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Nitro
| | Posted on Sunday, July 07, 2002 - 11:18 pm: | 
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I need a better understanding of the power multiplication of an antenna. Does this mean that if my antenna boasts 28x multiplication and I put 300watts to it I'll have a total of 8400watts (300x28) transmitted or are there other factors to consider when determining the total watts being transmitted? If so, what are they? |
bruce
| | Posted on Monday, July 08, 2002 - 7:43 am: |
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Nitro here are the facts
your correct if the "X" number is right its....
power * X =ERP ( the number you get is called efective radiated power )
NOW the problem is what is real gain...!
Back in the 1920's Mr YAGI and Mr Undila figured out that adding one element either a reflector or director gave about 4 db of gain over a driven element and then adding a 3rd elm either a director or reflector again added about 3 more.
So..... there numbers came out about like this...
3 elm beam 6 db 4X power
6 elm beam 10 db 10x power
given all other factors these numbers could change by a few db but to get 28X you would have to have 14 dbd and that is going to take at least 2 5 elem beams stacked its REAL SAD that gain numbers are so inflated. The best way to improve your station is by the antenna remember ANY gain you get on transmitt you ALSO get on recive! Now speaking of REAL gain back when i played with EME (MOONBOUNCE) on 2 meters i ran 4 17 elm beams in a h stack REAL gain was 20 dbd which meant with 900 watts CW my ERP was 90,000 watts small gain conpaired to the big boys who have erp's of 1,000,000 watts ! There are lots of good web sites on beams .... yagis or yagi-undila arays.
O one final note on verticals a 1/2 wave antenna has about 2 dbi gain about zero dbd and a 5/8 wave some real gain although you can get up to 3dbd if you get a very good ground plane under it.... ok call it 3 db but ive never see it except on VHF/UHF.
bruce |
DeadlyEyes
| | Posted on Monday, July 08, 2002 - 6:46 pm: |
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Sorry but you still have only the input power going out. The only thing a beam does is to focus the unused signal.
For example if the dbd gian of a beam is say 3. If you put 4 watts in a no gain quarter wave antenna it sounds like 4 watts. BUT if you put that same signal into the 3x beam it will sound like 12 watts and transmit actually only 4 watts. What is happening is that the beam is acting like the reflector on a flashlight to focus all the signal in a much tighter area.
But the gain is only one of sound not actual power.
By the way here is how you figure multiply factor. For every 3 db or full multiple of which you double power. So if the DBd gain is say 12.5 . There are 4 complete multiples of 3 plus a small part of a 5th. If you transmit 1 watt the signal will sound like a little over 16 watts. The first 3 db doubles 1 into 2. The second 3 db doubles 2 into 4. The third muliple of 3 multiples 4 into 8. The fourth/last multiple of 3 doubles 8 into 16. The little extra of dot 5 adds a few extra watts of power.
I hope I have not confused you too much.
DE |
Nitro
| | Posted on Monday, July 08, 2002 - 9:02 pm: |
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I have a Moonraker 4, it's specs. read as follows: 14.5db gain, power mult. 28x , 16.5 foot boom, but it has a quad reflector, the driven element and two directors. So it's not a five element much less two stacked. could it be that the Quad reflector and boom length could increase the gain? Or maybe the type of material? It boasts aviation grade aluminium. I chose this antenna because of the reviews I got on it, from USA and Canada the users said it was a killer antenna, do you think the gain and power mult. is exagerated?
Nitro. |
ss8541
| | Posted on Tuesday, July 09, 2002 - 12:11 am: |
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deadly eyes, erp(effective radiated power) is just that, it isn't prp(perceived radiated power). yes the radio may be putting out 4(for this example) watts, but if the antenna has 3db gain (2 times) then the radiated power is actually 8w in the center lobe of the radiated power. this is evident when using a field strength meter. the meter isn't measuring 'sound' but yet amps/sq.meter, or as what really matters, 'power'. that is why using a good beam is better than an amp.
i do have to say that was a pretty good way of describing an easy way to do db calculations. that little extra over 16x that you were talking about for 12.5db brings the multiplication up to 17.8db. 12.5db=17.8 multiplication factor, so your way was pretty close. |
bruce
| | Posted on Tuesday, July 09, 2002 - 5:19 am: |
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Nitro
I get yelled at all the time a 4 el quad MIGHT do 10 db MIGHT but no way will you get 14. If that was true all these guys running quad stacked 22 elem yagys for moonbounce would all be running (4) 4 elen quads ( 20 db gain ) NEVER beleve antenna gains unless they have the range tests under NBS standards to prove it.
HERE ARE SOME MEASURED RESULTS OF ANTENNA DONE CORECTLY GIVE A LOOK !
http://www.csvhfs.org/CSANT98.HTML
bruce
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Nitro
| | Posted on Tuesday, July 09, 2002 - 6:48 am: |
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This is really great stuff, I'll look at these equations more closely and try to understand them, I had the TX signal covered, much like a fireman can adjust the nozzle and spray water (omni-directional antenna) or make it more intense (like the beam), I also have an idea of how the RX signal travels along the directors onto the reflector, then bounces off the reflector and meet the signal coming off the directors at the driven and then down the radio (hope I have it right), but what I'd like to know is how the TX siganl behaves once it reaches the beam.
Nitro |
DeadlyEyes
| | Posted on Tuesday, July 09, 2002 - 1:53 pm: |
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RE ss85...
Power multiplication of the antenna is included in the ERP calculation sure. BUT also included are the negatives. Say you antenna has a db gain of 4 but you are using coax with a line loss of almost two due to the type of coax being used/the radio frequiency being used/and the length of the coax. The net ERP of the antenna system as a whole would then would be 2. The antenna 4 minus the line loss of 2. In order to get the 4 db gain out of the antenna you would have to run extra power to compensate for the transmission line loss.
Antennas should always be considered as a system composed of the antenna itself plus the coax plus any devices that cause insert losses. |
DeadlyEyes
| | Posted on Tuesday, July 09, 2002 - 1:58 pm: |
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RE Nitro 7/8/02
Was the gain stated in DBi or DBd?
DBi is gain referenced to a mathametical model of a perfect reference dipole in some perfect theoretical free space. The comparison will be close enough to real world but hmmm still skewed a bit.
DBd is the gain referenced to an actual physical no gain dipole. It is hardware vs hardware and more closely represents the real world.
Either is good enough for daily use. |
ss8541
| | Posted on Tuesday, July 09, 2002 - 6:08 pm: |
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deadlyeyes, working in the business band radio area professionally, i am very aware of losses in transmission lines and the devices on that line. some of our rptrs are running close to 200w to get 40w at the antenna to make up for the line loss, and losses through isolators, combiners, filters, etc. and on the rxing end, tower top amps to make up for the rx loss. this is mainly at uhf freqs(440mhz and up for us) due to the increased losses at these freqs.
as for cb radio(27mhz), someone running 100ft of rg58 would have a 2.3db loss. this is 40% loss compared to the 50% in your example. we could get technical and say that if the antenna had a bad swr, that the loss would increase.
my point is that i left this out of my last post for the fact that at cb freqs, there isn't much line loss at all. you have to run a long length of the smallest stuff for it to be noticed. 100ft of rg8/213(what most run for base stations) is a 1db loss(20%). so with a 4w carrier from the radio, this leaves 3.2w at the antenna. no one will ever notice the difference between a 4w carrier and 3.2w carrier. so you might as well just use the 4w carrier when calculating your erp.
and don't get me wrong, i have always preached the antenna system is what makes a station. and that definitely includes the coax. i only recommend rg213 or bigger for bases with over a 50ft run. but for a mobile with a 18ft run, i'll tell guys to slap some rg58 on it since the loss is neglible, and rg58 is cheaper and easier to run. now if they are running power, then that is a different story. |
bruce
| | Posted on Tuesday, July 09, 2002 - 6:22 pm: |
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I realy dont want to nit-pic this but it is rated in DBI (a useless number) the moonraker 4 is nothing more than a 4 elm beam good for about 10 DBD or 12.5 dbi thats a real gain of 10x not 28x also the quilty of the materials has little to do with gain at 27 mhz unless maby you might want to make it out of Gold? Ive seen computer models of yagis with very high Q elements and realy good gain but back to the real world alum. is the materal of choice and it is NOT a high Q materal. Well my choice CUSHCRAFT WHY ? im realy not a fan but i had many of them over 40 years and they work just like they say they will AND if you need a part you CAN get it! Here is a sample and its good for 18 DBI
http://www.cushcraft.com/amateur/details.asp?catid=170
Bruce
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Nitro
| | Posted on Tuesday, July 09, 2002 - 11:07 pm: |
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The spec. sheet doesn't indicate if it's DBi or DBd, it just says 14.5 dB. |
Nitro
| | Posted on Tuesday, July 09, 2002 - 11:17 pm: |
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Yeah DeadlyEyes I'm sure there are negatives but in the same way there are positives, for example there must be some significant advantage in using a Quad reflector for sure, this could account for some increase in gain, this antenna also uses aviation grade aluminium, ok, maybe that particular spec. may not give you bragging rights since other beams out there could be using the same material, but can't that fact also increase the gain? Pardon me here but I'm looking for the 4dB gain bruce stole from me. From the reviews these Moonraker 4's stand tall above the MACO 4's in performance, so bruce, are you willing to give me my full 14.5dB gain now?
Nitro |
bruce
| | Posted on Wednesday, July 10, 2002 - 4:53 am: |
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Nitro NO I WILL NOT GIVE YOU 4DB HA HA HA! 14 dbd on a 4 element array would inspire EME users !
You have a good antenna nothing wrong with it but the real world and antenna sp sheets rarly meet.
Its a 4 element beam the quad reflector is a gimmic just like the wire kits that they sell for thoes antennas. As for the Maco 4 inless im missing something i looked it up it looks just like your moonraker so gain should be almost the same FACT YAGI GAIN ( how much ) = NUMBER OF ELEM and BOOM LENGH ASUMMING THAT ITS TUNNED CORECTLY.
Here is my e-mail box wa4gch@yahoo.com its ALWAYS open.
bruce |
bruce
| | Posted on Wednesday, July 10, 2002 - 7:13 am: |
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THIS is a bunch but explanes truth or at least standards used by QST on yagi antenna gain if you are intrested in what is involved in "FAIR" gain reporting this should help
bruce
http://www.arrl.org/ads/antenna/
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DeadlEyes
| | Posted on Wednesday, July 10, 2002 - 8:13 am: |
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Re SS and Nitro....
First SS because he was first to reply. It is good that you knew what I meant about negaives in a system. However before we go too too far into the acutual numbers know that I pulled numbers out of the air just for the purposes of example.
And I agree that in the VHF and UHF regions of radio the type of line you use does make a very very big difference. One could be pumping power on the ground only to be heating up the coax with nothing but a trickle being actually sent into the antenna.
However in the CB range I have been using the RG8x or the mini 8 coax for some time now. I prefer the gray jacket stuff that copper sells because it is easier to work with. Overall, on the Ham Bands not too shabby for the price of the stuff. Granted not as good as the ultra low loss very expensive coax but still not bad.
Now to Nitro.
Absolutely a beam will help but the coax comes in when frequency and length of coax come into play. This is not a big problem with the CB Frequencies. But in the VHF and UHF frequencies it makes a big difference. If you were to use the mini 8 coax for UHF almost all your signal would go to keeping the coax warm. BUT if you used say Heliax (sp?) or some of the newer ultra low loss coax the loss is extremely reduced compared to the mini 8 losses. A loss in the transmission line means no signal out. But then again you would not have to worry about ice and snow building up on the coax in winter either :-)
DE |
Nitro
| | Posted on Thursday, July 11, 2002 - 6:03 am: |
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The info I've gotten from this discussion is really awesome and overwhelming in some cases, it's a good thing I asked, I'm relatively new to the world of CB so there's a whole lot more for me to learn, hey bruce, should I share your views (db gain) with all the guys I know with 'rakers? I think not, they'll want to round up a posse and come after you. What I now want to know is how the siganl behaves once it reaches the beam, like I said at the end of one of my posts, I know (or think I know) how the beam treats a RX signal. But I'm not sure how the beam treats the TX signal before sending it off the tip of the antenna and I don't want to start a seperate topic on it (or should I?).
Nitro. |
bruce
| | Posted on Thursday, July 11, 2002 - 9:55 am: |
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BRING THEM ON NITRO !!!! HA HA HA
OK LINCH ME but there are real world
using .2 wave spacing gain in dbd should be as follows:+/- 1db
2el = 3db
3el =6db
4el =8db
5el =10db
to get 13 db you need to go to about 10 elem 16 dbd about 20 elem
VERY GOOD QUESTIONS ! OK in short lets say your moonraker has 2 "S" units gain over a A-99 Your talking to TAZ on your a-99 he is s-5 you go the the moonraker he is s-7 On his end you would ALSO be 2"S" units stronger well a beam is nothing more tham a way to reshape the lobe of the antenna in doing so the signal gets stronger because it is now poited at your target. NOW on recive your incoming signal is treated the same way your transmit signal so the recive signal increases exactly as your transmitt signal does this is a dumb thing it dont care if it's a gointa or a goouta. Books have been writen hunderds of them on yagis some good some junk. Some good ones the william Orr antenna handbook, The ARRL antenna handbook and thr RSGB handbook.
Also Larson ( the founder of the antenna company ) wrote papers in the 70's going into great detail on designing them. The goverment NBS did a paper on them about 1978 and NBS findings are still good basic numbers when determing gain.
bruce |
Scrapiron63
| | Posted on Thursday, July 11, 2002 - 12:44 pm: |
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Nitro: Don't feel like the lone ranger, I've been messing with beam antennas longer that lots of these guys have been living, and I don't know "how' they work. I know what it takes to make them work right, and how to build'em, but thats another story. Look at the beam real close and you'll see something that really blows your mind. Your actually talking on the little 11 inch piece of gamma-match. That's all the center or hot side of your coax is hooked to. The signal is just radiating off the rest of the antenna. That's why any other metal objects, like guy wires that are not broken up with insulators, can mess with how efficiently your beam works. |
Hoosier Cardinal
| | Posted on Thursday, July 11, 2002 - 1:35 pm: |
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I dont care what they say about the rakers. I have a few sets but i dont give a you-know-what about the real gain figures because i know mine work and work well. All this technical BS actually takes the fun out of CB!!!! |
bruce
| | Posted on Friday, July 12, 2002 - 9:55 am: |
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Nitro LOOK at his graph HOW can you jump 3 db for ONE more element then 2 more for ONE more then only .5 for 4 more ????????? either this is a misprint OR the people who wrote it sell antennas HUMMMMMMM.
Like i said before there are JUNK websites There are only 2 rules to yagis gain doubles everytime you double the number of elements provided they are spaced and cut corectly..... check out
ARRL ANTENNA BOOKS
RSGB ANTENNA BOOKS
BILL ORR ANTENNA BOOKS
they are all in agreement
bruce |
bruce
| | Posted on Friday, July 12, 2002 - 11:13 am: |
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ok here is a 4 elem beam lets see what cushcraft clames
http://www.cushcraft.com/amateur/details.asp?catid=97
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Jellybean
| | Posted on Friday, July 12, 2002 - 6:11 pm: |
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I have a question, I'm getting ready to put up a beam. How far below the radials of the antenna should the guy wires be? If they're about 8' below, should I use non metalic guy wires, or would some sort of insulators be adequate?
Thanks, |
bruce
| | Posted on Friday, July 12, 2002 - 11:01 pm: |
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8 foot should be no problem |
Jellybean
| | Posted on Saturday, July 13, 2002 - 11:07 am: |
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Ok great, thanks bruce. |
Nitro
| | Posted on Saturday, July 13, 2002 - 1:41 pm: |
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Hey Jellybean, what type of beam is it? How high are you mounting it? Good luck!!! |
Nitro
| | Posted on Saturday, July 13, 2002 - 1:51 pm: |
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Thanks bruce for the info, I'll print it out and go through it. I see Husier Cardinal is one of those guys who thinks to get too technical is taking all the fun out of the hobby. That's alright though, you're entitled. As for me I can't see any fun in not knowing.
Nitro |
Jellybean
| | Posted on Saturday, July 13, 2002 - 7:27 pm: |
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Nitro, I picked up a Moonraker. I'm going to put it on my roof. My peak of roof is 26', I'm putting up a 10' section of mast with the rotor on it, then 10' of mast with the Moonraker. I was going to put a third section of 10' but thought that was too much. So my guy wires will only be about 3' below the tip of the verticle radials. I'm guying it at the base of the rotor to six points on the roof. I'm putting the base of the mast into a tripod. With my situation, I couldn't do a tower. To many trees around the house, and wife says, no more trees down.  |
Nitro
| | Posted on Sunday, July 14, 2002 - 8:50 am: |
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Fine business Jellybean, hope it performs,what type of material are you using for guy wires?
Are the moonraker 6's still around, I'd like to find one for a friend, he doesn't want anything under 6 elements, if you know where one can be had let me know.
Nitro. |
Taz
| | Posted on Sunday, July 14, 2002 - 2:03 pm: |
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yeah i no of a moonraker 6 sitting at 60 feet which is n olonget used and the tower it sits on it a beast! but he put a pool in his back yard and i cant get to it from the alley so i have to pluch it off of his property with a crane out of the street. |
Bigbob
| | Posted on Sunday, July 14, 2002 - 5:10 pm: |
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Does copper still sell MACO Super Laser500s,those are just like the moonraker 6s. |
Scrapiron63
| | Posted on Sunday, July 14, 2002 - 6:43 pm: |
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The laser 500 is a lot more beam than the moonraker 6. The moonraker 6 is just that, 6 elements each way. The 500 has 8 elements vertical and 8 flat, and is 40 feet long, almost 10 feet longer than the moonraker 6. It's also a lot better built in my opinion, and i've put both together. The laser 400 is about equal to the raker 6. |
Nitro
| | Posted on Sunday, July 14, 2002 - 10:20 pm: |
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Hey bruce, I ordered both the ARRL handbook 2002 and the ARRL Antenna book, I remembered ordering one couple years ago for a HAM student and it was really fantastic reading, I thought I'd own one of my own.
Nitro |
Nitro
| | Posted on Sunday, July 14, 2002 - 10:26 pm: |
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Are you going for that moonraker 6 Taz? I guess they don't sell anymore, only used. Why do you think they use those stainless steel rods at the ends of the moonraker 4 elements? Do you think they give some advantage over all-aluminium elements? Or just style?
Nitro. |
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