Markus, VLF,
Am 26.02.2011 14:27, schrieb Markus Vester:
DHO 23.4 kHz is received simultaneously by a small ferrite
antenna to lock the TX samplerate.
Maybe this should be pointed out a little more detailed.
While it was a quasi common thinking in the last months, that it is
impossible to receive a VLF MSK transmitter (like DHO38 or GQD) during
transmitting below 9 kHz (due to the very high field strengths
near the TX coil and wire), your and Gerhard's experiments show that it
is possible indeed, if a resonated ferrite antenna is used. I've built
the same and can receive DHO38 at 20 dB SNR in 3 Hz. The attenuation of
a 9 kHz signal against 23.4 kHz is about 40 dB. The dynamic range of
the soundcard allows another 80 dB before overload occurs. Additionally
there is a very narrow directivity of this antenna (-10 dB at +-30
deg).
The few VLF transmitting stations may use this method as an alternative
to a GPS locked VFO, if SpecLab is used to generate the TX frequency. I
will use this antenna as a redundant system to lock my VFO in the next
experiment. Maybe there are some advantages regarding EMC.
RX stations may use this method too since the strongest MSK transmitter
can be choosen, even if the RX loop antenna points into another
direction! (Stereo mode necessary)
A photo of my simple ferrite RX antenna for DHO38 is here:
http://dl.dropbox.com/u/19882028/DHO38%20ferrite%20RX%20antenna.JPG
34.3 nF is used to resonate to 23.4 kHz. The output winding has about
25 turns while the primary has about 200 turns.
73, Stefan/DK7FC
Markus (DF6NM)
Sent: Saturday, February 26, 2011 11:55 AM
Subject: Re: VLF: OE5ODL and OE3GHB active on 8970 Hz
Hi Stefan and group!
In the moment I'm running on GPS-Sync and will switch to DHO38-Lock in
a few minutes. I'm curious about the stability.
Antenna-current is as usual about 550-580mA.
Beside my plan to run a QRSS10 X-Band QSO with OK2BVG soon, no further
plans right now.
73
OE3GHB
Gerhard
Am Samstag, den 26.02.2011, 11:42 +0100 schrieb Stefan Schäfer:
LF,
The season is slowly passing, the average QRN is significantly
rising. But today the QRN is low and both Austrian VLF TX stations
are transmitting. OE3GHB is about 15 dB above noise in 424 uHz on
8969.98 Hz.
Some new projects on your side? There's not much activity these days...
73, Stefan/DK7FC
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