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Author Topic: 120 ft T2FD Antenna Build  (Read 662 times)

Offline ChrisSmolinski

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120 ft T2FD Antenna Build
« on: November 27, 2019, 1454 UTC »
A few months ago I built a 58 ft T2FD antenna. Happy with the results, I decided to build a larger one, the largest I could reasonably fit with the available trees. I have an Oak tree at the top of a hill, and decided to locate it there. The top support rope is about 85 ft high in the Oak, measured from the base of the tree. The ground slope down the hill gives me some additional vertical distance, while still allowing for about a 45 degree slope with a 120 ft antenna length with the current installation. I may be able to get the top end of the antenna a few feet higher, and bring the bottom end closer to the tree, for a steeper angle.

Below are my built notes. I'll start out by saying that a 120 ft T2FD was not twice as hard to build and erect as a 58 ft T2FD. It was probably ten times as much work  :)

The wire is 16 AWG stranded hookup wire, from a 500 ft spool I bought on eBay. I prefer using this type of wire now over traditional bare stranded antenna wire, it's much easier to work with and does not kink. It's probably not as strong, of course.

A reminder about the T2FD antenna layout, courtesy of this diagram from G4RAA:



Each side of my T2FD is 60 ft long. Each end was assembled on my driveway, then transported separately to the installation site. By transported I mean bundled up, carried over, and then untangled. The top end was hoisted up part way first, then the center pipe was attached to that, then the other end was attached. Then the rest of the antenna was hoisted up, while trying to keep it oriented correctly and not getting tangled in nearby branches. 

The center and end supports of the T2FD are made with 1" diameter schedule 40 PVC pipe. The spacers are made with 1/2" diameter PVC, for less weight, and are spaced every 10 ft. I got more 1/2" pipe than needed, as it was less expensive per piece to get ten of them, I'll use the extra pieces eventually for other projects. Or so I tell myself.




The 1/2" spaces cut to 5 ft lengths:



I drilled holes about 1" from the end of each piece of pipe for the wire to pass through. The holes are barely large enough for the wire. So the wire spacing is about 58 inches.



I then wrapped some duct tape around the wires on each end of each spacer, to help hold them in place, so they don't slide around:



On each end pipe, the wire is taped in place with duct tape:



The center pipe, again with duct tape on the wire to help hold it in place, it also passes through two small holes in the pipe and there is a knot as well:



Also visible is the 12:1 Cyclops Antenna Transformer which allows for a good match from the 900 ohm antenna impedance to 75 ohm RG-6 coax cable: https://www.blackcatsystems.com/rf-products/cyclops_rf_ham_shortwave_radio_matching_transformer.html

A Jellyfish matching transformer would work equally as well: https://www.blackcatsystems.com/rf-products/potted_matching-transformer-unun-balun-beverage-longwire-k9ay-flag-ewe-dipole-antenna-shortwave-ham-radio.html

The connections have wire nuts and then tape over them for moisture protection.

At the top end of the center space pipe is the 850 ohm termination resistor, also potted in resin like the transformer:



The coax cable attached. This coax happens to have a separate wire as part of the cable (probably to supply power in security camera applications). I don't use it electrically, but it does serve as an additional mechanical support. Hey, I got a good deal on a 1,000 ft spool of the cable at a hamfest.

A view looking up from the bottom end of the installed T2FD:



Rather than a complicated Vee made of rope at each end of the antenna, there is a single hole in the center of the PVC pipe, just large enough to pass the rope, which then has a very large knot on the opposite end, to hold it in place:



Top end of the T2FD:




An SWR plot courtesy of my Rig Expert Zero. The red plot is this T2FD, the green plot is the 58 ft T2FD. As expected the shorter T2FD has a flat SWR to about twice the frequency, although SWR is not everything:




I just finished installed it before sunset last night, so today is my first real use of it. It will take a while to determine how well it is working, I'll update the thread with some additional posts over time.
« Last Edit: November 27, 2019, 1645 UTC by ChrisSmolinski »
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 120 ft T2FD/ 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline Josh

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Re: 120 ft T2FD Antenna Build
« Reply #1 on: November 27, 2019, 2347 UTC »
From  the looks of the plot I imagine signal strength is going to be about the only diff.
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Offline Beerus Maximus

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Re: 120 ft T2FD Antenna Build
« Reply #2 on: February 02, 2020, 1806 UTC »
Chris, two questions -

- What resistor specifically did you use (wattage, etc).
- Any articles or hints on potting that you find informative? I've never done it and know nothing about how to do it.
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Offline ChrisSmolinski

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Re: 120 ft T2FD Antenna Build
« Reply #3 on: February 02, 2020, 1845 UTC »
Chris, two questions -

- What resistor specifically did you use (wattage, etc).

I used about ten 1/4 watt resistors in parallel, figuring that would help reduce the overall inductance, and provide a few watts of effective power dissipation to handle any large transients.

Quote
- Any articles or hints on potting that you find informative? I've never done it and know nothing about how to do it.

Trial and error :) 

The potting resin I buy has instructions on it that are pretty good, basically get your ducks in a row so you can work efficiently. The stuff takes hours to harden so you do not have to rush. I found silicone baking moulds work great.

I was considering selling a potted transformer and resistor pair if there is ay interest.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 120 ft T2FD/ 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline skeezix

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Re: 120 ft T2FD Antenna Build
« Reply #4 on: March 22, 2020, 2246 UTC »
I'm thinking about making one of these (as well as a cage dipole) and use it for tx/rx on the amateur bands, as well as general coverage rx.

In the the time that yours has been up, how has it worked for you and do you use it for tx?

How does the 120' T2FD perform compared too the 58'?

From what I've been able to find about this antenna: pick some convenient length, figure out the resistor by trial & error, and the wire spacing has some formula (which I don't have handy as I type this).  You found an impedance of 900 ohms, does that vary by length (and/or other factors)?

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Offline NJQA

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Re: 120 ft T2FD Antenna Build
« Reply #5 on: March 23, 2020, 1335 UTC »
The March/April 2020 issue of QEX has part 1 of an article on Broadband HF Antenna designs.  In the article they note that for a 30 foot long T2FD antenna, with 100 watts input to the antenna, 74 watts is lost in the resistor at 14 MHz, and 70 watts is lost at 29.7 MHz.

Unless a flat SWR over a very large bandwidth is of importance to you (e.g. ALE scanning), the T2FD would not be my first choice for a transmitting antenna.
« Last Edit: March 23, 2020, 1347 UTC by NJQA »

Offline skeezix

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Re: 120 ft T2FD Antenna Build
« Reply #6 on: March 23, 2020, 1355 UTC »
Thanks for the info... that's very interesting and a lot of power wasted.
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Offline Teotwaki

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Re: 120 ft T2FD Antenna Build
« Reply #7 on: March 23, 2020, 1429 UTC »
A few months ago I built a 58 ft T2FD antenna. Happy with the results, I decided to build a larger one, the largest I could reasonably fit with the available trees......................

Very cool! Thanks for all of the pictures!
Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline ChrisSmolinski

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Re: 120 ft T2FD Antenna Build
« Reply #8 on: March 23, 2020, 1636 UTC »
Yes, the T2FD is for reception only, not for transmitting. But it works pretty well. In fact I now have it connected to my KiwiSDR, if you want to give a listen: http://sdr.hfunderpants.com:8073/

It's better on the lower frequencies as expected, although it seems to work ok at least up to 12 MHz or so. I have not compared it against the 58 ft T2FD on 11m yet - the shorter one is excellent there.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 120 ft T2FD/ 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline Teotwaki

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Re: 120 ft T2FD Antenna Build
« Reply #9 on: March 24, 2020, 0407 UTC »
Yes, the T2FD is for reception only, not for transmitting. But it works pretty well. In fact I now have it connected to my KiwiSDR, if you want to give a listen: http://sdr.hfunderpants.com:8073/

It's better on the lower frequencies as expected, although it seems to work ok at least up to 12 MHz or so. I have not compared it against the 58 ft T2FD on 11m yet - the shorter one is excellent there.

Thanks for sharing access to it. I can hear Windy right now.   ;D
Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline ChrisSmolinski

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Re: 120 ft T2FD Antenna Build
« Reply #10 on: March 24, 2020, 1046 UTC »
Thanks for sharing access to it. I can hear Windy right now.   ;D

That's great, thanks for letting me know. Actually one of my motivations for installing it was better reception on the 4 MHz beacon band.  :)

In fact I just tuned in now (1046 UTC) and heard weak telemetry. Still no sign of A on 2097 unfortunately.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 120 ft T2FD/ 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop / Discone in a tree