T2FD antenna
Tero Ranta
Hi,
I¨m planning to build T2FD antenna (terminate folded dipole) for whole
HF spectrum (150kHz-30MHz). I would appreciate if you could give me
some dimensioning information.
Thanks in advance,
Tero Ranta.
S
In <333e84b1...@news.ttl.fi> tero....@icenet.fi (Tero Ranta)
writes:
I¨m planning to build T2FD antenna (terminate folded dipole) for whole
>HF spectrum (150kHz-30MHz). I would appreciate if you could give me
>some dimensioning information.
Great idea, great antenna...
T2FD antenna only covers ~5:1 freq range well, and maybe 6:1 with
reduced performance, so could design for ~6-30 MHz with some
performance down to ~3 MHz or perhaps 4-21 MHz with some down to ~2
MHz. On the high freq end, pattern gets too directional, on the low
freq end, antenna begins to look more and more like a resistor.
See Radio Nederland WWW site for dimensions/construction details, but
the short story is that the total sloper length in m is 100/fmin in MHz
so a 6-30 model is ~17m long, and the spacing is ~3/fmin in MHz, so the
6-30 model is ~50 cm wide. I like to use black plastic sewer pipe for
spreaders and center block strain relief/load covers. It is
inexpensive, lightweight, easy to work with and readily available in
the US. Some sources (~10yr old WRTH articles +?) also specify that
large diameter wire must be used, but the effective diameter of the
wire is modified by the spreader spacing, so I think that any diameter
of stranded Cu or Cu clad wire that is strong enough to hold up the
weight of the antenna is OK. Termination should be a non-inductive
resistor with at least 1/3 the rated power dissipation of the signal
applied if used for TX. (assumes <100 % duty cycle and/
or amplitude modulation) Practical feedpoint nominal impedances are
from ~300 to ~600 ohms. The terminating resistor should be slightly
higher than the feedpoint impedance, especially for lower feed
impedances. Guy Atkins recommends:
feedpoint termination
300 390
450 470
600 600
You can use a T2FD at lower than T2FD fmin design frequency as a
Marconi antenna by connecting both feeder wires in parallel and feeding
those wires off of ground and/or a counterpoise wire that is ~1/4
wavelength long along the ground. It isn't very efficient, and the S/N
advantages of the T2FD design are lost, but it is better than feeding a
T2FD that is too short direct to a balanced RX input or balun
transformer.
Note that T2FD performance is so broadband that the bandwidth of the
balun may be limiting factor if the wrong balun is used.
Note also that good VSWR is not an indication of good efficiency. For
instance my 450 ohm antenna is cut for 7 MHz fmin, terminated with 470
ohms and fed through 450 ohm balanced line to a 9:1 balun with useful
balun bandwidth ~1-50 MHz. The T2FD VSWR in 50 ohms as seen through
the balun remains generally low over ~1-50 MHz, but the antenna is very
inefficient below ~3.5 MHz. It looks more like a 9:1 balun with a ed
450 ohm transmission line to a 470 ohm load than an antenna at 1 MHz.
Between 1-50 MHz VSWR is generally below 3:1 at maxima, except for
several sharp resonances above ~13 MHz that I attribute to coupling to
nearby resonant metal objects.
S
Dave Gorz
In article <333e84b1...@news.ttl.fi>, tero....@icenet.fi (Tero Ranta)
writes:
> Hi,
> I¨m planning to build T2FD antenna (terminate folded dipole) for whole
> HF spectrum (150kHz-30MHz). I would appreciate if you could give me
> some dimensioning information.
>
>
>
> Tero Ranta.
Here's a description of one submitted by our man in Havana, Arnie Coro.
Sorry about it being in all capital letters, but that's the way it was
submitted.
Dave
EASY TO FOLLOW INSTRUCTIONS FOR BUILDING YOUR OWN BROADBAND
SHORTWAVE RECEIVING ANTENNA
"THE TILTED TERMINATED FOLDED DIPOLE, TTFD OR T2FD"
BY ARNIE CORO
RADIO AMATEUR CO2KK
HOST OF RADIO HAVANA CUBA'S " DXERS UNLIMITED "
RADIO HOBBY PROGRAM.
(THE INFORMATION IN THIS ARTICLE IS IN THE PUBLIC DOMAIN AND
MAY BE PASSED ALONG TO ANYONE WHO WANTS TO IMPROVE THEIR
SHORTWAVE RECEPTION )
PLEASE SEND YOUR COMMENTS TO: ARNIE CORO
DXERS UNLIMITED
RADIO HAVANA CUBA
PO BOX 6240
HAVANA CUBA
OR TO OUR E -MAIL ADDRESS: AC...@TINOTED.CU
INTRODUCTION: THE TILTED TERMINATED DIPOLE ANTENNA VERSION
FULLY TESTED HERE AT RADIO HAVANA CUBA HAS PROVEN TO BE THE
EASIEST BUILT , GENERAL PURPOSE , LOW NOISE ANTENNA OF THE
MANY THAT I HAVE TRIED FOR GENERAL SHORT WAVE RECEPTION..
THE ANTENNA IS BASICALLY A FOLDED DIPOLE OF ONE THIRD OF A
WAVELENGTH, OVERALL LENGTH, AT THE LOWEST FREQUENCY YOU WANT TO
LISTEN TO WITH MAXIMUM EFFICIENCY. THE ANTENNA WILL PERFORM
WITH LOWER EFFICIENCY AT FREQUENCIES LOWER THAN THE ABOVE, AND
WILL RETAIN ITS EXCELLENT LOW NOISE PICK-UP CHARACTERISTICS.
IF YOU ARE NOT FAMILIAR WITH SHORT WAVE ANTENNAS I RECOMMEND
YOU TAKE A LOOK AT AN ANTENNA HANDBOOOK OR AT THE RADIO
AMATEURS HANDBOOK ANTENNA SECTION SO THAT YOU CAN HAVE A CLEAR
PICTURE OF WHAT A *FOLDED DIPOLE * IS.
THE TTFD: TO CALCULATE THE LENGTH OF YOUR TTFD,IN METERS, USE THE
FOLLOWING :
FORMULA: 100 DIVIDED BY THE LOWEST FREQUENCY IN MEGAHERTZ.
HERE'S AN EXAMPLE: FOR GENERAL SHORT WAVE LISTENING,
A GOOD LOW FREQUENCY CUTOFF IS 7 MEGAHERTZ. SO 1OO/ 7 = 14.28 METERS.
FOR ALL PRACTICAL PURPOSES, YOUR ANTENNA LENGTH CAN BE 14.3 METERS.
NOW WE CALCULATE THE SEPARATION BETWEEN THE UPPER AND THE LOWER
PORTION OF THE FOLDED DIPOLE, USING THE FORMULA :
3 DIVIDED BY THE LOWEST AT WHICH WE WANT MAXIMUM EFFICIENCY
FREQUENCY IN MEGAHERTZ. FOR OUR 7 MEGAHERTZ EXAMPLE, IT'S SIMPLY
3/7= SEPARATION IN METERS. CALCULATING 3/7 = 0.42 METERS, WHICH
FOR ALL PRACTICAL PURPOSES IS 40 CENTIMETERS.
TO BUILD YOUR TTFD, YOU NEED COPPER WIRE. IT CAN
BE STANDARD ANTENNA WIRE NO.16 OR NO.14, OR YOU CAN USE
PVC COVERED HOUSEHOLD. TYPE WIRE, USED IN TYPICAL HOME ELECTRICAL
CIRCUITS. NO 14 OR NO. 16 PVC COVERED WIRE IS IDEAL FOR ANTENNAS
THAT ARE LESS THAN 30 METERS IN LENGTH.
THE TTFD IS A FOLDED DIPOLE, SO YOU MUST REALIZE THAT THE
TOP PORTION OF THE ANTENNA IS DIVIDED IN TWO BY AN
INSULATOR LOCATED EXACTLY AT THE MIDDLE OF THE TOP SECTION.
THAT INSULATOR IS BRIDGED BY A CARBON RESISTOR OF 390 OHMS
AND TWO WATT DISSIPATION, FOR AND ANTENNA THAT IS TO
BE USED ONLY FOR RECEIVING PURPOSES. THE 390-OHM CARBON
RESISTOR MUST BE CAREFULLY SOLDERED TO EACH SIDE OF THE ANTENNA
AND PROTECTED FROM THE WEATHER BY PLACING IT INSIDE A PIECE
OF PVC SPAGHETTI TUBING SEALED WITH EPOXY RESIN. OF COURSE
THAT YOU WILL NOT MAKE THE SMALL 390 OHM 2 WATT CARBON
RESISTOR HOLD BOTH WIRES TOGETHER, YOU MUST USE A HIGH QUALITY
ANTENNA INSULATOR TO HOLD THE TWO UPPER WIRES TOGETHER, AND THEN
BRIDGE THE INSULATOR WITH THE 390 OHM RESISTOR. MY ADVICE IS THAT
YOU PROTECT THE 390 OHM 2 WATT RESISTOR FROM THE EFFECTS OF THE
WEATHER INSIDE A SMALL SECTION OF PVC PLASTIC PIPE, SEAL THE ENDS
WITH SILICONE AND LET ONLY TWO FLEXIBLE LEADS COMING OUT OF THE
SECTION OF PVC TUBING. IF YOU CANNOT FIND A 390 OHM 2 WATT
CARBON RESISTOR, THEN YOU MAY USE A PAIR OF 680 OHM 1 WATT
OR 680 OHM 2 WATT RESISTORS CONNECTED IN PARARELL TO SUBSTITUTE
FOR THE 390 OHM RESISTOR. IF YOU ARE THINKING OF EVER USING THE
TTFD AS A TRANSMITTING ANTENNA, THEN THE TERMINATING RESISTOR
MUST BE MODIFIED ACCORDINGLY. MORE ABOUT USING THE TTFD FOR
TRANSMITTING LATER.
THE LOWER PORTION OF THE ANTENNA IS ALSO INTERRUPTED EXACTLY
AT ITS CENTER WITH AN INSULATOR. THE ANTENNA FEEDLINE CONNECTS
TO EACH SIDE OF THE INSULATOR. YOU MAY USE 3 TYPES
OF DOWNLEADS WITH THE TTFD. YOU MAY USE HEAVY DUTY 300 OHM
DUAL BALANCED TRANSMISSION LINE, WHICH MAY BE AVAILABLE AS
*LOW LOSS TV FOAM TWIN LEAD * OR YOU CAN USE A HOMEMADE
PARARELL FEEDLINE OF VERY LOW LOSS MADE FROM TWO 75 OHM
COAXIAL CABLES. THE OUTER SHEATH OR BRAID OF THE COAXIAL
CABLES IS JOINED TOGETHER RIGHT NEXT TO THE ANTENNA INSULATOR
AND THEN IT'S LEFT WITHOUT ANY CONNECTION. BUT PLEASE REMEMBER
TO SEAL IT FROM THE ADVERSE EFFECTS OF WEATHER USING SOME
KIND OF SILICONE CAULKING COMPOUND. THE CENTER OR INNER
CONDUCTORS OF THE COAXIAL CABLES ARE CONNECTED ONE TO EACH
SIDE OF THE ANTENNA. YOUR HOME-BREWED 150 OHM DUAL BALANCED
AND SHIELDED TRANSMISSION LINE IS TAKEN TO THE SHACK, WHERE
YOU CONNECT THE CENTER CONDUCTORS TO THE BALANCED INPUT OF
YOUR ANTENNA TUNER. THE OUTER SHEATS OR BRAIDS OF THE 2 CABLES
ARE ALSO JOINED TOGETHER AND SOLDERED, BUT HERE THEY ARE
CONNECTED TO YOUR RECEIVING SETUP GROUND CONNECTION.
THERE IS ANOTHER WAY TO FEED THE TTFD WITH JUST ONE SINGLE
75 OHM COAXIAL CABLE , AND THIS IS DONE BY CONNECTING
A 6-TO-1 BALANCED TO UNBALANCED ( BALUN ) TRANSFORMER
RIGHT AT THE ANTENNA TERMINALS. THE 6-TO-1 STEPDOWN BALUN
WILL PROVIDE A MATCH TO THE 450 OHM ANTENNA WHILE AT THE SAME
TIME PROVIDING A MATCH TO THE 75 OHM COAXIAL CABLE.
THE TTFD CONSTRUCTION INVOLVES THE USE OF AT LEAST SIX
FIBERGLASS OR PVC SPREADERS THAT KEEP THE UPPER AND LOWER
WIRES SEPARATED FROM EACH OTHER AT THE CALCULATED DISTANCE,
WHICH IN OUR EXAMPLE IS 40 CENTIMETERS. AT THE END SECTIONS
THE ANTENNA IS SUPPORTED USING HIGH QUALITY DACRON OR NYLON
FISHING LINES WHICH ACT AS VERY LONG INSULATORS.
THE TTFD ANTENNA MUST BE PLACED WITH ONE END AT THE TOP OF
THE MAST AND THE OTHER END AT A LOWER HEIGHT SO THAT THE
ANTENNA SLOPES AT AN ANGLE OF 30 TO 45 DEGREES, FROM
THE HORIZONTAL.
PLEASE NOTE THAT IT IS EASIER TO ASSEMBLE THE ANTENNA IF YOU
PREPARE THE WIRES FIRST BY CUTTING TWO IDENTICAL SECTIONS
WHICH FORM EACH SIDE, FROM THE TOP CENTER INSULATOR RIGHT
TO THE LOWER CENTER INSULATOR. IN OUR EXAMPLE, THE
LENGTH OF WIRE REQUIRED IS 14.6 METERS WHICH IS DISTRIBUTED
THE FOLLOWING WAY: 7.1 METERS FROM THE TOP CENTER INSULATOR
TO THE TOP END, 40 CENTIMETERS GOING DOWN, THEN 7.1 METERS
TO THE LOWER CENTER INSULATOR. IN PRACTICE YOU WOULD WANT
TO HAVE A LITTLE LEEWAY SO THAT YOU CAN WRAP THE ANTENNA
WIRE AROUND THE INSULATOR AT BOTH THE TOP AND LOWER SECTIONS.
PLEASE NOTE THAT YOU WILL NEED TWO IDENTICAL HALVES TO MAKE
YOUR ANTENNA.
THE FIBERGLASS INSULATORS OR SPREADERS THAT SEPARATE THE
UPPER AND LOWER WIRES ARE TIED USING NYLON FISHING LINE.
IF YOU WANT TO USE THE TTFD FOR AMATEUR BAND TRANSMITTING
PURPOSES YOU MUST REPLACE THE 390-OHM TWO-WATT CARBON RESISTOR
WITH A NON-INDUCTIVE RESISTOR OF 390 OHMS CAPABLE OF
DISSIPATING AT LEAST ONE FOURTH OF THE TRANSMITTER POWER
ON THE SSB MODE OR ONE THIRD OF THE TRANSMITTER POWER IN THE
CW OR RTTY MODE. THE RESISTOR CAN BE ASSEMBLED FROM A SERIES
PARALLEL COMBINATION OF TWO-WATT CARBON UNITS. FOR A TYPICAL
AMATEUR BAND 100-WATT TRANSCEIVER THE RESISTOR MUST BE
CAPABLE OF DISSIPATING ABOUT 36 WATTS.
SOME NOTES ABOUT THE TTFD: THE TTFD ANTENNA IS ESSENTIALLY
AN OMNIDIRECTIONAL RADIATOR. IT WILL PICK UP LESS NOISE THAN
A RANDOM WIRE, A DIPOLE OR A VERTICAL, OUTPERFORMING THE
TYPICAL WIRE ANTENNA ESPECIALLY IN NOISY DOWNTOWN LOCATIONS.
IF YOU HAVE ANY DOUBTS, PLEASE FELL FREE TO SEND THEM TO
ME VIA E-MAIL. I'LL DO MY BEST TO HELP YOU ENJOY BETTER
SHORTWAVE RECEPTION WITH THE TTFD.
WITH MY BEST 73 S
YOUR FRIEND IN HAVANA
ARNIE CORO CO-2-KK
P.S. AS A 6:1 BALUN IS NOT A STANDARD ITEM, AND MUST BE BUILT,
YOU MAY WANT TO USE A 4:1 BALUN TRANSFOMER, AN ITEM THAT MAY
BE BOUGHT OF THE SHELF FROM AMATEUR RADIO SUPPLY STORES.
SPECIFY A BALUN RATED FOR AT LEAST 250 WATTS POWER, AND WITH
A 4 TO 1 RATIO. THEY USUALLY COME IN A WELL SEALED BOX WITH
A FEMALE COAXIAL CONNECTOR FOR THE CABLE AND TWO WIRES FOR THE
BALANCED CONNECTION.
FEEDING THE TTFD WITH THE TWO 75 OHM COAXIAL CABLE BALANCED
SHIELDED TRANSMISSION LINE DESCRIBED ABOVE, IS SOMETHING THAT
YOU WONT FIND IN THE TECHNICAL LITERATURE , BUT THAT IS AN
EXCELLENT LOW COST SOLUTION, AS THE 75 OHM COAX OF GOOD
QUALITY IS MUCH CHEAPER THAN ANY OTHER TYPE OF ANTENNA DOWNLEAD
DUE TO MASSIVE PRODUCTION FOR TV CABLE DISTRIBUTION SYSTEMS
THAT KEEPS COSTS DOWN I.E. ECONOMIES OF SCALE !
IN CASE YOU USE THE TWO COAX CABLE BALANCED , SHIELDED TRANSMISSION
LINE, REMEMBER TO CONNECT THE SHIELDS OR BRAIDS TOGETHER AT THE
TWO ENDS OF THE LINE, AND THEN SEAL THEM AGAINST MOISTURE,
ESPECIALLY THE END OF THE LINE THAT IS EXPOSED TO THE WEAHTER.
THIS APPROACH REQUIRES THE USE OF A BALANCED ANTENNA TUNER,
OR AS AN ALTERNATIVE A LOW COST 4 TO 1 BALUN AT THE ANTENNA
TUNER INPUT. SOME ANTENNA TUNERS HAVE A BUILT-IN BALUN SO IN
THAT CASE YOU WONT NEED AN EXTERNAL UNIT.
GOOD LUCK BUILDING THE KK-11 VERSION OF THE TTFD !!
ARNIE
-----
--
Dave Gorz | Lightning flashes, sparks shower,
dg...@fs2.mar.lmco.com | In one blink of your eyes, you have missed seeing.
Steve
6:1 baluns are available from Amidon, (714) 850-4660. There rated for 1
kW and cost $70. Overkill for receiving. Build your own.
Dave Rickmers
On Tue, 01 Apr 1997 16:59:43 -0500, Steve <theb...@erols.com> wrote:
>6:1 baluns are available from Amidon, (714) 850-4660. There rated for 1
>kW and cost $70. Overkill for receiving. Build your own.
I can't believe you quoted all 198 lines in your reply...Palomar sells
a wide variety of baluns and ununs for $29.95. They are rated at 250W
PEP and epoxy encapsulated. See their ad in new MT for phone #.
dr
S
In <334532b6...@news.earthlink.net> ric...@earthlink.net (Dave
for 1
>>kW and cost $70. Overkill for receiving. Build your own.
>a wide variety of baluns and ununs for $29.95. They are rated at 250W
>PEP and epoxy encapsulated. See their ad in new MT for phone #.
Not only that, but what's with 6:1 balun anyway Ernie is a god guy,
but this sounds off base to me...for 390 ohm termination, feedpoint is
~300 ohms, feed w/ simpler 4:1 balun to 75 ohm (cheaper, lower loss)
coax and have 1.5:1 nominal VSWR mismatch to 50 ohm radio. Perfectly
acceptable for RX. Actual T2FD VSWR relative to 300 ohms at feedpoint
will vary over freq with maxima ~3:1 anyway, so if you need <= 1.5:1
VSWR for solid state TX, you will need tuner at radio anyhow. Baluns
built to integer squared impedance ratios are easier to build, cheaper
and more efficient.
300 ohms 4:1 to 75 ohms
450 9:1 50
600 9:1 75 is my advice.
Jim