Tom McDermott wrote:
>
>I use the Heil Pro+ headset with the HC-4 element, Writelog, and SSB
>messages with an FT1000MP. It works quite well, but it took some effort
>to get there.
>
>In general, computer soundcard levels are about 20-30 dB higher than
>microphone levels in most of the common amateur rigs. To boost the
>microphone levels to the point where it is digitized well (minimal
>noise) by the soundcard, I use a 20 dB audio amplifier powered by a 9V
>battery. It's a simple design and includes RC filters on the input and
>output to keep the RF out (1.5KW amplifier less than 12 inches away = no
>RFI). Battery power also helps to prevent RFI or grounding problems.
>This amp is in-line from the Heil headset to the soundcard mic input.
>Some soundcards have a programmable 20 dB gain boost on the mic input,
>but my WinXP software sometimes randomly turns it off. Even when this
>boost is on, it seems to introduce some noise. This setup works better
>with it off and instead using the external audio amplifier.
>
>Going from the soundcard to the phone-patch input, the problem is the
>opposite, lowering the soundcard level by 20 dB going to the radio. I
>use a small 1:1 transformer and a 20 dB attenuator (2 resistors). The
>transformer breaks up a ground loop that is heard as a once-per-second
>beep - it's caused by the RS-232 computer interface ground current when
>Writelog polls the rig for frequency and status. The RS-232 ground
>return currents share the audio ground path back to the computer unless
>you break up the audio path with the transformer. The 20 dB pad is
>ABSOLUTELY required; without it there is a lot of hum and other noise
>from the computer, with it, it is virtually impossible to distinguish
>"recorded audio" from "live audio" from "Heil directly to mic jack"
>audio.
Thanks for the info, Tom. There's a Heil-to-Icom preamp on my website
which is based on a dynamic-to-sound-card preamp that appeared in QST,
so it should do the job perfectly:
www.ifwtech.co.uk/g3sek/in-prac/best-of.htm#icom
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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