Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Reflector Vs Director
When modelling close spaced element antenma
assemblies it is possible that some elements are physically longer than the "driven" element. Is the length of a element sufficient enough to declare that element a " reflector" or are there other caveates involved.( i.e. phase) As background to this question I would point out that that it is possible to have two closed spaced (positioned) elements one of which is shorter and one of which is longer than the "driven " element, this combination being placed either forward or to the rear of the "driven " element. Regards Art |
#2
|
|||
|
|||
the length itself relative to the driven element length is not sufficient to
apply any particular label to an element of a parasitic antenna. it should be noted that the terms 'director' and 'reflector' are not necessarily scientific terms, they are more of a vague word description of how an element apparently works based on the observation of the antenna pattern. the real effect of each element of an antenna must be described by describing the current magnitudes and phases and the physical location of each element. a good example of this is a 2 element parasitic array, at one frequency the parasitic element may be a 'director' and at another frequency it could be described as a 'reflector'... without changing the length of either the driven or parasitic element. " wrote in message news:u85ge.72716$c24.9252@attbi_s72... When modelling close spaced element antenma assemblies it is possible that some elements are physically longer than the "driven" element. Is the length of a element sufficient enough to declare that element a " reflector" or are there other caveates involved.( i.e. phase) As background to this question I would point out that that it is possible to have two closed spaced (positioned) elements one of which is shorter and one of which is longer than the "driven " element, this combination being placed either forward or to the rear of the "driven " element. Regards Art |
#3
|
|||
|
|||
Dave
I was hoping that the IEEE would have a definition upon which I could hang my hat on. Hate to see another quabble like we had with TOA! In my particular case I have two elements coupled in such a way that even tho only one is driven the other is also of the same phase ie. additive, all other elements are longer than the driven element which suggests multiple reflectors, absent an accepted definition. Regards Art " wrote in message news:u85ge.72716$c24.9252@attbi_s72... When modelling close spaced element antenma assemblies it is possible that some elements are physically longer than the "driven" element. Is the length of a element sufficient enough to declare that element a " reflector" or are there other caveates involved.( i.e. phase) As background to this question I would point out that that it is possible to have two closed spaced (positioned) elements one of which is shorter and one of which is longer than the "driven " element, this combination being placed either forward or to the rear of the "driven " element. Regards Art |
#4
|
|||
|
|||
Art Unwin wrote:
"When modeling close spaced element antenna assemblies it is possible that some elements are physically longer than the "driven" element. Is the length of an element sufficient to declare a "reflector" or are there other caveats involved (i.e. phase)?" Art answered his own question. The element doesn`t care how it gets a leading (capacitive) current, or a lagging (inductive) current. In our broadcast curtain antenna arrays, we used an RCA WM-30A phase monitor for the current angle in the ibnductive parasitic reflectors. Phase was adjusted to spec with a short-circuit stub connected to where the feedpoint would be if it were a driven element. Kraus is unequivocal on page 245 of edition no. 3 of "Antennas": "When the halfwave parasitic element is inductive (longer than its resonant length) it acts as a reflector. When it is capacitive (shorter than its resonant length) it acts as a director." Best regards, Richard Harrison, KB5WZI |
#5
|
|||
|
|||
Interesting.
One respondent says position is a factor and the other says it is not according to Kraus ,who may well have been directing his comments at a Yagi model So I changed the feed point on my model, which is not a Yagi, to other elements to see if they lagging or leading. Surprise ! Some of the other elements were resonant also thus they could be fed in one or more places at the same time Since with the initial design they are not all directly fed these apparently do not fall into any catagory. I suppose literature in general can only apply definitions to that which is known by the author at the particular time Regards Art "Richard Harrison" wrote in message ... Art Unwin wrote: "When modeling close spaced element antenna assemblies it is possible that some elements are physically longer than the "driven" element. Is the length of an element sufficient to declare a "reflector" or are there other caveats involved (i.e. phase)?" Art answered his own question. The element doesn`t care how it gets a leading (capacitive) current, or a lagging (inductive) current. In our broadcast curtain antenna arrays, we used an RCA WM-30A phase monitor for the current angle in the ibnductive parasitic reflectors. Phase was adjusted to spec with a short-circuit stub connected to where the feedpoint would be if it were a driven element. Kraus is unequivocal on page 245 of edition no. 3 of "Antennas": "When the halfwave parasitic element is inductive (longer than its resonant length) it acts as a reflector. When it is capacitive (shorter than its resonant length) it acts as a director." Best regards, Richard Harrison, KB5WZI |
#6
|
|||
|
|||
Well, everything stated may be true... but I have never seen a beam where
you would confuse the reflectors from the directors by physical size... if in doubt and you wish to confirm this--just look up! Warmest regards, John -- Sit down the six-pack!!! STEP AWAY!!! ...and go do something... " wrote in message news:u85ge.72716$c24.9252@attbi_s72... | When modelling close spaced element antenma | assemblies it is possible that some elements are | physically longer than the "driven" element. | Is the length of a element sufficient enough to | declare that element a " reflector" or are there | other caveates involved.( i.e. phase) | As background to this question I would point | out that that it is possible to have two closed | spaced (positioned) elements one of which is | shorter and one of which is longer than | the "driven " element, this combination being | placed either forward or to the rear of the | "driven " element. | Regards | Art | | |
#7
|
|||
|
|||
John Smith wrote:
Well, everything stated may be true... but I have never seen a beam where you would confuse the reflectors from the directors by physical size... if in doubt and you wish to confirm this--just look up! Warmest regards, John Given a beam with two identical driven elements, which is the reflector and which is the director? :-) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#8
|
|||
|
|||
Well Cecil:
You know me and my fondness for "tweaking" electrical lengths grin... I suspect it is more than possible to have 'em the same length, and indeed, you seen the folded 1 wave monopole I played with, it did exhibit side "nulls." Now, as to if the gain of the beam you point out is exactly equal or better, I doubt--as opposed to one being longer/shorter director/reflector (remember, I still ponder the ethers part in all of this--and NONE of our formulas take it into account)... but besides all of this... I JUST HAVEN'T SEEN ONE!!!! And, you know I am a hopeless "Assumer"--I dare to assume if it were such a great idea, I'd see a bunch---but then, I am open to a discovery here!!! Come on Cecil, with so many after my scalp--I can't afford losing any hair to you!!! grin I gotta get some work done here--I am turning off message notification... I will read/respond to your come-back later... grin Warmest regards, John -- Sit down the six-pack!!! STEP AWAY!!! ...and go do something... "Cecil Moore" wrote in message ... | John Smith wrote: | | Well, everything stated may be true... but I have never seen a beam where | you would confuse the reflectors from the directors by physical size... if | in doubt and you wish to confirm this--just look up! Warmest regards, John | | Given a beam with two identical driven elements, which is the | reflector and which is the director? :-) | -- | 73, Cecil http://www.qsl.net/w5dxp | | ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- | http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups | ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#9
|
|||
|
|||
Seems to me Cecil that the terms "Reflector" and
"Director" are very poor words to describe antenna elements for an HF array . I have oft times changed a single element into two closely coupled elements and where one is short and one is long relative to a driven element I wonder who was the first to assign these terms Or was it a poor translation from Japanese ( Uda and Yagi) ? Regards Art Cecil Moore" wrote in message ... John Smith wrote: Well, everything stated may be true... but I have never seen a beam where you would confuse the reflectors from the directors by physical size... if in doubt and you wish to confirm this--just look up! Warmest regards, John Given a beam with two identical driven elements, which is the reflector and which is the director? :-) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#10
|
|||
|
|||
"John Smith" bravely wrote to "All" (11 May 05 09:21:00)
--- on the heady topic of " Reflector Vs Director" It's all about the frequency, physical length, and spacing... JS Reply-To: "John Smith" JS Xref: aeinews rec.radio.amateur.antenna:30111 JS Well, everything stated may be true... but I have never seen a beam JS where you would confuse the reflectors from the directors by physical JS size... if in doubt and you wish to confirm this--just look up! JS Warmest regards, JS John JS -- JS Sit down the six-pack!!! STEP AWAY!!! ...and go do something... JS " wrote in JS message news:u85ge.72716$c24.9252@attbi_s72... JS | When modelling close spaced element antenma JS | assemblies it is possible that some elements are JS | physically longer than the "driven" element. JS | Is the length of a element sufficient enough to JS | declare that element a " reflector" or are there JS | other caveates involved.( i.e. phase) JS | As background to this question I would point JS | out that that it is possible to have two closed JS | spaced (positioned) elements one of which is JS | shorter and one of which is longer than JS | the "driven " element, this combination being JS | placed either forward or to the rear of the JS | "driven " element. JS | Regards JS | Art .... There's always free cheese in a mousetrap. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
CHAMPAIGN-URBANA -- Assistant Director for Technology (Chief Engineer) WILL-AM-FM-TV | Broadcasting | |||
Hudson Division Director Race | General | |||
Hudson Division Director Race | Policy | |||
Hudson Division Director Race | CB | |||
Hudson Division Director Race | Shortwave |