Roger (K8RI) wrote:
> Dan Zimmerman N3OX wrote:
>
>> About a month ago (4 March), I posted about a newly hatched business plan of
>> mine and referred to a cage dipole that sold for $350 and had 5dBd claimed
>> gain. There was possibly an implication in my post that **any such claim**
>> was a **lie**, and that I had some specific knowledge that a factual
>> mis-statement must be taking place if such a statement is made.
>>
>> I have since been contacted by an individual whose company sells an antenna
>> meeting that description, and that individual assures me that the gain claim
>> for his company's antenna is truthful, based on an engineering analysis,
>> and he is concerned that my implication could be harmful to his business,
>> given the truthful nature of his gain claims for his company's antenna.
>>
>> So I feel I should apologize for any implication that those who sell cage
>> dipoles with with gain over dipoles are lying. I did not intend to
>> misrepresent the truth or falsehood of the claims of others.
>>
>>
> If it is truly a cage dipole then it has no gain over a regular dipole
> or 2.2 db gain over an isotropic source.
>
Thanks to the link that was provided I did go to the page advertising
the antenna. Basically I agree with their statements *except* for the
gain. Most could really do away with the tuner, but with a solid state
amp I'm limited to about 1.2:1 or less before the amp shuts down at
full power.
Antenna gain it not an easy thing to measure accurately and
particularly so on the lower bands. A lot of technique is involved even
on an antenna test range. Depending on conditions and set up any
particular antennas with similar characteristics such as variations of
dipoles (cage versus regular center fed) can, and often do show
considerable differences. So, I don't doubt that there is a strong
likely hood the outfit doing the measuring did in fact see a 5 dbd
difference. OTOH that is contrary to accepted theory and practice so
I'd have to question the methodology used by the company doing the
measuring as some one else has already mentioned.
That said and gain figures aside, a good size cage dipole is (can be) a
royal pain in the back side to build. Make a mistake and they turn into
the equivalent of a bait casting backlash. So, were time of the essence
I'd probably purchase one of these instead of doing all the cutting,
pruning, and swearing to build one myself. The 40 meter cage is a good
antenna and IIRC about 2 to 3' shorter than a regular dipole. (It's been
a long time since I had one, but that's my recollection and don't have
the ambition to go do the math for the L/D ratio at present) I had one
in the early 70's for a short time, but we also had a major ice storm
resulting in a relatively short life span for the cage. It worked well
and had a very broad band width but that's the extent of my first hand
"practical" experience.
As an aside, I did field strength measurements using an old Singer
Metrics set up for well over two decades where I worked in
instrumentation and calibrations standards so I'm well acquainted with
this type of work. OTOH it has been a long time.
> However the name "Cage Dipole" is a "common use"
> name with an established reference that goes back many years. It is
> generic to a family of dipoles made of wire, or tubing that effectively
> increases the diameter of the dipole thus lowering the Q and widening
> the bandwidth. It has been widely shown with widely available data to
> have no gain over a regular dipole, but a wider bandwidth based on
> diameter to length ratio.
>
> I've also seen a Yagi design using the cage dipole principle for the
> driven element, but that is a Yagi not a cage dipole antenna.
>
> Claims that a cage dipole has higher gain that those accepted are a bit
> more than optimistic.
>
But it is easily possible to come up with those results on a non
standard test. I'd have to see the methodology used, the area, and then
see if the results could be reproduced at various locations other than
the original site. There are just too many outside influences at any
particular station/location to make a truly valid test indicative of
what all stations could expect.
> As it is a well established principle/design it should not be
> patentable, but strange things do happen..
>
>
73 again,
Roger (K8RI)
> 73
>
> Roger (K8RI)
>
>> Based on long established, daily tested antenna physics, any such antenna is
>> impossible, since it would have to be around 300 percent efficient. I
>> cannot know and do not know, however, if those who claim such things are
>> truthful. I can only factually maintain that the antenna is impossible.
>>
>> However, do not take this retraction to mean that have given up on my
>> business plan of 4 March, as I think there's still a market, and in fact, I
>> am assured that I have fewer competitors than I thought.
>>
>>
>
>
>> 73
>> Dan
>> _______________________________________________
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