Keeping the simple in
simplex QRP 2M FM By Richard Fisher, KI6SN |
The
ARRL's Field Day is a periodic reminder to me that the world of QRP need not be
confined to the high-frequency bands: 1.8 to 30 MHz,
While
other operators are pounding CW frantically on 40 and 20 Meters, I make a point
to sneak away for some FM simplex work on the 2-meter band. Terrestrial operations on 146 MHz have
always been a fascination at KI6SN. It's a place where even modest antennas and
low power can produce some pretty , amazing results. That was certainly the
case during Field Day 2002.
Indeed:
for portable/vacation/business trip radio activity, 2-meter FM is one of the
most convenient plug-and-play QRP band and modes around.
With
the ARRL's September VHF QSO Party on 14-16 September 2002, this is a great
time to develop a VHF station and experiment with this band mode and the
antennas in popular use by radio amateurs on 2 Meters.
For
Field Day 2002 I used a three element homebrew beam made of metal rods and PVC
and mounted on a PVC mast about six feet off the ground. I was running 5 watts
with a Kenwood TM-261A transceiver. I was able to work dozens of FM'ers from
our Field Day location 8,000 feet high in the San Gabriel Mountains north of Los
Angeles.
Beams
can be a simple and wonderful solution for 46 MHz. But, without a rotor or a
permanent mast at home, I was seeking a simple solution to work simplex on a
more regular and reliable basis
The
classic J pole has long been a solid performer on 2-meter FM. it's
omni-directional, easy to tote and store and very inexpensive to build from
scratch Fundamentally, the J-pole consists of parallel matching section and a
carefully calculated feed point to present your HT or transceiver a 50 ohm
load.
I
was surprised, however, to learn that there are several variations of the
J-pole. Versions include the single-wire radiator, the top-wire radiator and
the loose-wire double-radiator, which I chose to focus upon for this month's
column.
While
reams of articles have been written about the 2-meter FM J-pole, the best
treatise I've seen on the subject is by L. B. Cebik, W4RNL, of Knoxville, TN.
He is one of the leading experts in antenna modeling and theory in Amateur
Radio today. His four part series “Some J Poles That I Have Known" is a
“must-read” on his Internet Site:
www.cebik.com.
Part
2, titled "The Varieties of Twin-lead J-Poles and Some Performance
Standards'* gives details on building the antenna described for this column
using inexpensive 300-ohm twin-lead you can find at most any hardware store or
Radio Shack.
I
was attracted to the Loose-Wire Double Radiator J-Pole (I’ll call the L-W-DR-J
for short) for a couple of reasons. First, I wanted to build an antenna that
could withstand being repeatedly rolled and unrolled and survive the rigors of
the road. With the L-W-DR- J, as can be seen in the accompanying diagram,
basically you're working with a single piece of twin-lead 56.5-inches long
pretty rugged!
|
Another
attraction was that the dimensions of the L-W-DR-J are in standard
inch-increments that can be measured using a hardware store wooden yardstick.
There's
a 34-inch radiator, a 22.5-inch parallel matching section and the feed-point is
2-inches above the base of the antenna.
The
half of the twin-lead separated above the 22.5-inch matching section is the
"loose wire." As W4RNL explains, this design "emerges from the
desire to use the twin-lead intact for added strength. Therefore, instead of
removing the wire that is parallel to the normal radiator (above the matching
section), we leave it in place, cutting out only a small portion to allow one
side of the matching section to be open."
While
this antenna can easily be constructed in an hour or so, great care must be
taken in dressing the 300 ohm twin-lead -- especially at the antenna's
feed-point.
For
the KI6SN version of the L-WDR-J, I chose to cut away a 3,4-inch long section
of insulation that creates a "window” -- not unlike those seen in standard
450 ohm ladder line, in which a standard RCA phono plug is soldered to accept
the coaxial feed-line.
In
this process, an Xacto knife was used to cut away the insulation between the
parallel stranded wire feed-line. Then a soldering iron was used to melt the
insulation remaining directly on the wires.
After
carefully trimming any excess bits of insulation, the builder will have a
3/4-inch length of insulation less parallel stranded wires. The rest of the
insulated 300-ohm twin-lead extends above and below this ¾-inch stretch of
parallel wires.
One
of the bare antenna wires is then soldered to the center post of the RCA phono
jack midway in the "window." Next, solder the opposite stranded
parallel wire to the ground post of the phono jack. There's your feed point.
The accompanying diagram shows how the jack is connected.
Next.
from those solder points measure and mink the 300-ohm twin-lead two inches
below the RCA phono jack. Cut the twin-lead there and trim about 1/2 inch of
insulation from the parallel stranded wires. Ultimately they'll be twisted
together and soldered. But let's not get ahead of ourselves.
From
that 2-inch cut measure back up the twin-lead, crossing over the phono jack
feed point, a total of 56.5 inches. Mark it there and, again, cut the
twin-lead.
Now,
identify the side of the twin-lead that is connected to the ground lug of the
RCA phono jack. This is the matching section side of the antenna. Measure 22.5
inches from the bottom of the antenna and mark it. Then measure 22.75 inches
from the bottom of the antenna and mark it. This is the point where you'll
remove a 1/4-inch section of one of the twin-lead wires. This simultaneously
creates the matching section and the "loose wire."
OK,
now we've got an RCA phono plug dangling from a ¾-inch section of
insulation-less twin-lead. That doesn't sound very sturdy, does it? A hot, glue
gun can provide a solid solution. Filling the void with glue not only secures
the wires and makes the RCA phono jack a solid foundation for the feed point,
it's also weatherproofing for the feed point.
The
last step is to twist and solder the twin-lead wires at the base of the 2-inch
stub. Before doing that, though, it's a good idea to check for shorts. Set your
digital multi-meter or VOM to “resistance" or "continuity."
Touch the meter's probes to each side of the antenna at its base. If you see a
short, you've got trouble. If not, you're in good shape and can now twist and
solder the twinlead wires at the base of the antenna.
One
caution: It’s extremely important to measure each element of the L-WDR-J
antenna precisely. And, remember that the electrical length of the antenna
begins at the tip of the twisted, soldered wires at the base of the antenna and
extends 56.5 inches up the twin-lead from that point.
I've
made lots of 2 meter FM simplex contacts on 146.52 MHz using the L-WDR-J
antenna suspended in a tree about 20-feet above ground at KI6SN. Signal reports
from more than 65 miles away have been solid with five watts output.
Since
my feed line has a run of about 35-feet to the TM-261A, a coaxial balun was
wound using the feed line coax to prevent coupling between the J-pole and feed
line. It is a simple matter of curling five turns of the feed line into a
4-inch diameter coil and securing it with electrical tape.
Richard
Fisher, KI6SN, can be reached by sending snail mail to 1940 Wetherly Dr.,
Riverside, CA 92506: or by sending e-mail to: [email protected].
This
article is reprinted from the September 2002 issue of Worldradio.
More on that
2-meter J-pole By Richard
Fisher, KI6SN |
September's
Worldradio QRP column on the construction of a 2-meter J pole antenna generated
a lot more than RF. The e-mail box at KI6SN was flooded with testimonials,
questions and comments about it.
The
Loose-Wire Double Radiator 300-ohm 2-Meter J Pole described in L.B. Cebik,
W4RNL's online series "Some J Poles I Have Known," is a simple,
inexpensive and portable antenna made from garden-variety 300-ohm twin lead and
can be built in less than an hour.
Many
who have constructed the KI6SN version featured in September say it works
great.
Typical of the success stories was that of Jim
Kephart, KD5QAG, who wrote from northeast of Oklahoma City: "As a new Ham,
I could hardly wait to build the J-pole you described," he said. "it
works great with my HT (handi-talkie)! I live in a rural area of Oklahoma
between Oklahoma City and Tulsa. Hitting any repeater from my home is a
challenge. With only the rubber duck on my Yaesu VX5R I could barely hit the
closest repeater in Stillwater, a distance of 35 miles over rolling
hills, and would receive marginal to poor signal reports on 5 watts. With the
J-pole hanging in my front window of my home I can now access all three of
Stillwater's 2-meter repeaters with 'full quieting' signal reports on 2.5
watts!
"I
actually pulled the J-pole, by a rope, up about 20 feet into an oak tree and
had good signal reports from Hams on an Oklahoma City repeater over 80 miles
away. Not bad for 5 watts and an HT! I could hit Oklahoma City before only
during 2-mater band openings.
"I'm
going to use the tree approach again and try simplex operation with some
amateur friends in Cushing, my closest town, and see how it works.
"Where
I live, frequent power outages intermittent phone service and tornado weather
are a fact of life. Amateur Radio has provided my family (my two sons, James
II, KD5QQN and Zach KD5THZ, are now both Hams) with another way to communicate.
"By
the way, I have requested frequency coordination for a 2-meter open repeater to
be placed on top of the hospital I work at in Cushing. I'm the respiratory
therapy manager. It will be supplied with emergency power access from the
hospital's generator and help with local emergency communications. One
enthusiastic Technician can make a difference! I have been studying and plan to
take the General Class theory and CW, exams soon."
Jim
wondered how much power this J-pole can handle. At KI6SN. I've powered up to 50
watts on occasion with no degradation in performance.
Meanwhile,
Lionel Mordecai, K6CEQ, of Chula Vista, CA wonders “why people don't make a
6-meter or even a 10-meter J-pole using similar construction?" The source
of my information for the loose wire J-pole came compliments of W4RNL, who is
one of Amateur Radio's foremost authorities on antenna construction and design.
If you visit his web site (www.cebik.com) and check out the four-part series
"Some J-Poles I Have Known," there’s a ton of background and
theoretical information that shows the J-pole will work nicely on a whole
variety of frequencies –including 6 and 10 Meters.
Ben
Bennett, N7IVM, of Olympia, WA writes: "My first 2-meter antenna was a
J-pole similar to yours, but made from 450 ohm ladder line.
"A
point which may be of interest to you was that we discovered that the VSWR was
a little better when we strapped each end of the 'loose wire' back to the main
radiator.
"I
don't know whether this was related to the fact the conductor separation is
greater in the 450 ohm line which I used because it was already in my
possession, whereas the only 300-ohm line was old style TV downlead:"
Mike
Greenfield, N9JIY. from Jackson, WI, writes to relay his experience with
2-meter simplex operation. "I've been monitoring and CQ'ing on 146.52
during drive times in the Milwaukee area for a couple of years now. Contacts
are very tough. Only maybe 40 call signs have been collected in the whole time.
Pitiful.
“A
buddy and I tried 2-meter simplex MCW (modulated CW) and it works very FB. The
MCW signal was 100 percent copyable when the FM voice signal was not even
detectable. I don't know why, because MCW is not narrow band.
"Two-meter
rigs are so cheap and plentiful, and 2-meter simplex is done so little it seems
like a great opportunity to experiment and develop."
Mike
suggests an award be developed to generate more interest in 2.meter simplex
operation.
John
La Sala, N2FWR, writes from Floral Park NY with a few concerns:
Q.
"Regarding the RCA plug, can I substitute it for an SO 239 connector so I
can feed it with a PL-259 connector? I am worried once the antenna is erected
the (RCA) plug will disconnect from the antenna.”
A.
There's nothing critical about the connector. You can use any size or style
that you'd like. I wrapped the RCA phono plug/feedline connection with
electrical tape at KI6SN. It has held together just fine.
Q.
'Do I need an antenna tuner? What is the SWR at 146.520 MHz?"
A.
I've used this antenna at KI6SN in the 145, 146 and 147 MHz portions of 2
Meters with great success. SWR measurements haven't been taken here, but I'd
welcome any reader's finding. An antenna tuner wouldn't hurt, but at KI6SN it
hasn't been necessary.
Q.
"Being a boater, if this works I will make (versions) for the marine band.
Do you have specifications? It would be appreciated."
A.
W4RNL's web site (www.cebik.com) posts formulas for calculating J poles for any
frequency.
Bill
Ross, K6MGO. writes from Marina Del Rey, CA that the construction hints in
September's column say "to measure down from the RCA jack 2 inches, strip
1/2 inch of insulation that will he twisted together and soldered.
"As
far is I can see. the shorted bottom of the antenna will now be 1 1/2 inch from
the jack, not 2 inches, or am I missing something? And what does this do to the
other dimensions referenced to the bottom?"
The
goal for MGO and any other builder; is to achieve the ELECTRICAL length of 56.5
inches for the total antenna. And the stub at the base of the antenna needs to
be an ELECTRICAL length of 2-inches as measured from the solder points at the
RCA plug down to the precise point where the shorted twinlead wires meet at the
Base.
But
Bill makes an excellent point If, in your construction, you'd feel more
comfortable adding a bit more fudge room to the stub dimension, by all means do
so. For example, cut it 2.5 inches below the RCA jack connection and that'll
give you an extra half-inch to play with. Just remember, when all is said and
done, the stub needs to be two inches from the solder point of the twisted base
wires to the point at which it's soldered to the RCA jack feed point.
When
cutting the twinlead during construction, always keep in mind that you're
trying to land on the exact ELECTRICAL lengths described in September’s column.
Richard
Fisher, KI6SN, can be reached by sending snail mail to. 1940 Wetherly Dr.
Riverside CA 92506; or by sending e-mail to: [email protected].
This article is reprinted from the October 2002 issue of Worldradio
GRUMMAN AMATEUR RADIO CLUB MINUTES OF GENERAL MEETING – 10/16/02 By Pete, N2PYV |
The
meeting was called to order by Pat at 5:42 PM. All present introduced
themselves.
Finances
continue to be in good shape.
REPEATER REPORT –
Gordon, KB2UB
Gordon
reported that he has ordered a new Hamtronics Repeater for the Bethpage site at
Plant 14. He gave the factory all the necessary parameters so that the repeater
should be a plug-in when received. The cost was $1,638.00.
NET REPORT –
Zak, WB2PUE
The
Wednesday 20-Meter Net was good this week. The Sunday 40-Meter Net was also
good.
VE REPORT –
Bob, W2ILP
There
were four applicants. Three were new hams who passed the Tech. Exam. One passed
the update to General.
WAG REPORT –
Bob, W2FPF
No
Activity
Bob,
W2ILP, gave an interesting lecture and demonstration about RTTY received and
transmitted using a computer connected to a HF transceiver.