Radio Mike Test

Radio mikes have become an essential tool. Demands of constantly moving cameras and the pressure of production schedules force us to rely on them more and more. Advances in radio technology and miniaturization have made this possible to the extent that some of us are now routinely working with radio booms.

We are making an evaluation of the latest systems from the perspective of working production mixers. We try to be scientific in our tests to obtain quantifiable and repeatable evaluations. But in addition to absolute performance, we also want to consider ease of use, cost-benefit analysis and service and reliability considerations. This is an ongoing project for us and we'll post updates from time to time. We also invite your participation; let us know your experiences and suggestions for the kind of tests you would like to see and we'll try to incorporate them.

Since a clear understanding of complex terms is important to interpret the features of various systems, we've provided a resource page with links to additional information and a glossary. Many of the terms are familiar, of course, but we will strive to provide precise definitions and an explanation of applicability. Just click on any underlined word to access the resource page.

A historical perspective of radio mike use and development can be useful in evaluating the current systems. For historical background click here.

Cost is always an important part of equipment evaluation. To see a table of current retail prices for the tested gear, click on RadioPrices.

There are many choices in radio systems. We've confined our initial tests to the most popular units in common use on motion pictures: VHF Vegas, VHF Lectrosonics, UHF Lectrosonics, and UHF Audio Limited. We are also beginning to evaluate the new, frequency agile systems as the FCC assignment of HDTV channels restricts the frequencies available for unimpeded broadcast. We hope to expand this inquiry to the newer UHF Vegas, Sennheiser radios, the new frequency agile Sony system, and systems available from Telex and others.

In comparing the older Vegas and current Lectrosonics and Audio Ltd. models there are advantages to some designs which are apparent even before the units are powered up. As the older design, the Vega is at a disadvantage here; more current models would probably fare better and, in fairness, we should make a test of the latest Vega in the near future.

The Vega Dynex II systems we worked with have transmitters encased in a rugged plastic shell. The transmitter output is 50mW FM, the maximum permissible by the FCC. The antenna is a 1/4 wavelength limp wire permanently attached to the case. A single 9-volt battery loads into a compartment in the bottom of the case accessible through a sliding plastic door. A plastic tab facilitates removal of the battery. Loading the battery is fast and easy but the compartment does not accept all 9-volt batteries. Remarkably, there is really no standard size for 9-volt batteries and the extended life lithium batteries tend to be slightly larger. The limp wire antenna has often been a source of trouble. When rigging an actor, it is important that the antenna wire not cross the mike lead or noise may result. Also, if the shield on the antenna becomes frayed, the signal will break up. This can be very aggravating because the signal can be just fine and then become noisy when a performer makes the slightest move. Receivers are housed in a solid metal case and powered by an external source or by 4 9-volts. Front panel switches are of good quality and a meter measures both audio and RF levels.

The Lectrosonics units offer several refinements. Measuring only 1.1" x 2.75" x 5.2", the Lectrosonics receiver is less than half the size of the Vega. This greatly facilitates mounting the receiver on video cameras and also bundling several receivers into a quad box of reasonable size and weight.

On the VHF transmitters, the shield on the mike cable serves as the antenna, greatly simplifying operation and removing a potential source of trouble. This antenna system doesn't work as well on UHF units and they employ a small, stiff wire antenna (1/4 wavelength, usually about 2"~3") which mounts with a screw connector. The design of the battery compartment is particularly ingenious. It permits one-hand operation, assures positive contact and correct polarity, and accommodates all the popular brands of 9-volt batteries. Metering audio level is accomplished with two LEDs; one light indicates a signal 20 db below limiting and the other shows operation of a gradually sloping limiter. In practice, one sets the gain so the -20 db light flickers regularly on normal dialog and the 0 db light flashes only occasionally on peaks. The transmitter has a fitted belt clip which is very useful but also the source of occasional aggravation. This is a ruggedly constructed variation on the belt clips found on pagers. The transmitter can often be attached to an actor's belt, eliminating the need for a belt-and-pouch kit. This can greatly simplify use of the transmitter but the advantage is almost completely offset by those occasions when the belt clip must be removed to maintain a low profile. Attachment is by two tiny screws held under tension from the spring and quickly attaching or detaching the clip is difficult.

[A wire-frame belt clip is now available from Lectrosonics as an accessory. This provides much of the functionality of the full-size belt clip while maintaining a lower transmitter profile.]

The Lectrosonics VHF receiver is very energy efficient (55mA for the 187 model, 70 mA for the 175) and requires only one 9-volt battery. Metering for audio level and RF strength is done with arrays of LEDs. On the VHF there are two lights for level (mirroring the lights on the transmitter) and one light for RF. If the RF light glows brightly, the signal is strong; if it is dim, RF is weak. Both the transmitter and the receiver are housed in well designed shells of extruded aluminum. The components have the look and feel of high quality equipment. Access to internal components is simple and easy.

The UHF Lectrosonics model transmitters are very similar in appearance to the VHF models. The previously mentioned stiff wire antenna attaches to the top of the case and the belt clip attaches with only one screw but there are no other significant observable differences. There are some significant electronic differences. Except for the model 190, all of the UHF Lectros are wide band designs with 75kHz deviation. This bandwidth is the "real estate" of the signal; all other things being equal, a 75 kHz bandwidth will yield noticeably improved audio quality when compared to the 15 kHz bandwidth of VHF. Power output is up to 70 mW and a special 200 mW unit is available. The UHF units also employ a more sophisticated compandor; the "dual-band compandor" uses two compandors, a high frequency unit and a low frequency unit with a cross-over network to more precisely match attack and release times to the needs of the program material.

A plug-on transmitter for regular microphones is available for both VHF and UHF Lectrosonics systems. These greatly enhance the utility of the system by making wireless booms possible.

The receivers are clearly from the same family as their VHF cousins but are also different in obvious ways. They are slightly larger (3.2"x1.22"x5.1") and chunkier in appearance. The front panel incorporates a 10-light LED array which measures both RF and audio, selectable by a switch. Power consumption is up to 140 mA and the battery compartment now holds 2 9-volt batteries. One battery is sufficient for operation but two provide additional run time. Audio output level is adjustable by a high-low switch at the rear of the unit and, within a limited range, by a trim pot on the front panel.

The receiver is available in both regular and diversity designs. The compact diversity receiver uses an antenna switching design to keep size and weight to a minimum. A "true-diversity" model is also available but this is very much larger and not often seen in mobile applications like a production sound cart.

The "frequency agile" model 200 is a new design fitted into the same case as the 195 receiver. An antenna-switching diversity system like the 195, this model offers the user the ability to set any of 256 different operating frequencies over a range of about 25 mHz. The transmitter and receiver each have two pots advancing and retarding the frequency in steps of 1.6 mHz and 100 kHz respectively. The receiver has a switch to disable the pilot tone squelch function. With the pilot disabled, it is possible to check for reception of competing signals by observing the RF reception lights. By switching up and down through the channels, one can find unused spectrum. The transmitter has 100 mW output. Power consumption rose dramatically and the model 200 receiver requires 400 mA. Consequently, there is no longer a battery compartment; the unit is powered from an AC adapter or another power source like a quad box or a block battery.

This power hunger is related the efforts by Lectrosonics engineers to maintain the same steeply notched filtration they use on single frequency models. A dedicated frequency radio will employ filters to sharply reduce its sensitivity to frequencies outside the reception channel. This helps minimize RFI. Some other frequency agile designs have used filters to minimize sensitivity outside the range of frequency agility but leave the operating range wide open. A frequency agile system working from 537 mHz to 563 mHz would be filtered above and below these limits but would be wide open within that 26 mHz range, although only 75 kHz is used by the radio at any one time. Lectrosonics engineers worked out a system of narrow filters which track with the selected frequency so the radio is finely tuned only to the selected frequency and has steep rejection of other RF energy even within the range of its frequency agility. This is a very worthwhile aspect to the design but, apparently, not conducive to energy efficiency.

[The Lectrosonics line has developed considerably since this was first written. The 205 model is no longer current. The UCR211 receiver, the closest equivalent, runs more efficiently and can be powered from 2 9-volt batteries. Many other models are now available including a "digital hybrid" system. Anyone seriously considering purchase should visit the Lectrosonics website.]

The newest model 205 frequency agile system offers some refinements to the model 200. Power consumption is down to 260 mA; still too much for an internal battery but less of a drain on the system. It also incorporates a newly designed squelch circuit with a "smart squelch" which minimizes transient noise in marginal reception conditions. Many "drop-outs" are accompanied by a "pfffttt" noise which spoils the track. This noise is usually caused by the squelch circuit suppressing the audio momentarily when the pilot tone is too weak for reception. The newly designed circuit minimizes these "hits" by holding squelch until a word is finished and by softening its action to prevent noise.

Quad boxes are available for all the Lectrosonics models. Typically they offer power from rechargeable gell cells and appropriate multicoupler hook-ups for the antennas. There are also rack mounts available.

In the Audio Ltd. world, there is really only one basic body-pack transmitter, the TX2000.

[Audio Ltd. has also been refining it's product line in the five years since we first wrote this. For the latest specifications, vist their web-site: Audio Ltd.]

This is a two-channel switchable device with 50 mW output. This makes some of the benefits of frequency agility available throughout the range of Audio Ltd. products; if problems arise on one frequency, one can switch to the other. However, the two frequencies are fairly close together; switching won't get clear of an HDTV station whose broadcast consumes an entire channel (a single TV channel spans 6 mHz). The body-pack transmitter operates on a 9-volt battery which is held in place by a flimsy, removable plastic door. These have a tendency to pop open and release the battery from the contacts at the worst possible moment. In practice, one tapes the battery compartment closed. A small panel of switches and metering lights are accessible after removing a plastic panel on top of the transmitter. Setting gain requires a greenie or small screwdriver but the dynamic range of the system is so great that one typically sets the gain to the sensitivity of the mike used and doesn't change it. Selected channel and audio level are indicated by LEDs which glow from below a plastic panel. The transmitter antenna is a stiff wire design very similar to the Lectrosonics. In fact, many users report that the antenna wire used is not rugged and they mount Lectrosonics antennas to their transmitters. The transmitter has a very useful belt clip. A simple stiff wire clip holds the unit to a belt or pocket and adds very little to the profile of the transmitter. If necessary, it can be removed or reattached in a moment with no tools.

A frequency agile design has recently been released with 32 frequencies available in a single unit. The first model we examined operated within a range of about 6.75 mHz. Audio Ltd. has engineered the frequencies to advance in unequal steps, minimizing the likelihood of one channel's intermodular signal interfering with another. However, a system working in range of about 6.75 mHz or little more than one TV channel is very limited. By comparison the Lectro frequency agile system works in equal steps but spans a range of about 26 mHz or 4 1/2 channels. The Audio Ltd. has the edge if the goal is to work with many units in the same range, the Lectrosonics has the edge in finding an unused channel in various locations. This is not a inconsequential difference. Checking a particular model 2020 Audio Ltd. radio, we find that its operating frequencies (565.550-572.300 mHz) are already N.G. in Indianapolis. Worse, based on FCC channel assignments for HDTV, that range will soon be unusable in Baltimore, Boston, Cincinnati, Dallas/Ft. Worth, Hartford/New Haven, Miami, Philadelphia, Pittsburgh and San Francisco. It's bad enough to find many markets proscribed with regular single frequency radios, it would be a serious limitation to have that many off-limits after paying the extra money for a frequency agile system.

We understand that most of the Audio Ltd. 2020 production models now shipping have a much broader range of frequencies available. The standard model 2020 should operate in a range of about 12 mHz. This is about 2 TV channels but, because the points of demarcation are unlikely to exactly match FCC channel allocations, 12 mHz should cover 3 channels. This is still only half the frequency range of the Lectrosonics frequency agile system but it should be sufficiently broad to find clear air in most markets.

Audio Ltd. also has a special transmitter designed to work with the Schoeps microphone system. This directly accepts the screw-on Schoeps capsules to make a high quality radio boom mike. This combination works so well that many mixers use it as their primary recording configuration. An associate made a test with two Schoeps mikes mounted on a pole, one hard wired and one using the HX 2000 Audio Ltd. transmitter. Switching back and forth between them during a scene he was unable to hear any difference.

The transmitter can be matched to two basic receivers, the MX 2000 2 channel receiver and the DX 2000 two channel diversity receiver. (The frequency agile DX 2020 is identical to the two channel DX 2000 except for the frequency agile feature.) The DX 2000 receiver is a true diversity design. Somehow Audio Ltd. managed to squeeze two complete receivers into a space only 147 x 64 x 20mm. (5" x 2.4" x .8" approx.) A remarkable accomplishment in miniaturization.

The MX receiver is powered from an internal 9-volt battery and has no provision for external power. There are work-arounds available from other manufacturers for getting power in through the 9-volt contacts but there is no external power provision available from Audio Ltd. The DX diversity receiver requires either external power or power from several DL 123A lithium batteries. These batteries provide 10 hours of reliable operation but cost about $7 each. In practice, most people use the DX receiver in a quad box and power them through the box. It's worth noting, however, that even the frequency agile Audio Ltd. receiver can be operated from internal batteries, albeit very expensive lithium cells.

In the Lectrosonics models, the radios were complete unto themselves and the quad box was just a device to house the units and provide power and antenna amplification. The Audio Ltd. quad box does all this as well but also supplements many of the features of the radios. The receivers have very little in the way of metering for audio, RF or battery condition. However, these functions are well handled by a bank of lights on the quad box. Switches allow one to accurately monitor any condition in any of the mounted receivers and their associated transmitters. It is even possible to remotely monitor the battery condition in the transmitter. The box is designed to work with external power from either a battery source or AC. However, it also holds 6 internal D-cells for those occasions when the unit must be used remote from a cart. Both transmitters and receivers are housed in beautifully machined metal cases which are wedge-shaped at the edges. The receivers slip into wedge shaped receptacles in the quad box, automatically making connections for power, audio and RF. A rack mount offering similar connections for two radios is also available. The diversity Audio Ltd. radios are very cumbersome or expensive (in batteries) to use by themselves but very elegantly realized with the quad box. However, this is a very expensive system. A package of four diversity radios with a quad box is at least $20,000.00.

The extraordinary performance of the Audio Ltd. system is rapidly becoming legendary. We set out to see how it compares to familiar designs and to the latest from Lectrosonics. For our first test of these systems we evaluated the standard Lectrosonics 185 VHF, the UHF diversity Lectrosonics, and the DX2000 Audio Ltd. Each radio was tested with only standard whip antennae and each was connected to a Sonotrim mike. Recording was done on a Tascam DA88 so we could discretely record all three systems simultaneously. A Cooper mixer fed the signals to the Tascam. As expected, the VHF unit had the least range. The antenna diversity Lectrosonics had significantly increased range compared to the VHF unit. The true-diversity Audio Ltd. had, by far, the greatest range.

Recordings were done at normal reading levels. Listening to the tracks, we were impressed by how alike they sounded. In a normal recording, there was no audible difference between the UHF Lectrosonics and the Audio Ltd. And the audio from the VHF Lectrosonics was very nearly the same as its UHF competitors. By listening carefully we were able to identify a slightly more nasal quality in the VHF recording, probably indicative of a more limited frequency response. However, this was a relatively subtle distinction and the resulting track could easily be EQ'd to match either of the other recordings. This test only evaluated the radios under rather undemanding conditions without much variation in line delivery. We also needed to look at how well the units performed under more difficult circumstances and with greater range in line delivery. First, we decided to look at the frequency response of the various systems.

In conjunction with the radio mic test, it seemed reasonable to look at the Sonotrim mic head itself to provide reference point so we could identify how the radio systems might color the response. There are many lavalier mics out there to choose from but the Sonotrim seemed like a good place to start. Since microphones do change their characteristics over a period of time, we allocated a brand new microphone for these tests. It had never been used except in testing so the results are reasonably consistent and typical for that type of mike. The mike was tested in an anechoic chamber and its response was measured in different configurations without moving the mike.

Reproductions of the print-out graphs are available on the Test_Graph page. Just click anywhere you see Test_Graph to see the charts. (Special thanks to Dave Missal, Ed Somers and Marc Lesonsky at LSC for performing these tests. To go to LSC Home Page, click here )

We first tested the Sonotrim in an anechoic chamber powered by a hard-wired PSC power supply. This was our reference standard. The result was a smooth, flat response from 100 Hz to 1 kHz. At 1 kHz there is a presence rise of nearly 5 db which subsides to flat by about 8 kHz. This gradual presence rise is typical both of this mike and this kind of mike. Test_Graph Sonotrim

The same Sonotrim microphone operating through an early series Lectrosonics 185 VHF radio transmitter/receiver was plotted. The bottom end is no longer flat, down 5 db at 100 Hz., but the response otherwise was a reasonable approximation of the hard wire pattern. Test_Graph Lectro185

The Lectrosonics 195 transmitter/receiver set showed the same low end roll off of 5 db @ 100 Hz but otherwise matched the performance of the hard wire system. Test_Graph Lectro195

When we tested the Audio Ltd. system it was a very nearly identical match to the output of the microphone when connected to a hard-wire, PSC power supply. If one holds the two graphs up to the light and superimposes them, the trace lines lie exactly on top of one another. A demonstration of audio excellence available with unlimited money. Test_Graph Audio Ltd.

For our follow-up test, we used a Vega, VHF Lectro, UHF Audio Ltd. diversity set and the newest model 205 Lectrosonics frequency agile system. We worked under good conditions outdoors; we were at least 75 feet from a road or any utility poles and we maintained clear line-of-sight between the transmitters and the receiving antennas. We were, however, still in an urban environment in North Hollywood only a mile from the Burbank Airport. All transmitters had fresh batteries from the same batch. For this test the Audio Ltd. system may have been operating at a disadvantage. Several months had elapsed since our first test and NBC had begun HDTV transmission on channel 36 (602-608 mHz), possibly interfering with the Audio Ltd. signal.

We tried making actual measurements of the range of the various systems. There are some limitations to this kind of undertaking. First, remember that we are testing single units of each radio; other units at different operating frequencies may yield somewhat different results. We did check several findings with a second radio but it was usually operating at a nearby frequency to the first. Also, the range isn't an absolute number. A radio would begin to experience drop outs at one spot and then operate well for another 20 feet beyond. We tried to make a good judgment evaluation of where each radio was getting to the end of its range.

The Vega (169.925 mHz) was the first to drop out around 175 feet.

The Lectrosonics VHF (169.505 mHz) lasted a little longer to about 200 feet.

Using a Comtek "phase right" antenna added about 25 ~ 50 feet to the range of the Lectrosonics. (We didn't test it with the Vega.)

Using a Yagi antenna added an additional 25~50 feet to the range of the Lectrosonics. Even with the Yagi, the Lectrosonics fell well short of 300 feet.

Both the Lectrosonics 205 and the Audio Ltd. were able to work reliably to about 350 feet with just whip antennas mounted directly. Using "batwing" Yagi antennas we were able to get at least 450 feet of reliable range from both systems. At that point the RF indicator lights were about half extinguished but the units were working well. We had run out of straight line real estate but we think that the reliable range is not much greater for either unit in an urban environment. Turning a corner which required transmission to work through a building, each unit worked for about another 50 feet and then began to experience drop outs.

We concluded that the operating range was about the same for the Lectro 205 and the Audio Ltd. and that this range was really adequate for nearly any shot one is likely to face on a set. Of course, it's not quite good enough to rig the actors and then stay at base camp while the rest of the crew goes off to do a tow shot with an insert car (always a pleasant fantasy). But it is good enough to get most any shot where the actors are visible and identifiable. If the performers are so far away that one can't really identify them, then even if the camera has a 500 mm lens mounted, they'll be so far away that sync sound isn't important.

We also did some critical listening to the two high-end systems. We listened through a Cooper mixing panel with one system on the left track and the other on the right. One could make immediate A-B comparisons with ease. The systems sounded identical under most circumstances. We listened at a normal level, at a whisper and at a sudden yell and could distinguish no difference at all. The slight "pumping" sound of the compandor or the limiter which is sometimes audible on the Lectrosonics 195 was not apparent on the 205. However, there was one difference we did observe; when the Lectrosonics was operating very near the limit of its range, its response was no longer flat. At 300 feet range it was a match for the Audio Ltd., at 350~400 feet there was a noticeable loss of bottom end and some loss at the high end as well. It still sounded "pretty good" but the warm tone was gone and the loss was clearly apparent in comparison with the Audio Ltd. which held its tone until the signal dropped out.

Our preliminary conclusion is that the Audio Ltd. still offers the absolute best performance. However, at only a little more than half the price, the Lectrosonics 205 frequency agile system is clearly the best value. It is more user friendly, has local repair facilities, is manufactured locally (New Mexico) and matches the performance over most of its range.

If you have any comments, experiences to share or contributions of any kind, please e-mail us.