[Elecraft] HM-14 Microphone

[Ron D'Eau Claire]

It's not possible to have a "low percent modulation" on SSB. The percent
refers to the sideband (or audio component) level compared to the
carrier level. Since no carrier is transmitted in SSB, the concept of
"percent modulation" becomes meaningless.

What DOES happen if you don't have enough audio is that you don't get
full power output in SSB. That's easily checked. Load up (into a dummy
load) and transmit with the POWER control at 10 watts. Your bargraph
should just flicker to 10 watts from time to time on the peaks. The
human voice has a very large average to peak ratio so only a very
occasional peak will actually hit 10 watts. Most of the power will be in
the 2 to 6 watt range with the compression off (SSbC 1-1 on the menu).
You can turn the compressor on (SSbC 2-1 or 3-1 or even 4-1). That will
raise the average to peak ratio by compressing the peaks. That makes you
sound louder at the other end but you also sound less natural because
the signal is being distorted by the compressor. 

Another way to check to see if you are getting full RF output from your
mic is to put the bargraph is ALC mode. (Press and hold DISPLAY). Now it
will read right to left (backwards) to remind you that you are in ALC
mode. The bargraph now shows the ALC action that is controlling the
output of the K2 to hold it down to the requested power level. If at
least one bar flickers occasionally while transmitting in SSB, you have
all the mic gain you can use. The K2 is achieving full output.. 

It's good to check your mic gain on 10 meters because that's the band
where the most audio is needed to drive the K2 to full 10 watts output
in SSB. If you get 10 watts there, you'll have 10 watts anywhere <G>. 

10 k sounds big for a resistor to the electret element, but may not the
THAT big! I've used anything from 1 to 15k with various electret
elements. It only need to provide the correct voltage to the element.
Too big of a resistor may result in too low of a voltage and low output
and perhaps distortion. 

The size of the resistor can have a large effect on the amount of audio
the mic makes, not just because of the voltage but because it is a load
impedance in parallel with the mic element. The end of the resistor away
from the element (that connects to the +5 from the rig) is at audio
ground. So the resistance is across the audio signal coming from the
mic. 

The K2 has an input impedance of about 1K for audio (there is a 1 k
resistor right across the input to the speech compressor). So the size
of resistor you are using should not have an affect on the audio level. 

Ron AC7AC
K2 #1289

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The manual on the SSB Option does not list the HM-14 / HM-15 nor to
describe the bias resistor to use.  I used a 10K resistor.  Is this
right or wrong?  I noticed that the SSB manual indicated approx. 800 ohm
resistor for use with the HM-7.  

I am concerned that I am not putting out a properly modulated (low
percent modulation) single on SSB.  I check into a 28.440 Net every
Sunday here in Northern New Mexico and the folks tell me that I am not
'moving the needle' but am readable.  Any help would be appreciated.
Michael, KD5HVL