Wirless Mic Channels


We just got in the new rack of the ULX's the night before opening night. In a mad rush to get them setup and out to actors I just set them on group 1 and went channels 1-6. Tonight after rehersal I am going to draw out frequencies to select from. For the show, we are going to run 18 mics. We have 6 Shure UC's, 6 SLX's, and 6 ULX's. What is the best way to balance them out so they don't all collide. We are in Dublin, OH (a subarb right outside of Columbus)

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so i take it you use a digital board?


Wireless Guy
Premium Member
I'm not sure where the original poster said anything about a digital board...

In order to avoid problems, you need to use a program to do intermodulation calculations. The information you'll need is the frequency range and frequency steps each system offers. For instance, the ULX is available in the J1 and M1 range (M1 = 662-698 MHz, I don't know what the J1 is off of the top of my head). The SLX is available in H5 and another one I believe. Both the ULX and SLX can step in 25 kHz increments. I'm not very familar with the UC series, but this information is in the manual and on Shure's website.

You'll also need a list of TV stations in your area, both analog and digital. This information can be gleaned from a number of sources, but a sure bet is the FCC website <http://www.fcc.gov/mb/video/tvq.html>. Just search for stations within about 50-75 miles of your location.

The best program currently available to do these calculations is Sennheiser's SIFM application, which is available at Sennehiser's website for free <http://www.sennheiser.com/sennheiser/icm_eng.nsf/root/products_wireless-systems_sifm_software>. Plug in your frequency blocks, step increments, and local TV stations, and walla, out pop usuable frequencies. For the ULX and SLX you'll need to enter into manual mode and enter the frequency directly. There is a table of frequencies in the SLX and ULX manuals.

While the program is very good and should work, the real world isn't always perfect and you should check your mics thoroughly before the show starts. Henry Cohen of Production Radio Rentals recently posted some great advice (with reference to another person's wireless issues) to the Theatre-Sound mailing list:

Henry Cohen said:
There are several items to look at, starting first with the SIFM program:
1) Are the parameters correct? Specifically, how far away from tuned
frequencies are 3rd and 5th order products being restricted - A minimum of
100KHz for 3rds and 75KHz for 5ths is recommended to start. Have *all*
wireless devices in the same general spectrum present in the venue been
entered into SIFM (other mics, coms, IEMs and IFBs)? Are the chosen
bandsplits correct?

2) Calculating in analog TV is one thing; did you consider the pilot tone of
any strong nearby digital TV stations (.310MHz above the
channel's lower frequency edge)?

3) Did you check the FCC website to confirm all analog and digital TV
stations that might be problematic for your location? Remember that several
DTV stations surrounding your bandsplits raises the overall RF noise floor.

As to the equipment itself:
4) In order to simulate as close as possible to 'real world' intermodulation
interference, spread out all your transmitters within the performance area,
keeping them separated by at least two feet, and turn them all on. Now turn
one off and look at it's receiver; does the RF signal indicator show a
complete loss of RF or at least an energy level below the squelch threshold?
If yes, good; turn the transmitter back on, go to the next one and repeat
the process for all transmitter/receiver combinations. If no, there is then
an intermod issue, a faulty/misaligned receiver front end or one of the
transmitters still on is faulty.

5) You indicate the "The mics are right in front of the stage, which is
elevated about 3 feet, so I'd say they have a pretty clear line of sight,
and the distance from the receivers to the transmitters is never more than
maybe 30 or 35 feet": Are you using individual antennas on each receiver or
an antenna multicoupler(s) with remote antennas? If the former, ensure both
antennas of each receiver face the performance area and the receivers are
separated enough so that each pair of receiver antennas are at least one
wave length (of the lowest frequency used) apart. If the latter, What kind
of antennas are used? In this case, directional *UN-amplified* log
periodic, band limited 'paddles' would be the best option.

6) If using directional antennas, where are those antennas facing in
relation to TV broadcast towers?

7) Do the "drop outs" consistently occur at the same point in the production
or is it random? Drop outs occurring at the same point in the production may
indicate that performers in front are physically blocking upstage

8) Where are the transmitters located on the performers; are the performers
wearing any metal (or have any implanted)? Are antennas straight and
vertical? Are the antennas coming in direct contact with skin?

Lastly, a simple check that all TX and RX electronics, antennas, coax and
connections is in proper working order is an often overlooked part wireless

Henry Cohen
Production Radio Rentals

Let us know how things go, and don't hesistate to ask if you have more questions.
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i was assuming that theydo have digital. they said "group 1" i'm not entirly sure though.


Wireless Guy
Premium Member
By Group 1, the original poster was referring to Shure's preset groups of channels in the ULX system.
oh ok I see
Thanks for clearing that up for me!!

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