Foxhunt gear – offset attenuators

Filed Under (Antennas, Dayton Hamvention 2010, Homebrew, Kits, VHF/UHF) by Jonathan on 08-07-2010

I attended a great fox hunting presentation at Dayton this year, hence a few posts on the topic.

I had some posts in the past about tape measure beam antennas.  Really neat antennas and they have multiple purpose use (they are GREAT for hitting distant repeaters when you orient them vertically!).  Much like the picture on the right (courtesy of Joe Moell K0OV) they are more useful for fox hunting when you add the active attenuator to your setup.  FYI, Joe is the co-author of the great book “TRANSMITTER HUNTING, Radio Direction Finding Simplified” available where most ham books are sold.  His website has more information on the book at and he contributes to CQ and CQ VHF.

So….. just what is an offset attenuator?  Joe explains it on his “Homing in” site as:

An RF attenuator is a device that goes between antenna and receiver to reduce the signal strength down to within the range that the receiver S-meter can handle. Without one, you may think you’re close to the fox when you’re still far away. You won’t be able to get close enough to a camouflaged hidden T to identify it. The amount of attenuation should be adjustable so that you can add just a little when your S-meter first pins, up to a lot as you get within a few feet. Special ARDF receivers used by champion foxhunters have electronic attenuation built in, but ordinary handi-talkies don’t. Adding it would require major micro-surgery in the HT.

His attenuator page is:

I recommend his site in general, many great projects:

On his attenuator page, he has full schematics to make an offset attenuator.

But wait…… there’s more!

Further on his page, you see one made in a sweet Pomona box.  I like this box and thought it was a bit pricey at first, until I did the math and figured out the cost/time to do it myself.  These boxes are shielded with the connector of your choosing (BNC/SMA/259, etc).

They generally cost around $25 or so and are shielded!  Great to have.  When you add the cost of connectors and such, it isn’t really so expensive after all.

I really advise using such a case or a metal case in general, makes things work out much smoother in the end.  More information on this box at:

But wait….. there’s even more!

Marvin Johnston KE6HTS is now offering a “semi-kit” for this attenuator on his website.  I’ve seen this kit when I was at Dayton this year and encouraged a friend to pick it up and build.  I may end up running a buildathon here in CT on these attenuators.

The price is really not bad at $22.00.  You can purchase them built for a few dollars more.

Information on the kits and pre-built models are at:

And yep……. there’s even more (again!).

If you would like to “roll your own” from parts you may have on your bench, but don’t want to make a circuit board, you can get one from……. you guessed it…… Far circuits.  I picked one up and am going this route myself.

There are a few boards/projects on the Far circuits website at:

There are a ton of great resources out there on the web, these will really get you going right from the start.  Fox hunting is a really fun and useful part of our hobby and one that doesn’t cost a ton of money to get started in.  If there are no active fox hunts in your area – start ’em!  There are plenty of options as far as transmitters and such and really doesn’t cost a club much money to get started.

The Montreal Doppler

Filed Under (Dayton Hamvention 2010, Homebrew, VHF/UHF) by Jonathan on 17-06-2010

So, here I was at Dayton a few weeks ago and decided to check out the fox hunting/amateur radio direction finding (ARDF) forum.  I forgot who did the forum, but it was actually very well done.  One of the projects I learned about was “The Montreal Doppler”.  This is a really neat project designed by Jacques Brodeur, VE2EMM.

I saw many neat attenuators, offset attenuators….. but this….. well…. it has LEDS!  Pretty lights…. OK, I digress.  Working with a bunch of these LED’s is pretty kewl and looks sweet.  This is a project that is well documented on the web and I’ll provide links below.

The biggest question I had was, where do I get the microcontrollers and firmware.  Not only was I able to acquire the PICS (microcontrollers), but I was able to get PC boards and the LCD for a very reasonable price from FAR Circuits!  I know I picked up the last one he had at Dayton, but he may be able to do more (they cost $45.00).  Check out the FAR circuits website at

A little about this project from VE2EMM’s website, list of features:

–   36 LEDs display; center LED when green = good signal, when red = no signal ,  the direction is frozen to the last good signal.
–   Uses 3 PICs; a PIC16F628A for the display, a PIC18F4520 as the main processor and a PIC12F675 as a frequency divider.
–   Filters; a Max 267, the best bandpass filter that I have ever seen, followed by the Roanoke switch cap filter for very narrow band width (+/- 0.5Hz).
–   My DopplerII integrating and phase detection software in the main PIC.
–   LM386 for monitoring the audio independently from the doppler.
–   Simpler menu selection, turning a selection pot and a pushing a DO switch.
–   It will switch 4 antennas with a + or – going signal, 4 antennas differential, 8 antennas with a + or – going signal.
–   Pushing the DO PB sends the direction to APRS.  The protocol is:  <cr><lf>%359/Q<cr><lf>. The Q (0<8) is the quality of the signal just before the
extraction of the phase information.
–   GPS information goes through the doppler, it will be instantly interrupted when the doppler sends a DF to APRS on a PC.
–   Faster main processor, PIC18F4520.    **** NEW ****  June 06

The model I saw really intrigued me and there are a few really well done websites devoted to this project (it has quite the cult following).

The original site is at:

Here is another page on Jacques site that has some examples from other builders:

KA7OEI has a neat page with a bunch of information on this project:

He has a lot of information about an alternate firmware that looks like the image below:

The alternate firmware page is at:

If you have any more information on this project, resources or anything of the sort, please comment below.

Free grid mapping software for all you VHF’ers (and up!) – WorkedGrids from Bertrand Zauhar, VE2ZAZ

Filed Under (Software, Space Communications, VHF/UHF) by Jonathan on 08-06-2010

Every now and then, a little gem comes along, something that just works right.

I recently stumbled on a piece of software called “WorkedGrids” by Bertrand Zauhar, VE2ZAZ.  This software, of course, is geared towards those of you in the VHF and up crowd.  Satellite, VHF/UHF/Microwave sidebanders and such.  Bertrand describes it as:

WorkedGrids is a Windows application that displays a map showing the amateur radio grid squares contacted and logged in using a third-party logging program. WorkedGrids uses colors to display information on a per-band basis. Up to four bands can be displayed concurrently.

As you can see by the image on your right, there are plenty of color coded grid squares telling you how you worked a station.  Swell stuff really!  Being a “1 call”, I thought it was neat that the image he uses on his site was centered right on my area.  Some of those spots are indeed hard to work, but I digress…….

The beauty of this software is it’s not “logging” software, it’s really QSO mapping software.  You use your logging program of choice.  If it doesn’t have a similar feature, you can export your log and then load it into this program and Voila!  All set.

System requirements:

Operating System: Any 32-bit version of Windows from Windows 95 to Windows Vista. Most likely 64-bit versions of XP and Vista as well, but untested so far.
Minimum CPU Hardware: Pentium-Class CPU, preferably Pentium-II or faster for quicker map refresh.
Display: 640×480 or higher resolution, 256 colors or more.
Disk usage: 1MB
Typical RAM usage: < 10MB, varies as a function of Map window size.

So why not give this gem a try?  You can find it at:

VHF/UHF and microwave antennas de G4CQM

Filed Under (Antennas, Homebrew, New Ham Primer, Six Meters, VHF/UHF) by Jonathan on 29-03-2010

If you’ve been reading this blog for awhile, you know I’m a huge fan of not only making your own gear, but projects that can help new hams get started making their own gear.

G4CQM has a great compendium of VHF/UHF and microwave antennas that any new ham can build and use.  There are some great antennas for 2M that can be used for either hitting a distant repeater, making a good haul on “52” or even satellite work.

Many of the antennas in the microwave area can be modified for computer/wifi use as well.  Really neat stuff.

Some examples are:

6 Meter antennas from 5-11 elements

2 Meter 3-11 elements

70, 23 and 13cm antennas

Information on feeding, stacking and feed loss

The overall construction articles are well written with plenty of nice drawings as well as antenna plots.

If you would like to check out G4CWM’s Yagi antenna site, point your browser to:

Link update:

G4CQM has sent me a new link as he has changed ISP’s:

Thank you Derek for keeping me honest!

More satellite antenna projects/improvements

Filed Under (Antennas, Homebrew, Space Communications, VHF/UHF, YouTube Antenna Goodness, YouTube Goodness!, YouTube Space Comms Goodness) by Jonathan on 07-12-2009

OK, not to sound like Rod Serling, but…..

Today, I humbly submit, for your approval, an incredible AzEl project from Dave Matthews, KI4PSR.

Dave has submitted a project to Parallax (the microcontrolller/stamp  people)  This is a neat AzEl setup that you can build from off the shelf parts (mostly) that allows you to use your computer to track the birds as they fly overhead.

It doesn’t get easier than this, but the project seems really neat.  He lists the materials he’s using as well as sites where you can obtain parts.

Might I add, he also brings my favorite Ham Radio Deluxe into the mix!

For project info, schematics and such, check out the Parallax website at:

That might be a bit technical for some, but here are some other great projects/mods I’ve found recently.

K7PAR has some tips for improving an Arrow (or Arrow like) antenna at:

KI0AG has a neat micro duplexer for the Arrow.  He specifies that this is indeed maximized for the Arrow antenna itself.

What makes his project neat is he really documented the information well, so it is incredibly educational.  Check out his project at:

Finally, let’s not forget Randy, K7AGE and his mod to hold a dual band antenna.

As always, if you have more ideas, post them below.


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