[Elecraft] Hum on TX audio w/ CM500 headset on KX3

[Frank O'Donnell]

For my CM500 headset with the KX3, I referred to Walter Underwood 
K6WRU's blog posts to order the adapter allowing the CM500 mic plug and 
a PTT switch to share the radio's mic jack. I also followed his 
checklist from a second blog post to set TX EQ and mic bias.

While adjusting the mic gain with the TX power set to 0.0, I noticed hum 
on my audio from the CM500 mic. This was audible regardless of whether I 
had the PTT cable attached, or if I left it detached and tapped the XMIT 
button. The hum also appeared regardless of whether I used the CM500 
phones vs other headphones. If I unplug the adapter and use the handheld 
mic that came with the KX3, the hum does *not* appear.

Any suggestions on what I should look at to run this down?

Thanks and 73,

Frank K6FOD



On 5/5/20 9:15 PM, Don Wilhelm wrote:
> On the KX3, look in the manual for the MIC jack connections. It should 
> tell you why you need to be aware of the situation that the CM500 plug 
> can present.
>
> Walt Underwood K6WRU has presented a link to an adapter that will 
> allow you to plug the CM500 mic plug into a jack leaving the other 
> jack available for us as PTT. Use of that adapter does not require you 
> to set MIC BTN to off.
>
> Be careful, not just any adapter will do - some are simple splitters 
> that put both the tip and ring on both jacks.
>
> 73,
> Don W3FPR
>