[ARDF] Smart Phones for Smart ARDF?

[Charles Scharlau]

About 15 months ago I brought up the subject of implementing an ARDF
receiver using a handheld computing product, such as the iPhone or other
members of Apple's family of iOS devices. My posting raised more questions
than answers, but today, I think some of the most vexing questions have been
answered.

In early June of 2010 I launched a free "Software Defined Radio" iOS App,
named iSDR, on the App Store. Now, after 5 updates, and more than 5000
downloads, the question of whether the iPhone, iPod touch, and iPad are
capable of performing SDR duties has been answered with an indisputable
"yes". Actually, overall they seem to work better for this purpose than I
had hoped going into the project.

So, today, for those who are willing to build a simple $20 kit, it is
possible to transform their Apple iOS devices into a simple (but
surprisingly sophisticated) receiver for your HF band of choice.

But many questions remain regarding the use of these products for ARDF.
Currently, the iSDR app is not optimized for ARDF in any way. But that
should start to change in 2011. Also, now that the most fundamental software
questions have been answered, it is time to start addressing the hardware
questions: can a "quadrature sampling detector (QSD)" device be built to
perform as a high-performance ARDF RF front end? What will it take?

A back-of-the-envelope analysis suggests that the answer is probably "yes" -
in fact an SDR using such a device in conjunction with an Apple iOS device
running an appropriate app, might provide features and performance and
simplicity that is unachieved and unimaginable in all ARDF receiver designs
to date. And it can probably be done at a lower cost than virtually any
other ARDF receiver design (if you exclude the cost of the Apple product
itself).

If you are interested in developing, testing or building the ARDF RF front
end hardware, please contact me.

=====

If you're confused about what software defined radio is, or how it can be
applied to ARDF, then I suggest you download the iSDR app (still free, and
always will be) and give it a try. (If you don't own an iOS product, then
visit a friend - or the local Apple Store - and ask them to demo it for
you!) In a few weeks iSDR version 2.0 will be launched. In addition to a new
S-meter, iSDR v2.0 will contain another first that should be of interest to
the ARDF community: a virtual fox hunt.

The virtual fox hunt in iSDR version 2.0 is just a simple demo, that lets
you use iSDR to listen to a full 5-minute sequence of CW fox transmitters.
This is not a recording: the fox signals are generated by the iSDR software
itself, and iSDR has full control over their timing, frequency and
amplitude. Listening to the virtual signals, you will find them
indistinguishable from live signals.

What this demonstrates is that we now have all the ingredients to create a
very realistic "Virtual Reality Fox Hunt (VRFH)". It might work like this:
download the VRFH app to your iPhone, start it up, enter 5 GPS coordinates
(one for each fox), and off you go. The virtual reality fox hunt would allow
you to navigate to each fox by listening to its signal strength, and
determining the direction to each signal by waving your iPhone just as you
would wave an ARDF sniffer. (In fact, when you're not hunting virtually, you
can use the same app to hunt live signals!) The difficulty level could be
selectable for each participant: setting each transmitter to transmit
continuously on different frequencies (beginner), or full ARDF rules
(expert). Simulated ARDF practices could be held without transmitters,
receivers, flags, or printed maps! Putting on such an event would be simply
a matter of finding GPS coordinates for suitable fox locations, and a place
to start/finish. Think of VRFH as an ARDF style of geocaching.

VRFH doesn't exist today - so far as I know! But if you'd like to be a part
of making it happen in 2011, please contact me.

73,
Charles
NZ0I
charles.scharlau at gmail.com