THE WOBBLER
A Mystery Radio Signal
Procedures
This page last updated January 21, 2006
Radio Tuning Technique
After considerable experimentation as I tried to improve reception of
the Wobbler signal, I determined a particular tuning procedure which
seemed to always work well and considerably enhanced the ability to
detect the signal.
I will present the procedure as first a general description and then
the details of my specific approach.
- General Tuning
Technique - Most
important is the use of the Upper Sideband capability of the
receiver. By detuning downward by 700 Hz and with USB selected,
the Wobbler signal literally jumps out of the noise and broadcast
content that might accompany it. To listen for a Wobbler on 910
KHz , you would tune to 909.3 KHz in USB mode. You can also tune
up channel to say 911 KHz and use LSB, but I have not found that to
work as consistently as the procedure above. It also helps to
isolate the Wobbler if you can set a narrow bandwidth.
- JRC NRD-535D
and Similar SWL Receiver Tuning - What follows is specific to
my NRD-535D, but can easily be adapted to most general coverage
receivers.
- Tune down 700 Hz from the desired BCB channel
[i.e. for 910
KHz, tune to 909.3 KHz]. This doesn't have to be exact, but does
need to be detuned enough to produce a good signal.
- Set USB mode. As I noted above, LSB
mode requires detuning up band and for me has not worked as
consistently.
- Turn PBS (Passband Selector) fully CCW.
This seems to help eliminate other audio.
- Turn BWC (BandWidth Control) to mid
range. If using a Narrow bandwidth filter, this control may have
no effect.
- Set bandwidth to Intermediate (or Narrow).
- Turn RF Gain down until AGC (S-Meter) settles
just above the
average signal level. This isn't necessary but I think it
minimizes the passage of superfluous signals through the DSP processor
(next item). I also think it improves listening in general,
removing some of the chugging of weak signals.
- Not
part of the 535D, but immensely effective for this purpose
is an external DSP audio processor. I use the GAP and set it to
the maximum processing mode (#7). This silences all the
heterodynes introduced by the tuning technique, as well as background
broadcast signals, but lets the Wobbler blast through in all its glory.
I have found this technique will bring the Wobbler signal up out of
even moderate on channel audio. When the Wobbler really gets
going, it can be heard over the other audio, even without processing,
but that is a far less common occurrence.
Reception &
Processing
The configuration of radio equipment I am using is:
- JRC NRD-535D General Coverage Receiver
- LF Engineering H-800 & M-601 Active
Vertical Antennas
- Radio Plus+ Quantum Phaser
- ANC-4 Noise Canceler
- MFJ 784B DSP Audio Processor
- Archos Gmini 220 MP3 Digital Audio Recorder
For direction finding activities the equipment is:
- Palstar R30 Receiver
- Quantum QX Loop Antenna
For computer controlled monitoring:
- Ten-Tec RX-320D Receiver
- GAP DSP Audio Processor
Computer signal processing was done with:
- Audacity Audio Editor
- MP3DirectCut MP3 Editor
- Spectrogram & Spectran Signal Analysis Programs
© W. Curt Deegan, 2005-2006