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RF issues
. Skywire Audio cables are said to contain the best of 20 years of continuous research embodied in the best Highwire designs but developed further still. Skywire brings particular attention to bear on the suppression of radio frequencies around their cables. This is accomplished by encircling the signal conductors with an efficient electromagnetic RF-absorptive material to reduce radio-frequency ringing and noise which, according Palmer, leads to a significant improvement in sound. The effects of radio-frequency energy in hifi cables does not show up in steady-state audio frequency testing such as a sine-wave sweep. However Don Palmer believes it can be audible during music reproduction by way of intermodulation distortion (IMD). Even small amounts of IMD can raise the overall noise and distortion to audible levels. Palmer draws our attention to the fact that distorted music will sound louder than undistorted music and that sometimes distortion can be mistaken for increased dynamics. There are a number of items one can listen for that will indicate RF noise and intermodulation distortion such as veiling, artificial airiness, blurring, softening and an overall homogenization of the sound. These artifacts may combine into a sense of increased space and detail but cannot actually increase the amount of information.

According to Palmer, the true disadvantages of unshielded radio frequencies are the lack of dead-quiet backgrounds and the loss of recorded ambiance. Instruments are not as well separated and distinct from each other nor portrayed in their own sound bubbles. This can lead to congestion particularly with complex music such as orchestral and choral works. An excess of radio-frequency interference can also create non-linear dynamics across various bands of the audible bandwidth. Therefore certain ranges can sound louder, sharper and more forward than others. Palmer’s conviction about the sonic benefits from lowered radio frequency is nicely illustrated by the common sonic improvements when all unnecessary domestic cables and power cords are unplugged (including TV power cords and telephone lines).

Palmer’s design theory is based on the fact that RF energy inside a cable will reflect from its ends. This sets up sustained ringing wherever the wavelength of the RF energy is at odd or even multiples of the cable length. By reducing sustained ringing in audio cables, noise is reduced and the reproduction of low-level audio signals improved. According to Skywire Audio, several conditions must be in place for sustained ringing to occur. First RF energy has to be present in the system and cables to initiate the ringing. Audible audio frequencies between 20Hz–20kHz won’t have enough high frequency content to initiate it themselves. However sources of analog RF signal, noise and high-speed digital pulses will introduce it. There are usually numerous such sources of RF and electromagnetic contamination in any domestic environment. DVD players, FM tuners, TV sets, wireless telephones, digital answering machines, computers, fax machines, microwave ovens, variable light dimmers and other household electronics leak RF both into the air and power grid. Within the audio system itself there are the high-frequency digital pulse generators in CD transports and players, S/PDIF digital cables and remote-control circuits. Power supplies and fluorescent displays also are sources of significant RF noise. Then there are ham radios, commercial AM and FM stations, cell phone towers, local police and taxi communications plus contamination from nearby residential and industrial equipment. RF noise can enter an audio system through the power lines, be generated within the system itself and be picked up by the signal cables and power cords which simply act as receiving antennae. Damn, this massive omnipresent RF presence could become a justification for elevated prices of high-end wires after all…

The second condition for sustained ringing is that the cable’s conductive resistance must be low enough to minimize resistive losses. With high resistive loss in the conductors the ringing energy dissipates as heat. Most hifi cables have relatively low resistance but some are intentionally made with highly resistive conductors. These can use very fine wire or high-resistance materials to reduce ringing but cause other sonic side effects.

The third condition for sustained ringing is an RF impedance mismatch between the cable and the send/receive connectors at either end. At radio frequencies the impedance is equal to the voltage divided by the current. The cable, connectors, source and  load each have an RF impedance. The impedance for a steady-state direct current is the same as the resistance. For alternating current and RF the impedance can have resistive, capacitive and inductive elements. An audio cable may have a fraction of an ohm DC resistance but a 75Ω impedance at RF.

The impedance determines the energy flow. Where RF encounters an impedance mismatch (change), some energy is reflected. A cable with mismatches at both ends is like two mirrors set up to reflect each other. Any disturbance bounces back and forth many times. In an audio cable the impedances of the wire and connectors are not designed to match the RF impedances of the equipment at the input and the output. The most common methods for optimizing cables for audio applications result in very real mismatches at RF wavelengths.

Skywire’s design. All of Skywire’s 2020 Series cables share common features. My loaner set of digital and analog interconnects and speaker cables had gold-plated terminations, the same 19 x 14-gauge strands of pure silver-plated soft  copper conductors, the same low-loss Teflon dielectric, dual-layer electrostatic shields for lowest noise and maximum RF attenuation. They also shared the same elegant white livery that confers a rather classy appearance to these cables.