Field-Friendly Phone Interfaces
Appeared in Radio World 4/1/98
by Paul Kaminski
The dial-up "plain old telephone system" or POTS, remains the least-expensive
system for transmission or reception of audio, albeit with limited audio frequency response.
With last-minute remotes, breaking news stories, increased program demands and budgetary
pressures, some radio users still depend on POTS for transmission and reception. Most people
producing such programs or news coverage are not technicians. An easy way to hook equipment
to the phone system is a big plus.
Handset answer
This article focuses primarily on handset replacement products. Calls to manufacturers
and dealers turned up the model mentioned here. If you make or use a model not shown, let
me know and I'll write about it in a future article.
Handset replacement devices plug up or into the handset port on a POTS telephone. They
replace the telephone handset microphone, and sometimes the receiver, either with an enhanced
microphone or with a provision that lets you connect a broadcast mic and headphones to the
telephone instrument. The replacement devices do not act like a telephone hybrid, splitting
the signal into separate transmit and receive paths. Nor, with a few exceptions, do they
plug up to standard telephone RJ-11 jacks, or work with phones in which the dial pad is
in the handset. You still need to dial with the dial pad of the instrument. The handset,
by design, allows leakage between the send and receive paths ("side tone").
John Lynch, a sales representative for Broadcast Supply West [Worldwide] of Tacoma, Wash.,
said handset replacement devices are not designed to record or put two way conversations
on the air. "It can be done, but the quality will never be as good as that available
with a telephone hybrid," he said. If you do one thing at a time with them, just send
or receive audio, you can get acceptable results, Lynch said. According to Lynch, handset
replacement devices are attractive to broadcasters on a budget, because they allow those
broadcasters to "do a remote using any telephone that has a handset that can be disconnected...
...JK Audio makes similar passive handset interfaces. The THAT-1 and THAT-2 allow users
to send or receive audio, from equipment ranging from full-blown mixers to cassette recorders.
The THAT-1 has a simple interface, with RCA jacks for inputs and outputs and a handset mute
switch that replaces the handset on an electronic phone (not the old carbon mic style).
The THAT-2 adds volume controls, XLR line in and line out, and a handset switch that allows
it electrically to match handsets from old-style carbon mics to digital PBX. The XLR mic-level
telephone output allows an easy interface to professional equipment. Both units provide
a mix of send and receive audio on their outputs.
JK Audio makes a receive-only unit called the QuickTap IFB that provides and XLR line-level
connection and a 1/8-inch mono output jack for listen-line audio ? a good tool when you
need to feed pre-delay cue to a headphone amp or a talent ear piece.
Mixing, too...
...You also can choose units that include mixing capability.
JK Audio addresses the high-dollar end of this market, with the RemoteMix, RemoteMix C+
and the RemoteMix 3. The latter model blurs the line between handset replacement devices
and telephone hybrids. If you need a three-input portable mixer and handset replacement
device/phone line hybrid (hooks to both RJ-11 and handset jacks) with VU meter, squawk-box
intercom style talkback and a touch-tone dial, this is your box.
The next JK iteration of the RemoteMix 3 is called the 3.m, which adds a clean mixer feed
(without telephone receive audio) to its other capabilities, without an increase in price.
With an audio response of 8Hz to 15 kHz, it works well for basic field mixing to record
to a MiniDisc or High-end tape recorder. JK also has an even more advanced model, the Remote
Mix 3x4, which allows not only a hot backup system for an ISDN/POTS codec or RPU, but also
the ability to produce a remote call-in talk show in the field.
Versatility
The versatility of these devices can help broadcasters solve telephone and remote-feed
problems using POTS. While the system audio response is band-width-limited, the transmitted
audio benefits from the addition of a better microphone. Your news product can benefit,
too. If your competitor covers an event with a voice report, and you cover the same event
with a wraparound report, including actuality of the subject matter, expert or newsmaker,
your station will be perceived as the one that brings an extra perspective to the story.
To summarize the reasons for handset replacement devices: The cost is low compared to POTS
codecs, frequency extenders, RPUs and satellite transmission equipment. Some units are less
than $100.
They offer relatively easy connection to any hard-wired telephone with a detachable headset.
With digital PBXs, it may be the only option if you go hard-wired.
They allow recording or transmitting of enhanced dial-up POTS audio (but not both simultaneously
with any quality).
They allow a hot backup to an RPU/POTS or ISDN codec or other feed (reduce make-goods on
that must-run, big-dollar remote).
Higher-end handset replacement devices ($260 and higher) include rudimentary mixing of
mic-and line-level send audio, a separate line-level feed, an output for recording from
the telephone line and other features, depending on the box.
The marginal cost of transmission per minute is low compared to cellular phones.
Paul Kaminski is the Motor Sports Radio Network news director and host of its syndicated
weekly programs "Race Talk" and "Radio Road Test." |
