Re: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012

[Russ Edmunds <wb2bjh@xxxxxxxxx>]

You have already described it yourself. The terminology dates back to the 1960's-70's when offsets were measured using trace oscilloscopes to see the visual representation of the frequency difference between two stations close in frequency. An audible heterodyne was often not present with differences of a few kHz, thus 'subaudible'. Visually, you could 'see' the offset, and sometimes the beat between the two signals which might or more likely not be audible. So you saw the SAH on the scope. You used the same equipment to determine the actual offset value.

You could also manually count the beats - audibly or visually, as applicable - to determine the offset.

Russ Edmunds
15 mi NNW of Philadelphia  
Grid FN20id
<wb2bjh@xxxxxxxxx>
FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'; Grundig G8
AM:  Modified Sony ICF 2010's barefoot


--- On Fri, 9/7/12, Tim Tromp <kilokat7@xxxxxxxxx> wrote:

> From: Tim Tromp <kilokat7@xxxxxxxxx>
> Subject: [IRCA] 738 & SAH's from Michigan - Friday morning 9/7/2012
> To: "irca@xxxxxxxxxxxxxxxx" <irca@xxxxxxxxxxxxxxxx>
> Cc: "ABDX" <ABDX@xxxxxxxxxxxxxxx>
> Date: Friday, September 7, 2012, 6:51 AM
> 738 Tahiti is already in this morning
> @ 1030 UTC with some audio, but
> I'm plagued with t-storm noise right now.  I'm also
> seeing a carrier
> fading in and out on 737.8 - has anyone noticed this
> before?  It's been
> here the last few mornings and always disappears or fades
> out completely
> by 1100 UTC.  The fading would suggest that it isn't
> local, but I could
> find no reference to anything being so far off frequency
> here.
> 
> I see a lot of talk about SAH's (sub-audible hets I
> presume?).  Can
> someone provide good audio demonstrating this phenomena?
> 
> Thanks,
> Tim Tromp
> West Michigan
> 
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