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From: "Alan Melia" <alan.melia@btinternet.com>
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>
Date: Fri, 6 Jul 2012 00:14:39 +0100
MIME-Version: 1.0
Subject: Re: LF: RE: Analog oscillators
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Hi Stefan I may be shot down here but I believe you must avoid toroids as 
the tuning element in a stable oscillator. It is difficilt to be sure of the 
mechanical stability of the winding and ferrites have a high tempco, iron 
dust are better but not as good as an air core. My old fashioned idea is 
that ceramic tube formers are the thing, I am not sure about styroform for 
RF, I would use NPO ceramic. You will probably need to trim the temp 
coefficints to get drift under control.

Lookinf at your requirements of 4times I doubt you would get enough swing 
mixing 2 oscillators to 2MHz. If you do you will have to start in the 
overtone range say 35MHz I think. I've not tried it so high.

Alan.
----- Original Message ----- 
From: "Stefan Schäfer" <Stefan.Schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, July 05, 2012 11:24 PM
Subject: Re: LF: RE: Analog oscillators


> Hello again,
>
> It is a bit disapointing. The oscillator is drifting several 100 Hz when 
> looking to the divide by 4 side, i.e. the PA output i.e. close to 475 kHz.
>
> Does someone have the circuit of the 137 kHz oscillator of DJ2EY? It must 
> have been published in the CQDL in 2003 i think. This oscillator was very 
> simple and reasonable stable.
>
> I used 9 turns on a FT37-43. No Amidon cores of the T50 or T37 series are 
> available in the moment. For the JFET is used the BF862 which may be not 
> the best choice since the drain currents are quite high due to the high 
> gain. I also used styroflex Cs but don't know if it is a good choice.
>
> Varactor diodes, yes, another idea. But the drift problems may be the 
> same. I can accept a drift of < 20 Hz after switching the VFO on (1 
> minute).
>
> So maybe i have to find a suitable pair of xtals and build a similar 
> design than Ha-Jo does.
>
> Ah BTW, what is the name of that popular DDS VFO IC. Not the SI570. It has 
> to work without any programming and USB interface and all that PC stuff. 
> However a DDS IC that operates on a frequency defined by external parts 
> (potentiometer) will have the same problems, or not?
>
> Any suggestions.
>
> 73, Stefan/DK7FC
>
> Am 05.07.2012 22:42, schrieb Roelof Bakker:
>> Hello Stefan,
>>
>> The NE602 works very well as oscillator and delivers a clean and low 
>> noise signal.
>> One of the main problem in building VFO's is the mechanical design.
>> It can be done, but it is not trivial when you use a tuning capacitor and 
>> gearbox.
>> Mechanical rigidity and freedom from micropfonics requires a solid 
>> enclosure which with the gearbox need to be mounted on the frontpanel, 
>> rather than on the chassis.
>>
>> As the frequency range is small, it will be mechanically much easier to 
>> use varactor tuning in conjunction with a ten turn potmeter. I have been 
>> there and done it all.
>> I have build a 40 m receiver with varactor tuning and it is rock stable.
>>
>> Building VFO's is fun!
>>
>> 73,
>> Roelof, pa0rdt
>>
>