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(copy of email for archival interest - MSE 3/2014)

Date: Mon, 07 Mar 2011 15:04:25 -0500
To: hftoa@yahoogroups.com
From: Joe Taylor <joe@Princeton.EDU>
Subject: HFTOA: first radiolocation results

Hi all,

I'm happy to report that last week four of us (AA6E, K1JT, K9AN, and
W3PM) successfully measured the location of a radio transmitter by
time-of-arrival measurements. Our "unknown" was the broadcast station
WCKY in Cincinnati, at 1530 kHz. Details of the measurements and
analysis procedure are posted at
http://www.physics.princeton.edu/pulsar/K1JT/HFTOA_2.pdf .

If you no longer wish to participate in this project, you may stop
reading here. (Send me a brief note and I'll remove your address from
the email list.)


Otherwise, ... read on.

We'd like to try another test soon, perhaps this week. This time it
would be good to use a test signal at HF. We'll want a signal
predictably copyable by many of us. One possibility is the SSB bulletin
broadcast nearly every evening at 0245 UTC by the ARRL headquarters
station, W1AW. Frequencies for the voice bulletin are 1.855, 3.990,
7.290, and 14.290 MHz. Ordinarily in this project we'll want everyone
tuned to the same frequency, but since W1AW will have identical
modulation on all four bands, we should get nearly equivalent results if
everyone uses the band on which they copy W1AW best at the appointed time.

[Note: if you have another good suggestion for a predictable HF test
signal, please share it with the group. A shortwave broadcast station?
(Any modulation type, including DRM, would be OK.) A cooperative ham
with a good signal who would put a signal on the air at a specified time
and do something like read from QST for a few minutes? A net with a
known schedule and lots of good signals, especially from the net control?]

The suggested data-taking software is called "hftoa.exe", which operates
in a manner similar to "wwv.exe". You can download it from

http://www.physics.princeton.edu/pulsar/K1JT/hftoa.exe .

Install it in the same directory where you already have WSPR and 'wwv'.
Typing the program name at the command prompt gives you a brief usage
message identifying 4 required arguments:

C> hftoa
Usage: hftoa <f_kHz> <mode> <nsec> <tstart>
Example: hftoa 3990 AM 300 0200

The parameters are as follows:

f_kHz - Rx frequency (kHz)
mode - Rx mode (AM, USB, or LSB)
nsec - Duration of recording (s)
tstart - UTC start time (HHMM)

Thus, for a five-minute recording of the W1AW bulletin on 3990 kHz the
command would be:

C> hftoa 3990 AM 300 0245

Please note that we want recordings in *AM mode*, even though the
transmission is SSB! That means you will be listening to the bulletin
in "Donald Duck" mode.

You radio should be configured as for the 'wwv' tests: mode=AM,
bandwidth around 6 kHz, RF gain reduced as needed. The 1 PPS pulses
from your GPS receiver should be clearly audible but not so strong that
they pump the AGC.

You can brief test observations by typing something like:

C> hftoa 3990 AM 10 -1

This will cause hftoa to make a 10-second recording; the "-1" start time
means "starting immediately". At the end of the 10 seconds the program
will report the average, rms, and maximum absolute values of the 16-bit
integer samples, something like this:

Ave: 0.3 Rms: 355.9 Max: 2721.0

Signal level is not critical, but good target values have "Rms" around
several hundred and "Max" maybe 10 times larger. (This is for the
combination of an over-the-air signal and your 1 PPS pulse.) Aim for
"Max" to be much larger than 10000.

At the end of an observation there will be a wave file with a name like

K1JT_110307_024500.wav

... that is, MyCall_YYMMDD_HHMMSS.wav

When we get to the point of making a scheduled test run, this is the
file that should be sent to me as an email attachment. We'll do the
cross-correlations to determine differential propagation delays for each
pair of receiving stations.

Finally: Martin, AA6E, has set up an a "HF Time of Arrival Project"
Yahoo group at http://groups.yahoo.com/group/hftoa/ for those who wish
to continue with the project. The email address is
hftoa@yahoogroups.com. Please join that group to discuss progress and
receive future communications relevant to HFTOA.

-- 73, Joe, K1JT