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From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <KOEAKFKINDBIGKCFCJEDGEBJCAAA.victor13@online.nl> <7E7DFBB4D102A04DB5ADC88D66628A4A0FAB99CC@ICTS-S-MBX5.luna.kuleuven.be> <1SmrFA-199XcW0@fwd21.t-online.de> <4FF5EB68.9040507@iup.uni-heidelberg.de> <op.wgzqhb2nyzqh0k@pc-roelof> <4FF61402.6000703@iup.uni-heidelberg.de> <C1BC2599448542E39E69412F3FC0A53A@JimPC> <4FF6EE70.2040600@iup.uni-heidelberg.de> <804F85B8E2764C8C9D9007462F586A67@JimPC> <4FF8A5F5.5020200@iup.uni-heidelberg.de> <500AE796.9090408@iup.uni-heidelberg.de>
In-Reply-To: <500AE796.9090408@iup.uni-heidelberg.de>
Date: Sat, 21 Jul 2012 18:47:53 +0100
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Subject: Re: LF: RE: Analog oscillators
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All  you  can  do  with  thermal  drift is  heat  the assembly  to a 
temperature , where  you  can control  the core  temperature by ensuring 
the  thermal  gradient is steep  enough  not to be  affected  by the 
ambient changes and the  parasitic heat input  from the  energised 
components  ...   oven will  take many times the  oscillator  wattage

Or place in a bath of  insulating / heat conducting  fluid , so the 
opposite applies , enlarging  the  thermal  heat sink and  reducing the 
gradients , reducing  the  affect of  point  heat source , will  drift , but 
more  slowly ..

G..

--------------------------------------------------
From: "Stefan Schäfer" <Stefan.Schaefer@iup.uni-heidelberg.de>
Sent: Saturday, July 21, 2012 6:32 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: RE: Analog oscillators

> MF,
>
> Another episode about my analog oscillator for MF story.
>
> After the hints from the LF group i have now collected a Amidon T50-6 iron 
> dust toroid to wind the coil for a free running analog oscillator. The 
> oscillator runs on 1900 kHz and is intended to drive my 472...479 kHz PA. 
> This PA has an internal divide by 4 IC inside, so it can alternatively be 
> driven from a conventional HF TRX on the 160m band range.
>
> The idea to have a very small analog oscillator covering the 630m band 
> comes from the need for low power consumtion for /p MF test and volume 
> limitations in a backpack. My PA was designed to run on 12V DC directly 
> (https://dl.dropbox.com/u/19882028/MF/100W%20475kHz%20PA.png) and 
> especially to be very COMPACT. The efficiency is arround 85%, including 
> the driver power.
>
> For normal CW operation, a drift of say 20 Hz in 5 minutes can be 
> accepted.
>
> First i took a FT37-77 ferrite core to build the resonsnce coil. All the 
> capacitors are "Styroflex types". The drift of the oscillator was not 
> acceptable. See https://dl.dropbox.com/u/19882028/MF/Drift%20FT37-77.png
>
> The new coil which uses about 60 turns of 0.22 mm diameter enameled Cu 
> wire produces this drift (same scroll rate and displayed range in the 
> spectrogram): https://dl.dropbox.com/u/19882028/MF/Drift%20T50-6.png
>
> That looks much better :-)
>
> After running the VFO for 15 minutes, the drift is stabilized to 2 Hz in 
> 10 minutes! See 
> https://dl.dropbox.com/u/19882028/MF/Drift%20T50-6_Langzeitdrift.png
>
> That is very satisfying and so the VFO which uses a 33pF variable 
> capacitor to cover 472...479 kHz is well suitable for CW!
>
> Of course there will be a higher drift if the supply voltage is changing 
> or the ambient temperature. And i hope the RF will not affect the transmit 
> frequency significantly..
>
> This evening i want to test the VFO on the band. Maybe there will be some 
> QSO partners? :-)
>
> Thanks for the explanations about the temp drifting components. If you 
> have further useful suggestions, don't hesitate to tell them.
>
> 73, Stefan/DK7FC
>
>
>
>
>
> Am 07.07.2012 23:11, schrieb Stefan Schäfer:
>> Hello Jim,
>>
>> Am 07.07.2012 20:55, schrieb James Moritz:
>>> When you replace the existing inductor with a high-Q one, you will find 
>>> that the loop gain of the circuit is increased due to the higher Q, and 
>>> you will be able to use a lower gain/reduced transistor bias current.
>> Give me some days. Soon i will report about the progress. A T50-6 os at 
>> my parents QTH where i will be in some days.
>>
>>>
>>> For CW enthusiasts, I am suprised more use is not made of simple LC 
>>> VFOs. A drift of +/- 100Hz during the time taken for a QSO is usually 
>>> not noticeable,
>> Oh i would say 100 Hz is a bit hard but 20 Hz should be OK in my opinion.
>>
>>> and it is easy to achieve this in the LF/MF range. Also, the narrow 
>>> tuning range means an elaborate tuning mechanism with reduction gearing 
>>> is not needed - just a knob with a simple hand-marked scale is adequate.
>> EXACTLY!!!!
>>
>>
>>
>> 73, Stefan/DK7FC
>>
>>> It is much simpler than the schemes needed to obtain an LF/MF signal by 
>>> dividing/mixing down the output of an HF rig, etc. A VFO is also a much 
>>> better practical choice than a crystal oscillator, which leaves you 
>>> stuck on a fixed frequency.
>>>
>>> Cheers, Jim Moritz
>>> 73 de M0BMU
>