Dear Peter, LF Group,
(still trying to catch up with my E-mails....)
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From PE1E:-
Any other antenna suggestion for my ( top floor ) condo at 100' a.s.l. ?
BTW : I am forbidden to span a longwire on top of the building :-(
My first step was to buy a ( professional, be it vintage, all solid
state ) LF receiver today.
And that's where my second question is about..
It is a Telefunken ELK 639 with LF as from 9.8 Khz until 570 Khz in 5
bands.
I wonder if any list member uses or has been using this Telefunken ELK
639 as well...
...I am eager to learn about the possible experiences on this one.
E.g. : is its stability sufficient for the very narrow QRSS QSO's ?
Should I ( try to ) lock the LO's to my frequency reference ?
If this does make sense, I could ( try to ) lock my Schomandl ( with
very low phase noise ) or HP 3336B to my e-11 HP frequency standard,
thus ensuring ( more than - sic - ) sufficient frequency stability )...
Any comment and/or suggestion on the use of the ELK 639 for 136 Khz is
most welcome.
Any other advices as well.
Thanks.
Peter, PE1E.
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I have an ELK639 RX and have used it on 136k - Selectivity is very good, and
you should have no problem with out-of-band QRM. It is also unusual in that
a wire or loop antenna can be connected to one of the various antenna inputs
directly, without requiring an external tuner or preamp to achieve good
sensitivity - the dedicated LF front end has been designed to do this.
Since it is a mechanically tuned, free-running oscillator, the stability is
not nearly as good as a synthesised receiver. But it is adequate for the
faster QRSS speeds like QRSS3, and similar "visual" modes. The RX has an
external oscillator input which you could use with an external synthesiser,
but to achieve a significant improvement in stability you would also have to
do something about the 525kHz BFO, which is also a free-running oscillator.
Or you could attach a synthesised receiver which tunes 525kHz to the IF
output. Strangely, the ELK639 does not have a product detector, it just
feeds the BFO signal into the AM detector - with AGC on, the IF signal into
the detector is too high for good demodulation. But provided you operate it
with the AGC off, audio gain turned up high, and just sufficient RF gain to
get good SNR, it works OK. This would definitely be something worth
modifying.
As far as antennas go, the problem with a receive antenna close to a
building is that the local QRM level is often very high due to noise picked
up from mains wiring. If this is the case, I would try active whip and/or
loop antennas in different positions around your apartment to try and find
the least noisy location - probably on the roof or balcony if you can get
access...
Good luck on 136k,
Cheers, Jim Moritz
73 de M0BMU
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