[karc] So-called sub-audible tones
- From: Phil Somers <pwsomers@xxxxxxxx>
- To: KARC FreeList <karc@xxxxxxxxxxxxx>
- Date: Sun, 11 Oct 2009 17:27:10 -0700 (PDT)
Ever wonder why they are called "sub-audible" tones? Your ear has been hearing
60 cycle (60 Hz) hum for years. Why wouldn't it be able to hear 151.4 Hz? Well,
of course it can. Apparently VHF receivers are designed with filters that block
from about 67 Hz to 254.1 Hz, some better than others. My IC-746PRO is
primarily an HF rig but also includes 6m and 2m. On 2m FM, it does not filter
out these low frequencies. They are easily discernible as a low hum, for
example when I am listening to the 94 repeater or the input on 34 where users
are also using 151.4. VE3DZE, VA3AKY and I just did some tests on 52 with and
without tones, and tones from the low end 67 Hz to the top end 254.1 Hz. Big
range of responses from various rigs. On some rigs, the 254.1 tone was very
loud and annoying.
So if you are hearing some "hum" on the repeater, but not on direct on 52,
etc., it may well be the so-called sub-audible 151.4 tone.
... Phil VE3HST
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