Date: Thu, 4 Jan 2001 23:11:41 -0500 From: "Tony Fegan VE3QF" Subject: [Elecraft] Choice of Microphone for K2 (long) A well chosen microphone can make a big difference in your success and enjoyment with the K2 on SSB. Here are some notes that I made some time ago: Choosing a microphone for QRP SSB use is not a simple task, as we are not all blessed, (or cursed) with the same voice characteristics. With QRP SSB we are trying to achieve the most intelligible signal for the power available. Listen on the bands and you will find that some signals stand out, even if they are not the strongest. These are usually transmissions that accentuate the higher voice frequencies and attenuate the lower frequencies. Most of the intelligence of the human voice is carried in a band of frequencies around 2 KHz. The lower frequencies add some personal voice characteristics but the amplitude of these is not as important for communication. If the microphone has a near linear response to the voice, then much of the available power will be wasted transmitting these low frequencies instead of concentrating on the higher frequencies. The microphones shipped with many rigs, even some expensive ones, usually have far too much low frequency response and so are more suitable for local contacts where voice fidelity rather than communication quality might be preferred. Some years ago I purchased the Heil HC4 and HC5 microphone inserts to use with my Kenwood TS950S. I was amazed at the improvement in transmitted audio clarity (especially with the HC4). The Heil microphones have a peak in the audio response around 2 KHz and a low cut-off of 500 Hz (HC4) or 350 Hz (HC5). The HC4 insert is well suited when using speech processing, especially when audio processing is used rather than RF processing. This is because harmonics are produced in any non-linear amplifier and some of these lower frequency harmonics fall within the audio passband. With the low frequencies of the voice, attenuated before processing, the resulting processed signal is much cleaner (less mush) and far more useful compression can be applied before distortion becomes a problem. With the K2 I now use the Heil headset with an HC4 insert (needs a pre-amp). Sometimes I use an old Shure microphone, (model # 444, no suffix), which works well if a series capacitor of between .005 uF and .01 uF is used to attenuate the lower frequencies. I am sure other microphones can be 'doctored' in a similar way. The value of series capacitor will depend on your voice. Use a smaller value capacitor if you have a deep voice. As a bonus, with low frequency attenuation, the higher pitched audio makes your transmission easier for your contact to accurately tune in. This in turn helps you with the intelligibility of his transmission as he is now transmitting on your frequency and so there is no need to use your RIT. The correct 'tuning in' of an SSB signal is another story. 72 / 73 and enjoy Tony Fegan VE3QF K2 # 490 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Fri, 05 Jan 2001 09:41:00 -0600 From: ny9h Subject: Re: [Elecraft] Choice of Microphone for K2 (long) VERY WELL PUT !! Tony's info sounds exactly like the instructions that came with my 1976 G3lll rf clipper, which went into the if strip of the yaesu ft101; the need was to get the power out of the lower audio frequencies, before you completely overloaded ( permanently) the sweep outputs and the power transformer. Since electrets are so inexpensive; a little eq :roll off the bottom below 400, boost at 3k...and listen on another receiver. ( the g3lll rf clipper really worked well & it specified the shure 444 and the low cut cap Tony described... experiment ,,, or if you gotta buy another finished product, look up w2ihy gate/3eq. Another tactic, if you can take your dynamic mike apart, checkout covering over, partially or completely any ports on the back of the mike element. Listen to your audio as it will changes the response curve, Listen to your 4$ mike become a ==== $150 dx special.