[time-nuts] 4046 variations (was EPE GPS....)
robert8rpi at yahoo.co.uk
Sun Sep 27 12:03:30 UTC 2009
The old King Radio (then Bendix-King now part of Honeywell) Silver crown aircraft radios used 4046's in some of the synthesisers. The one in the VHF com had a different King part number to that in the ADF (MF direction finder). While trouble shooting we tried an ADF chip in a VHF (didn't have the VHF part in stock). It sort of worked but was slow to lock-up at the ends of the frequency range. Ordered some of the correct parts, both ADF and VHF. They all had the same manufacturer's part number and date code but different King numbers overstamped. Appaently the selected then at the factory for low noise (ADF) or wide pull-in (VHF).
--- On Sun, 27/9/09, Joe McElvenney <ximac at btinternet.com> wrote:
> From: Joe McElvenney <ximac at btinternet.com>
> Subject: [time-nuts] Egg on Face (was EPE - GPS Frequency Reference Project)
> To: "Time Nuts Digest" <time-nuts at febo.com>
> Date: Sunday, 27 September, 2009, 11:00 AM
> >There's a subtle difference between 3rd phase detectors
> in the 74HC4046A
> >(Philips/NXP, ON, TI) and the 74HC4046 (Fairchild, NS)
> >The 3rd Phase detector in the 74HC4046A works as the
> designer intended
> >in the GPSDO circuit, the 3rd phase detector in the
> 74HC4046 does not.
> >The 74HC4046 uses an RS flipflop for the 3rd phase
> detector and requires
> >narrow pulses on the R and S inputs.
> >The 74HC4046A uses extra internal gates to ensure that
> only narrow
> >pulses are seen by the RS flipflop in the 3rd phase
> You are perfectly correct. I hadn't noticed that there was
> a 74HC4046A
> fitted to the board in the article but just a plain
> 74HC4046 shown in
> the parts list. However, it is something to watch out for
> as this will
> be a popular project among those, like myself, who do not
> need to slice
> time quite so finely.
> Cheers - Joe G3LLV
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