Inverted V, Vertical Rhombic
Jeff Young (N8CMQ)
on
January 10, 2010
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I was looking at alternate antenna designs for low band operations, and I saw the vertical rhombic design. What piqued my interest is it is an end fed inverted V, but with a counterpoise ground wire. The apex angle is larger, so the height is lower.
Why a rhombic? Gain. A rhombic has one or two lobes of radiation, depending on construction.
So a support good for a 40 Meter inverted V could also be used for an 80 Meter vertical rhombic.
The two antennas can share the same support, but I would orient them at a 90 degree angle to reduce interaction.
OR, two vertical rhombics oriented in favorite directions as the rhombic is mono or bi-directional depending on construction.
And if you add a little extra effort, you can make the rhombic a mono-directional in both directions. You just need a couple of relays and power resistors.
A little higher support, and you could have a 160 Meter vertical rhombic!
The only drawback in making the rhombic a mono-directional antenna is half the power is turned into heat in the power resistor.
If you decide to try this design, be sure to use the return ground wire.
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Inverted V, Vertical Rhombic
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by K9TY on January 10, 2010
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Good morning!
Well, you too piqued my interest, so I went and did some searching on what is usually called the "vertical 1/2 rhombic". So you feed it at ground level at one end, goes up to a single apex support (large obtuse angle there) and back down to the ground. On the far end one can install the 600 ohm non-inductive resistor to make it uni-directional (shooting from feedpoint to that end). Or forget the resistor and it'll be bi-directional. And of course, install some counterpoise wire on the ground as 1/2 of you rhombic is missing! :-D
A couple issues as I see it: Rhombics are loooonnnnng antennas -- usually a couple/few WAVELENGHTS long, so unless you have lots of land.... (this is not a half-wavelength antenna; it's HALF A RHOMBIC!). And then there's that resistor on the end -- as you said, it needs to be able to soak up alot of power. And you have to find a truly non-inductive resistor.
Anyway, it is a cool design. Most of my web searches found this antenna in military field manuals. There a half-rhombic for VHF is now like a normal HF antenna in length. Much tougher to really do it on the lower HF bands.
Happy hamming in 2010.
Dave - K9TY
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Inverted V, Vertical Rhombic
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by NY7Q on January 10, 2010
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In the Navy, we used shipboard vertical Rhombics and ashore we used ""big"" Rhombics...they all worked great.
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Inverted V, Vertical Rhombic- TRY it on 6M!
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by K0FF on January 10, 2010
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Antenna gain comes from warping the pattern so that less energy goes in some direction in favor of it "bunching up" in the favored direction.
In this sense, "direction" is a 3 dimensional quantity, including azimuth AND elevation (2 pi steradian).
Antennas exhibit reciprocal behavior, simply meaning what applies to transmit also applies to receive ( with notable exceptions; don't try transmitting into your Beverage!).
In the receive mode, an advantageously directional antenna improves strength but also disproportionately improves signal-to-noise ratio (picks up less noise from unwanted direction)
We are aware of the occasional need for an east/west sort of directivity, but the up/down directivity can be used to advantage ( or disadvantage) to set the angle of radiation.
Different types of propagation benefit more or less at a particular angle of takeoff.
On HF this is pretty much understood. Long haul requires a lower angle and "local" requires higher angles.
The long antenna as referred to on HF becomes a really long antenna if it is also used at VHF.
Some of the strongest signals I've ever heard on 6 meters have come from 160 Meter antennas! These become "wave antennas" on 6M, giving tremendous gain in one direction.
The Rhombic is also useful on 2 meters, with some long haul and even EME being done with them. A Rhombic cut for 2M can fit on a rooftop.
Most HF rigs made today also include at least 6 Meters too. Let me encourage operators with such a radio to try the band, with whatever antennas are at hand, Of course observe the SWR to make sure the rig is happy first.
It has long been known that a Mosley tribander works pretty well on 6M, but the directivity is reversed!
See you on 6M
K0FF
K0VHF
K0EME
6M DXCC, EME, WAS, WAC from the "Black Hole".
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Inverted V, Vertical Rhombic
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by WB2WIK on January 10, 2010
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If the antenna is really just a 1/2-wave inverted vee but fed against a horizontal ground wire directly under it, it's way too short to be any sort of "rhombic."
B&W sells a terminated antenna kind of like this, and I've used it a few times: One of the worst antennas I've ever used! Of course, it, too, is way too short at only about 100' overall length. I experimented a lot with the ground wire (when everything's connected, it's like a delta loop fed at one lower corner, terminated in the opposite corner at ground level, with the horizontal part of the loop literally laying on the ground), the termination, the feedpoint transformer and everything I could think of and it still did not perform nearly as well as a plain old inverted vee using the same apex support but fed in the middle.
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RE: Inverted V, Vertical Rhombic
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by WY3X on January 10, 2010
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OK, I ran some calculations. If you build one for 28.4 MHz with a 20 degree wave angle- you're looking at 148 feet on a side. A rhombic has two sides, so you'd need a support structure that is roughly half of 148 feet tall, or 74 feet tall. Entirely do-able for a 10M half-rhombic. (Assuming you hang one element in the air and the other element is a radial at ground level, or just under the ground, beneath the aerial element.)
Now- the author suggests an 80M vertical rhombic. Let's see how long THAT support structure would need to be...
3.9MHz, same (20 degree) wave angle, you need about 1,078 feet on a side. This requires a support structure a whopping 539 feet tall!!! This is not really within the realm of practical application for the "average" ham op.
Admittedly, I'm taking the figures for a full-size rhombic, and squeezing the ends together so that the tower is at the apex of the antenna, and each side is drooping down to some point on the ground where feedline and resistor connections are made. Or am I missing something the author wants us to know? A drawing of sorts would have helped explain things...
I love experimenting with antennas, and if this was practical and there was some usable gain to be had... (much more than a couple of dB)... I might look into it. I have a nice resistor bought for the purpose of a rhombic just in case some day I lived on enough real estate to install one.
73, -KR4WM
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Inverted V, Vertical Rhombic
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by K9ZF on January 10, 2010
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Sounds like an interesting experiment. It may not be the best antenna in the world, but that doesn't mean it's not worth trying.
How about giving it a shot, keep track of the dimensions and such, take some good photos, and reporting back with the results. Preferably compared to a "known" reference antenna. Or better yet, have several folks try the same experiment and publish results here:-)
Have fun!
73
Dan
--
Amateur Radio Emergency Service, Clark County Indiana. EM78el
K9ZF /R no budget Rover ***QRP-l #1269 Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla> List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
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Inverted V, Vertical Rhombic
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by NA4IT on January 10, 2010
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I have used one of these for a portable operation. It was 110 feet long for the "V" element, and 80 feet for the counterpoise. Terminate one end with a 600 ohm termination load, and the other feed with a 12:1 balun fed with coax. No tuner needed. It is basically a dummy load that has a lot of leakage, but it DOES work. We used it for Winlink on 40M and made solid S-9+ contacts out of state. Works well on other bands too. Buxcomm has the balun and the termination resistor.
de NA4IT
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RE: Inverted V, Vertical Rhombic
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by W4VR on January 10, 2010
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This antenna appears in many military publications but I don't believe it's used by hams or commercial installations. For military use, it's easy and fast to install and provides a broader radiation pattern than a horizontal rhombic for a given length. It would be worth a try on 160 meters, but you should have something to compare it to..such as a dipole or inverted-L.
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RE: Inverted V, Vertical Rhombic
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by AA4PB on January 10, 2010
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Remember this about the termination resistor. It makes the antenna radiate in only the one direction because it absorbs (and turns to heat) all the power that would have been reflected back to the reverse direction. It doesn't add that power to the forward lobe giving the antenna more gain in the forward direction. Depending on your particular application, you might be better off not terminating the antenna so that you can work stations to the rear rather than changing that lobe to heat.
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Inverted V, Vertical Rhombic
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by K1DA on January 11, 2010
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I think my Heathkit "Cantenna" has one of those resistors in it.
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RE: Inverted V, Vertical Rhombic
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by K0FF on January 11, 2010
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K1DA said:
"I think my Heathkit "Cantenna" has one of those resistors in it. "
These terminated antennas need higher value resistances, 600 or 300 Ohms depending on the configuration.
After WW2 when surplus electronics abounded in the US, 600 Ohm resistors that look like broom handles, about a foot long were available for a dollar or two. Many were ganged together to make superb 50 Ohm loads, after an article by K7GCO.
I still have a hand full of them and use them in sealed PVC pipes to terminated the ends of experimental antennas.
The terminated VEE beam is one example.
Fortunately 12:1 baluns were also available surplus and I was able to snag one of those. Used on some ships, the housings weighed in at about 50 pounds or more. I refitted mine into a modern Fiberglas NEMA box with home made feedthru insulators.
http://www.qsl.net/k0ff/Baluns/12%20to%201%20TX/
Geo:K0FF
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Inverted V, Vertical Rhombic
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by AI2IA on January 11, 2010
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It is a wise ham indeed, who knows his limit when it comes to extreme attempts to obtain or improve operation on the HF bands.
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RE: Inverted V, Vertical Rhombic
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by K6LHA on January 11, 2010
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W4VR wrote on January 10, 2010:
"This antenna appears in many military publications but I don't believe it's used by hams or commercial installations. For military use, it's easy and fast to install and provides a broader radiation pattern than a horizontal rhombic for a given length. It would be worth a try on 160 meters, but you should have something to compare it to..such as a dipole or inverted-L."
A Vertical Rhombic was in the antenna kit of some AN/GRC-26 military transportable field radio stations of the 1950s...in a hut on the bed of a deuce-and-a-half (2 1/2 ton truck) with the famous/infamous BC-610 half-gallon Tx and a tow-behind motor-generator. As a separate antenna kit, one was made for the AN/TRC-1 70 to 90 MHz radio relay set and used in Europe during the Berlin Blockade to jump into Berlin from the edges of (then) West Germany.
Never used/played with either, just the horizontal rhombics 70 feet high, rather long, and with iron wire tapered-feed-line terminating resistor for HF. Had a bunch of those over a 2 square mile antenna farm in Tokyo. They work great on known direction radio paths with each leg about 3 wavelengths (or more)...:-) If one has the land, fine, but it doesn't fit in a typical urban dwelling lot unless one has a full acre or more of flat lot land. <shrug>
For at least 3 decades the land forces haven't bothered with rhombics in field conditions, just used NVIS whips for high-HF/low-VHF frequencies. For comparison in amateur radio use, a simple vertical would be a known-characteristic comparison antenna.
73, Len K6LHA (who was AF6AY before 8 Jan 10)
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RE: Inverted V, Vertical Rhombic
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by K1DA on January 12, 2010
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I have a 12/1 from a Navy inverted discone, uses a hardline connector the size of a firehose. BTW my Cantenna comment was a "suggestion" to look closely at anything which turns RF generated at great cost and expense into heat. Remember that "wideband" dipole with the resistor inside the center connector?
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RE: Inverted V, Vertical Rhombic
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by K0FF on January 12, 2010
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RR.
Yes I remember the dipole with the reistor across the feedpoint!
I try to look at every antenna and see its good points along with its disadvantages.
No one antenna is perfect for every use or every location.
Trap Tribanders are called "rotatable dummy loads" by many but look at the millions of contacts and buckets of fun they provide.
Geo>K0FF
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Inverted V, Vertical Rhombic
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by TF3Y on January 13, 2010
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Check out http://www.tf4m.com , i.e. Thor's TF4M website. He has Rhombic farm and his website carries a lot of info and links related to Rhombics.
73, Yngvi TF3Y
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RE: Inverted V, Vertical Rhombic
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by W8JI on January 16, 2010
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I had a "Vertical Half-Rhombic" which is actually called an Inverted V in old textbooks. It was on a broadcast tower in a swampy area with standing water in sandy black loam.
Even though it was 2 wavelengths per leg it never did show any gain over a dipole, although it had good F/B ratio.
That was in the 70's.
When I moved here in 1998 I was going to try again. I tried modeling Rhombics and V's of all types and never could find anything with worthwhile gain. Losses in the system, from the really physically long conductors and earth below the conductors, and half the power being lost in the termination (or wasted in the wrong direction if left unterminated) just eats the system up on HF.
If anyone can show a model that has more gain I'd appreciate a file or accurate description of the antenna, because I sure can't find one.
I summarized my results that includes models of antennas here:
http://www.w8ji.com/rhombic_antennas.htm
73 , Tom
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