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Author Topic: 80 meter Foxhunting  (Read 107089 times)

Posts: 340


« on: February 15, 2008, 02:52:36 PM »

I couldn't help but notice that almost every post on this thread has to do with 2 meter or UHF foxhunting. Doesn't ANYONE do H.F. foxhunting any more?  It's far more challenging, and covers a lot more real estate.  The 80 meter foxhunts we did in L.A. were a blast...and they sometimes went all weekend.

80 meter foxhunting doesn't take huge antennas, according to popular opinion...but it does take some serious SKILLS, and some experience.


Posts: 17476

« Reply #1 on: February 15, 2008, 09:28:06 PM »

Yes, there are still folks who do it.  If you notice the thread just below
this one about the National ARDF Championships (from last year), that
included competitions on both 80m and 2m, as does the upcoming
championships in Texas in May.  You can find more information about
these events and 80m hunting at  80m is used
in the international competitions as well.

But generally, 80m isn't used nearly as much for vehicle  hunting as
it used to, for a number of reasons.  First, virtually all hams have 2m
equipment, and the transmitter operator can have just a technician
license.  This probably has been one of the biggest reasons for the
shift to VHF/UHF over the years, as well as the availability of hand-held
receivers that can be used.  (Even a Ten-Tec Argonaut from the late
1970's was still far larger than a 2m mobile of the same vintage.)  I got
started hunting on 75m SSB, but as most clubs shifted their nets from
75m to 2m repeaters, it made sense for the transmitter hunts to shift
frequencies as well.

Distances?  The longest (airline distance) transmitter hunt that  I know
of was around 400 miles, and it was on 2m.  With a bit of elevation it
isn't hard to hear a 2m signal further than ground wave can propagate
a 80m signal of the same power level.  While 80m NVIS propagation
can cover longer distances, that is VERY DIFFICULT for most hams to DF.

On the other hand, 80m is very convenient for hunting on foot where
the maximum distance to the transmitter is a few miles.  A QRP CW
transmitter is easy to build with perhaps 1 to 5 watts output to a vertical
wire and gives plenty of signal - cheaper than building a 2m transmitter.  
An 80m hand-held DF receiver isn't difficult to build, especially
using direct conversion (though a superhet isn't that much more
difficult and gives much better performance.)  But even for a mobile
hunt, it isn't that hard to build a loop antenna for a HF receiver.  I've
done it before to track down some interference.  It is just a matter of
getting enough people willing to try it.

Traditionally, hunts held during the day used 80m vs. 10m for night hunts.
We don't see many 10m hunts, either, but that might be something to
try as well.

Posts: 340


« Reply #2 on: March 14, 2008, 09:28:28 AM »

Well that's good to know.  I'm thinking of resurrecting 80 meter DFing up here.  Should be fun!

Posts: 24

« Reply #3 on: March 20, 2008, 09:52:20 PM »

I you would like to experience 80-meter foxhunting, please come to the USA ARDF Championships in Texas this May.  If you don't have 80m foxhunting gear, you can probably borrow it there.  See my other message to this forum on that topic.

Joe Moell K0OV

Posts: 104

« Reply #4 on: April 15, 2009, 08:14:16 PM »

I think that 3.910 where the CBer's are during the afternoon and the interfering stations that disrupt the Marconi net on 3.872 would be great for 80 meter fox hunting practice.  

Posts: 38

« Reply #5 on: May 11, 2015, 03:27:51 PM »

I would love to do some foxhunting in Inman SC on 40 meters, with a car load of Hams, extra class only

Posts: 17476

« Reply #6 on: May 11, 2015, 03:44:59 PM »

Go right ahead and do it.  3 turns of wire on a frame perhaps 9" square (or 12" on the diagonal)
and tuned with a mica trimmer capacitor will work for an antenna, and it is small enough that
you can stick it out the passenger window if you don't have a sunroof.  Add a single turn link
in the middle that is about half the diameter of the main tuned loop and couple it to your coax.
Adjust the capacitor for maximum signal strength, and the nulls should be broadside to the loop.

Posts: 1090

« Reply #7 on: May 12, 2015, 01:52:25 PM »

I don't think it was as low as 80 meters. But one of the local old timers was telling me about foxhunts they had on the lower bands years ago. Said the fox would park under some power lines, the lines would resonate in another location and throw the hunters off.

Posts: 17476

« Reply #8 on: May 12, 2015, 02:16:12 PM »

80m and 160m used to be common for transmitter hunts, particularly during the day when coverage
was primarily local.  My local radio club hunted on 75m, which is where I got started.  That was
before 2m FM became so common.

I'm glad I didn't try to do it on foot back then, however - the HW-12 was a pain to try to run
on batteries!

Posts: 305

« Reply #9 on: July 31, 2015, 02:46:01 AM »

I really like the idea of 80 meters or lower fox hunting.  simple circuits could be built and should be fun for walking in urban or park areas.

Wonder if anyone has tried magnetic loops for this purpose. 

perhaps we can generate some dialog about homebrew units, antenna etc perhaps even for the new very low freq bands

stan ak0b

Posts: 17476

« Reply #10 on: July 31, 2015, 09:44:59 AM »

Tuned loops are the standard for DF antennas in the lower HF and MF bands.  Mine are typically 6" to 8"
diameter, made using plastic tubing bent into a circle with multiple wires running inside.  Ferrite rods are
good for more compact loops, but the ferrite grade has to be properly chosen:  many rods from AM BC
radios can be lossy at 80m, but they would make much more sense below 500kHz.

Yes, we get funny looks while walking through the park with such sets, but we're used to it by now.
They aren't as funny looking to the general public as a 2m yagi.

Direct conversion receivers can work well - I published one in QST  a few years ago - but they tend
to be prone to instabilities of various sorts:  one of my prototypes shifts frequency about 1.5 kHz
when I switch in the sense antenna.  But as a quick way to get started they can be quite usable. 

Such receivers aren't always friendly to other nearby hunters, as the local oscillator radiates.
International competitions require that such interference be inaudible at a distance of 10m, and my
designs were measured at just 8m due to radiation through the case.  (The cascode RF amp helps
to isolate the loop antenna from the oscillator signal.)

A very useful improvement is to change to a half-frequency injection mixer.  Somebody has done this
with my published design, but I lost track of who it was.  It solves a lot of the direct conversion
problems - it's on my list of experiments when I get time...

My current super-het design is a simple cascode RF amp + SA612 + 455kHz ceramic filter + SA612 + LM386
and really isn't much more difficult to build than the direct conversion types if you have the parts.
The common 10.7 MHz IF transformers work well on 80m with added capacitance across the main winding,
though the only signal-frequency tuned circuit in mine is the main antenna loop.

Sensitivity is good - I can hear a 1W transmitter with wire tossed over a tree branch as far as I'm likely
to run to find it.  Main nulls are deep, and the sense antenna is easy to adjust to a very deep null.  (These
characteristics apply to the direct conversion receivers as well.)

Further improvements?  An audio S-meter to indicate signal strength by a change in pitch, because it is much
easier to detect a small change in frequency than a change in loudness.

Posts: 305

« Reply #11 on: August 03, 2015, 11:21:49 AM »

thanks wb6byu --  very interesting do you have a web site with more details or pictures.

I love the idea of a 6 to 8 inch loop.

Thanks  Stan AK0b    w9ifz at yahoo dot com

Posts: 228

« Reply #12 on: August 07, 2015, 09:46:52 AM »

QRP fox hunting is alive and well on 20, 40 and 80M.  For more information:


Posts: 17476

« Reply #13 on: August 08, 2015, 02:19:36 PM »

Here are some links to articles on hand-held 80m DF receivers:

K0OV's overview article on 80m hunting from 2000: some links may be out of date

My direct-conversion receiver article, "A Simple Direction-Finding Receiver for 80m", appeared in QST for September 2005, and is available (for members) from the ARRL archive.

DF1FO has some very sophisticated receiver designs, though most of the available information is in German:

The "Junior 80" is a simple but optimized 80m receiver by DL5NBZ.  It is a direct-conversion receiver using a half-frequency injection mixer to avoid many of the common problems with DC receivers.  (in German, of course, but you can still understand the drawings and read the schematic):

An excellent article (in English, even!) on 80m DF loop antennas:

PA0NHC has an English description of his receiver:

DL7VDB has a comprehensive list of articles, including older ones from European journals - again in German, but Google and others will translate it for you:


Posts: 17476

« Reply #14 on: August 08, 2015, 02:47:30 PM »

My nominal loop construction uses a 6" to 8" loop of plastic tubing, secured through
holes in each side of the receiver case with hot melt glue.  Generally I use the milky-
white "poly" tubing common in most home repair stores, which is cheap and relatively
stiff to hold its shape, but lots of other types will work, too.

My "standard" size is 6" diameter.  With 4 turns on the main loop, this requires around
220 - 270pf to tune 80m.  I've built them from 4" to 12" - larger loops pick up more
signal and are less convenient in the brush.  4" will want more gain, and probably is
about minimum before switching to a ferrite-core design.  Increasing the number of
turns in the tuned loop also increases received signal strength, but also affects the
load impedance on the loop.

To make a 4-turn loop, I make a bundle of 5 individual wires + a length of RG-174
coax taped together and thread it through the tubing.  It really helps to use different
colors of wire here, but you can get by with marking the ends of each piece with felt
pens.  Wire diameter is usually around #22 stranded, insulated, though it can get a bit
tight in the smaller tubing sizes.

Select 4 of the wires and connect them in series end-to-end (this is much easier than
trying to pass a single wire through the tubing 4 times!).  For example, the connections
likely would look something like this:

                 left side connects       right side connects to
Wire 1:       tuning capacitor          wire 2 (left)
Wire 2:       wire 1 (right)              ground
Wire 3:       ground                       wire 4 (left)
Wire 4:       wire 3 (right)              other side of tuning capacitor

That gives a 4-turn winding with the center tap grounded.  It's difficult to predict the
resulting resonant frequency due to changes in the inter-turn capacitance, but coupling
a dip meter to it should clearly indicate the resonant frequency with a capacitor across it.

The 5th wire is used to couple the sense antenna:  this method provides the required 90
degree phase shift via transformer coupling, making adjustment much simpler.

One end of the coax attaches to the receiver input.  At the other end I trim back the braid
and connect the center conductor to ground.  This gives a 1-turn shielded coupling loop.
Yes, it would be technically better to ground the shield at both ends and break it in the middle
to improve the balance, but that hasn't seemed to be a problem.

I feed this into a preamp with an input impedance of around 1500 ohms - I don't know how
optimum that is, but even the simple receivers are more than sensitive enough.  Too low of
an impedance will drag down performance.

Most other designs I've seen use just main tuned winding and connect it to an FET preamp
with high input impedance (often two FETs in push-pull to maintain balance.)

The big mobile loop I built used (I think) 6 turns on a 12" diameter loop with a single turn
link.  I ran it straight into my TS-450 and it worked OK, though, of course, it wasn't particularly

There is nothing magic in these dimensions or construction methods - you can make a cross
using 1x2 wood and attach the wires to it with staples if you want.  Try it and see.
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