[TenTec] D-104

[geraldj@ames.net (Dr. Gerald N. Johnson, P.E.)]

The D-104 has always been designed for AM with a strong rising frequency
response. That was intended to overcome receiver selectivity by
supplying audio preemphasis to the high frequency components, especially
in the days of a rounded receiver selectivity curve. There weren't any
D-104 with a flat response, the rising response was intentional.

And like I've said before that rising response means most of the output
power of the microphone is outside the transmit filter in a SSB rig so
any audio processing before the balanced modulator and filter is screwed
up and in some radios those high frequency components drive the audio
and modulator into distortion leading to distortion products that pass
through the filter.

The relative phase response of the microphone, audio stages, and the
transmit filter are important to punch as limited by the transmitter PA
stages and ALC. Some microphones and filters (and voices) lead to a
signal that has a poor peak to average ratio and some are much better. I
find the EV 664 works well with my Yeasu FT-726 though I have a battle
ship rated Turner hand mike (weighs a ton) does better. The microphones
supplied by Yaesu have a lousy peak to average ratio. The Shure R5 does
well on my S-line and Corsair II.

I've not found that the Shure R5 element (used in the 520 "Dispatcher"
microphone eons ago) is still available. Distributor catalogs don't show
it but also don't show it as obsolete. I have my local distributor
checking...

73, Jerry, K0CQ

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