Hi all,
It is a problem that you have to attenuate 138.8 and the lower shift frequency, which is active
every tenth seconds or so. So I agree to the solution Hans-Joachim suggest using bandpassfilter.
A tuned two stage filter is fairly simple, but it is also an idea to use high Q
frame antennas,
my frame antennas attenuate 138.9 by 26dB when listening to 136.0kHz
73,
Jan-Martin, LA8AK
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J M Nøding, Datakvalitet, TTS, Kristiansand
Telefon 0047-380-52660, 9077-7126 (QTH: 0047-380-87178)
-----Opprinnelig melding-----
Fra: Hans-Joachim Brandt [mailto:[email protected]]
Sendt: 17. januar 2003 13:35
Til: [email protected]
Emne: Re: LF: Notch for DCF39
Hi all,
as I had to design a group-delay controlled band-pass filter once, needing two
pole circuits at both sides of the pass-band I have also been designing such a
filter for the amateur LF band using the ARRL Radio Designer, but have not
completed it, because I am living in the southeast of Germany (JN68GN) and do
not need it. But concerning the LF activity in eastern Germany I have also
thought that DCF39 at Burg, close to Magdeburg, would severely hinder such
activity.
When DL2HRE, Edgar, located at Bernburg, half way between Magdeburg and Halle, appeared on the LF band, I have asked him how he has managed to listen on LF. He is using an rx input filter consisting of seven resonant circuits employing pot cores, capacitively top-coupled, centered at 136.4 kHz. I also feel that this should not be the optimum solution; a filter with poles (one for DCF39 and perhaps another for SVX) would be better, but so far Edgar does not seem to look for a filter employing poles.
Anyway, his rx sensitivity on the LF band using his 250 meters long antenna seems to be very good. He has become the utmost station in the northeast of Germany which I can contact reliably on LF in normal CW. So far I have not found a comparable station in the northwest of Germany. DL2HRE has also told me of another east German LF station at Plauen (the callsign I have not noted, sri) but so far I have not heard it.
DL2HRE has no internet connection.
73 Ha-Jo, DJ1ZB
"Alan Melia" <[email protected]> schrieb:
Hi all, a belated Chrismas present to the Group. As a result of a discussion
with Hugh M0WYE, I calculated, and simulated a Bridged-T Notch Filter for
136kHz, which should reduce the level of DCF39 by about 30dB which only
giving about 2 or 3 dB loss at the top of the band. Hugh has made up the
filter and from workbench tests it seems promising. It occurs to me that
this may be of interest to those living closer to Burg that we do.
Details on http://www.alan.melia.btinternet.co.uk/BR-t-Notch.htm
We would be interested if anyone finds it useful.
Cheers de Alan G3NYK
[email protected]
http://www.alan.melia.btinternet.co.uk
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