[ARDF] Fun and Frustration

[Charles Scharlau]

Not to extend this subject too far, but I would like to clarify my suggested
SDR solution.

First let's consider an 80m receiver design. Take a simple SDR front end
that samples a 3.5 MHz signal down to an audio I/Q signal. Feed the I/Q
audio into the stereo microphone input of an iPhone (or an iPod/iTouch).
Inside the iPhone the audio gets sampled at 44kHz, and functions provided in
the iPhone SDK let the software grab the ADC output from the sound card,
massage it, and display it on a color graphics display, while sending it
over a Bluetooth interface to a wireless earphone or stereo headset.

To handle 2M signals a down converter from 144MHz to 3.5Mhz might be used. I
suspect that a down converter suitable for ARDF would be difficult to
design, mostly because of the need for a large dynamic range. But with the
iPhone controlling gain and attenuation (via USB) it seems that a reasonable
ARDF converter might be feasible at a reasonable cost.

The 3.5 MHz SDR front end isn't exactly a low-power device, but in my
experiments it hasn't shown itself to be a power hog either. It seems to run
for quite a few hours on a 9V battery; so I suspect it can sip juice from
the iPhone's USB port without being too big a nuisance.

iPhone 3GS users say their phone batteries last for at least a full day of
heavy use. When being used as an ARDF receiver (no phone calls) it seems
that its battery life would probably be adequate for an ARDF competition.

As far as using a cell phone in competition, it is far too early to be
concerned about that. This is just a concept discussion. I can't prove that
it will even work... but so far I haven't seen strong evidence that it
won't. But if an iPhone SDR is made to work, it should also work on one of
the new generation iTouch (iPod) devices, or on one of the many competing
products currently in the pipeline that are likely to be as suitable as
Apple products for this type of application. But, honestly, communication
devices have gotten so small and ubiquitous that the ARDF rule makers are
fighting a losing battle against them, and should probably be looking at
ways to eliminate any advantage to be had from shared information... but I
digress.

Receivers capable of combining and presenting information the way an
iPhone/iPod does could go a long way toward removing some of the ARDF
frustration. It is not hard to imagine the receiver, compass, and map all
being provided by one easy-to-carry device. The possibilities of letting the
receiver process all the information are potentially revolutionary. Imagine
an application that searches automatically for all foxes and homing beacons
on the air, and identifies each signal uniquely by its frequency and CW
identifier, records antenna orientation (accelerometer) heading (digital
compass) and signal strength (receiver) information automatically; processes
it, and displays the best fit for bearing and range to each transmitter in
almost real time... and tracks your progress toward the nearest fox
(accelerometer, compass). I won't even touch on what can be done if you
include GPS data. It sounds futuristic, but all the parts are there and
mostly integrated for us already. Like they say where I work: Now it's just
a matter of software :-)

73,
NZ0I