[ARDF] Fun and Frustration

Wed Oct 7 05:27:47 PDT 2009

I've been following this discussion with some interest.

My own feeling, and I'm happy to be contradicted, is that power consumption, and to a lesser degree cost, often overlooked till it's too late, is the killer for battery powered s/w defined radio solutions at this stage.

We've looked at FPGA (much lower frequency apps than this would be) solutions over microprocessor solutions for various products at work, and it always comes back to power consumption, esp. if you are running off batteries. Phillips had a series called "cool running" FPGAs that I think they sold off to one of the big boys (Altera or Xilinx), but even then you are looking at an order of magnitude increase over a discrete RF or microcontroller solution.
With a receiver, as distinct from a transmitter, you'd also need an ADC capable of 300MHz operation (for 2*sampling at 2m), and that takes serious current (and cost). This is outside the FPGA itself.
Also, don't forget to add the support chips. A RAM based FPGA (probably the case at the speeds we are talking), you have to add an SPI or IIC serial flash eprom. Then you still need the microcontroller to do the user interface (pretty much any serious ARDF receiver would have one now anyway). Yes, you can get VHDL defined micros or special micros embedded in the FPGA (eg ARM or PowerPC), but again, power consumption is worse than the plain silicon version.

Perhaps a solution where you sample at audio frequencies, or zero IF (with I and Q) could be a useful 1/2way SDR solution, but then you still need the associated RF components (front end, rf filter, IQ linear mixer and PLL VCO) that you'd have had with the 'discrete' solution, so unless you have a driving need for it (eg. software programmable IF filter bandwidths or special DSP tone detection/FFT etc), then you almost certainly have a more costly and complicated solution, and probably having to lug around a bigger battery/LiIon cells as well.

Dale's idea of a separate RF and CPU board is perhaps the most currently helpful idea, but bear in mind that is exactly what the "Ultra Sniffer" kit David VK3XJH and I designed years ago was, and it hardly took the world by storm. Frankly, there is little incentive for anyone to create such a thing for you. There simply aren't the sales in ARDF to make it worthwhile. It is not really practical to do this these days using pin-through components, so we're certainly looking at surface mount. It's very hard to do this for a kit, and almost as much work to make the kits up as to just pick and place the board anyway !  I know...I've been there.
You are wecome to the circuit and layouts for the old Ultra sniffer RF board if you want. It could still form the basis for a solid performing ARDF receiver, and it can double as a FoxOr transmitter too ! The micro board however, by today's standards, is crap.

Lastly, I'd be very surprised if an iPhone can directly do a SDR without an external downconversion. See above comment about needing lots of stuff to do even that.

That's my 2c. As I said, happy to be contradicted as there could be now developments of which I'm unaware, as I don't work directly in RF anymore, but for now, I concur with Dale.

Bruce, VK3TJN

On Wed, 7 Oct 2009 03:05 am, Charles Scharlau wrote:
> One brief update on my comments:
>
> I'm seeing some strong evidence that it *might* be possible to create a
> downloadable application that would turn an Apple iTouch into the
> "computer" part of an SDR. So possibly taking an iTouch (or iPhone) loaded
> with the right application, plugging an SDR front end into the microphone
> port, and adding a directional antenna, you've got an all-mode ARDF
> receiver.
>
> Not to go off the deep end with futuristic ideas, but if this were
> implemented using an iPhone 3G (which includes a built-in digital compass,
> lots of memory and the ability to display maps), you could have one device
> that serves as receiver, map, and compass... not to mention music player,
> web browser, cell phone, etc. etc. etc., with a Bluetooth interface to use
> with your cordless headphones. The total cost could be well under $100 for
> those who happen to already own the phone.
>
> Just thought I'd mention that in case it motivates anyone else to more
> closely examine the possibilities of an SDR ARDF receiver. Again, please
> let me know if you might be interested in collaborating on an experimental
> design.
> OK, I'll stop my monologue now.
>
> -NZ0I
> On Sun, Oct 4, 2009 at 8:09 PM, Charles Scharlau
> <charles.scharlau at gmail.com
>
> > wrote:
> >
> > In an earlier post I suggested that ARDF needed to evolve, including the
> > equipment we use. I hadn't commented with thoughts about equipment
> > evolution, but I thought I'd go ahead and post some thoughts... even if
> > no one asked :-) I think the subject fits the original subject because
> > the current situation with receivers contributes to the frustration of
> > the sport for both newcomers and those who have been playing the sport
> > for years.
> >
> > I see three problems that need to be addressed: 1) availability - where
> > to find quality ARDF receivers in particular, 2) cost 3) complexity. Yes,
> > I know one can put out feelers and others will gladly identify someone,
> > somewhere who is selling a receiver. But that only serves to illustrate
> > the frustration of obtaining equipment: it is very much a treasure hunt,
> > and a buyer beware activity. When searching for a quality receiver one
> > must either buy a used receiver of uncertain condition, sans warranty,
> > and sans manual, or contact a foreign builder with uncertain product
> > availability (often uncertain product specs!), and all the problems that
> > can go along with communicating and remitting payment to an overseas
> > entity. After being in the sport for a while one tends to get numb to
> > this situation, but I'm always reminded when I must explain to a newbie
> > the hoops that he/she must jump through to purchase ARDF equipment.
> >
> > Loaner receivers are great, and shifts the issues of availability and
> > cost to the one doing the loaning, but it does nothing to reduce the
> > complexity of the sport... especially for the technology challenged.
> >
> > I believe that receiver evolution is needed sooner than later, especially
> > in countries where the sport has little or no history, and no domestic
> > receiver suppliers exist. But I think there might be the beginnings of a
> > solution to the receiver situation beginning to take shape: SDR or
> > Software Defined Radio.
> >
> > There is a cottage industry of SDR front ends. See
> > http://groups.yahoo.com/group/softrock40/ for links to information on how
> > the concept works and sources of kits. The remarkable things about the
> > SDR concept are the low parts count (ignoring the computer for now), the
> > high performance (including huge dynamic range, and high selectivity),
> > and the ability of the radio to gain new capabilities or
> > performance improvements with just a change to its software.
> >
> > Currently, the need to lug along a laptop makes an SDR totally
> > impractical as an ARDF receiver. One solution would be to substitute a
> > handheld computer instead of a laptop. But so far I've yet to identify a
> > suitable handheld with the requisite two-channel sound card. Another
> > solution would be to build a stand-alone SDR by interfacing the SDR
> > front-end with a high performance digital signal controller (i.e., an
> > all-in-one DSP + microcontroller IC). Such a stand-alone SDR holds the
> > promise of an overall parts count (and parts cost) well below any
> > similarly capable receivers available today. Also, with the appropriate
> > software installed, it could operate on any mode (AM, FM, CW, etc.), and
> > possess features specifically for the sport of ARDF (or for any other
> > purpose that one can imagine). Come up with your own whizzbang feature
> > set for simplifying ARDF receiver operation, or gaining an edge in ARDF
> > competition, and most likely it can be supported in the same SDR hardware
> > in combination with the right software.
> >
> > I believe that a publicly-available hardware design using standard parts,
> > and an open source software effort, could eventually resolve all three of
> > the ARDF equipment issues I've listed - in the USA and elsewhere.
> >
> > Others more knowledgable than myself have probably considered the SDR
> > possibilities. I would be interested to hear/read your thoughts and
> > ideas. I would be especially interested to hear from anyone with DSP or
> > hardware design experience who might be interested in collaborating on an
> > experimental design. Feel free to contact me offline if your post doesn't
> > seem of general interest: charles.scharlau at gmail.com.
> >
> > 73,
> > NZ0I
>
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-- 
Cheers,
Bruce