K2 mic gain super low on 20 meters

[Mark Newbold]

Hi all,

I acquired a secondhand K2/100 with KAT100 ATU a while back. The amp and ATU are in a separate
enclosure. I have used it mostly for CW, but lately I have been using it for digital with a MicroHam
DXP interface. When operating digital I keep an eye on the transmitter ALC level, where I expect to
see 1 bar. I noticed recently that on 20 meters I can't get even 1 bar on the ALC meter, even
turning the DXP's TX audio level up a lot. The RF output meter shows very low output power. No
similar problem on 80, 40, 30 meters.

I plugged in a Heil Proset mic and observed the same behavior -- when I speak into the mic there is
plenty of TX audio on 80 and 40 meters (too much in fact, even speaking very softly). On 20 meters I
have to yell into the mic to get 1 bar of ALC.

This is with the output power set to 50 watts, Mic gain set to "2" (choices are "1", "2" and "3"),
compression set to "1", ATU disabled (set to CAL).

Any ideas of why the mic gain would be super low on just one band?

--Mark K7NEW

--
Mark Newbold
Port Angeles, Washington, USA
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[Bill Coleman-2]

The transmitter gain of the K2 is definitely not uniform, but different on every band. This is problematic when trying to run digital modes, where the audio input needs to be adjusted on every band.

I wonder if you have lower gain on 20m because you have a transmitter alignment problem — perhaps one of the 20m tuned circuits needs to be adjusted.

Gain seems to fall off on higher bands — I wonder how well you fare on 15 or 10m.

You also don’t say which mic you have on your Heil Proset. It it one with the older crystal HC-4 or HC-5 elements? These have pretty low output.

I have two headsets (one BM-10 and one Proset) originally with the HC-4 elements. I had to modify my K2 to get acceptable output. (I changed KSB2 R14 from 1k to 3.9k)

The element in the BM-10 died, and I replaced it with an electret mic element. I’ve also switched to another headset with an electret mic that has a lot of output (Yamaha CM500) and had to reverse the modification.

> On Dec 18, 2020, at 6:14 PM, Mark Newbold <[hidden email]> wrote:
>
> Hi all,
>
> I acquired a secondhand K2/100 with KAT100 ATU a while back. The amp and ATU are in a separate enclosure. I have used it mostly for CW, but lately I have been using it for digital with a MicroHam DXP interface. When operating digital I keep an eye on the transmitter ALC level, where I expect to see 1 bar. I noticed recently that on 20 meters I can't get even 1 bar on the ALC meter, even turning the DXP's TX audio level up a lot. The RF output meter shows very low output power. No similar problem on 80, 40, 30 meters.
>
> I plugged in a Heil Proset mic and observed the same behavior -- when I speak into the mic there is plenty of TX audio on 80 and 40 meters (too much in fact, even speaking very softly). On 20 meters I have to yell into the mic to get 1 bar of ALC.
>
> This is with the output power set to 50 watts, Mic gain set to "2" (choices are "1", "2" and "3"), compression set to "1", ATU disabled (set to CAL).
>
> Any ideas of why the mic gain would be super low on just one band?
>
> --Mark K7NEW
>
> --
> Mark Newbold
> Port Angeles, Washington, USA
> ______________________________________________________________
> Elecraft mailing list
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>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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