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DK8KW > VLF 29.03.99 06:42l 82 Lines 4243 Bytes #-9683 (0) @ EU
BID : F9CA55DK0MAV
Read: DL9EM GUEST DO1KHS
Subj: MV61 Level-Meter as LF-Receiver
Path: DB0ZKA<DB0ABH<DB0SRS<DB0MW<DB0ERF<DB0ABZ<DK0MAV
Sent: 990329/0437z @:DK0MAV.#NDS.DEU.EU [Peine] DP5.07 $:F9CA55DK0MAV
From: DK8KW @ DK0MAV.#NDS.DEU.EU (Holger/'geri')
To: VLF @ EU
Hello Lowfers,
many of us use(d) a normal short-wave transceiver to listen on the new
long-waveband (135.700 to 137.800 kHz). Most of those receivers are
not made for long-wave and suffer from bad sensitivity (according to
my own experience, the IC-751 is one of the exceptions). When using
a pre-amplifier, a problem arises from selectivity. A big part left and
right of the band is filled with very strong signals (for example
138.830 kHz: DBF39 with a signal strength up to 50 over S9 here in
Northern DL). Converters using the SO42P (such as the Datong) do a good
job regarding sensitivity, however, they have the same problems with
intermodulation.
A week ago or so I bought an old, East German made selective level meter,
ranging from 200 Hz to 2.1 MHz ("MV 61 Universal-Pegelmesser" made by
"Praecitronic"). Although nothing indicates, that this is a receiver,
I gave it a try. Indeed, it is an excellent receiving piece of equipment
if used properly.
The unit has got the capability to measure (on the receiving frequency
or throughout the entire band) the level in dBm, ranging from -130 dBm
(this is in the 0.5 uV range) up to +20 dBm (this is in the Volt-range
at 50 Ohm). To achieve this, an attanuator can be switched, both, in steps
of 10 dB as well as 1 dB (cascaded).
An additional analog readout allows to read the signal strength up to
+/- 0.1 dBm. Additionally, the unit has a voltage output of +/- 2.5 Volt,
referring to the signal strength, so here I see a good possibility to do
long-term QSB observations, e.g. on the unidentifid 137 kHz RTTY signal.
Two excellent filters (I do not yet have the full documentation, so I don't
know, what kind of filters it is) can be switched to either 1.7 kHz or
0.1 kHz bandwidth. The 0.1 kHz filter has got 100 Hz/3 dB and 450
Hz/60 dB shape factor.
The frequency can be either adjusted by a internal VFO (good long-term
stability, ability to adjust frequency with an accuracy of +/- 10 Hz)
and uses a funny way of measuring the VFO frequency by using a combination
of digital readout with an analog DC-meter. However, the Unit also accepts
an external oscillator between 4000 kHz and 6100 kHz to cover the entire
range of 200 Hz to 2.1 MHz. I use the same DDS VFO that I use for
transmitting to cover the 4135.7 - 4137.8 kHz frequency necessary
to align the frequency with an accuracty of +/- 1Hz.
The unit has no decoding capability for SSB or CW, only for AM. However,
it has an IF output at 200 kHz, so I feed my IC-746 with all filters
and DSP goodies (250 Hz/500 Hz cascaded CW filter plus DSP 80 Hz filter,
noise reduction, etc.) with this frequency. Originally, the sensitivity
of the IC-746 is not good in this frequency range but using the
selective level meter as a converter I nearly got rid of all the DBF39
and related problems, at a high level of sensitivity. I copied stations
in aural CW that I could not even detect before with the Datong converter,
e.g. G3KEV with 8 to 12 dB over the noise.
For those of you who like to listen for stations above and below our band:
I can copy signals down to 16.000 kHz, that I can identify (FSK), below
there is a lot of noise/unidentified transmissions, e.g. 50 Hz humming
plus harmonics in the 200 Hz to 1 kHz range! Beacons between 200
and 400 kHz can be received very clear.
I have seen the MV 61 on several rallies and flee-markets here in Germany,
I am sure they also swapped over to other European countries. I had never
considered them being receivers, so I never thought to buy one for longwave,
however, I gave it a try.
With this message I want to encourage everyone interested in longwave
activity to look for those selective level meters (there are other
s, made by HP or Wandel & Goltermann, etc., but I did not try them)
and make use of them as LF/VLF receivers. I only paid 60.- DM (approximately
30 Euro/20 pounds/35 US$) for mine! The only disadvantage of this
unit: it's big (like everything we look at LF should be!), it's 19" wide
(but looks great in the shack, makes much more impression than a simple
Datong converter!).
Best 73, have fum, cu on LF!
Geri, DK8KW (W1KW)
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