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WB8WFK Foxfinder 80-Meter ARDF Receiver


Current Foxfinder news

6/12/2003 Current OZMOD board has components to make the foxfinder 80 PLL tuned. Current plan is to evaluate A PLL tuned foxfinder after the ARDF games in August. Next a new foxfinder board layout which uses the new IF design will be done.

2/15/2003 A revised IF design is currently being evaluated for use at the 2003 region II ARDF championships by team Albuquerque. Preliminary testing indicates major improvement in the operation of the IF stage and the receiver.

About this page

This page contains updates, feedback and circuit modifications relating to the foxfinder-80 ARDF receiver article that appeared in the November, 2000 issue of 73's amateur radio today.  The design data posted at this site reflects the version used at the 2002 championships in Georgia.

Source for circuit boards

As the article was being published the layout of a circuit board was in process. The circuit board layout for the foxfinder-80 was provided by Far circuits. To obtain a circuit board order direct from Far circuits. The price is $5.00 per board plus $1.50 shipping per order. I have also provided a LINK to the far circuits web site.  To email Far circuits the address is farcir@ais.net. The phone number is 847-836-9148. I will be assembling one of the boards for checkout in early November. The current artwork revision marked on the PC board artwork is ARDF RECEIVER 10/3/00. 

Revised Parts List

Some minor typos managed to make it into the parts list published in the article. Click to Download a revised parts list

Please read this before building the receiver!

Some errors  managed to get into the original article. The most important change is the number of turns in the DF loop. A revised web version  of the article along with modifications that  has occurred since the original publication can be downloaded. Please download and read before building. 

 click to down load A revised web version of the article.    (big file ~ 1.7MB)
 click to download schematic sheet1 (~50KB)
 click to download schematic sheet2 (~19Kb)
 click to download schematic sheet3 (~15KB)

Notes about circuit board version 10/03/00

I found that I had to add a pad capacitor across C20 to get T1 to resonate.  The cause for this is most likely due to the following: 

Reduced distributed capacitance in the circuit board layout and how the layout of the parts around T1 was done. The layout and wiring of the hand wired prototype was different.  Any variations on how T1 is wound.  Spacing between board and copper foil shield on box. The pad consisted of two capacitors connected across C20. The values 120Pf and 68Pf where used. 

Other important  modifications are covered in the PDF web update. 

Notes about sense antenna

Also tried a suggestion by Jack Loflin to make the sense antenna flexible. I use a section of 1-inch wide tape measure materiel to replace the sense antenna section above the loop and it works great. Easy to fold upand pack away the unit. 

Dale Hunt WB6BYU Has the following recommendation. I would be interested in any feedback from anyone who has tried it on a Foxfinder-80. I'm using the wire sense antenna on my VK4BRG 80m receiver. The original sense antenna was a telescoping whip which was attached with an insulated bolt through the bottom of the case.  Instead, I put a lug on the end of a piece of #16 insulated wire and connected it under the head of the bolt on the outside of the case.  (Suitably insulated, of course, with a few thicknesses of heat shrink tubing at the lug to protect the joint.) 


If you have performed any modifications to a foxfinder-80 and want them posted on this page please email Jerry, WB8WFK