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Strange Antenna Suddenly Appeared




 
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WA2SQQ
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« on: August 24, 2020, 03:43:19 PM »

Got a text today from a friend asking if I knew what kind of antenna this was. It suddenly appeared, via a helicopter on a second tower, adjacent where I have a 440 repeater near William Paterson College in NJ.

We’ve since determined that is made by Rhode & Schwarz. I’m going up to the site on Friday to photograph it and hopefully find out who owns it.

https://www.rohde-schwarz.com/us/product/hl451-productstartpage_63493-9051.html

I would think, something this large, has to be in some FCC data base? Any ideas?


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Steve - K4HX
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« Reply #1 on: August 24, 2020, 04:09:08 PM »

Pretty typical HF log periodic antenna. Other manufactures make similar.

If it is to only be used for reception, would it need any FCC paperwork?
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W1ITT
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« Reply #2 on: August 24, 2020, 04:17:15 PM »

It's an HF log periodic.  It's pointing to the left hand side of the page..  I saw that model a few years ago at an installation overseas and was surprised at the lightness of its construction.  It was on the ground and had failed in a storm.  I was surprised because, generally, anything that Rhode and Shwartz makes is top notch material.  Until the cootie-virus shut things down, I was going worldwide putting up log periodics for an American manufacturer.
Despite my previous comments, if an R&S LP suddenly appeared over my back yard, I'd run some coax to it in a hurry.  I've put a couple of "my" LPs on the air with a ham rig and they are fun and, of course, frequency agile.  Who might be running this particular aerial in NJ would be interesting to find out.  The FCC database might not be of much help as they mostly list towers, not what's bolted onto them.  There are a few people out there who are using HF for trading arbitrage because radio is usually quicker between two given points than the internet with its inherent latency.  There are folks who do high speed trading in such a manner that the small interval  makes a difference.  Don't let anyone tell you that HF is old school and out of date.

73 de Norm W1ITT
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W1ITT
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« Reply #3 on: August 24, 2020, 07:57:27 PM »

Taking a second look at that installation, I don't see a rotor, which would indicate point-to-point.  When you go up to look at it, see what the azimuth is and then see what's on that great circle bearing.  Some of the arbitrageurs are doing business with European exchanges.

73 de Norm W1ITT
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« Reply #4 on: August 26, 2020, 01:25:26 AM »

trading crypto via ALE on HF LOL
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« Reply #5 on: August 26, 2020, 08:01:15 AM »

Norm,....you're very perceptive,......(nudge nudge, wink wink.)
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« Reply #6 on: August 26, 2020, 04:31:07 PM »

Imagine what would happen if you connected the strange antenna in this subject line to the Strange Homebrew Amplifier a couple lines down??? The strangeness would be multiplied by a factor of two at least! Or maybe 3 Db?

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K1JJ
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« Reply #7 on: August 26, 2020, 05:48:55 PM »

Considering the rather elaborate and unconventional boom structure to support those log cell wires, I'd think a single boom with standard aluminum elements would be both stronger and less maintenance from wx damage.  And maybe cheaper to build.   Also, the feedline is openwire line which is not only more fragile but not a good impedance match to the usual 50 ohm elements. A real log uses a 50 ohm feedline consisting of aluminum angle spaced 3/8" apart or whatever.  Or use a split boom as the feedline.   I know, I designed and built pair of 16 el  in a stack for 13.9- 30 MHz on 60' booms each weighing 300 pounds for my 110' tower. Worked very FB.

Chuck's four stacked logs is a good example...

T

This is what those guys shuda put up:   Wink


* K1KW Log Stack.jpg (26.26 KB, 800x600 - viewed 69 times.)

* K1KW Logs (1).jpg (240.76 KB, 480x640 - viewed 84 times.)
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« Reply #8 on: August 26, 2020, 06:03:00 PM »

Tom..
The log periodic has many design options.  I have worked  frequently with the big TCI LP, a 4-30 mhz unit.  It runs a 200 ohm feedline, and a four to one balun back at the center support point to 50 ohms through the rotary joint.  The wire elements that go to the side catenaries are designed to work nicely with this impedance.  The 200 ohm line over the boom (which is a triangular tower) is also aluminum angle stock.  Although the antenna is only specified down to 4 mhz, I have run it on 75 meters and had a really swell time.  If it's good enough for our Uncle, it's good enough for me.  A cool feature is that it is rotated hydraulically with all the rotation controls on the ground where they are easy to access.  LPs DO walk the dog.

73 de Norm W1ITT
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K1JJ
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« Reply #9 on: August 26, 2020, 06:13:05 PM »

Hi Norm,

Yes, there are some logs out there using openwire and high impedance feedlines. It has been a debate for sometime now, but it was hammered into my head that the very best technique is to use a very low impedance balanced feedline to match the existing ~50 ohm element cells. I'm not sure of the reason to run an intentional mismatch of 4:1 or higher when it can be current fed at its characteristic impedance. Maybe because a heavy 50 ohm aluminum angle feedline would be physically impractical for a wire log.    I went thru great pains to mount an insulated set of aluminum 50 ohm angles on my 4" boom... and had to insulate the elements from the boom too.

Either way models out OK, but I like the 50 ohm approach better myself.

** One thing occurred to me:  At any given frequency within the range of the log cell, there is only one element that is 50 ohms j0, for example.  The elements after and before this one element  either are too short or too long, so they exhibit capacitive reactance or inductive reactance respectively.  Perhaps the thinking is to use a higher impedance feedline to find an "average" of the cell elements. I am not sure. I'll axe one of my ant guru buddies...


T
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« Reply #10 on: August 26, 2020, 08:36:51 PM »

Another reason for the wire vertical elements is to get a specific pattern.

KVOH in Simi has a very large TCI suspended between a few towers.  It points 'up'.  The target audience is central and south America.

--Shane
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Chuck...K1KW
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« Reply #11 on: August 26, 2020, 09:01:43 PM »

Well, you did it.  Managed to get me out of the woodwork as they say....

On LP's, before you design one, you need specifications!  What did the customer want/need?

This "strange" antenna was designed for 4 - 30 MHz, who knows what mechanical requirements were nor the power level needed, if one, or the desired target with no rotator as Norm observed.  Height above ground would also be an important parameter in determining the optimum wave angle.

My logs were designed for 14 - 30 MHz and all my extensive modeling was based on this frequency range and a desired F/B ratio of over 25 dB.  Other constraints on the design were boom length (guy wires in the way) and number of elements due to the tower being in the middle.  The 4 stack came about due to the requirement to control radiation angle which is important in this frequency range.  My antenna was designed for hammy hambone radio with the most flexibility at the expense of perhaps a db or 2.  These are highly modified Tennadyne T-10's.  I decided to optimize an existing design to make the job of sourcing materials MUCH easier.  Tennadyne was great and met my requirements.

Now onto some LP basics as a result of my modeling many designs:

Two design parameters define the performance of LPDA's  

1) Tau, the taper factor, how quickly the element lengths taper down to the high frequency end.  This factor is typically in the 0.85 to 0.95 range and is applied to the previous element length to get the next element length higher in frequency

2) Sigma, the relative spacing factor which defines how the element spacing reduces towards the high frequency end.  This factor is typically in the 0.05 to 0.15 range and is applied to the previous element spacing to get the spacing for the next high frequency element.

These two coupled with the frequency range determine the boom length for a LPDA.

The interconnecting feedline impedance determines gain and F/B ratio.  I found that a lower interconnecting feedline impedance increases gain at the expense of F/B ratio so here is a trade off.  I opted to get 25 dB of F/B with less than a dB of forward gain loss.  With my design parameters it's about 45 ohms. On my last stack of 18E logs on 62 ft booms, the interconnecting impedance was 70 ohms.

I suspect with a 10:1 frequency range and wire elements a much higher interconnecting feedline impedance would be needed to optimize performance.

One other note.  The Length to diameter ratio of each element at its resonant frequency needs to be the same for proper power distribution with a constant interconnecting feedline impedance.  I suspect that this is why I see some designs with a tapered feedline to accommodate the lack of maintaining the constant L/D ratio over the 10:1 frequency range with wire elements.

Last comment.  The typical LPDA curves relating Tau and Sigma you see in almost all the literature are WRONG!  These were done so many years ago and copied from one source.  Contemporary modeling shows that they are in error by as much as 4 dB on gain and over 17 db on F/B with no consideration for optimizing the interconnecting feedline impedance.  

Done...

Chuck  
 

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73, Chuck...K1KW
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« Reply #12 on: August 26, 2020, 09:11:52 PM »

Hi Shane..
I can't offhand recall the model number of that high-incidence wire LP you mentioned, but I last tuned one in Costa Rica for SW broadcast.   Get the input matching section right and the log array takes care of itself.   Those multitower catenary supported logs are in a different family from the big rotary logs.  If one had a few towers in the right spots, or even tall trees, they'd not be too hard to duplicate. I recall a series of articles, probably in Ham Radio Magazine in the 80s with a pile of wire log designs, both vertical and horizontal polarization, but I don't recall ever hearing a homebrew fixed log on the air.  For ham use, where we want to be able to transmit all over the compass, they have their limitations.  
I'm eager to hear what the azimuth is found to be for the aforementioned Rhode and Schwartz log in NJ.  I have done a bit of work with point to point HF arrays for a firm that was doing fast commodity trading, but a nondisclosure prohibits any specifics.  I can say that there are more than just a handful out there doing it.  

73 de Norm W1ITT
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K1JJ
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« Reply #13 on: August 26, 2020, 10:09:35 PM »

Thanks for the info, Chuck.

I found the tubing length to diameter ratio very hard to keep constant in the real world.  The big elements in the rear of the log were fat and had a lot of taper, while the ones in the front started to get too thin.   I finally got the ratio pretty close thruout the entire 60' log.  This coupled with the ice loading and wind stress modeling and then if that's not enuff, finding the proper diameter tubing and sleeve material at the metal scrap yard was challenging. A juggling act.   Bought a used South Bend lathe especially for the job. The local metal shop wanted $5000 to do the sleeving for two antennas, booms included.  I paid $500 for the lathe and did it myself. DIY.

I can understand how wire logs have very little control over this L/D ratio (since all the wire is the same diameter) and how a tapered feedline is the only fix.

Making up fiberglass plates to hold the insulated elements onto the boom was sporting and added a lot of weigh. I rented a TIG welder and actually welded alum straps from the feedline to the elements.  They held up quite well.

Those two logs were probably the best antennas I've ever used up on the higher bands, including a pair of 20M 60' boom Yagis I built. The f-b on the log was tremendous when I turned it towards SA and then could hear little when beaming 90 degrees or 180 off.  I used a prop pitch rotator with a MOSFET controller from M2.

I remember putting a few hundred watts into the log when it was a few feet off the ground. I could light a florescent bulb in the cell area for each frequency.  For example, the bulb lit brightly on 15M near the center of the log, maybe 5-6 elements wide and the energy was gone when measured farther away. The power found its way to the proper cell depending on frequency.  The number of elements were not more than an equivalent  4 element Yagi beam in length for this 16 element 60' long log.

OK on the 45 ohm and 70 Ohms feedline. Interesting on the feedline induced f-b/ forward gain tradeoff.   I remember seeing those 62' logs sitting on chairs nearly completed in your backyard. Musta been about 1992 or so?

Norm, I actually put up a 5 element wire log for 75M about 120 feet high back around 1988. Openwire feeder.  For some reason it did not work well and I replaced it with a standard wire horiz Yagi which did.  In hindsight it was in the vertical plane and probably needed a ground screen.

Fun times.

T

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« Reply #14 on: August 26, 2020, 11:58:07 PM »

Norm,

It's a TCI 516-A3...  Maybe a 3A, I can't remember.

Sits on a bluff over Los Angeles, CA.

I went for a motorcycle ride once, decided I was going to drive the hundred miles there and see what I could find.  While riding up a dirt road, was greeted by the station engineer coming back down.  Started a multi year friendship after spending 6 hours at the local diner babbling about the station, etc. 

IIRC, the towers are about 130 feet tall.  Nothing jn comparison to k1jj or W8JI (lol), but pretty impressive none the less.

I looked my notes up on the TX...  It's a 100kw ampliphase.  I previously reported it was a 250.  Memory is starting to fade I guess.

--Shane
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« Reply #15 on: August 27, 2020, 11:27:19 AM »

That setup is not unconventional. I've seen many logs with similar arrangements and wire elements. Pretty standard for decades now.

Considering the rather elaborate and unconventional boom structure to support those log cell wires, I'd think a single boom with standard aluminum elements would be both stronger and less maintenance from wx damage.  And maybe cheaper to build.   Also, the feedline is openwire line which is not only more fragile but not a good impedance match to the usual 50 ohm elements. A real log uses a 50 ohm feedline consisting of aluminum angle spaced 3/8" apart or whatever.  Or use a split boom as the feedline.   I know, I designed and built pair of 16 el  in a stack for 13.9- 30 MHz on 60' booms each weighing 300 pounds for my 110' tower. Worked very FB.

Chuck's four stacked logs is a good example...

T

This is what those guys shuda put up:   Wink

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« Reply #16 on: August 27, 2020, 11:39:50 AM »

I dunno, Steve.  Looks like a spider web to me. Lots going on. There are countless failure points within the wires for feedline, wire elements, boom supports, etc.  In contrast, an aluminum tubing log built like a Yagi is so much less to maintain.

I'm thinking in terms of a hambone who has to climb that tower and fix things after a windstorm...  Grin   A commercial operation with a crane or helicopter can get away with that stuff.  

T
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Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #17 on: August 28, 2020, 11:42:05 AM »

Mil and gov sites have been using these for a long time. I don't know, but I'm guessing they are reliable.

https://www.tcibr.com/product/tci-model-521-rotatable-log-periodic-antenna/

https://antennaproducts.com/product/lph-89/

https://comsystems.com/product/log-periodic-mod-730/

https://www.kratosdefense.com/products/space/antennas/hf-antennas/rotatable-directional-hf-antennas
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« Reply #18 on: August 28, 2020, 12:38:35 PM »

Yep, there are plenty of wire log arrays out there.  I guess I am just biased towards using tubing.  My 75M 2el wire delta loops on 40' booms at 190' have been up for over 10 years now without any failure, so maybe I should be more forgiving of wire designs.  

Did you ever notice that in nature, the fern plant is designed just like a log periodic?  The pattern goes from macro to micro which is even more amazing.

The plant forms a big log cell, then the leaflets form smaller logs themselves, and if you look closely at each little finger of the leaflets, they too form tiny logs.  It's an interesting design that supports from the rear and can take a lot of wind abuse.  Pick one up next time in the woods and study it closely.  Brrrr... the fern is a very old buzzard going back to the dinosaurs so it knows the score..  Wink


T


* Log Periodic in Nature.jpg (11.6 KB, 225x225 - viewed 58 times.)
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #19 on: August 29, 2020, 06:41:24 AM »

Fractal
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Bob
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« Reply #20 on: August 29, 2020, 01:33:59 PM »

Visited the site at William Paterson College yesterday. I was able to get within about 100 ft from the base of the tower. Here is a series of photos.


* WP_Ant 01.jpg (1656.99 KB, 2000x2000 - viewed 91 times.)

* WP_Ant 02.jpg (1323.77 KB, 2000x2000 - viewed 120 times.)
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WA2SQQ
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« Reply #21 on: August 29, 2020, 01:35:08 PM »

More ...


* WP_Ant 03.jpg (1927.84 KB, 2000x1333 - viewed 105 times.)

* WP_Ant 04.jpg (598.26 KB, 2000x1333 - viewed 109 times.)
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WA2SQQ
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« Reply #22 on: August 29, 2020, 01:37:12 PM »

Last two ...
Definitely looks like its pointing in the general direction of Europe.

Interesting that the sign mentioned that FCC registration was not required.


* WP_Ant 05.jpg (588.76 KB, 924x2000 - viewed 108 times.)

* WP_Ant 06.jpg (178.67 KB, 924x2000 - viewed 84 times.)
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« Reply #23 on: August 29, 2020, 05:30:00 PM »

Zoom in on the second photograph in this latest site visit series and notice the little squigly things twisting about the wire elements.  Those are some sort of UV resistant plastic and they are included to absorb energy from vortex shedding that makes wires dance in the wind and cause metal fatigue.  It's a nice addition to the R&S design.
Large wire logs have been around at least since the 70s that I know about.  I have installed a slew of TCIs and refurbished a number of Antenna Products logs at sites for our Uncle and others.  The nice thing about the wire logs is that they are field repairable if necessary, by regular GI tower-dogs, with locally sourced or expedient materials.  The tubular element logs, such as the Allgons, use specific sized tubing to maintain element length to diameter ratio down through the boom, and they are not  often easily available at a military base out back of beyond.  In a conflict situation this could become even more critical.
Based on that compass bearing, I'm sticking with my guess that they are traders.  Having dealt with a couple of those outfits, I suspect it will be difficult to get anyone to talk much as they are big on nondisclosure agreements.  Again, it's cool to see people Making HF Great Again.
73 de Norm W1ITT
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« Reply #24 on: October 16, 2020, 08:05:44 AM »

Visited the site at William Paterson College yesterday. I was able to get within about 100 ft from the base of the tower. Here is a series of photos.

Check this out, the webinars and papers are interesting... look at the video’s title image...

https://www.rohde-schwarz.com/us/campaigns/rsa/adt/hf-learning-center_253628.html?cid=802_us_sma_GOV_facebook_20-10_i______HFLC__&fbclid=IwAR3IA1twhmVVSUrAYkOhzwd-6G-ypT4RdWvyT7S1ShjQjW10Ii8rFnpqnRk

Ed
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