I am confused by some of the posts relating to microphones to be used with a
K3.
Jim (K9YC) wrote in his appendix on Ham audio about why communication
microphones have been designed with emphasis on higher frequencies above 2
KHz. This was to overcome most transmitters implementation of a sever roll
off above 2 KHz. This was standard practice.
I presume (but am unsure) that the K3 does not have a severe roll off above
2 KHz in the transmit-audio chain but is instead relatively flat within the
audio pass band. The roofing filter then limits the total bandwidth of the
transmitted energy but doesn't add shape until you get to the edges. If so
the K3 is a horse of a different color.
There has been a lot of discussion about microphone selection and I find it
all unclear with regards to past amateur practices (what worked great with
different rigs and microphones) and perhaps what we should be doing with a
K3. I understand that people are getting good audio reports with all kinds
of setups. I am too. I don't want to start a war of my audio sounds great so
that the way it is. I want to start with what is correct from an engineering
perspective then tweak from there.
So if the K3 does not roll off in frequency per the old standard then it
seems to me that the ideal microphone set up might be one of the following
two initial setups (then tweaked for personal desires or circumstances):
1. Studio (or other microphone with flat frequency response) and no Tx audio
equalization.
2. Communication microphone such as Heil that has high frequency
pre-emphasis coupled with Tx equalization that de-emphasizes high
frequencies to flatten the audio back out.
As Jim explained the old reason to have a microphone peaked above 2 KHz was
to counteract the microphone input circuit roll off. If the K3 does not have
that roll off then to get back to where you were with a prior rig you have
to cut the above 2 KHz response down.
For different situations, equalization might be contemplated for DX with a
greater low frequency roll off for example. Communications microphones seem
to already have low frequency roll off built in and perhaps the
configuration #1 above needs to think more carefully on the low frequency
side.
Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
K3-100 #508/ KX1 #1311
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