HFU HF Underground
Technical Topics => Equipment => Topic started by: ChrisSmolinski on July 26, 2019, 1913 UTC
-
I previously had a 132 ft long T2FD antenna circa 2008-2015 or so, that was eventually destroyed in a storm. It was a reasonably good performing antenna, and I've wanted to put another back up, which I just did this morning.
The new antenna is shorter, it is about 58 ft long, I made it with the wire from an 80 mb dipole that I was never really happy with, because it was fairly low, and the location wasn't great for getting it higher due to nearby trees. It's made with #16 insulated hookup wire, my antenna wire of choice lately. You can get 500 ft spools on eBay for about $30 shipped if you watch for deals.
The spacers are 20 inch long pieces of 1" PVC pipe, because I happened to have some of that length as leftovers from another project. Each has two small holes drilled near each end for the wire to pass through. The old T2FD used wooded spacers, which eventually broke. There are 5 of them one in the center (which also supports the balun), one on each end, and one in the middle of each span.
The balun is a 4:1 [EDIT: I think it is really a 9:1], actually the one from the old T2FD. I'd normally use one of my Jellyfish transformers but I am out of them right now and didn't want to make a new one and wait for the resin to harden ;D I think a slightly higher impedance ratio will be better, so it will be interesting to switch out the balun in a few days and see what the difference is. Coax feed is my usual 75 ohm RG-6 which goes from the balun down to a grounding block, underground in conduit, comes above ground with another grounding block, then up to the shack.
The terminating resistor is made from a pair of very old carbon composition resistors, 1 watt each, which are just over 900 ohms when used in parallel.
I did some research online as to the optimum tilt angle, as well as running some antenna models. It seems the best performance is from a nearly vertical orientation, not tilted at 45 degrees or so as many do. The old T2FD was actually not very far from nearly horizontal, as it was 132 ft long and I don't happen to have any redwoods in my yard. ;D
I shot a line over a tree last night with the EZ Hang (it went over perfectly first time, how often does that happen?). Based on the known length of the antenna and the measurements I was able to take at ground level, I could estimate that the top of the T2FD is about 59 ft high. The low end is 3 ft high and 15 ft horizontally from a vertical orientation. That works out to about a 15 degree tilt from vertical, oriented to the northeast.
Performance:
I'm surprised how well it works actually, given the size. It works even down to the MW band, I was able to hear 530 from Canada at 1700 UTC in the afternoon. And the 1620 pirate from about 10 miles away. Both with signal levels equal to the NE beverage antenna. And on the high end of HF, it's incredible on the 11m band. Much stronger signals than my other antennas. On the 49m band it picks up CFRX 6070 and WBCQ 6160 (the only signals there now) about the same as my 43/48m folded dipole antenna, perhaps 6160 is even a hair better. Difficult to tell with 6070 as the signal is so strong anyway. It will be more telling shortly when the European DX starts to roll in on 49 meters, and eventually pirates on 48 and 43 meters. I'll write a followup reply post with more performance information after using it for a while.
-
Nice work, thanks for reporting it. I was gonna say to test for the optimal load via a variable resistor but if it's that far up in the air it'll be fun tweaking the pot every time you want to run a test. I think the normal load is 600 or 400, where the balun you used would seem more practical, maybe you stumbled onto the secret combination.
-
SWR and impedance plots taken with the RigExpert here in the shack. I updated the first post to mention my use of 75 ohm RG6 coax.
(https://i.imgur.com/ZvZdq74.png)
(https://i.imgur.com/BRdDFOC.png)
-
Well I think you've found the sweet spot.
-
Well I think you've found the sweet spot.
Yeah at this point I am hesitant to change anything.
-
Do you have any ferrets on the feedline to decouple it from the antennae?
-
Do you have any ferrets on the feedline to decouple it from the antennae?
No, that's what the balun is for ;D
-
That's a pleasant thought.
-
Nice! I'm a big fan of the T2FD for a receiving antenna. I used the RF Systems version a number of years ago, very, very low noise even in a suburban location with a wide coverage range, as you pointed out. I'd try building one myself but I still have two brand new RF System T2FDs that I bought on closeout so no point really.
Interesting about the angle you used (vertical). I found that reception was equally good either near horizontal or tilted close to 30 degrees. Maybe Countryman's original 30 degree design was in regards to transmitting for his intended purpose?
-
Does your coax drop straight down from the feedpoint?
-
The coax comes off the balun at about a 45 degree angle. Speaking of the balun... I was puzzled about how good the impedance match / SWR was, especially since the impedance of the T2FD should be around 900 ohms. I thought about the history of that balun again, and now I think it is a 9:1 not 4:1. If I lower the T2FD for some reason I will measure the impedance ratio.
Cebik's analysis of the t2FD doesn't show much benefit for tilting it: http://the-eye.eu/public/Books/Electronic%20Archive/ModelingTheT2fd.pdf
Nothing in the models shows any advantage to tilting the antenna with respect to skip communications or reception. Perhaps the only advantage may be mechanical, for those lacking a suitable high support from which to hang the antenna vertically.
I like to think of the T2FD as having the low angle pattern benefits of a vertical antenna, without the usual warts that make verticals unsatisfactory in most cases (more noise, and difficult or nearly impossible to get a decent ground radial system without a huge effort).
What are the dimensions of the T2FDs you have?
I'm pretty happy so far with the performance. I am tempted to try tilting it to the south, to see if it really does change directionality. I can just use the other end of rope over the tree.
If I set up a second KiwiSDR, I think this antenna might go on it.
-
I found that reception was equally good either near horizontal or tilted close to 30 degrees. Maybe Countryman's original 30 degree design was in regards to transmitting for his intended purpose?
The original Countryman T2FD antenna (http://hflink.com/antenna/#T2FD) was tilted to help offset the imbalance problems the design had due to its high impedance open wire feed.
In other words, they had a lot of transmission line radiation that showed up as nulls and peaks in the measured radiation pattern.
Tilting the flat top helped to fill in those nulls.
There was no balun in the original designs.
The open wire feedline was not decoupled from the antenna at all.
Ferrite baluns, which came along later, were applied in updated Terminated Folded Dipole designs.
Using a ferrite balun provides feedline isolation over a broad spectrum, eliminating feedline radiation in the TFD.
There is no magic tilt (and no need for tilt) in a TFD that has a balun.
-
As I recall, USN NRL (Naval Radio Labs) devised the T2FD for shore station listening posts and the NSA picked up on the design as being much more portable than the typical rhombics then favored by signals intelligence orgs. One slang for the T2FD is squashed rhombic, perhaps the desirable features of rhombii were criterion for a new design that featured portability and ease of installation over the rhombii for field use. Much easier to install the lowly T2FD above a embassy or other govt building than a full size rhombic.
Collins Radio took a look at rhombics for some clandestine bcaster and decided to do away with the loss of the terminating resistor. They made a dual rhombic with a matching network in place of the load and doubled their output over rhombics by reflecting the rf back to the antenna rather than heating a load. Of course, that then eliminated the aperiodic nature of the rhombic.
From the swr graphs, with particular respect towards the lack of peaks and nulls, it seems Mr Smolinksi has perfected the art of the T2FD aperiodic antenna.
-
I can't stand a 60' T2FD on end at my QTH, but I could slant one that is significantly longer, so my question is: what do I lose from breaking from vertical, and what do I gain from adding length to the antenna? Does length add gain to lower frequencies? Does less slant make it more omnidirectional?
-
Does length add gain to lower frequencies?
My B&W T2FD was 90ft long, covered 160m and up. Their shorter version was good from 80m. They seem to have a sharp knee in the swr that rises dramatically at the low end of the spectrum as a function of the design, this can be seen in Mr Smolinksi's charts.
-
On T2FD "directionality", I suspect the local ground plays a part. Some users see a diff between horizontal and slanted or vertical, while others report no diff. I also suspect the supporting structure as well as other antennae or conductors in the nearfield also play a role.
On the termination position with reference to the feedpoint, I suppose this is where the T2FD acts like a rhombic in that energy coming from the feedpoint is absorbed by the load, energy from elsewhere along the antenna not being absorbed as much, wich may also explain a lot about why the T2FD is legendary for poor tx performance. With a rhombic, you aim the termination and feedpoint inline with the target reception area - termination towards target, the antenna then rejects signals coming from the back.
Who knows, fun to consider and experiment with anyway.
-
Some additional data points:
The signal level is generally a bit on the low side. This is not an issue with the AFE822x which has an adjustable gain pre-amp, it's a little more of an issue with say the KiwiSDR which does not, especially with very weak signals.
I briefly played around with changing the tilt angle, making it closer to around 45 degrees. I did not notice any obvious change in signal strengths when looking at the MW band. I recorded a 500 kHz chunk at the upper and, and made the change about half way through (which was quick and easy to do - just untie the support rope at ground level and move it to another location). A quick check at HF, CRFX 6070, did not show any appreciable change in signal levels either. According to Cebik's analysis tilting the antenna does change the pattern and make it less symmetrical, but does not seem to improve the low angle radiation in any direction.
So I suspect a vertical orientation is still ideal, but tilt as needed. The question is where is the tradeoff? Your tree(s) are a fixed height. If you want to make the T2FD longer (for better low frequency performance), you need to tilt it more. When does making it longer but more horizontal start to hurt you? OTOH if your receiver has sufficient sensitivity, you do not need more signal, so you don't need to make it longer. ;D
-
On T2FD "directionality", I suspect the local ground plays a part. Some users see a diff between horizontal and slanted or vertical, while others report no diff. I also suspect the supporting structure as well as other antennae or conductors in the nearfield also play a role.
Yes, I suspect there's a lot of known unknowns as well as unknown unknowns affecting antenna performance. One reason you just have to "build and see how it works".
-
Generally speaking, the radiation pattern for a T2FD antenna with a balun is the same shape as a dipole of the same length.
The only difference is in the efficiency gain or amplitude of the curve.
On HF, it is advantageous to get the feedpoint as high as possible, especially to get the radiation center above ground clutter and above receive RFI sources.
For a single support, the Inverted-V configuration gets the feedpoint at the top.
And it turns out that the TFD tends to do very well as an Inverted-V.
Structurally, the inverted-v configuration helps to manage the weight and wind loading of the coaxial cable, balun, spreaders, and termination resistor.
The inverted-v TFD is the most commonly seen HF antenna throughout most of South America and Southeast Asia, as radio ops who travel there have probably noticed :)
-
Just for my understanding, I take it this is the direction the antenna 'looks' with the tilt?
Top
/
North <- / South
/
Bottom
-
The bottom of the antenna is about 15 ft to the north of the top. Whether this is giving me any real directionality is another story ;D
-
Gotcha.
I still have my RF Systems T2FD...I never thought to hang it vertically, but could do so at a decent height with the pine trees I have (at least the full length of the 45'antenna if not higher ~70' possibly). Hmm...might have to try it again to see if it will minimize the some of the local RFI I've been fighting with my vertical setup.
-
Since reading this thread I've been giving the T2FD some serious consideration and research. Of particular interest is the function of the resistor at the "far end" of the antenna. Understanding its purpose should help in designing my own T2FD.
I found a very old post from this very forum describing (at least a portion) of the resistor's function which suggests why so many report the TF2D as having lower noise and better S/N than monoband dipoles:
The balancing resistor keeps the elements in perfect balance all the time in relation to the feedpoint, and THAT does a very effective job of canceling out local noise.
Having read elsewhere that "dummy loads have extremely flat SWR curves" and noting the T2FD is very wide-banded, the concern is how much energy is lost and how to minimize it. The same post from above includes this:
In addition, at MOST, the balancing resistor might cause a 3 dB drop in signal (1/2 an S-unit). Most of the time, it absorbs little, if any signal. Almost all signal is fed to the feedpoint through the folded dipoles because of the slightly lower resistance at the feedpoint that at the balance point. That is why for a 500 ohm feedpoint, you use a 540 to 600 ohm resistor in a terminated folded dipole.
As noted elsewhere in this thread, good performance from a T2FD depends heavily on the resistor value. The above post gives an explanation for why that is.
Is finding the feedpoint impedance simply a matter of deploying a T2FD, running the shortest possible 50-ohm coax to an analyzer and noting the R in an R,X scan?
-
The resistor closes the loop with resistance, this is what makes the T2FD broadbanded aka aperiodic. If the resistor was replaced with wire, creating a folded dipole aka loop, the antennae would have swr peaks and nulls akin to other dipoles, but rejecting energy at twice the tuned frequency - a main characteristic of a folded dipole.
here are some vids on folded dipole experiments;
https://www.youtube.com/watch?v=WwJnXTVUrgI
https://www.youtube.com/watch?v=dsyuotZyU_g
https://www.youtube.com/watch?v=HmaLvSJKCOc
-
I had something *vaguely* like this in the 80's and it was quite a nice antenna. I had RG8 on it instead of RG6 and no balun, but it was very similar to this antenna. I think that one had a 600 ohm resistor at the feedpoint. It was *almost* as good as my >400' random-chaos longwire but it was a lot quieter. Granted, QRM was nothing like we deal with now. But my mom had a pair of touch-lamps which plagued the longwire, and the terminated dipole was practically immune to it.
I may just try one of these!
Edit: The antenna I used was built from a long chunk of 2-conductor wire that was laying on the ground beneath power lines. I always assumed by it's small gauge that it was some kind of phone line. It was like two separated 24 g wires but very hard to bend. I had probably 75' of it. Had no plans for building it whatsoever, it was just an experiment after reading about folded dipoles in Pop Comm. Turns out Chris' post brought that old antenna out of my memory. It worked quite well so I never messed with it.
-
Another interesting youtube video on the T2FD ......https://www.youtube.com/watch?v=Y473hOmif-E
-
I had something *vaguely* like this in the 80's and it was quite a nice antenna. I had RG8 on it instead of RG6 and no balun, but it was very similar to this antenna. I think that one had a 600 ohm resistor at the feedpoint. It was *almost* as good as my >400' random-chaos longwire but it was a lot quieter. Granted, QRM was nothing like we deal with now. But my mom had a pair of touch-lamps which plagued the longwire, and the terminated dipole was practically immune to it.
I may just try one of these!
Edit: The antenna I used was built from a long chunk of 2-conductor wire that was laying on the ground beneath power lines. I always assumed by it's small gauge that it was some kind of phone line. It was like two separated 24 g wires but very hard to bend. I had probably 75' of it. Had no plans for building it whatsoever, it was just an experiment after reading about folded dipoles in Pop Comm. Turns out Chris' post brought that old antenna out of my memory. It worked quite well so I never messed with it.
Yep, two conductor phone line. You could have made fish hooks and pierced ears with that stress hardened copper.
A friend gave me three partial reels of the stuff in the 90's. I've still got most of two. The size makes it great for stealth antennas in HOA afflicted areas.
If you can find a multi-conductor reel there is usually a light blue coated wire. You can't see an antenna made of that stuff day or night unless you know exactly where you're looking.
-
If you can find a multi-conductor reel there is usually a light blue coated wire. You can't see an antenna made of that stuff day or night unless you know exactly where you're looking.
There is a bundle of old phone line wires (bundle of about 25 wires) that run all through this house. Just the reg copper, but they must have put it in for alarm sensors or something, because they run into every room and the separate garage. I'll probably try to pull them all out when we redo the walls but it'll probably be some time before I can afford that project.
At my old place, the chaos longwire was sky blue wire and it was practically invisible from right beneath it.
-
I shudder involuntarily when someone mentions touch lamps.
So glad those things are out of style.
-
I did an experiment today. Well, two experiments. First yesterday I moved the T2FD to a new location, about twice as far from the house, to hopefully reduce any RFI pickup. The new location also has more open space, so I can play with the antenna orientation. The top of the antenna is about the same height as before.
The experiment today: I set up the AFE822x SDR recording the upper end of the MW band. This gives me a number of relatively stable signals to monitor. I let it record for about 15 minutes, then I moved the bottom of the antenna, so instead of being nearly vertical, it is at about a 35 degree angle from vertical, with the bottom aimed roughly to the north, perhaps slightly east of north. Then let it record another 15 or so minutes.
I plotted out the carrier signal strength (2 kHz wide bandwidth) for several MW stations from the recording. Here are those plots, vertical axis is signal in dBm, horizontal is time, sorry no ticks, but each graph is the same length, and again the change is about midway:
Baseline noise 1715 kHz:
(https://i.imgur.com/lCSTbc5.png)
My semi local 1620 pirate WEDG which is to my north:
(https://i.imgur.com/fGtdCg7.png)
1470 WTTR which is about 10 miles to my south:
(https://i.imgur.com/1vgMqTm.png)
1480 WEEO 39 miles to my northwest:
(https://i.imgur.com/Noa5akI.png)
1490 WARK which is 40 miles to my west:
(https://i.imgur.com/G3vLrbR.png)
1500 WFED 46 miles to my south:
(https://i.imgur.com/OBK3bmp.png)
1510 WWSM 49 miles to my northeast:
(https://i.imgur.com/RHoCsQH.png)
1520 WTRI 43 miles to my west south west:
(https://i.imgur.com/EoBohOh.png)
1530 WCTR 58 miles to my east south east:
(https://i.imgur.com/qKSyAS9.png)
1540 WACA 48 miles to my south:
(https://i.imgur.com/LhRT8J6.png)
1570 WNST 30 miles to my east south east:
(https://i.imgur.com/jdEeUdA.png)
1650 WHKT 204 miles to my south:
(https://i.imgur.com/bsLYVGO.png)
1660 WWRU 172 miles to my northeast:
(https://i.imgur.com/3ppVa4F.png)
1680 WTTM 105 miles to my east:
(https://i.imgur.com/FDUykiv.png)
1690 WPTX 101 miles to my south-southeast:
(https://i.imgur.com/kuzrpKO.png)
1700 WRCR about 180? miles to my northeast:
(https://i.imgur.com/l0RGj1T.png)
-
In the speriment it looks like 1680 is the only loser with the rest staying same or even increasing in gain.
Was just about to post some q for you too.
How does the T2FD noise floor compare to other antennae, such as your groundloop, skyloop, bev, perhaps if you have an active type. Say noise floor of each and signal level of the same signal on each ant at or close to the same time.
-
How does the T2FD noise floor compare to other antennae, such as your groundloop, skyloop, bev, perhaps if you have an active type. Say noise floor of each and signal level of the same signal on each ant at or close to the same time.
Enquiring minds want to know. I intend to raise a dedicated SWL antenna this fall along the edge of my property. The engineering and logistics of a T2FD is higher than for a dipole. Is it worth it?
-
How does the T2FD noise floor compare to other antennae, such as your groundloop, skyloop, bev, perhaps if you have an active type. Say noise floor of each and signal level of the same signal on each ant at or close to the same time.
I await funding for this experiment ;D
-
Enquiring minds want to know. I intend to raise a dedicated SWL antenna this fall along the edge of my property. The engineering and logistics of a T2FD is higher than for a dipole. Is it worth it?
My general experience with this T2FD is:
It works very well for the size. Performance is great down on MW, and up on 11 meters. If you have limited space and can only put up one fairly small footprint antenna, this may be the one. But you need to mount it nearly vertical (see below) for best results. This is good in that you don't need a lot of yard area vs a horizontal dipole. But you do need a tall tree, basically 85% of the length of the antenna assuming a 30 or 35 degree tilt from vertical. This means that in general you do not select the length of the antenna based on the band(s) of interest as with most antennas. Instead you find your tallest tree, get a rope over it, measure the length at that angle, and design your antenna appropriately.
It is not as good as a dedicated antenna for most single bands. My 43/48 meter band folded dipole wins on those bands, and nearby.
I *think* you want to mount it so that it is at about a 30 degree from vertical orientation, based on the signal plots in my previous post. I am not 100% sure the few dB of signal increase was due to the tilt, it is possible it was because the antenna was slightly higher overall. But further increasing the tilt angle *lowered* signal levels slightly, so I'd say I am 99% sure it was due to the tilt. I need to do some more experiments to see. Also this was on MW, it is possible results on HF are different. It's tricker to test on HF due to the typical fading of signals, longer measurement periods will likely be needed. But I think it's a safe bet that this is close enough to ideal.
It's not too much more difficult vs a traditional dipole. You do need twice as much wire and some spacers, I found 1" PVC worked great. And you want a 9:1 or 12:1 balun vs the usual 1:1 balun. In one way it is *easier* than a normal dipole - you only need to get one end way up high in a tree, the other end is tied off at the ground.
I am beginning to think two, or even four, T2FD antennas much be interesting for diversity reception. I had been considering doing this for some time using vertical antennas, but we know that traditional verticals, are, well, typically not as good (I am trying to avoid using profanity when describing vertical antennas) in the real world as theory suggests, mostly because you can rarely get a good enough ground system for them (unless your idea of fun is ripping up your yard to bury 50 or 100 or so quarter wavelength radials). But a few T2FD antennas is much easier to install. And they actually work! :)
-
How does the T2FD noise floor compare to other antennae, such as your groundloop, skyloop, bev, perhaps if you have an active type. Say noise floor of each and signal level of the same signal on each ant at or close to the same time.
I await funding for this experiment ;D
Check's in the mail.
-
I've tried using a slingshot and fishing wire to get rope up high, and it doesn't work out well for me. Do you have any advice in this regard?
-
I've tried using a slingshot and fishing wire to get rope up high, and it doesn't work out well for me. Do you have any advice in this regard?
That's exactly what I use, but I went with a heavier weight than what was supplied with the EZ Hang, I got some 2 oz weights from eBay, that helped with taller trees.
-
Some HAMs swear by tennis balls in spud guns, with fishing line to start with.
-
I bought a cheap child’s bow and arrow set and screwed a heavy nut onto the tip of the arrow. Then I tied a pull string right behind the fletchings and shot it over a limb. Then I tied the guy cord to the end of the pull string, pulled the guy cord and then attached the guy cord to the T2FD.
-
Wrist rocket, 1-2 oz. egg sinker, a good old Zebco 202 reel rewound with 60 lb. test mono, and you're in business. Stay away from sycamores, the things are killers. They're nice and tall with big branches high and in the open, but they're as hollow and punky as the trunks themselves. Quite a few people have been killed by falling branches strolling under them on windy days.
There's no way I'd try to haul a heavy antenna up one.
As far as launching antennas in trees, it takes practice. Those first few times are frustrating as it comes, as that weight you aimed at the branch in one tree goes sailing through five others to God knows where. It gets easier, but you'll still manage to screw it up now and then over the decades. Just remember to check what's downrange of where you're launching that sinker, a two oz. weight can be lethal at wrist-rocket speeds and it doesn't respect power lines. I don't think monofilament conducts electricity? I don't want to find out at my age.
Good luck, Young Edison!
-
Ah ah! I'm going to use a DRONE to firstly survey the top of a very tall tree and then take a line weighted down up very high over the tree top and then land on my house roof.
Will let you know how it goes!
Str.
-
Ah ah! I'm going to use a DRONE to firstly survey the top of a very tall tree and then take a line weighted down up very high over the tree top and then land on my house roof.
Will let you know how it goes!
Str.
I've considered the drone approach, let us know how it goes!
-
Meet the TL2V (Terminated Linear Loaded Vertical);
https://g8jnj.net/broadbandhfvertical.htm
http://www.tc2m.info/TC2M%20HF%20Vertical%20G8JNJ.pdf
More or less one half a T2FD with the other half grounded.
-
Meet the TL2V (Terminated Linear Loaded Vertical);
https://g8jnj.net/broadbandhfvertical.htm
http://www.tc2m.info/TC2M%20HF%20Vertical%20G8JNJ.pdf
More or less one half a T2FD with the other half grounded.
I see it suffers from the "install a cumbersome ground radial system or suffer from poor efficiency" problem inherent with vertical antennas:
GROUND SCREEN. In order to operate in an efficient manner, this antenna (as is the case with all vertical monopole antennas) needs to be fed against an appropriately dimensioned ground screen (ground plane, radials or counterpoise wires). Ideally this would take the form of a continuously conductive metal sheet, extending out to beyond 1/4 of a wavelength at the lowest required operating frequency. However in most cases this would not be practical to implement.
Not practical. Quite the understatement :P
The next best solution would is a series of wire spokes extending out away from the base of the antenna out to beyond 1/4 wavelength at the lowest required operating frequency. A minimum of 8 buried wires would seem to offer the best compromise between cost, effort and efficiency.
Eight quarter wavelength (minimum length) radials. Buried. Sure, let me get right on that.
(https://i.imgur.com/6DLu3BC.png)
-
She got otherworldly hints on antenna design from astrologers, so she would know.
-
Any one remember the old "El Toro" antennas hams made out of ladder-line with the high point on the TV mast on the roof? The bottom end of the ladder-line would be hooked to the center conductor of the coax and the outer braid soldered and clamped to the outdoor spigot as a ground. The center of the ladder-line would be pulled as far from vertical as the postage stamp lots of those post-war developments allowed.
Those guys got out. Oddly, regulations on rf output filtering came along about the time interest in antennas like the "El Toro" peaked.
-
Drone survey complete but because of the angle of vision my drone pilot failed to get it over the very top so will try again today.
I have a very 'Tree congested' garden and the far side of the tree is a childrens playground so definataely inable to take off/land in either.
Will take off from my roof top, flu over the tree top, dip down 20' and then turn and land in the lane to the side of the tree.
Tricky manoeuvre!
The monofilimant line must trial from a weight suspended under the drone otherwise the line will get caught in the props, again, tricky business...
Str.
-
Drone survey complete but because of the angle of vision my drone pilot failed to get it over the very top so will try again today.
I have a very 'Tree congested' garden and the far side of the tree is a childrens playground so definataely inable to take off/land in either.
Will take off from my roof top, flu over the tree top, dip down 20' and then turn and land in the lane to the side of the tree.
Tricky manoeuvre!
The monofilimant line must trial from a weight suspended under the drone otherwise the line will get caught in the props, again, tricky business...
Str.
Thanks for the update!
I was wondering if using a weight to keep the fishing line down below the props would help. Let us know how things go, I'm considering getting one of the kids to try using their quadcopter to take some line over a tree.
-
I'd make a video but am too busy guiding the pilot and feeding out the line from a multiplier reel...
Str.
-
3rd time lucky and after a few attempts and having gained a bit of experience it was quite simple. Flew up some 12lb monofilament, followed by some 80lb. However the rope I've tied to the 80lb won't go through the branches. Will have to use wire rather than rope?
The tree is an 80'+ eucalyptus, growing 5' a year.
Str.
-
Congrats! Any tips on the technique you used to lift the fishing line over the tree? Maybe some step by step instructions?
I've found that when a rope won't go through a tree (I use a sling shot to shoot the fishing line over), it is often because a knot is hitting a branch, Often pulling back and forth a bunch of times will allow the knot to eventually slip past the obstruction.
-
Fly drone over tree and land on other side!
A small weight is suspended 12" below with the line off that to keep away from props as drone decends.
I've smoothed the knots out and the transistion from line to rope with much insulation tape, still no good..
I'm going to get some dacron to smooth the transition.
Str.
-
Perfect, thank you, I got it now :)
-
Cool. Definitely the future of wire antenna deployment!
Str.
-
it is often because a knot is hitting a branch
In cases like these I send a "carrier wave oscillation" up the rope orthogonal to the plane of the branch and rope. This can "jump" the knot over the branch, however these operations have always been within 40'. I doubt I could get the wave to travel all the way up 80' with enough amplitude to jump the knot over.
-
Indeed I had the same thought and tried it from the open window but not enough oomph on it. I'll have to get out on the roof at weekend, will hopefully be cooler as I burned my hand and rear cheeks as it was so hot! Somewhat rare for the UK!
Str.
-
For the drone deployment, I highly recommend going up 2 times the height of the tree plus the width of the tree.
This should prevent a situation where the drone can't make it back down to the ground if the line gets snagged in the tree.
Also, make sure the attached weight is centered, so that the drone isn't trying to compensate (drift) for the unbalance. (especially if flying in close proximity to tree limbs).
-
This is droning on and on!
I want to see specs on noise floor and signal levels for each antenna at casa del smolinksi!
:D
-
I repaired the T2FD after some storm damage. I replaced the generic ham radio balun I was using with a custom 12:1 version of my Cyclops potted matching transformer, fed into 75 ohm RG-6 it provides an ideal 900 ohm feedpoint impedance. Also a potted 850 ohm termination resistor.
Works great, I am hearing my semi local (I suspect they are about 5 or 10 miles away) pirate on 1620, WEDG The Wedge, playing Christmas Music. Heck, they might even be a Part 15 station, or close to it.
https://www.blackcatsystems.com/rf-products/cyclops_rf_ham_shortwave_radio_matching_transformer.html
(https://i.imgur.com/Fp0IRNo.png)
-
Zombie thread I know but antenna discussion are always undead!
Chris, I notice that your Kiwi is noted as a 120 T2FD ... did you change from the short one to the big version ? I've been using your kiwi on and off for the last week or so and am really impressed with the results. I have an acre of trees out back , some of which are probably pushing 100'. The usual issue is there's too many trees and it's a struggle to find an antenna path. On the other hand, I own a Stihl chainsaw......
WIth your 59 foot version of this antenna, did you scale the wire to wire spacing to the new shorter length? I'm guessing yes, but I wanted to confirm before I get out the soldering iron and tape measure.
-
I played around with antennas on the Kiwis and ended up with the 120 ft T2FD on http://sdr.hfunderpants.com:8073/ and the 500 ft beverage on http://sdr.hfunderpants.com:8074/
The 120 ft really works well overall, from MW up through HF and is not even that bad on 11 meters.
Yes, the spacing for the T2FD antennas is scaled based on the length.
I found (and some websites with T2FD info/modeling confirm this) that the ideal orientation is really vertical vs tilted, you tilt only because your trees are not tall enough for the antenna length ;D
-
Thanks Chris. How high up is the 120' T2FD (tilted?) I'm really impressed at its s/n even with stormy wx here in SE
-
Thanks Chris. How high up is the 120' T2FD (tilted?) I'm really impressed at its s/n even with stormy wx here in SE
It's installed going down a hill, roughly to the east. The high end is maybe 85 ft up and low low end is perhaps 5 ft high, the bottom of the hill is perhaps 20 ft lower than the top. So at roughly a 45 degree angle. Obviously my trees were not tall enough :) But I wanted something significantly longer than the 58 ft to make it worth installing. I will say that 120 ft is probably the upper end of what is feasible before it becomes completely unwieldy (I think I mentioned this before). Also you really need a support rope down the center to take all the stress off the wires.
But yes, it's a great performer, and I am glad I built it. It's significantly better than the 58 ft T2FD. Much more than just twice as good. Someone out west with a 200 ft Redwood needs to put up a real T2FD ;D
-
I may have to settle for the smaller T2 that you describe, although I think I could fit a 90' version in between the trees.
I was surprised that my RTLSDR doing 10M QRSS decodes managed to live though a very stormy summer season here with no damage (I choked the DC feed and put gas discharge devices on power and RF input).
Too bad that they're so poor at direct sampling . I'm hesitant to potentially sacrifice a kiwi but I might but a RSP1 out there and let it go.
I"m using a 30M ammo can to house the radios and the PI that is beaming the data in to the house via a RF transparent window I cut and covered in the mil can. So far, so good including a 2 month straight run with no downtime. The can is bolted to the ground rod with the radio and computer inside.
I'm just using a 10M dipole which works well, but I'm thinking of the T2FD for multiband SWL only .
-
Cool. Definitely the future of wire antenna deployment!
Str.
I do the sling shot, fishing reel and monofilament with a small fishing sinker. I've gotten pretty good at it though there's a fair share of marooned sinkers in various trees. I too use it to pull a heavier "haul line" back over.
Eucalyptus are good in the sense that they're mostly vertical as opposed to more low, globe shaped trees. Kinda surprised to find that they're found out your way
-
Received some bamboo "spreaders" Friday. Will get to work on one of these before long.
I found the original CQ article (1956?) about these in my old magazine stash.