For wireless users not familiar with Helical antennas, particularly those with wireless personal monitor systems, their first experience can be deceptively simple. Plug it in, aim it, and it works. What works about it is that if they’ve been using a whip antenna or even a paddle at longer distances, for the first time, they get no dropouts.
Operationally, Helicals are as easy to use as “paddle” or “shark fin” antennas. A two-way mounting block is threaded on both ends: 5/8-inch for American mic stands on one side and 3/8 European on the other. Simply attach a length of co-ax to the Helical’s right-angle BNC connector and aim it towards the performance area.
Helical antennas theoretically have 14 dB of forward gain without using an RF amp, plenty to overcome cable loss from long runs and still “pump it up.” Passive “paddle” (LPDA) antennas, by contrast, only have 7 dB of forward gain, often just enough to make up for cable loss in longer runs, and only are polarized in one plane — more on that later.
Super Bowl Origins
Helical antennas have been around for years, but they became popular after PWS founder James Stoffo began successfully deploying them at the Super Bowl over a dozen years ago, where they’ve been used since, due to the event’s high RF channel count (1,000+), demanding RF environment and mission-critical nature.
The now-familiar “top-hat” profile of the original PWS Helical Antenna — made of rugged, clear polycarbonate (Lexan) — combines a 14-inch round back-plane with a 14-inch tube extending from the disk’s center with a spiral band of copper wound around four times inside. PWS’ standard 8089 UHF Helical (470 to 900 MHz) is 6 inches in diameter. A smaller 8241 Helical has a higher-tuned 4-inch tube for 900 MHz equipment, such as Lectrosonics’ Quadra digital IEM.
As mentioned, Helicals can be particularly useful for IEMs, the majority of which are non-diversity receivers, meaning they’re inherently susceptible to dropouts. Stereo transmissions are further compromised by the simple fact that the MPX side band (L-R) that creates the stereo signal is lower in level, so that long before a dropout, as SNR decreases, the audio’s stereo separation is reduced.
After first hearing about Helical antennas, I still doubted their value. Stoffo made me an offer I couldn’t refuse. “Use it for a month; then, on the last day, go back to using a whip or paddle,” he said. “Then call me.” After a dropout-free month, I was surprised how even minor dropouts became irritating. “That’s how your musician feels all the time,” Stoffo pointed out.
Helical antenna benefits include a wide bandwidth, but most importantly, they transmit circularly polarized RF, and receive transmissions through all 360 degrees.
Give and Take
To understand this ultimate benefit of a helical antenna, you must first understand that antennas are reciprocal and can both receive and transmit. In order for them to receive well, the receive antenna and transmit antennas must be oriented the same direction. That’s why, since hand-held mics are usually held up-and-down, their receive antennas also work best in a generally vertical position.
In pro audio, there are three common types of antennas. First are simple whip antennas — the free ones that came with your receiver — that are either quarter- or half-wave, depending on their length. While their directionality is almost omni, it resembles a donut-shaped field around the antenna’s length, though weak in the direction the antenna points. The difference is shorter quarter-wave antennas must be attached to the equipment chassis (or its metal equipment rack).
The second type of common pro-audio antenna is the “paddle” or “shark fin” directional antennas (actually called Log Periodic Dipole Array or LPDA), seen at many concert events, which provide rejection to their rear, allowing them to reduce nearby sources of interference while also providing about 6 dB of forward gain, making up for weaker signals, longer cable runs and BNC couplers. RF Venue’s Diversity Fin is an interesting combo of these two — whip and fin.
We mentioned that receive antennas not oriented on the same axis as their transmit antenna, such as holding a handheld horizontal or turning whip antennas sideways, produce dropouts. That’s why RF operators fan out stacked individual receiver’s antennas in a dual 45-degree pattern to put each receiver’s antennas equally in both planes of polarization.
Because they’re directional, paddles can give you a false sense of security, unless you employ best practices and also orient each paddle in its own plane — one vertical, one horizontal (or at least at 90° to each other).
All 360 Degrees
Helical Antennas’ dual advantage is that they’re not only directional with 14 dB of forward gain, but they also transmit or receive through all 360 degrees of polarization — especially important for many non-diversity wireless IEMs.
I recently used the PWS Domed Helical for Micheal W. Smith’s Christmas symphony pops show where he was backed up by LaFayette, LA-based four-piece band, L’Angelus (langelus.com) at Jacksonville’s Moran Theater. Drummer Johnny Rees, who was actually closest to the side-stage monitor mix position, reported dropouts, so we changed his quarter-wave whip to a paddle, even though he was only 10 feet away and that cleared it up.
Meanwhile, the PWS Helical Dome worked flawlessly on Smith all across the stage and the rest of L’Angelus across the downstage edge, who were on a four-way combiner feeding the Dome. We also had my old 8089 “top-hat” Helical, and a walk test comparing both of them showed the new Dome, which employs two turns instead of four, to have a slightly wider coverage pattern, about 75° instead of 70°.
Though especially valuable as an IEM transmit antenna, Domes also excel when used in pairs for diversity receivers. I’ve since done a few other gigs with the Domed Helical. The Dome’s rear rejection and forward gain also make it a perfect choice for mission critical wireless receivers, such as lead vocals and guitars. When compared to the high cost of premium wireless products (plus a spare), the Domed Helical is a bargain. (The original Helical sells for $450 and the Domed Helical sells for $650).
As a final note, those familiar with the original Helical know that, although they’re rugged, finding a big-enough case can be challenging. The Dome neatly fits into a SKB or Gator 14-inch snare case with room to coil a few lengths of BNC co-ax cable. Buying a 4-mix IEM system without a Helical antenna would be like apple pie without the cheese.
