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HF Explorer Help
-----------------------------------------------------------------------
Command Line Switches:
-c DDC center frequency, set band.
-c 7.2e6 or -c 7.2M for 40 meter ham band.
Default is 3.9e6 80 meter ham band.
Example:
hfx.py -c 9500k
starts up in the 31 meter band.
-a Audio output file. Output file for 32kHz two channel
signed word audio. Two channels are used for
independent sideband. This file can be converted
to a wav file with sox. Example:
sox -c 2 -r 3200 file.sw file.wav
sox needs the .sw extension to indicate file type.
If not specified no audio file is created.
-r Radio output file. File to write RF data to for later
demodulation. Records the entire band to disk, width
determined by sample rate/decimation. Be sure to
note the decimation and center freq for later use!
Example:
hfx.py -c 900e3 -d 80 -r rf_data_AM-c900e3-d80
writes a pre-demod rf file centered on 900kHz with a
bandwidth of 800kHz (That's 80 AM stations!). The
center and decimation could be put in the filename for
proper use later.
If not specified no rf data file is created.
At default 250 decimation disk usage is about
8Gb / hour.
-i Radio input file. Use to play back a previously
recorded rf data file. Example:
hfx.py -c 900e3 -d 80 -i rf_data_AM-c900e3-d80
plays back the previously recorded band, no
usrp hardware needed. Tune about the 800kHz wide band.
When playing a recorded file, time controls
fast-forward and rewind are available.
-d Decimation. Sets sample rate and bandwidth.
This is the factor that the usrp sample rate, 64e6,
is divided by. Default is 250 for 256kHz bandwidth
which is enough to record a ham band without
eating up disk space too fast. The 64e6 sample
rate limits the upper practical frequency to 32MHz.
The Basic RX transformer limits the lower frequency
to about 200kHz.
Powermate Knob:
A Powermate knob is recommended but not necessary. If a knob
is used, it is in one of 3 or 4 modes controlling frequency,
volume, filter and (if playing a recorded file) time.
Pushing the knob switches mode and the buttons on the HFX panel
change to show which mode is in effect. Then just turn the knob
to set frequency, volume, filter or go fast forward or rewind.
Bandswitch:
Across the top are a set of predefined bands and buttons
to rapidly switch to the center of that band. To change a band,
type the frequency in Hz into the box under "Center Frequency",
then press "Set" on the left, then the button you want to
program. From then on (untill the program is exited) pushing
that button takes you to that band. To make a band button
permenant edit the hfx.py script with whatever frequency you
want assigned to what button.
Frequency:
There are 6 ways to set the frequency.
1) Move the slider with the mouse
2) Use the Spin Control up/down arrows (very fine 1Hz control)
3) Type the frequency in Hz into the Spin Control
4) Turn the Powermate knob
5) Web control.
6) Clicking on the FFT display to set demod center. This is very
convenient for tuning +-15kHz when you see a signal on the
display. If in Lower Sideband, clicking just to the right of
a signal will tune to it immediately. Clicking several times
on the far right right or left of the display will rapidly
tune up or down the band.
Volume:
Move the volume slider with the mouse, or push the Powermate knob
untill the volume button is active, or click on the volume button,
then turn the knob. Volume can also be set by web control if web
control is setup and enabled.
Filter:
Similar to volume, switches in any of 30 audio filters from 600
to 3600Hz in Sideband or up to 5kHz in AM.
Mode:
Demodulation modes are chosen by clicking on the buttons for
Lower Sideband, Upper Sideband, or AM.
PGA:
PGA slider sets the rf gain in the Analog-to-Digital converter
before digitizing. 0 to 20db gain easily shows up on the FFT
display.
Time:
When playing back a recorded RF data file, you can enjoy the
freedom of rewinding or fast-forwarding. Replay a weak signal
or skip through annoying AM commercials.
Antennas and Preamps:
The USRP Basic RX board is not sensitive enough for anything but
the strongest signals. In my experience about 40 db of small
signal gain is required to make the HFX as sensitive as other
receivers. Some working amplifiers are the Ramsey PR-2 with 20db
gain, fairly low noise and more bandwidth than we can use here.
Also the amp modules from Advanced Receiver Research are nice.
I use an ARR 7-7.4MHz GaAsFET 29db amp with .5db noise at the
apex of a 40 meter dipole with excellent results. Another
amp I like is a Minicircuits ZHL-32A 29db amp but they are
expensive and hard to find. Also it may help to use some filters
to keep strong local signals from the ADC, or limit rf input
to the band of interest, etc.
Resonant outdoor antennas, like a dipole, in a low-noise (away
from consumer electronics) environment are nice. Long random wires
with a tuner work. I like a small indoor tuned loop made from 10ft
of 1/4" copper tube, a 365pf tuning cap and a pickup loop connected
to rg-58.
Web Control:
To control your radio remotely, ensure you have a web server
(Apache, etc) working and a compatible directory structure in
place. Directories /var/www/cgi-bin/commands and
/var/www/cgi-bin/state must already exist. You will need a
home page with forms and a set of scripts to put commands in
and put the current state on the home page. email me for further
help. Setting WEB_CONTROL to True in hfx.py turns on the timers
that check for commands and update the state.
IF Output:
There is a provision for outputting un-demodulated complex
through the audio out in stereo for use with Digital Radio
Mondial (DRM) or using a seperate demodulation program like
SDRadio (by I2PHD).
Set IF_OUTPUT to True in weaver_isb_am1_usrp4.py.
--Good luck and happy LW/MW/SW Exploring.
Chuck
chuckek@musicriver.homeunix.com
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