[ARDF] Piccon mods

[Kenneth E. Harker]

I've now run three tests on modified piccons, each running for several hours.

* Test 1: 3.579545 MHz crystal with 22 pF caps to ground: 
  slow by 2.3 seconds/hour.

* Test 2: 3.579545 MHz crystal with no caps: 
  slow by 2.3 seconds/hour.

* Test 3: 3.579545 MHz crystal with no caps, 1MHz resistor across crystal: 
  slow by 3.2 seconds/hour.

Any ideas?  Test 3, BTW, is what the schematics for PicCon 1.0 show,
but of course PicCon 1.0 used a different DTMF decoder chip and a different
revision of the PIC firmware.  Adding the resistor actually made things worse.

I couldn't tell any difference (just looking at the WWV-synced clock) between
tests 1 and 2.


I guess I should modify another one of my PicCons just to compare.


On Mon, Nov 14, 2005 at 05:55:45PM -0500, David Ward wrote:
> I had a very similar experience with the same results. Using the ceramic 
> resonator the controller ran slow by about 20 seconds per hour (~ 5500 
> PPM). I then replaced the resonator with a 3.579 MHz crystal with 15 pf 
> capacitors. It now runs slow by about 2 seconds per hour (~500 ppm). I 
> haven't got around to replacing the caps with smaller values yet but from 
> what I read I'm not sure any value will be enough to overcome the 500 ppm.
> 
> One thing I wondered about was whether the crystal should be a series or 
> parallel mode. Anyone have any opinions?
> 
> Dave
> VE3BIP
> 
> 
> ----- Original Message ----- 
> From: "Kenneth E. Harker" <kenharker at kenharker.com>
> To: <ardf at kkn.net>
> Sent: Monday, November 14, 2005 1:35 PM
> Subject: [ARDF] Piccon mods
> 
> 
> >    I've modified one of my piccons by desoldering the ceramic resonator
> >and replacing it with a 3.579545 MHz crystal and two small 22pF caps.
> >See my photos:
> >
> >http://www.wm5r.org/piccon/
> >
> >    Unfortunately, the controller is still running slow - at the
> >rate of about 2.3 seconds per hour.  This is an order of magntiude
> >improvement compared to the worst I experienced with the ceramic
> >resonator, but it's still not good enough.  The IARU rules specify
> >that the maximum deviation of the transmitting periods is only five
> >seconds for the entire competition (which could be eight or nine
> >hours.)
> >
> >    Any ideas?  Should I try changing the caps to a different value?
> >Would I increase the value? (27 pF? higher?)   Decrease the value? (18pF?
> >lower?)  Do I need to add resistance anywhere?
> >
> >
> >    I am mildly annoyed that I have to do any of this just to get a
> >timing controller that can keep proper time.
> >
> >-- 
> >Kenneth E. Harker WM5R
> >kenharker at kenharker.com
> >http://www.kenharker.com/
> >
> >_______________________________________________
> >ARDF mailing list
> >ARDF at kkn.net
> >http://www.kkn.net/mailman/listinfo/ardf
> >
> 
> 
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-- 
Kenneth E. Harker WM5R
kenharker at kenharker.com
http://www.kenharker.com/