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| To: | <[email protected]> |
|---|---|
| Subject: | Re: LF: RE: Analog oscillators |
| From: | "James Moritz" <[email protected]> |
| Date: | Sat, 7 Jul 2012 19:55:37 +0100 |
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| In-reply-to: | <[email protected]> |
| References: | <[email protected]> <7E7DFBB4D102A04DB5ADC88D66628A4A0FAB99CC@ICTS-S-MBX5.luna.kuleuven.be> <[email protected]> <[email protected]> <op.wgzqhb2nyzqh0k@pc-roelof> <[email protected]> <C1BC2599448542E39E69412F3FC0A53A@JimPC> <[email protected]> |
| Reply-to: | [email protected] |
| Sender: | [email protected] |
Dear Stefan, LF Group, One more question: Currently i use the BF862 since it was on hand. However i could use a normal BF245 instead. I thought it could have an advantage since the housing is bigger and so the temperature differences should be smaller. Also the BF862 has a relative high Id, so the power dissipation and hence the temperatures may be higher. Vdd=5V and the osc didn't start to oscillate when using a source resistor of 100 Ohm. When using 50 Ohm then it runs and the DC source voltage is 0.4V, i.e. 8 mA DC drain current. Could be a bit lower. 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. 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, 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. 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 Moritz73 de M0BMU |
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