T2FD results (58 ft)

[syfr]

Thanks to Chris, I built a 58 ft T2FD and got it hung in the back yard in test.   The high end is up at about 48 ft  with the antenna sloping at about 25 degrees with the low end up about 5 ft.  The antenna is at the end of about 175 ft of 52 ohm coax heading to my Kiwis though a homebrew active splitter.  I used a 900 ohm resistor and there's currently no balun.

Chris and I are only 120 miles apart or so, and it's interesting to compare results in our installations. While I'm super impressed with Chris's 120 ft T2, I'm not sure I could actually get that installed by myself.

My reference antenna (one that I left hooked up all the time to the Kiwis) was a trap dipole in the attic (30' up) that was only so so, and prone to lots of noise being emitted by all the junk in the house. 

There's some "industrialization" that needs to happen to keep this thing in the air, but I'm impressed so far.  S/N is MUCH improved over the noisy attic antenna.  I'm looking forward to the nighttime results on 40M as my benchmark.

Thanks to Chris for the inspiration.

[RobRich]

Nice. :)

Note without a balun your coax is technically a transformer due to the substantial mismatch. If you want a quick fix until buying or building a proper balun, even a cheap 4:1 television transformer probably would help.

[syfr]

I have one of Chris's baluns, but forgot to install it when I hoisted up the antenna.   :-)

It's just a temporary rig as it is.  I wonder if there'll be a noticeable diff with the balun?

[ChrisSmolinski]

Besides a better impedance match, the transformer will help stop the coax shield from acting like part of the antenna.

[syfr]

Thanks Chris.  The impedance transformation makes for higher efficiency power transfer, so I get that.   When I replace the "haul line"  I'll put the balun in place and see what happens.  I suppose that the impedance of the antenna as it varies over frequency is swamped by the 900 ohm resistor and I should choose a squid tap close to that?

I'm hoping I stayed clear of the poison ivy patch I discovered back there.  After getting the antenna up I went full Agent Orange on that area.

[ChrisSmolinski]

Thanks Chris.  The impedance transformation makes for higher efficiency power transfer, so I get that.   When I replace the "haul line"  I'll put the balun in place and see what happens.  I suppose that the impedance of the antenna as it varies over frequency is swamped by the 900 ohm resistor and I should choose a squid tap close to that?

Yes, that's an excellent starting point. If you have a VNA, you can look at the impedance or even SWR plot, and change taps for the best/flattest response. Since this is a a receive only antenna, it's not super critical to get a perfect match, I think both of my T2FDs are generally 2:1 or less.  The termination resistor is part of the equation as well, and affects the SWR.

I'm hoping I stayed clear of the poison ivy patch I discovered back there.  After getting the antenna up I went full Agent Orange on that area.

Yeah, terrible stuff. I've cleared out the big patches of it and am in continuous mode now of looking for any new growth and killing it. Just got a few small plants yesterday. I use a bush axe to cut them at the roots, and keep the blade super sharp, just sharpened it the other day.  Let's me keep a safe distance from the leaves 

I discovered a video a while back about how to clean up after possible exposure to poison ivy (the guy used to work in the forests). He showed a great example, he put axle grease on his hands then tried to clean it off with just soap and water. Of course his hands were still black with grease...

He said what you need is lots of friction to get the poison ivy oil off your skin, along with the soap. So use a washcloth, and a really good soap - I use dish detergent. Scrub Scrub Scrub. I've been following his protocol and so far all has been good.

[syfr]

Later that week....


I discovered that I had neglected to connect the terminating resistor! 

Down came the antenna and it's back up again with the termination .  I'm quite pleased with the antenna, though I'm getting slammed by interference from a local (1- 2 miles away) AM station on 1090 which creates mixing products across the spectrum . Even with that, the T2 is quite good.   I'll look forward to writing it out tonight.  I don't have a suitable enclosure for the balun yet, so there's a pretty big mismatch at the feedpoint still.

It's kind of interesting to connect to Chris's Kiwi with the 58 ft T2 and mine , and tune to the same station. There's a very noticeable diversity receiver effect as we're about 120-140 miles apart I'd guess.   If you offset the tuning (on CW especially) by 100 hz or so the effect is really cool.

Feel free to try :   mykiwisdr.hopto.org:8073 or 8074.       It'll be gone during thunderstorms but generally back on ASAP. 

[RobRich]

You had a linear-loaded dipole probably resonant somewhere around 5-6MHz.

Given the 58' footprint your T2FD should start rolling off well above MW. The balun might even help with the MW station, as like Chris noted, your coax - especially at 175' and even more so if unburied - is acting as part of the antenna right now due to a lack of common mode isolation.

You might want to wind some coax on a mix 31 or 43 ferrite as a choke closer to the the receiver end, too.

http://www.karinya.net/g3txq/chokes/

[syfr]

Thanks! I'll give that a try. Probably half of that coax is underground...say 75' or so. It's more than I'll use in its permanent installation, which will probably shave 50' off the total.

[syfr]

I took the T2FD down and installed a 450 foot loop.  So far, the loop is the clear winner, performance wise. I purchased screw in insulators and spent about 6 hours going up and down ladders installing the lag bolts into trees at the 20-30 foot level (and chopping branches, removing small trees, etc etc).

It's a remarkable improvement . Need to play with the balun to determine best taps for it. Any suggestions?

[Ray Lalleu]

Probably any antenna that far from the house, with a buried coax line,
would give better results than an attic antenna.

With a MW station so close, the best bet is to put up an antenna designed for horizontal polarization only. Beware, an horizontal dipole pick up some vertical polarization, mainly by the ends, also from the coax is there is no balun.

Even without a MW TX neighbor, a good design with an horizontal dipole is to use a bifilar line along the central pole down to the ground level or so, then use a balun to connect the buried coax. The down line would be part of the tuned antenna, so this would be a shortened dipole folded by the middle, with balun at the low end of the folding. Can be made with long bamboo poles, or with fishing rods.

[syfr]

Yes, you're right, no question re: attic antenna improvement. Homes are full of RF noise generators.

The local 1090 is a real problem that may never be resolvable, as it's just too strong and too close. Being medium wave makes the geometry of solutions difficult (quarter wave stubs, etc). I had the T2 mostly vertical, which really exacerbated the coupling of the AM  RF.

I'll try and get a look at the antenna with the VNA and see what it looks like, though life is pretty busy right now. 

I have a 40M dipole (an element of a 4 element yagi) at 45' and I can see the dramatic difference in the BCB coupling when I select that antenna, but it's a pretty poor general purpose SWL antenna, which is what I hope to use the loop for.  It's great for pirates at 39M though :-)

[ChrisSmolinski]

The local 1090 is a real problem that may never be resolvable, as it's just too strong and too close. Being medium wave makes the geometry of solutions difficult (quarter wave stubs, etc). I had the T2 mostly vertical, which really exacerbated the coupling of the AM  RF.

Have you tried an LC notch filter on 1090? Just knocking it down a few tens of dB or so may help immensely.

[ChrisSmolinski]

I took the T2FD down and installed a 450 foot loop.  So far, the loop is the clear winner, performance wise. I purchased screw in insulators and spent about 6 hours going up and down ladders installing the lag bolts into trees at the 20-30 foot level (and chopping branches, removing small trees, etc etc).

It's a remarkable improvement . Need to play with the balun to determine best taps for it. Any suggestions?

I use a 4:1 (I think? It's beed a while) balun feeding 75 ohm RG-6 on my 900 ft sky loop. I can load it up on 160-40 meters with a tuner for ham use, above that things are not happy For receiving though it's fine throughout all of HF.

[syfr]

Chris, it was your SkyLoop performance that got me interested in trying one. This is the first loop antenna I've ever used, and so far so good. It's not as high up as yours but the noise floor is SO low, that it's a pleasure to listen to.

Now I'm going to work at lowering the noise floor.  This will involve moving a computer out to a shed, etc, but it should be an additional improvement.