[ARDF] ARDF Digest, Vol 76, Issue 12

Gerald Boyd wb8wfk at worldnet.att.net
Tue Oct 6 21:12:41 PDT 2009

Hi Charles,

I have been experimenting with FPGA's for a SDR application for sometime now
and just finished the design of a SDR based signal processor for a multimode
ARDF transmitter (it does FM, AM CW keyed FM Keyed AM etc). 

I would recommend FPGA's over any processor based application. In FPGAs you
can enjoy the world of true concurrent processing and total control of your
design! Microprocessors suffer from the ability of only processing things in
a sequence and lock you into a fixed instruction set and architecture. 

In the FPGA world you can define a custom processor your own architecture
that can taylor itself to the application in hand and have true real time

In my recent ARDF transmitter project there are several processes that are
running at the same time.
(yes they are running at the same time, no time slicing!)

Two processes are running at 200 MHz (the phase accumulators) and every
thing else is only running at 40 MHz, Modern SDR receivers are now using
FPGA's. There was a QST add for a SDR a few months back and after reviewing
the photo I discovered that they are using the same FPGA that I am using in
my transmitter design. 

I am using a $10 FPGA. 

VHDL ( that's the programming language for designing FPGA's) is easy to
learn are there are free development tools on the internet from ACTEL and
Xilinx (the two major FPGA venders).  You can also use cheep eval boards to
do your code development and experimentation on. I used a $59 eval board to
develop my first SDR code before making the SDR ARDF transmitter PCB that I
demonstrated in Boston.

Don't get held back by using a Uprocessor for real time processing. Our
design uses the FPGA for all the real time stuff and the PIC for the user
interface and ADRF formatting stuff. For more info on our SDR project see
http://nm-arts.ning.com/group/ardfsoftwaredefinedradio   and join ARTS and
the SDR project group to track the project.

Now that the Signal processor is done, Mike K5ATM will be working on the
finishing efforts on the PIC user interface stuff in the upcoming months.

When the SDR transmitter stuff is all done I have been thinking about
starting a FPGA SDR receiver group on ARTS. 

Yes I concur that the parts count for a SDR receiver can be low. Some of the
transmitter stuff should be able to be re-used for a receiver? 

Also a simple hardware platform PCB ( FPGA ,PIC processor and LCD diaplay)
could make a low cost receiver.

Also been looking into how to make an Ipod like interface panel for an ARDF

Just my 2 cents comment.

Jerry WB8WFK

-----Original Message-----
From: ardf-bounces at kkn.net [mailto:ardf-bounces at kkn.net] On Behalf Of
Charles Scharlau
Sent: Sunday, October 04, 2009 6:10 PM
To: ardf at kkn.net
Subject: Re: [ARDF] ARDF Digest, Vol 76, Issue 12

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

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.

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