Message-ID: <4EF49A75.7040405@iup.uni-heidelberg.de>
Date: Fri, 23 Dec 2011 16:12:53 +0100
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <4EF3689B.1030902@iup.uni-heidelberg.de> <805AC05E834C4F7DA019C36A04013479@JimPC>
In-Reply-To: <805AC05E834C4F7DA019C36A04013479@JimPC>
Subject: Re: LF: Re: Automatic Variometer adjustment at DK7FC
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
X-AOL-SCOLL-URL_COUNT: 0  
x-aol-sid: 3039ac1db4054ef49b2d3d4a
X-AOL-IP: 195.171.43.25
X-AOL-SPF: domain : blacksheep.org SPF : none


Hello Jim,

Thank you.
I ran the circuit unattended over night with a somewhat cautious feeling 
but the system is still fine ;-) Now beeing here on the Grabber PC again 
and watch how it works in operation. Nearly perfect.

There are some transient overshootings when rapidly reaching the 
resonance point. Two short impulses occurr when crossing the resonance 
point (to far beyond the optimal point, then a bit back and a smaller 
bit back again) This happens since i had to reduce the 33 Ohm resistor 
because the engine stucked yesterday in the evening. The engines 
stucking may have to do with different meachanical forces at different 
coil angles and just the cold outside. So now i could simply decrease 
the gain a bit, ie. increase the dead band. But what i want to do is to 
make the resistor smaller and reduce the output voltage a bit, making 
the behaviour of the source come closer to an ideal voltage source 
instead of a current source. I will simply add a 7808 or 7806 and a 
1000uF cap in front of the 7667. Then i have to add a voltage divider in 
front of the 7667 to keep the input voltage below the supply voltage. 
Also this will make the inpit LOW level a bit closer to 0V.

I found some further minor things that could be changed or optimised in 
the circuit.
-Of course i do not need 2x a 680 Ohm resistor for the LEDs, one is enough.
-Also ordinary 1N4148 diodes instead of the BAT42 will work as well. 
Matching is uncritical.
-A RC circuit with a time constant of about 1 ms (10n, 100k) between 
output of the amp stage and the comparators may help to reduce unwanted 
short active impulses during pressing or releasing the PTT (sometimes 
seen here).

BTW i observed no EMC problems here with the circuit. The functionality 
is the same at 1% or 100% TX power.

73, Stefan/DK7FC



Am 23.12.2011 12:17, schrieb James Moritz:
> Dear Stefan,
>
> That is a nice simple circuit - I may well try something very similar 
> at my QTH over the Christmas holiday, if time allows...
>
> I suppose one advantage of a passive, "signal powered" phase detector 
> for this scheme is that the phase detector output automatically 
> becomes zero when the transmit signal is not present, which will 
> prevent unwanted tuner operation on receive. As well as the BAT42 
> diodes providing a dead zone in servo operation close to the resonance 
> point, I guess the inertia of the motor and gearbox will produce some 
> hysteresis, moving the variometer to a very slightly over-adjusted 
> position after the motor drive is removed, which will also help to 
> prevent the system continuously searching around the correct tuning 
> point. I expect one can optimise the resistor in series with the 
> motor, as well as the amplifier gain, to get the best operation  of 
> this feature.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>