Re: U2 with V2.03 firmware working FB
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Make sure you get the correct heater for the job as these xtal specs are unknown and too much or too little heat will make it worse. Perhaps Hans can tell you the source and you can get the correct heater for it.
? Digitally signed mail - M0ELS
From: Andy Cutland
To: "QRPLabs@..."
Sent: Wednesday, 31 July 2013, 17:23
Subject: Re: [QRPLabs] U2 with V2.03 firmware working FB
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Hi John,
Yes the kit already sits in a nice polystyrene box but in the shack (garden shed) the temperature swing can be massive during a sunny day so even the polystyrene box isn't enough for stacking of the signal to be possible. Therefore an oven at around 40c will be required to keep things perfect in between gps frequency adjustments.
73's De Andy
From: John Randall
To: "QRPLabs@..."
Sent: Wednesday, July 31, 2013 5:15 PM
Subject: Re: [QRPLabs] U2 with V2.03 firmware working FB
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Its a lot cheaper to simply place a styrofoam sock over the crystal which will keep it nice and cosy.
73 John
? Digitally signed mail - M0ELS
From: Andy Cutland To: "qrplabs@..."
Sent: Wednesday, 31 July 2013, 17:11
Subject: [QRPLabs] U2 with V2.03 firmware working FB
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Just installed V2.03 and can report that this is the most stable version so far. I have soak tested it with the trimble gps unit on 28mhz and can confirm that on fskcw mode my U2 drifted only a couple of hz over a 24 hour period after 2 hour warm up. That will do me !
My next task is to oven the oscillator can for faster stability. My cunning plan is to use a spare 3.3v regulator as the heat source which will be switched on and off by a 2n3904 with a thermistor between base and emitter as part of the bias circuit. I did investigate purchasing an ovened oscillator but the GBP 250 price tag put me off somewhat.? I will let you know how i get on as
a homebrew oven for a few quid sounds much more appealing.
73's De Andy
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