Message-ID: <4CCD3B87.9050301@iup.uni-heidelberg.de>
Date: Sun, 31 Oct 2010 10:48:55 +0100
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: Re: SBL-3+
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Hi Alan,

Thank you. Yes, i know your website from the early 2000s (as i was=20
young) where i have read all i have found in the web ;-)
Yes, a notch filter for 125 kHz is not so critical than a band pass=20
filter for 12.7 kHz regarding temp drifting. The special thing is that=20
my circuit has to handle several 10 K temp drift (maybe 50 K). The whole=
=20
RX is in the housing of the active antenna, so i have 3 cables coming=20
into this box (+12V, LO, IF). But even if i would decide to separate the=
=20
filter part and place it near the PC the difference would be marginal=20
since this floor of the building is not heated.....

In interesting field but i should hurry since the "active season" is=20
coming now and i do not want to provide a deaf grabber ;-) But there=20
have been some improvements since friday i think. Currently it is=20
runnning with a fast AGC but that's just for a few weeks maybe...


73, Stefan

Am 31.10.2010 01:32, schrieb Alan Melia:
> Hi Stefan No, you are right you do need low frequency paths on both side=
s of
> the mixer. I have a "lateral" approach to technical questions which star=
ts
> by saying "why do you want to do it that way"!
>
> I guess the SBL-3 unit you wanted will solve the problem. If you need mo=
re
> reduction in the 125kHz, look at my web site for a bridged-T passive not=
ch
> which was designed for 139kHz but would tune easily to 125. It might giv=
e
> you 25 to 30 dB rejection of the
> LO. Watch the load requirements though....I seem to rememebr you may nee=
d to
> terminate with a high impedance buffer......emitter follower....to get=
 best
> results from it.
> http://www.alan.melia.btinternet.co.uk/BR-t-Notch.htm
> It wont matter if this drifts a bit :-))
>
> I am a little surprised the filter drifts that badly with
> temperature.....wrong type of ferrite ?? You didnt have DC passing throu=
gh
> any of the windings I suppose....that might give trouble.
>
> Great experimentation.....well done
>
> Alan G3NYK
>
>
> ----- Original Message -----
> From: "Stefan Sch=E4fer"<schaefer@iup.uni-heidelberg.de>
> To:<rsgb_lf_group@blacksheep.org>
> Sent: Saturday, October 30, 2010 11:59 PM
> Subject: Re: LF: Re: SBL-3+
>
>
> Hi Alan,
>
> I want to try an alternative to the BF981 which runs in my current LF
> grabber RX. It downconverts 137 kHz to 12 kHz and feeds the soundcard
> with this 12 kHz signal. It is running not too bad but i have some
> problems with temperature drifting bandpass filters (since weeks) and
> have thrown them out of the Drain-to-Plus path. So, now the setup is
> running with a 2 stage RC LPF. I have had some problems with a to high
> 125 kHz level on the soundcard input and have applied a series LC
> circuit for 125 kHz now which reasonably solved the problem. But the LF
> noise is now just about 10 dB above the soundcard noise, in the
> afternoon. There is still a lack of sensitivity. This RX QTH should be
> very well for a grabber antenna but currently the setup is the problem.
> So i want to try something different, like a DBM. I am not an expert
> here and can/have to learn a lot, it seems ;-)
>
> 73, Stefan
>
> Am 31.10.2010 00:41, schrieb Alan Melia:
>   =20
>> Hi Stefan why a difficult to get mixer?? the IF port on most DBMs is DC
>> coupled so feed the siganl in there and (i presume) mix up ?? Or is the
>> RF/LO response still too high on the easily available ones?
>>
>> Alan G3NYK
>> ----- Original Message -----
>> From: "Stefan Sch=E4fer"<schaefer@iup.uni-heidelberg.de>
>> To:<rsgb_lf_group@blacksheep.org>
>> Sent: Saturday, October 30, 2010 9:29 PM
>> Subject: LF: SBL-3+
>>
>>
>>
>>     =20
>>> Dear LF,
>>>
>>> I want to try a LF converter using this mixer. Does anybody know a
>>> (cheep!) distributor in Germany or EU for 1...3 pieces of it? I've jus=
t
>>> found one where it costs about 40 Euro and this is to much!!
>>>
>>> 73, Stefan/DK7FC
>>>
>>>
>>>       =20
>>     =20
>   =20