In addition to Nick's comments, these days "cheap" and "nonstandard" are no longer synonyms. Like optics and other highly-complex precision manufacturing processes, automation has brought the price of high-quality mic elements down to a few dollars. Almost all the various microphones sold for communications purposes use the same low-cost elements. The difference in price is mostly the packaging and, occasonally, the name on the package.
I picked up a Radio Shack electtret element that I mounted in a hand-held mobile microphone enclosure. The original enclosure held a dynamic element about 1 inch in diameter that fit snugly in a ring moulded in the case behind the grille. I wrapped the tiny electret module in soft sticky foam tape until the diameter matched the moulded ring, then pressed in place so the element is suspended by the encircling foam. The impedance the K2 audio input sees is defined by the 1,000 ohm biasing resistor required by the electret element. Complete hookup instructions come with the mic element. The output is adequate to drive the K2 to full output on all bands. You'll notice that on most K2's the demands on audio from the mic is greatest on 10 meters. That's because the transmit RF chain overall gain is lowest on 10 meters. You can easily determine whether you have adequate gain by switching the bargraph from RF to ALC mode. If one bar flickers slightly in ALC mode, you are making all the RF you can. More bars just mean that the system is backing down the gain more on bands where the overall gain is higher. You can tell if you're making full output by whether the 10 (or 100 watt if you have a K2/100) bar on the RF meter just flickers on peaks, but it's usually easier to see whether a bar is flickering in ALC display mode. Lest I be accused of belittling many of the excellent (and expensive) communications microphones out there, let me add a couple of observations. The electret element sold by RS (and most others) is a "hi-fi" element, providing an essentially flat frequency response from a few HZ to well over 10 kHz. That means that the audio bandwidth transmitted is determined entirely by the crystal filters in the K2. In the 'old days' of conventional A.M. few rigs used filtering. The audio response was quite broad and limited more by the microphone than anything else. For those rigs, microphones that rolled off the audio below about 200 Hz and above 5 kHz were highly-desirable for best communications quality audio. The microphone's characteristics were aided a bit by the selection of components in the audio circuits that helped establish the frequency response, but most of the shaping came from the mic. Many of the most popular microphones of that period had a shaped audio characteristic that rose from about 200 Hz to about a 6 dB peak at around 3,000 Hz before dropping off again. That produced a little "brilliance" or high-frequency emphasis to most voices that made them easier to copy under noisy conditions. I've tried such mics with the K2 (using a suitable transformer since, as Nick said, the impedance of these mics is usually quite high - 50,000 ohms is common). In my estimation, there's no real advantage to using such mics with the K2 because the filters in the K2 can be adjusted to product the desired characteristic with a flat response from the microphone. The high impedance makes the microphone more susceptible to RF intrusion and requires a matching device between the mic element and the rig: a transformer or audio pre-amplifier. But, for those who love their prized D-104 or other vintage mic, they do an excellent job if the impedance is properly matched to the K2. A good friend once sent me a beautiful Astatic D-104 as a gift. I happened to be doing some work on his 1950's vintage E.F. Johnson Viking Ranger AM/CW transmitter and, after playing with the mic on my K2, I couldn't help but send the mic back to him with the repaired "Ranger". Some things just belong together. Sort of electronic Feng Shui, I guess. Other things that justify the cost of many mics are the nice packaging with an attractive and convenient desk stand, boom arrangement our headphone boom mounting. Also, well-designned "noise cancelling" microphones earn their price when used in very noisy environments. Typically, they have special elements with a baffle arrangement that directs your voice to only one side of the mic element while allowing sound travelling from around you to strike both sides of the mic element simultaneously. Sound waves striking both sides of the diaphragm simultaneously will produce very little movement and little or no output from the mic. Some exotic designs use two mic elements and add their outputs together to cancel the noise while attenuating your voice only sliightly. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
