Peter, DJ8WL wrote:
From recent examinations at a friends place close-by I can only recommend
the use of an attenuator (switchable in 5 db- steps) between such a tall
antenna and the RX-input to check overloading of the RX. Quite a few of us
have to do this - including me (I have about 1,5...2 volts RF across 50
Ohm
RX-input from LF-transmitters 25 and 45 km away!). Unfortuna-
tely their tx-frequencies are too close to our band to use sharp
cutoff-filters. A solution might be a narrow crystal filter at the front
(RF) end.
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"). 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, and it fulfills several of the requirements
Peter mentioned
in his mail.
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 DC meter allows to read the signal strength up to 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 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 either1.7 kHz and 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 ba using a combination of digita readout with a
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 now to cover the 4135.7 -4147.8 kHz frequency
necessary
to check 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 goodis (250
Hz/500 Hz plus
noise reduction, etc.) with this frequency.
With this combination of selective level meter and Transceiver I nearly got
rid of all
the DBF39 and related problems. I copied stations in aural CW that I could
not even
detect before with the Datong converter, e.g. G4KEV with 6 dB over the
noise.
For those of you who like to listen for stations below our band as well as
beacons:
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 Holland or Belgium. I had never considered them
being
receivers, so I never thought to buy one, however, I gave it a try. With
thi message I want
to encourage everyone to look for those selective level meters and make
use of them as
LF/VLF receivers. I only paid 60.- DM (approximately 20 pounds/35 US$) for
mine! The only
disadvantage of this unit: it's big (like everything we look at 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
Geri, DK8KW (W1KW)
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