[Elecraft] Replacement Hand Microphone

[Ron D'Eau Claire]

Paul Gates wrote:

I guess all the mikes for our rigs today have to be low impedance but I am 
wondering how a D-104 would sound if we could get it to work! They have 
untold punch!

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I just finished refurbishing a D-104 for a buddy to use on his 1950's era
E.F. Johnson Viking Ranger AM/CW transmitter and played around with it a
bit.

The later D-104's included a built-in preamplifier for use with modern rigs.
The amp provides the necessary impedance matching since the D-104 uses a
very high impedance crystal element. The amp is also important because
modern rigs require a much higher audio level at the mic input than most of
the old vacuum-tube jobs did. 

The D-104 has a peak in its response at about 3 kHz. Compared to the output
at 1 kHz, the output is down about 10 db at 100 Hz and 6 kHz. The peak in
the response at 3 kHz is up about 12 db. That 12-db "hump" gave the mic its
characteristically bright sound that made the sibilances (s-sounds) in words
very pronounced. In general, that helps with intelligibility. 

Audio shaping like that was far more important in the days of A.M. rigs
because the audio amps in the rigs themselves seldom did much audio shaping.
A little low frequency roll-off was usually provided by using low-valued
coupling caps, but that was about all. 

Audio shaping for best voice intelligibility is still very important, but
with the K2 it can be done largely by adjusting the BFO frequency and
choosing the right filter bandwidth. 

The bandwidth of the K2's OPT1 filter used for SSB transmission is fixed,
but it can be changed using the mod kits available from Elecraft. The K2
comes "stock" with an OPT1 filter bandwidth near 2 kHz because that provides
optimum "punch" for most voices. That's especially important when running
QRP. Wider bandwidths help some voices sound more natural.

The most critical adjustment of the SSB filter is the position of that
bandwidth in the audio spectrum. That defines the low and high frequency
roll-off points. That's adjusted with the BFO using CAL FIL. That is why the
SSB module setup instructions recommend listening to your signal on another
receiver to choose the final settings for the BFO frequencies. 

That procedure is more complicated than just buying a good
communications-quality mic like the D-104, but it allows the audio response
to be much better tailored to an individual's voice than the old rigs did.
While the K2 doesn't provide a peak in the mid-range, setting the roll-off
points at the high and low ends of the audio range provides the same
benefits. 

Ron AC7AC