[Elecraft] Using an ICOM HM-36 mike with the K2

[Dale Boresz]

Hello Dave,

To cut to the chase, after lots of experimenting, the ICOM HM-12 and 
HM-36 have become my microphone(s) of choice for use with the K2 - 
despite the fact that I really dislike using a hand mic. (Well, 
actually, I'm primaily a cw op, so I'm not all that thrilled about using 
any mic. ;) 

I have installed all of the KI6WX mod's (2.5KHz), and for what it's 
worth, here is a summary of my microphone experiments:

I have tried the Heil HC5, HC4, iCM, and 'Classic' microphones, as well 
as an assortment of Radio Shack communications headsets, and the ICOM 
hand microphones - both the HM-36 which came with my IC-746PRO, and the 
HM-12 which came with my IC-728.

The way I tested them was to run the K2 into a dummy load, while 
monitoring the signal on the 746PRO which is capable of exceptional 
fidelity on ssb. The output of the 746PRO was run to a Turtle Beach 
sound card, and digitally recorded via 'Cool Edit 2000'. Then I was able 
to easily switch between recordings and listen to the differences.

The results (to my ear) are as follows:
HC5, HC4: if I screamed loud enough, I could get decent output, but at a 
normal speaking level (which for me is admittedly below the norm) the 
audio was weak. It acts like there is a threshold above which the output 
quickly rises, but below which it quickly drops. I'm fairly certain I'm 
just hearing the action of the compressor and the noise-gate, 
respectively, both of which are part of the functionality contained in 
U3 (Analog Devices SSM2165-1). However, if I spoke loud enough, the 
articulation of both microphones was very good. However, in my opinion, 
the HC5 is much gentler on the ears, compared to the HC4, which can be 
quite ear-piercing (and is kinda designed to be so).

iCM and 'Classic': both contained *way* too much bass and sounded 
muffled. Additional research indicates that both of these microphones 
are intended to be equalized. When I use the 'Classic' on my 746PRO, I 
have to decrease the bass by -5db and boost the treble by +3db in order 
to get it to sound balanced. I suspect they're just not compatible with 
my voice characteristics; other may find them to be very acceptable. 
Both have plenty of output - just too much bottom end for my voice.

The Radio Shack headsets sound okay, but the articulation wasn't nearly 
as good as the HC5. Sound output level was acceptable, but seemed prone 
to over-driving.

Both the ICOM HM-12 and the HM-36 both sounded terrific. The 
articulation was as good as the HC5, and both have plenty of output. No 
need to raise my voice at all. Between the two I prefer the HM-12, but 
the difference is so small that I had to keep going back and forth 
between the recordings before I could decide which one to pick. If the 
HM-12 quit working for some reason, I'd be perfectly satisfied with 
using the HM-36. Overall balance was very nice, with no emphasis of low 
frequencies. I've had great success using the mic for chasing dx in 
pileups, and I've also received numerous unsolicited favorable comments 
from other op's concerning the clarity of the audio.

Regarding the connections for the microphone, see "Table 2. P1 Wiring 
for Selected Microphones" on page 18 of the KSB2 manual, which contains 
connection information specifically for the HM-12/22/23/36 microphones. 
I used a 10K resistor from microphone pin 1 to +5v, and no connection on 
microphone pin 2.

Good luck with your K2 and HM-36 combination. I think you'll be pleased 
with the results!

73,
Dale / wa8sra



DAVE HEALY wrote:

>...I'm left with the gut feeling it's a bad mike so I want to prove it and the only other mike I have is on my ICOM IC-746, a MH-36.
>
>So I have to re-wire the mike header for this mike, and here is the question......
>
>
>  
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