Hi Alan,
Thank you. Yes, i know your website from the early 2000s (as i was
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
filter for 12.7 kHz regarding temp drifting. The special thing is that
my circuit has to handle several 10 K temp drift (maybe 50 K). The whole
RX is in the housing of the active antenna, so i have 3 cables coming
into this box (+12V, LO, IF). But even if i would decide to separate the
filter part and place it near the PC the difference would be marginal
since this floor of the building is not heated.....
In interesting field but i should hurry since the "active season" is
coming now and i do not want to provide a deaf grabber ;-) But there
have been some improvements since friday i think. Currently it is
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 sides of
the mixer. I have a "lateral" approach to technical questions which starts
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 more
reduction in the 125kHz, look at my web site for a bridged-T passive notch
which was designed for 139kHz but would tune easily to 125. It might give
you 25 to 30 dB rejection of the
LO. Watch the load requirements though....I seem to rememebr you may need 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 through
any of the windings I suppose....that might give trouble.
Great experimentation.....well done
Alan G3NYK
----- Original Message -----
From: "Stefan Schäfer"<[email protected]>
To:<[email protected]>
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:
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 Schäfer"<[email protected]>
To:<[email protected]>
Sent: Saturday, October 30, 2010 9:29 PM
Subject: LF: SBL-3+
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 just
found one where it costs about 40 Euro and this is to much!!
73, Stefan/DK7FC
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