on some
20 stations in California, New Mexico, Illinois, Minnesota, and Wisconsin. Others are operating in various places
throughout the U.S. as well as overseas. The encoder is a Windows XP two rack-unit computer
with Lynx audio and SCA generator cards. CD players, Flying Cows, Optimod-PCs, or other digital sources plug
into the XLR inputs which accept AES or S/PDIF signals. One can also directly stream Internet audio through the
system using an Orban Opticodec.
Installation is quick and simple.
• The encoder has a BNC output connector.
• Just connect that to an SCA input on the exciter.
• Then drive away to see how far the signal goes.
Adding two digital stereo stations to existing analog stereo stations in as little as 20 minutes says this technology
is easy to work with. Yes, I timed one install from opening the transmitter site gate to driving away!
EVALUATING COVERAGE
Testing with a number of stations, I drove hundreds of miles to check the coverage in various directions. The
antenna used was a quarter-wave whip with a magnetic mount, placed in the middle of the roof to minimize
directional effects.
Typically, the first dropout would be at about the 60 dBu contour unless there was a big hill close in the way.
Reasonable reception would then continue to the 50 dBu contour – and beyond in most cases.
The results have been excellent. I had worried that a digital SCA might be somewhat fragile and have holes
when listening in a moving vehicle, even fairly close to the transmitter. However, that did not happen. One of the
reasons is that there are a couple of seconds of buffering, sort of like satellite radios have for when the signal is
briefly blocked
RECEIVERS
Radios have been slow in coming, but it is expected that production radios should become available about
the time you read this. As HD Radio manufacturers also discovered, digital receivers tend to generate
RF noise which has proven difficult to keep out of the tuner’s front end. But that has been solved in the FMeXtra
radios now. The recent prototype is more sensitive than my trusty Technics ST-9030, is far more selective, and
has great sound. I love this radio.
OPERATIONAL MODES
FMeXtra uses COFDM-type multicarrier modulation techniques with error correction and IF equalization in the
receiver to minimize multipath effects. Several different modes of operation with different data densities are available,
as are the bandwidth and number of bits allocated to each channel, wide or narrow, that is part of the data
stream. Additionally, FMeXtra is remarkably flexible as to where the bits are placed in the FM baseband spectrum.
Best of all, the signal appears as white noise, so there are no birdies or other effects on the main channel programming
under multipath conditions
A mono station could literally use the entire spectrum from 20-99 kHz for a gigantic data stream of up to, say, 300 kbps at one of the higher densities. Stereo stations may want to use 55 to 99 kHz, or 61 to 99 kHz if they are
running RDS. Indeed, by mixing and matching mono and stereo channels, along with differing sample and bit rates, it is
possible to add at least four digital channels to an existing stereo station or even more if the station is in mono, all with
decent sonic fidelity. A narrower data stream at 67 or 92 kHz can also be selected if an analog SCA must remain.
One of those can carry two channels at 20 kbps using low density, more at higher density. Stations will thus have many options depending on intended use. Some may even want to send a stream pointto-point to feed an AM, for example. This fixed type of operation can stack the data deeper than what might be appropriate if mobile reception is the goal.
A BETTER REPLACEMENT FOR TRADITIONAL SCA
Stations will certainly be interested in adding more stereo program channels to their signal, but there are many
other possible uses. One owner I talked with plans to carry his AM signal in stereo on one of the FMeXtra channels of his wide
coverage FM station. This will really help the AM coverage, especially at night.
other possibilities are today’s traditional SCA users, such as services for the blind, shut-in, and foreign language broadcasters. Since many of the latter like to operate
on a subscription basis, FMeXtra offers encryption and receiver addressability – if the subscriber does not pay the
monthly fee, the radio stops working. Regarding compatibility with IBOC, I understand that digital radios can be built to receive both IBOC and FMeXtra at no additional parts cost. It is just lines of code in software. As indicated above, my observations regarding coverage are experiential at this point. A follow-up article will provide more detailed information, measured data,
and comparisons. A slight disclaimer/disclosure: I do not sell FMeXtra or represent DRE, but am doing minimal consulting for them related to interfacing with typical radio station gear.
Lyle Henry, aka The Radio Doctor, is a Los Angeles-based engineer who has consulted on FM and SCA issues all over the
world. Contact Lyle at
[email protected]
