Message-ID: <009401cd676b$cec15230$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
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>
Date: Sat, 21 Jul 2012 18:08:18 -0000
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Subject: Re: LF: RE: Analog oscillators
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Stefan
Great news and detail about your oscillator. Let us know when you take your
last Breath !!

----- Original Message -----
From: "Stefan Schäfer" <Stefan.Schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Saturday, July 21, 2012 5:32 PM
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