Too good to be true?

[RolandSWL]

http://www.ebay.com/itm/All-Band-multiband-HF-VHF-Vertical-antenna-Ham-Radio-Amateur-/111199520706?nma=true&si=PBKFIEAzSfnR1KOc%252B9ytHcni2FM%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

[W1ITT]

What the seller fails to mention is that you have to reapply the expensive dilithium swr grease once every 28 days, more often if you are using continuous carrier modes such as RTTY or AM.  Save your money.  There's no free lunch in the antenna world, though many have been offered.

[KD6VXI]

600 watts carrier of am,  with 1.6kw pep rating.

Methinks this guy doesn't operate am much.   Nobody wants to listen to approximately 60 percent audio.

Lots of marketing.   No technical writing in his ad.

Not to mention......  Who wants an antenna tuner that requires a heat sink (his newest models don't.   I guess a bigger resistor?

--Shane
KD6VXI

[W4EWH]

If it sounds too good to be true, it probably is.

[K1JJ]

Modern day Gotham vertical with a  X 29  inflation factor.    ($16.95 > $500)

At least the Gotham had an accessible base loading coil and tap. (equal to a good strapping mobile whip)

I used to be an apt dweller too - and feel sorry for the poor bastards who have to go thru this expensive learning curve.

T

[WQ9E]

Sounds like resistive matching is used so depending upon frequency quite a bit of the RF is going into heating a resistor.  I believe B&W was one of the first commercially successful designs with their inverted V and later folded dipole setups and they still sell these rather expensive antennas.

Of course a dummy load with leaky coax will radiate a pretty good signal under the right conditions.  When I was a new ham we had an old timer on the coast who was insistent on always using a dummy load for tune up (and that is good amateur practice) but he built his own load and cables that weren't very well constructed and it was a running joke that he got out better on his dummy load than some guys did with their compact space antennas.  His high point was working a SM0 in the ARRL phone DX contest on his dummy load after he forgot to switch back to his vertical after an excursion to 15 meters necessitated re-tuning his T-4XB/L-4B setup  

[W1ITT]

Last winter I was over at one of our joint bases in Europe and saw a resistively loaded broadband butterfly dipole thing.  It was supplied by an American manufacturer for temporary use, and it "worked" in that it radiated at least a bit.  The military occasionally uses these things for tactical and temporary backup uses.  They are frequency agile which makes the ALE stuff happy.  After we got finisihed installing some omnis and rotary log periodics, those air cooled antennas were scrapped.

By the way, I have the aluminum from an original Gotham vertical stored in the rafters.  I telescoped it in years ago and used it on 20 meters as a quarter wave.  One of these days I'll put it up again, as a backup, either on 20m or 30m.  It worked fine, but I don't recall being breathless at all the DX it magically pulled in like the advertising copy told about.  I'll probably mount it up on the stink pipe....

[N0WEK]

No big surprises here, I'll just cross post this from a discussion of this antenna over on AR15.com....

"I asked him on ebay...My question and his response....Shall we toy with him??

Dear mugbug,

Hello, you can call it a smart load, not a dummy load as a dummy load does not radiate. The matching is a non resonate antenna design to consume all wasted energy that a tuner, balun, trap coils, earth losses combined do anyway. This design effectively radiates the magnetic RF field that is created from this design. It is a closed efficient circuit. The current and voltages generated by the transmitter are FORCED to go completely through the 24 foot element and back to ground. What is left after the magnetic RF field is generated is dissipated through the resistive device that is heatsinked on the side of the antenna box. This has not ever been effectively done before now. You can check my log book on QRZ.COM with all of the contacts made using this antenna design. Thank you for your question and interest, I have been waiting for this discussion and I am most certain it will not end here. There is a lot of old school theory that has been around since the beginning of radio that is undisputable. But there is still a whole lot more to discover and prove there are more ways to do the same thing better.
- carlh1979Click "respond" to reply through Messages, or go to your email to reply




Dear carlh1979,

Can you please explain in detail the need for the very substantial heat sink?

Looking at your schematic it appears to me you have built a 25ft tall dummy load.

I am sure it presents a nice match across all bands (resistors do that) but I honestly cant see how it can be resonant on all bands as you claim or even effectively radiate. "

http://www.ar15.com/archive/topic.html?b=10&f=22&t=665685

[KB2WIG]

Floor wax or a dessert topping?


klc

[n1ps]

I think...buying technical stuff on ebay is not my favorite means of on-line buying.  The feedback seems to be more about the transaction and the comments are restricted by something like 100 characters or so.  Amazon and similar seem to be better in that at least there are detailed reviews. 

So Norm's advice re the dilithium grease may apply 

p

[W2VW]

Positive feedback on this item is powered by folks who equate low SWR with actual performance.

[AB2EZ]

There is an article that was published in the NY Times on November 7, titled: "The Unbelievable Skepticism of the Amazing Randi"

The Amazing Randi is a magician who has devoted himself to debunking magicians who claim to have supernatural powers... rather than being very skilled at the art of "slight of hand", creating clever illusions, etc.

I met the Amazing Randi in 1972 (roughly), when he was the guest speaker at a small meeting I attended in Rumson NJ.

What the article describes is how difficult it is to prove to people that supernatural powers do not exist.

I think the article is relevant to the never ending discussions of antennas with magical capabilities.

It is certainly true that you can make lots of contacts using an electrically short antenna*.

It is also true that including a resistor in the antenna structure can, in certain antenna configurations, be helpful. For example, in obtaining the maximum RF current along the radiating conductors of an electrically short antenna, and/or in producing an impedance, looking into the antenna, that the feedline + the transmitter can "live with"... particularly as an alternative to using the same size antenna without a resistor, and without an antenna tuner.

But, when one makes claims about an electrically short antenna having a radiation efficiency that is comparable to a full length dipole... well, that's entering the realm of the supernatural.

You can prove that creating such an antenna is impossible for the same reason that building a perpetual motion machine is not possible. I.e. if you could build such an antenna, you could use it to do things that violate the laws of thermal dynamics... e.g. conservation of energy. However, most hams don't have the specialized knowledge to understand the proof. Although most hams would not invest in a company that claims to be able to produce perpetual motion machines, the lure of a magic antenna is often irresistible.

*My antenna is now limited to a coax-fed doublet running along the 2nd floor ceiling (with one end sloping down along the staircase to the 1st floor) of my house in Princeton, that is a total of 45 feet long. I make lots of contacts on 40m.

Stu

[W3RSW]

I think the maker spied a rhombic terminated by a 200 ohm resistor ( of half the design power btw and for good reason)  and confused himself into believing terminated 25 ft. Would radiate as well as several hundred feet of a directional diamond.

Regardless, the hocus-pocus is just on the cusp of believability for the uninformed.

[RolandSWL]

But it got a 5 outta' 5 on EHAM !

[WD8BIL]

No complicated add ons, No tuners, No ground radials, No Baluns, No Traps, No coils or taps to mess with, no adjustments needed.

NO SIGNAL!

[Opcom]

It reminds me of the 'alll band no tuning" antenna the ARRL investigated and x-rayed which had a fake pcb, RF transformer, and dissipative resistor inside a potted box.