Frequently Asked Questions - Wireless

FAQs - Wireless

The finish on the MM is a nickle -Teflon coating that has some very desirable qualities. It is conductive, very scratch resistant and very protective of the aluminum body in the presence of salt water or sweat. It does form a thin layer of nickle tarnish over time and exposure to corrosive elements. The tarnish is not harmful but is a cosmetic fault. We tried other none tarnishing finishes such as smooth nickle, chrome over nickle and gold over nickle and found that they looked great but a small pinhole in the finish allowed major destruction of the aluminum under the finish. A small pinhole rapidly grew into a large blister in the presence of salt water. The Teflon nickle finish kept the damage isolated to the original pinhole. 

We tried 6 tarnish removers and found one that works very well, is readily available, and has been around for more than a hundred years. Other polishes worked but not as easily or well. The tarnish remover is Wright's Silver Polish and can be found in almost any grocery. It's also available on the web.

Wright's site

Simply follow the directions on the container.

The Sanken CUB-01 boundary mic does not seem to have the usual FET output stage and also seems to have a large capacitor across the power supply lead (bias lead). This means that it can't be wired as the usual three wire microphone with the SM. The wiring below seems to work well and is fully compatible with our other transmitters.

  • Our pin 1 to Sanken shield (ground).
  • Our pin 2 to Sanken black wire (5 Volt power).
  • Our pin 3 to a 511 Ohm resistor and the other end to Sanken white wire (audio). This matches well to our 300 Ohm input input while providing a satisfactory 811 Ohms to the Sanken mic.
  • Our pins 4 and 5 no connections.

The color of the antenna caps or bands correspond to the last digit of the block number of the system. The universal color code used for resistors was picked for the code.


512.000 to 537.500




537.600 to 563.100

Brown 4.74"
22 563.200 to 588.700 Red 4.48"
23 588.800 to 614.300 Orange 4.24"
24 614.400 to 639.900 Yellow 4.01"
25 640.000 to 665.500 Green 3.81"
26 665.600 to 691.100 Blue 3.62"
27 691.200 to 716.700 Violet (Pink) 3.46"
28 716.800 to 742.300 Gray 3.31"
29 742.400 to 767.900 White 3.18"
30 768.000 to 793.500 Black (with label) 3.08"
31 793.600 to 819.100

Black (with label)

32 819.200 to 844.700

Black (with label)

33 844.800 to 865.000

Black (with label)


Score the insulation of a 50 Ohm coax such as RG58 (RG174 is OK if it is less than 5 feet) one quarter wavelength from the end of the cable. Do it very gently and don't score or even scratch the stranded shield wires since they will easily break off. Remove the outer insulation. Pull the shield down so that it has some slack in it with a bulge near the remaining outer insulation of the coax. Poke an opening in the shield with a blunt tool near the remaining insulation. The hole should large enough to pull the center conductor with the inner insulation on it through the opening. Straighten the shield so that you have a quarter wavelength shield wire and a quarter wavelength center conductor. These are the two arms of your dipole. Fold the shield back along the outer insulation of the coax cable. The center conductor is left pointing in its original direction. Now cover the center conductor and the shield with a half wavelength or more of shrink tubing to make it look nice. This antenna works best if the center conductor and the folded back shield are both in the open air since both the folded back shield and the center conductor radiate.

The times given are for turn on till shutdown (failure) of the respective transmitter. Times on alkaline AA's will drop greatly if the batteries are below room temperature. These times are typical and not guaranteed. Also note that the batteries were fresh and in excellent shape. 

The SM or MM transmitter will operate for slightly less than 2 hours on one Eveready or Panasonic alkaline AA battery, for 4 hours and 5 minutes on an Eveready 2200 mAh NiMh battery and for 6 hours and 30 minutes on an Eveready lithium battery.

The SMd dual battery 100 mW transmitter will operate for slightly less than 6 hours on two Eveready or Panasonic alkaline AA batteries, for 8 hours and 30 minutes on two Eveready 2200 mAh NiMh batteries and for more than 14 hours on two Eveready lithium batteries.

The SMq dual battery 250 mW transmitter will operate for slightly less than 2 hours on two Eveready or Panasonic alkaline AA batteries, for 5 hours on two Eveready 2200 mAh NiMh batteries and for 7 1/2 hour on two Eveready lithiums.

The variable power SMv transmitter will operate at 50 mW for 2 hours on an alkaline AA, for 4:45 on a 2200mAh NiMh AA, and for 7:20 on an Eveready lithium AA.

The variable power SMqv dual battery transmitter will operate at 50 mW for 5:50 hours on two alkaline AA's, for 9 hours on two 2200mAh NiMh AA's, and for 14:40 on two Eveready lithium AA's.

Your mileage may vary, See FAQ#087-WIRELESS.

An Eveready brand alkaline battery will power the LM for a little over 6 hours at room temperature. This time is from turn on until the transmitter shuts off. Lower temperatures, stale batteries or different brands will affect the operating time.

Since this was posted on 2006-03-02, we have come up with a third solution for interrupting the ground loop. See Isolating Battery Eliminator

What's happening is that the switching power supplies inside the UM400 transmitters create noise on the ground plane. This noise then has two paths because of the dual ground paths: one through the DC power and one through the audio ground connected by the mixer. Although mixers often have a transformer balanced output, some transformers have capacitance which can couple pins 1 and 2 to ground at high frequencies (such as hiss from DC switching supplies).

The solutions to this are as follows:

  • Use external isolating transformers at your mixer outputs.
  • Run a wire between the antenna connectors on the UM400 transmitters. One way to do this is to take a length of 18 ga. wire and crimp hoop lugs on each end. Then, using the SMA connectors for the whip (or external) antennas, lock the lugs onto the transmitters.

The range is not really limited by how loud the RM is or how the gain is set on the SM though these do have some affect. The limit on range is reflections from other surfaces. This effectively limits the range to 8 feet or less with maximum output on the RM and maximum audio gain on the SM. Even outdoors this short range is true since generally both the talent and the operator are standing on the ground and this is a reflective surface. The reflections cause the SM to receive echos of the transmitted tones so that the SM is trying to decode the proper sequence of tones and a delayed version of the tones. Amplifying the tones does no good at all since it is reflections that cause the failure of the decoding.

There is a positive aspect to this in that it is difficult for one RM to activate two transmitters at once which could lead to unintended results. More importantly, some prankster can't play the tones through the PA system and cause havoc. It is possible to to play the tones through a 2 way radio and allow very remote control. Cell phones don't work very well in this application due to the large amount of signal distortion (destruction?) that goes on.

The link shown below has loss numbers for just about every kind of coaxial cable that there is. The loss is per 100 feet of cable so if you have only 50 feet of cable you will have half the loss and so forth. Note that the loss figures are different at different frequencies.The frequencies are across the top going from 1 Mhz to 5000 MHz. The types of cable are grouped together in families vertically on the left side.

Click here for chart on cable losses

Some digital recorders have high levels of radiated RF and some have moderate levels of radiated RF but all radiate some RF. In any case, if the RF is the same as the operating frequency of the receiver, the range will always be affected. In most cases that particular frequency will be unusable. Some older digital recorders were so bad and radiated on so many frequencies simultaneously that any selected frequency was unusable. The only reasonable solution was to put the recorder in a trash compactor and then engage the crush mode, preferably multiple times. Modern digital recorders are much better but again, all radiate some RF.

The only current solution is to get the receiver antennas as far away from the recorder as possible. Increasing the separation by even a few additional inches may really pay off. We have some co-ax antennas that can be mounted on the straps of a bag system that will really help also. Things are easier on a cart setup since the antennas can be flown overhead to dramatically increase separation.

Here's a link to the Sound Devices site that discusses the problem in a nicely neutral manner.

Sound Devices Tech Note on RF