sceiv

Joe Moel/, PE., KOOV
PO. Box 2508
Ful/et1Ot1 CA 92633
Bag Those Foxes:
Antenna and Hunt Ideas
Whal's the fastest growing special
interest group in amateur radio? It's
hard 10 say for sure, but it just mighf
be radio direction finding (ROF) contesters.
You'll hear lhem called hidden
lransmitter hunters, loxhunters, bunny
hunters, or Simply T-/1unters.
Hams leam ROF techniques so they
can solve RFI problems or track down
Jammers and boolleggers, then dis­
COV1H lIlal it's a 101 01 fun to go mobile
DA ng Just for the sport of it. In the Iasl
month, I've heard lrom newly formed
or growing T·hunt groups In EI Cajon
(CA), Memphis (TN), Dayton (OH),
l o s Gatos (CA), Amherst (NY),
Coiul1'tlus (01-1), arx;l Fremonl (CA).
I
Radio Direction Finding
ue VOid left by the partly open window.
Build Of Buy?
Ya\jS are also popular as T-hunt antennas
on 144 101Hz aoo up. 'rnree- 10
si x-element home statiOn models by
Gusheraft and KlM have been used
with success by bunters in my area.
One disadvantage they share is that
they aren'l made to be Quickly disassembled
and siorec be tween hunts.
That's why I was interested when MFJ
EnterpriSeS (P.O. Box 494, Mississippi
State. MS 39762; 601-323-5869) annot.nCed
a new portable thtee element
beam.
Unlike most VHF yagis, the MFJ·
1763 boom Is not maoe of aluminum
tubing. II Is a long box·like enclosure
with threaded Inserts to accept the elements.
They attach or detach in seconds.
Your feedllne connects to ' he
50·239 at the rear. Inside the boom
er to tum by haoo when $lOpped, c0mpared
10 my usual lour-etement QUad.
But when driving at highway speeds,
the boom box makes It ' weather
vane: Because me mast connection
pojnt is behind the driven element, it
wantecic point 10 the rear. It took alot
01 lorce to keep it pointed any other
...,.
Since successtul hunte rs spend
most 01 the time moving toward the T
instead 01 away lrom t , I tried to oIlset
this ellect by OOIIIng a verticat vane d
thin alumifllm sheet to the rear of the
boom, using the holes provided lor
rear mast mounting. II took aoout 20
SQuare inches 01 material 10 eumoate
lIle tendency to point backwards.
T he ac id test for the MFJ-1763
cam e on tne Southe rn c enterma
"Palllfinoor" transmiller hunt in MaruI.
WA60PS and I sllccessJuIIy founcl lhe
T, but we didn't have the lowest
mileage. We got fooled by some dead·
end streets. but the MFJ beam can't
be blamed for met
Hiders AF60 and Kl6FG were 21 air
miles away from lhe starting hilltop.
running onl y a few walls on a rocky
power line access road. Because ot
the wide spacing, the MFJ.1 763 has
about the same gain as th e typical
rccr-ereeeor Quads tha t are popular
with local hunters. II picked up and
tracked this fox Just fine.
Photo B. WAORW$ Qevised this root
rack mount because /he rigid heacliner
in hiS wagon eliminated /he possibility
of a through-roof hole. Note the
plastic panel to keep weather OlJl.
within an hour after breakfast. Everything
else is unpredictable, and that's
the way they like It.
Such an atblude leads some teams
to searcl1lor opportunities to be outJa·
Photo A. If you tum on a hidden transmitter near Bolivar, Missouri, you'll be found
in shoff order. Jim Strader KFOOL and Gal)' Hamson WADRW$ are ready 10
hunt.
Traditional mobIle VHF T-hunts Involve
a sngIe we i hiddeti "'hare" arx;l a
group 01 "tx:lund'" vehicles I~ to find
iI. To win, they must gel there in the
shortest time or with the fewest maes
traveled, depending on the rules. uscally,
all hunters start trom a common
hilltop, although "stert anywhere" is
practical lor li rsHincler·wins events.
You don't neve 10 live In a big city to
have toen unt l un. There a re only
4,000 households in Bolivar, Missourt,
but regular hunt competilions are on
the ham club's calendar mere. Gary
Hamson WA0RWS sent me photos 01
the 2 meter ROF equipment they use.
Hand·rotated etnmq-wlre Quads are
the antenna of choice (PlOto A). They
are easy 10 make lrom PVC pipe and
fi>erVlaS spreaoers.
Rather than 001 a hole thl'OlJ!1l the
rooI' d tis wagon. Gary came l4' with
a cle ver window mount using jnexpensive
PVC pipe (Photo B). II attaches
to the roof rack wiItl hose clamps
so it's easy 10 remove after the nunt
He can hunlln almost any weather because
he made a Plexiglas panel 10 nn
74 73 Amateur Radio Today · June, 1992
box are a matching capacitor and a
lerrite bead balun. The ba lun gives excellent
leeclline decoupling tor a good
pattern, which is important for ROF
use.
MFJ uses a chemicallilm process to
protect all the aluminum parts. In my
area, outdoor aluminum antennas are
pitied and corrad ed in Just a lew
months by sail air. so If wiI be inl8f8st·
ing 10 see if the process prevents that
from happening 10 this one.
I mou nted the MFJ· 1763 alop the
van wiltl a PVC pipe mast, )ust fike the
other antennas I've tesled over the
years (Photo C). The teecnne goes
down the mast, running o nly 4·1/2
inches lrom the driven element, but
'his did not appear to anect the yagi
pauem . For regular use, however, It
would be better to route the co ax
down betincl the reflector.
The ImnHo-back ratiO was 14 dB,
which Isn't stellar, but If's adequate.
It's the dilference between 314·scale
and near zero on s -meters in most
VHF·FM rigs.
The portable vagi Is lighler arc eas i-
Free-For-All Contesting
Southern c antcmra r -nuotere-cmany
01 whom believe that the longer
a hunt lasts, ire more lun If is--have
just invented a new way to have a full
day 01 RDF enjoymert.
The Free-F o r-All (FFA) hunt is
uniQue because each hunting team is
also a hiding team. The fun begins
, early Saturday a' a restaurant in the
central part 0 1 the hunt area. After
breaktast. each team leaves to hide its
transmitter.
About an hour later, th e Southern
CsUomia coordinaled T-hunt lreQuerlcy
(146.565 Wizl co",es alive, as one
by one the lox-boxes begin their transmissionS.
After activating its hidden T.
each team rushes oll to try to be the
first to fmd all the others.
Each 01 the recent FFA hunts has
brought c ut about a dozen vehicles.
Despite the need to deposit lheir 'r's
QUiCkly so they can start hunting, the
teams ma nage 10 find challenging
spots to place them, usuaDy by scout·
Ing in advance 01hunl day_
11 you tNnk ltVs sounds .ke Jun, your
club may wanl to consider some rules
lor the hunt, to suit you r area and the
skills of your local ROFers, You could
set up oounoartes. limits on irensrnlssion
durationlliming. and some sort 01
scoring sys'em.
To the FFA alicionados 01 Southem
Califomia. however, boundaries and
rul es a re unnecessary a nd a nutsarce.
The lew rules that may be imposed
on a partiCular FFA are made
up over colfea on hunt moming. Usually,
the only requirement Is that each
team must hide at least ore T before
starting to hunt. It should be on lhe air
Photo C. I tested the MFJ· 1763 yagi
with a PVC pipe mast on the T-hunt
van. You can ha ve horizontal polariza·
tion by uSing the other set of holes for
the u-oon.
geous. Foxes with packet uansrrsssions
arr:! lraction-ol·a·seeond pulses
have been used. Some tea ms hide
multiple transmitters , within ya rds 01
each other Ot miles apart. Hiders rave
used c1oCll-\imers on Iow-power Ts at
dista nt mountaintops, limed 10 start
transmitting shortly atter breakfast.
Organized Chaos
A dozen T s on one IreQuency? Ir s
lricky. but practicaL Each T beeps for
crit a lew seconds, then It's SiIeot lor
a mnute or so. Hiders progra m their
controllers (see the sidebar) with dif·
rerent onIolf .anoe. so the transmis·
SiOns of the various T s are out 01 sync
and "doubles" are random.
Hiders leave clipboards or notebooks
near their 'r'e so hunters can
sign in as they arrive. The hunl ends