The original T2FD design

[KM1H]

Ive had requests to show the 3 magazine articles mentioned in the Cage Dipole thread so here goes. They are not perfect and if someone has a jpeg editing programent go for it.
The articles are in QST June 1949,  CQ November 1951,  and CQ February 1953.

Note the dimensional difference compared to what passes as a commercial T2FD these days as well as other critical points.
Also review the signal reports while understanding that S meters back then were not very accurate; OTOH the human ear can tell about a 1 to 1.5dB difference.

Here is the QST one

Carl

[KM1H]

November 1951 Pages 1, 2

[KM1H]

November 1951 pages 3 and 4.

[KM1H]

Feburary 1953 all 3 pages.

Once the weather improves I intend to build a pair for transmitting, one for 40-10M, another for 80M to whever it tops out. Maybe modify to cover 160 at a later time. The 90' one Ive been using all along for general coverage receiving has been a pleasant surprise.

Since I dont have any high power 600 Ohm real non inductive resistors it will either be with what I can find at hamfests/Fleabay or prchase from someone on here. I do have 450 Ohm 750W Carborundums to swap for like; these are unused from Gulf War 1 antennas.

For those with modeling programs: After a good evaluation I may string the 40M one off a section of guywire cut for 40M and see if the Close Coupled Antenna approach works, maybe 1-2" spacing. It might be a way to boost the low end efficiency.

Constructive comments welcome     

[KC2ZFA]

you can use your 450 ohm beasts with a 450 ohm feeder (per the third article) ! If you want to sell me one please let me know.

Peter

[ke7trp]

I wanted to try one of those antennas a few years back but the old kodgers told me the problem was that a huge part of the transmitter power is gobbled up by the resistor. 

C

[Steve - K4HX]

Thanks for posting Carl.

If the resistor is involved, why would the dimensions be so critical?

[W2PFY]

Thanks Carl, I copied your pages and printed them. There's also a lot of stuff via Google on these antennas. I have a large TMC resistor mounted in a box that was for terminating a rhombic antenna. It says on the tag that it is 600 ohms at 1800 watts but it measures 800 ohms? I have also seen terminating resistors for high power rhombic antennas constructed with nichrome wire. These were straight pieces of nichrome several feet long as I recall. Would there be a way to use such wire in the T2FD antennas?

[Steve - K4HX]

Did some modeling over average ground. Using the dimensions in the first article the T2FD was down 4 dB compared to a similarly dimensioned single wire dipole at 7 MHz. The T2FD was down 10 dB at 3.5 MHz.

The single wire sloping dipole was down about 4-6 dB compared to a flat top dipole.

Seems the sloping results in more loss.

So I modeled the T2FD as a flat top and compared to a flat top dipole. The T2FD was 3 dB down at 7 MHz and about 10 dB at 3.5 MHz.

The flat top results are almost exactly what I say with the B&W unit at 1.8 and 3.5 MHz. The B&W is twice the length of the T2FD in the first article.

Looks like the SWR curve is better with a 900 Ohm resistor. With a 16:1 balun, the SWR is less than 2:1 over the 3-15 MHz ranges, except for the 6-8 MHz range. See the attached PNG. I think you could juggle the length and maybe the spacing to get the low SWR parts of the curve to fall in the 7 MHz range.

The efficiency never gets over 40 percent.

f                     % Eff

3                     4.5
4                     13.9
5                     27.2
6                     36.3
7                     38.6
8                     36.9
9                     33.5
10                    30.6
11                    26.1
12                    22.5
13                    20.9
14                    24.3
15                    32.6

[ke7trp]

Thats about in line with what I was told. It works on all bands but... Its way down from a simple dipole.

C

[Opcom]

November 1951 Pages 1, 2

These antennas remind me of the B&W all band folded dipole, still sold today. 80FT long and a 600 or 900 Ohm load.

A bonus of showing that article is that C&H Sales co. as advertised in the 2nd page of the 2nd article is still in business in Duarte, moved from Pasadena. Sorry i love the old ads, and could afford none of it as a kid.

[W2PFY]

RATS, No free lunch

[VE3LYX]

I would try one before giving it a yes or no. "Experts" rarely have any actual experience. And sometimes an antenna that is so so in one QTH can be wonderful in another. Modeling is a wonderful tool but is only as good as its input. If the "inputter" (progam designer)  has no T2FD actual testing or experience then the results are meaningless no matter how much we would like to think otherwise.
Or as my P Eng Dad (Collins, GE and PYE) always said to me when I prejudged something like this. "One thing is for sure! If you don't try it, it won't work."
Don VE3LYX

[KB2WIG]

"
"One thing is for sure! If you don't try it, it won't work."
                                                                              "

The Wayne Gretzky school of enginering. --  "You miss 100% of the shots you don't take."


klc

[ke7trp]

Thats a really good point Don.

C

[K1JJ]

f                     % Eff

3                     4.5
4                     13.9

Whether we believe the pattern modeling or not, the modeling program should be reasonably accurate about antenna efficiency, since we are dealing with established physics formulas.  For a ham, it's quite a disadvantage to start with an antenna that is only about 10% efficient on 80M...  This is about equivalent to a good mobile whip installation on 80M.  I have measured my mobile to be down about 12-15dB from a standard full size dipole.

I think the utility of this design is perhaps for a military field operation. They could care less about being strapping. They just want to communicate and cover all freqs without tuning and hassles -  and is easy to put up and take down.


T

[Steve - K4HX]

Or the ancient Roman school of engineering - shoot the messenger. Then again, just blindly trying something in the hopes of finding something that will work could hardly be considered engineering or even logical.

The antenna was modeled using the exact dimensions from the article and compared to a standard half-wave dipole. What conditions could be changed that would make up for as much as a 10 dB difference?

There is no doubt that better results may be obtained at one location versus another with a T2FD. Those locational differences would likely make any antenna better at the better location. Thus, the dipole would still be better than the T2FD at the better location.

It's interesting how modeling gets pooh-pooed when it doesn't yield the preconceived answers.

Finally, nowhere in my post did I state, "Do not try it."

"
"One thing is for sure! If you don't try it, it won't work."
                                                                              "

The Wayne Gretzky school of enginering. --  "You miss 100% of the shots you don't take."


klc

[W3RSW]

The antenna was cut for 40 meters if I read it right, not 80, so looks like the model using digital derivatives of mesh and node theory at discrete intervals is doing its job well.  80 meters ought to be and is well down.

How's that for a mouthful of almost accurate sounding theory ?

I find modern antenna modeling programs to be fascinating and more accurate, taking in more variables partially related to each other than our poor minds and simplified algorithm "slide rules" can grasp.

Also in a more recent QST article I seem to remember that the center resistor ought to be more like 90 percent of power inputted, not 25.

[KM1H]

A model is only as good as the ability of the inputter to follow the design specs. I dont believe that EZNEC has an optimizer for efficiency?

I find it hard to dismiss the published results of the various military and commercial users back then without at least building one. Im sure their existing dipoles werent made of stainless steel wire as is the B$W military excuse. The standard USN wire aboard ship anyway was phosphor bronze of about 3/8" thick.

In going thru some more junk earlier I came across a Globar CX 600 Ohm 250W (rated in oil) or 50W CCS in air. That wll be a lot easier to experiment with and the article claims a bit over 600 is the best efficiency. Altho I detest open wire line I have almost a 1000' roll of #16 enameled copper and plenty of ceramic insulators Ive picked up over the decades.

Antenna weather has arrived and I have some PM and repairs to do first.

I want to compare between a true balanced tuner and a balun which I suspect causes problems.

Im also going to start at some length well below the lowest TX frequency. That means about 55' per leg for 3 KHz and 3.28' spacing, not the 17" of the B$W and others.

[Steve - K4HX]

One does not need a modeling program to know that placing the end of a dipole only 5 feet off the ground will results in losses, especially at the lower frequencies.

One does not need a modeling program to know that a sloping dipole does not yield an omnidirectional pattern, especially at the higher frequencies.

I saw no specific information on the results the Navy obtained on these antennas in the articles. The one specific given was that the antenna was completely vertical and a ground screen was used. That is a much different configuration than sloping over lossy ground. It would be informative to see the Navy reports. Can you post these?

It's interesting how modeling gets pooh-pooed when it doesn't yield the preconceived answers.

[Steve - K4HX]

An interesting analysis here.

http://myweb.tiscali.co.uk/g8hqp/radio/termdipole.pdf

[Opcom]

Since I dont have any high power 600 Ohm real non inductive resistors it will either be with what I can find at hamfests/Fleabay or prchase from someone on here. I do have 450 Ohm 750W Carborundums to swap for like; these are unused from Gulf War 1 antennas.

I have a big box of NI res.. carborundms or equivalent. If there is a 600 of 300+ watts in there I'll PM.

[KG4DAG]

One of the better evaluations I've seen on the terminated folded dipole is  by Cebick W4RNL
here: http://pe2bz.philpem.me.uk/Comm/-%20Antenna/Info-907-AntennaBasics-Advise/ModelingTheT2FD/t2fd.html

I made one with a 820 Ohm terminating resistor as a receive antenna and it seems to do the
job as a lower noise wide band receive antenna. For a transmitting antenna, I have my doubts.


( FWIW, I'm rebuilding an FT-102 and sooner or later I will be on the air on AM with it!)

[KM1H]

One does not need a modeling program to know that placing the end of a dipole only 5 feet off the ground will results in losses, especially at the lower frequencies.

** Yet a sloper is a favorite with DXers and contesters with limited real estate. I came in a very close second place in an ARRL CW DX Contest 80M only entry one year using 3 slopers with the ends about 4' above ground. The #1 was using a 4 square in a former farm field full of black earth and about 15 miles away.

Several years later I blew away a huge 160M pileup with one call for an Antarctic area island DXCC country that had never been activated on 160 before. The op made a point at Dayton of stating I was at least 10dB above the din. The antenna was an inverted vee with the apex at 50' and ends at about 2-3'.


One does not need a modeling program to know that a sloping dipole does not yield an omnidirectional pattern, especially at the higher frequencies.

** Yet an 80M sloper does yield a close approximation of exactly that similar to an inverted vee also with th ends close to earth. At higher harmonics all antennas have differing patterns.

I saw no specific information on the results the Navy obtained on these antennas in the articles. The one specific given was that the antenna was completely vertical and a ground screen was used. That is a much different configuration than sloping over lossy ground. It would be informative to see the Navy reports. Can you post these?

** I guess you didnt get past the first article. In 1949 or so specifics were based upon actual experiments and not a keyboard.

It's interesting how modeling gets pooh-pooed when it doesn't yield the preconceived answers.

** Any engineer worth the name doesnt depend upon the PC to have the last word. The ones who do nothing but clog up forums and create web sites with never having built and tested their design are close to useless to the non engineering ham wishing to duplicate.
To give Cebik due credit, he did a fine CYA with his T2FD article even though he didnt come close to modeling the original or try to optimize for the lower ham bands at least. I read that article years ago and my opinion hasnt changed with a reread.

I never said the T2FD was a superior antenna. My purpose for this thread is to try and get a few off their butts and build one and then report results as compared to a test antenna. Also report receiving results. Follow the article formulas first and then try to optimize for 160-40 or 80-20 depending upon height available. Remember that technology was a lot different in 1949 when cut and try was the rule. Today we appear to know more but do less in the way of hands on but talk a lot more with our fingers.

What I build on a hilltop rock pile will likely perform different than those with other local conditions.  Common sense says that, but the stupid models dont know better with the consumer software available.

Carl

[W2VW]

Hey Carl did you play cowbell for the Beatles too?