[ARDF] advanced Receiver Design

[Dale Hunt WB6BYU]

I've changed the thread name to make it easier for those who want
to skip the discussion...

Actually an 80m receiver could be built into a helmet, with one or two
loop antennas, electronic compass, and perhaps even some sort of
Head-Up display (at least a ring of LEDs around the visible part to
indicate the direction to the transmitter.  By using two loops you can
determine the bearing without rotating the loops.  The helmet also
means that your hands are free to read the map and/or scramble
through rough terrain.  (You could even use my  RIGHT/LEFT
80m circuit and indicator, which only requires a single loop antenna.)

For 2m or other applications where a fixed antenna array might not
have sufficient sensitivity you could put the minimum necessary
circuitry into the hand-held receiver with a Bluetooth or similar link
to a receiver worn on the body.  (Actually I talked with Bryan about
a similar design, probably at Lake Tahoe.)  The main receiver could
be designed to work with hand-held units for various frequencies,
giving a common interface.  The hand-held unit would not need any
controls, and could be completely sealed for weather.  (If you wanted
to be clever you could use the antenna connector to charge the
internal battery.)


While this has some possibilities for a future rig, my current efforts
are looking more towards what would be inexpensive and simple
to get people started.  I'm imagining a basic receiver (preamp,
VFO, mixer, if amp, filter, detector, gain control, VCO for audio
signal strength) that can be built using standard manual controls,
or interfaced to an external processor (of whatever type) for those
who want to experiment in that direction.  With a functional circuit
that can be built using easily available parts we have the ability
to build loaner receivers.  Those who want to customize the
features or performance can do so without having to build the
entire receiver from scratch.  I'd imagine this being available as
a circuit board, but would love to have someone willing to pick it
up for a kit / pre-built unit for those who don't like melting solder.
(Actually there are a number of receivers out there already that
might qualify for this, including DF1FO's and Valerie's from Montreal.)

Meanwhile I found an ideal extruded aluminum receiver housing,
though just a hair too small to squeeze a 9V battery into.  I'll have
to see if  can come up with a suitable receiver for competition next
year.  Might require some surface mount parts.

For anyone who wants to try using fiberglass rods for an antenna,
Harbor Freight sells 39" rods with threaded brass ends on them
to screw together to pull wires through conduits.  I've got a couple
elements built for my first attempt and when finished will test them
to see if the rods are durable enough.  By cutting the rods in half
I have screw-in half-elements for the yagi that easily fit in my
carry-on luggage.

Lots of ideas...


	- Dale WB6BYU






On 07 Oct 2009, at 13:57, Charles Scharlau wrote:

> 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
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