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Tech237
Moderator
Username: Tech237
Post Number: 755
Registered: 4-2004
| | Posted on Sunday, April 29, 2007 - 6:44 pm: | 
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As an experiment on the effect of antenna spacing take two CB antennas a beam and a vertical. Mount the vertical directly above the beam, about 1 ft above.
Attach a CB to the beam and a FSM or CB on recieve to the vertical. Now transmit on the beam and watch the FSM/S-meter - I would be very surprised if you do not get almost fullscale reading on the FSM. To reduce the meter reading to a neglibgable level the vertical would have to be around 10ft above the beam. Now transmit on the vertical - the meter reading should be less due to most radiation going out in an upward direction, but the meter will still read incoming signal.
Now if you can move the two antennas apart in a horizontal method and you find that it will take much more distance between the two antennas before the received signal drops to a low enough level not to be a problem.
I can give an actual example of this situation. A Water Rescue Base had 2 x 27MHz Marine radios (yes in Australia), 2 x VHF Marine radios and 1 HF Marine radio. when I joined this group the two 27MHZ antennas were on a common cross arm spaced about 6ft apart. if you transmitted on one radio you had no chance of hearing any signal on the other one. The same situation occured with the VHF marine radios
I moved one 27MHz antenna and one VHF radio antenna by exchanging them to the other mast. We could now talk on any radio without causing any problems on its mate. The two mast were around 30ft apart.
Later I improved the situation even further by raising one 27MHz and one VHF antenna to 65Ft high and left the other antennas at 30ft.
When I get chance I'll try to locate the relevant data on antenna spacing and add to this thread.
Simon
Tech237
KD7IEB
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Penrider
Member
Username: Penrider
Post Number: 95
Registered: 1-2007
| | Posted on Sunday, April 29, 2007 - 10:26 pm: |
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thanks, Simon...good info...someone suggested that I try stacking an Imax above a 3 or 4 element horizontal beam(use a 4 position switch to use either/or or Both), and I had wondered how far above the beam to put the Imax to keep interference to a minimum...to make sure I read correctly, you say approx. 10 feet from beam to feedpoint of Imax?....is that the best, or would I have to play with it from there?...
Moderator Note!
Check out Tech291's Pictures (Members Picture Area) of his MACO V58 mounted 3' 1" above his beams.
Posted on Sunday, November 13, 2005 - 8:43 pm:
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ok,
a quick rundown.
42' tower with thrust bering on top to support the weight.
21'of 1-1/2"sched40 galvanised pipe for mast plus a reducer and 3' 1" galv so Maco V58 could go on top.
53'agl to the pl connector on the Maco
43'agl to the center of the boom for the beam.
CDE AR-22xl rotator
104'SWI rg-213 for the beam
140'Times LMR-240 for the Maco(excess coiled in attic)
Volt-Guard 8 line surge supressor for rotator
2 Altelicon lightning supressors for coax
3 9'copperclad groundrods buried horizontal(tablerock at 4')
still not done with it yet,been messing with it since june when time or weather allowed.
Sean
CEF867
CVC81
"Keep smiling, it makes people wonder what you're up to!!"
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Tech237
Moderator
Username: Tech237
Post Number: 757
Registered: 4-2004
| | Posted on Monday, April 30, 2007 - 9:00 am: |
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As another Moderator noted less can work - sometimes, BUT for absolute surity a quarter wave at the highest frequency is best.
Take a look at the ARRL or RSGB Handbooks they both specifiy at least that quarterwave spacing.
I have used less (where space limitation dictated) and got away with it but not often. IN one such case, we were setting up a temporary radio base for a 6 day sporting event and only had 5ft of horizontal spacing to play with. IN that spacing we mounted (in order) 2m vertical (G7 for voice), 10m vertical(A-99 voice), 2m Vertical (5/8 wave for data), a 70cm (stacked 3 dipoles for voice) and a thrid G7 for the second 2m voice net. By keeping the two 2m voice nets 1MHz apart (one around 146MHz and the 147.5Mhz) and running the data net at 144.9MHz we kept inteference to a minimum.
After the event, and out of curiosity we removed all but the two G7s and even if we transmitted at 144MHz and listened at 147.9 then interference between the two radios was then unbelievable. Somehow the other antennas that we had inbetween were acting as a sheild.
Antennas are funny things - sometimes a setup that you KNOW should not work does and one that on paper looks like a sure thing is a bust. Thats is one reason I have always loved experimenting with them.
Simon
Tech237
KD7IEB
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Patzerozero
Senior Member
Username: Patzerozero
Post Number: 3653
Registered: 7-2004
| | Posted on Monday, April 30, 2007 - 4:34 pm: |
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regarding the moderators note to penriders question-if you go to http://www.copperelectronics.com/cgi-bin/discus4/show.cgi?tpc=77380&post=112932#POST112932, dennis states that the feedpoint of the maco v5/8 is 10' higher then the midpoint of the boom of the m104.
if you leave the groundplane OFF the maco v5/8, somewhere between 0'-3' above the beam, the beam acts as the groundplane for the vertical omni antenna. keeping the factory groundplane installed requires a greater distance....i thought more like 1/2 wavelength, but dennis seems to have NO PROBLEMS with 1/4+ wavelength separation. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 3654
Registered: 7-2004
| | Posted on Monday, April 30, 2007 - 5:54 pm: |
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'53'agl to the pl connector on the Maco
43'agl to the center of the boom for the beam.
CDE AR-22xl rotator'
'21'of 1-1/2"sched40 galvanised pipe for mast plus a reducer and 3' 1" galv so Maco V58 could go on top'-if you look at the pics posted on 11/12/05, you can see the short piece spliced to the top of the sched 40 galvanized pipe. the sched 40 goes down into the tower a ways, & with the thrust bearing, reduces the strain on the rotator. the pic (of dennis?) standing on the tower shows his head not even 1/2 way to the SPLICE, which has another 3 feet above it. the top pic shows the beam mounted maybe 1' over the tower. therefore, dennis is either 2' tall, or as HE posted, '53'agl to the pl connector on the Maco
43'agl to the center of the boom for the beam.
CDE AR-22xl rotator', which is 10' between the feeds & since the beam is horizontally mounted, that puts the v5/8 10 feet above the beam. |
Penrider
Member
Username: Penrider
Post Number: 97
Registered: 1-2007
| | Posted on Monday, April 30, 2007 - 7:26 pm: |
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Thanks, Simon and Pat..(and moderator, don't know which one)...even I understood all that, which is just unusual to say the least....with my tower, I MAY be able to run pretty close to the same disances(feedpoint of the beam would be the issue, Imax would be no problem)...the way things are right now, I know I could put the feedpoint of the beam at 36ft(Full Wave, correct??) then 10ft(1/4 wave or so, correct??) to the feedpoint of the Imax(No GPK, correct??)...that would give me 66ft to the tip of the Imax... I don't Think a certain nosy/rude ham a few blocks away could spot 6ft of extra height from the street(although he already Accused me of it once, tip of A-99 is at 54ft right now)...
This seems like an experiment that would actually Work(use Imax to find 'em, and beam to bring 'em in)...and I Might not even screw it up, LOL....once again, Thanks
Sean
CEF867
CVC81
"Keep smiling, it makes people wonder what you're up to!!"
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Henry_hpsd
New member
Username: Henry_hpsd
Post Number: 4
Registered: 2-2007
| | Posted on Tuesday, May 08, 2007 - 1:44 pm: |
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Hello,
About the stacking idea...when we stack antennas (wich are not identical as is the case with the Imax vertical and a 4 el yagi horizontal) both antennas will "sent" half of the transmitted signal. Vica versa counts for reception.
The only improvement you will notice is an improvement in QSB (sometimes signals vertical polorized are stronger horizontal and the opposite is possible aswell this is due wave reflections in the atmosphere) stacking a vertical and a horizontal antenna might give you an edge when this happens.
But overall your signal will get weaker its as simple as when you put 100 watt in to one antenna all the power is transmitted through that antenna but in this case only 50 watts is transmitted. And since all rules apply to reception aswell you will notice a slight drop.
The distance between antennas is not "at least a quater wave" this is a very old rule wich has been taken over and over the years by many. Since the 90's this statement has been brought down by many. For all situations different distances can be expected. (some reasons: Do you still want front to back or are you just going for gain?, at wich distance from your stations do you want to have the strongest signal?, at wich height are the ariels errected, etc..)
There are great antenna modeling programmas availible like Eznec are 4NEC2 wich will give you a great impression of what the systems does.
Hopefully i brought you down from your thoughts to stack a imax and a yagi.
take care 73s Henry |
Tech833
Moderator
Username: Tech833
Post Number: 1678
Registered: 8-2002
| | Posted on Wednesday, May 09, 2007 - 12:31 am: |
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Well, you're half right Henry.
Yes, when you stack antennas, each gets half the transmitter power. However, if the antennas are stacked one above the other, the amount of power on the horizon is doubled! A true 3 dB gain over a single antenna.
If the antennas are half wave spaced, the amount of power going straight up and down is nearly zero. If they are full wave spaced, gain on the horizon improves slightly with the addition of minor lobes above and below the major lobe on the horizon.
As you double the amount of antennas you stack, the gain doubles (3 dB) as well. |
Penrider
Intermediate Member
Username: Penrider
Post Number: 108
Registered: 1-2007
| | Posted on Wednesday, May 09, 2007 - 2:04 am: |
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Brought me down??? I Hate climbing towers, so I ain't coming down until it's finished!... If someone had read All of the topic posts, they would know that the idea wasn't to multiply gain, it was to use the omni to find signals, then use the beam or both to zero it in....I wasn't sure about the gain Paul is speaking of, but I knew there wouldn't be any loss other than that of two lengths of coax unless I used mismatched types or lengths of coax or had bad connections...also, as everyone stated the setup uses the beam as a groundplane for the Imax...that's Gain right there, isn't it?...even if it Didn't work, I could use the Imax for 11m and the beam for 10m...win/win either way
Sean
CEF867
CVC81
"Keep smiling, it makes people wonder what you're up to!!"
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Tech237
Moderator
Username: Tech237
Post Number: 772
Registered: 4-2004
| | Posted on Wednesday, May 09, 2007 - 1:14 pm: |
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Tech833 is perfectly correct ASUMING you are feeding both antennas at the sametime. In my description you are only feeding RF to one antenna at a time, which is more likely when using antennas of differing polarity, in which case each antenna would receive 100% of the power (alright ignoring feedline losses).
Simon
Tech237
KD7IEB
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Tech833
Moderator
Username: Tech833
Post Number: 1679
Registered: 8-2002
| | Posted on Thursday, May 10, 2007 - 11:25 am: |
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If you are only feeding one antenna at a time, that's different. Let's take the example of an omni antenna mounted above a horizontal yagi (beam). You can mount the vertical as close to the beam as you want. When you run the vertical, the beam acts like a ground plane for the omni. When you run the beam, the omni acts like more mast sticking up above the boom of the yagi. No interaction at all.
I thought Henry was talking about running two antennas at once, so I answered based on his comments. |
Henry_hpsd
New member
Username: Henry_hpsd
Post Number: 5
Registered: 2-2007
| | Posted on Thursday, May 10, 2007 - 2:25 pm: |
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Hi there!
Stacking indeed can provide you about 2,7dB gain above a single antenna, agreed. (keeping in mind both are indentical and in the same polarity)
But, I was under the impression that when you
stack a vertical and horizontal antenna (let alone non identical antennas) there will be no gain. Only loss. Ive I am wrong I would really appriciated an explination on forum.
Thanks in advance!
Henry |
Penrider
Intermediate Member
Username: Penrider
Post Number: 112
Registered: 1-2007
| | Posted on Friday, May 11, 2007 - 2:25 am: |
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now all of ya have me confused...I already understood how running two separate types of antennas on the same tower Independantly works, and stacking two identical antennas for gain isn't a new concept either...what I was originally trying to find out is... 1. how much distance was required between the two(that was answered quickly and easily)...2. when running two different antennas together(vertical above a beam) for the main purpose of Seeking and bringing in DX, will the Imax still act as an Omni(to detect signals) while rotating the beam to find the strongest signal source???....I was, and still am under the impression that if both antennas are properly tuned, equal lengths of same type coax are used with good connections, and a good quality switch box then there would be a minimum of loss(only the loss of "X"ft of coax)...if combining vertical and horizontal polarization causes loss, then how does a Yagi with Both work??
Sean
CEF867
CVC81
"Keep smiling, it makes people wonder what you're up to!!"
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Tech237
Moderator
Username: Tech237
Post Number: 775
Registered: 4-2004
| | Posted on Friday, May 11, 2007 - 8:32 am: |
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Penrider,
A combined verticla/Horizontal yagi/quad etc will still have gain - the same amount of gain a single antenna of the same style and number of elements. Where the "loss" comes in is that if the two are fed simultaneuosly each one will only get half of the available power.
For example say we feed 10 watt into a yagi with 10db of actual gain, the effective radiated power (supplied power x gain) becomes 10w x 1db (10db is 10 times power which is why I picked that value) or 100w effective power.
Now feed that same 10w into two cross polarized yagis each of which has 10db gain. No what is our effective radiated power? Each antenna only receives half of the supplied 10w or 5w (ignoring feed loss, inequalities in the phasing harness etc). So each antenna radiates 5w x 10db or 50w effective. Notice the 100w effective is still there except half is vertically polarized and half is horizontally polarized. Hence the apparent power loss on each part of the signal.
The above is a simplified look as othe factors can come into effect, but I hope it helps you understand a little better.
Simon
Tech237
KD7IEB
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Henry_hpsd
New member
Username: Henry_hpsd
Post Number: 6
Registered: 2-2007
| | Posted on Friday, May 11, 2007 - 9:21 am: |
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Hi!
With your present situation you have a winning team..
You will use your vertical for omni direction reception. And when you know where the DX is comming from you point your beam in that direction and then switch between the two.
When you were going to feed both antennas at the same time. You will bring loss to your system. Though there is a advantage aswell: Radiosignals have qsb sometimes caused by the polarity switches due to propagation you will see there is less QSB in this system.
Your comment on a (cb)yagi wich does both at the same time...there isnt or it will have loss compared to a normal horizontal or vertical antenna (but most of the time there is a switch to switch between vertical and horizontal)
There are omnidirectonal yagis (both horizontal/vertical) but they are used only for "propagation" in wich polarity varies alot. A helical antenna is an example.
Its easy to explain the loss, when you look to it in a transmitting way. Your power now is devided in the vertical AND horizontal plane.
When it would only be in the horizontal or vertical pattern it will be stronger. Look at it like when u held up a paper and pres with one a t-spoon you push right through it, when you will push with the teapot you will need to add force to brake the paper.
Best of luck.
henry 19sd348 |
Thehobo
Intermediate Member
Username: Thehobo
Post Number: 118
Registered: 2-2004
| | Posted on Friday, May 11, 2007 - 11:55 am: |
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penrider, i believe your confussing your self with the great amount of input your getting?? lol. but like the rest, and you stated you had a antenna switchbox, so now im assumming that each antenna has the full output of your system, when the switchbox is at one position or the other, it will feed that antenna with just coax loss!! now, being as ive used the setuip of a imax over a flat 4, the one thing i noticed, and it wasnt alot, is that the imax tended to be alittle directional as to were the front ond rear of the beam was pointing?? as i dont want to over load you with more stuff, ill say this, imo, both antennas will work if all other is ok?? like swr, and the resnonce?? use the set up for awhile then tell us your experance with it!! enjoy them as i did, find the signal lock on with the beam, talk up a storm.. lol..
thehobo
269150 am
monitor ch |
Penrider
Intermediate Member
Username: Penrider
Post Number: 114
Registered: 1-2007
| | Posted on Friday, May 11, 2007 - 9:24 pm: |
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I'm only confused about the Loss part...I understand the Split power aspect...what I don't get is how that constitutes as Loss?...The combination becomes Directional with the gain of a 5-element Beam instead of a 4-element beam or a single element omni(although it is Less gain than a single polarity 5-element beam)...lowest swr and matching resonance would be Required to run the setup anyway...and by the way, there are Three(3) different Dual Polarity Beams/Yagis for sale at copper with Significant front to back ratios...that makes them Unidirectional, not Omni
Sean
CEF867
CVC81
"Keep smiling, it makes people wonder what you're up to!!"
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Henry_hpsd
New member
Username: Henry_hpsd
Post Number: 7
Registered: 2-2007
| | Posted on Saturday, May 12, 2007 - 5:39 am: |
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Right about omni thank you for improving my Englisch!
It is an intresting subject isnt it?.
On Eznec i ran some test with a vertical (groundplane and horizontal (2el yagi) both fed. Everytime the gain was lower (in the order of 3dB) compared to the individual antennas.
So my opion remains that besides the power splitting there still is loss when u use (keywords) different antennas combined in different planes.
For those intrested i can sent the files. (They are larger then 50kb)
Besides this, working DX means your looking for that real weak signal far away. With both fed it will be more difficult, the front to back and front to side of the yagi will "disapear" cause the vertical gives you noises from all over the globe. There will be additional vertical lobs wich cause additional noises aswell.
If that was a winning situation whey dont we see it often ?
In anyway i look at it i would stick to the switching situation.
Was hoping some of the guys can confirm all this or improve my thoughts, after all we are here to learn and help!
Best regards!
Henry |
Tech237
Moderator
Username: Tech237
Post Number: 779
Registered: 4-2004
| | Posted on Saturday, May 12, 2007 - 8:52 am: |
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Penrider,
The combination does not become a 5 element beam simply because one supposed element is not in the same plane as the others and thus does not add to the gain of the array. To increas the gain all the elements have to be in the same plane (either horizintal or vertical) and spaced the correct distance apart.
Take a flashlight and tape a piece of card over the light with a single horizontal slit in it. Now shine it onto a wall. You should get a horizontal line of light on the wall. Leaving that first piece of cardboard in place, add a second one with a vertical slit in it. Now reshine the light onto the wall and notice the difference. This is a similar effect to running a vertical and horizontal antenna fed from the same source.
So even if they are fed in phase you still have a 4 element yagi getting half of the power while the other half goes to the vertical. THe yagi will still have the same gain it always has had but it's effective output is only half of what it would be if fed singularly because it is only getting half of the power. It is this reduction in power that produces the effective loss - of 3db or half power.
Simon
Tech237
KD7IEB
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Penrider
Intermediate Member
Username: Penrider
Post Number: 116
Registered: 1-2007
| | Posted on Saturday, May 12, 2007 - 2:31 pm: |
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thanks simon, that explains the power loss....so, use both for Receive, then find the signal and use the beam alone for TX
still kinda confuzzled as to how the beams with both horiz. and vert. elements work?...or is that a completely different concept?
Sean
CEF867
CVC81
"Keep smiling, it makes people wonder what you're up to!!"
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Tech237
Moderator
Username: Tech237
Post Number: 781
Registered: 4-2004
| | Posted on Saturday, May 12, 2007 - 11:21 pm: |
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NOpe same concept they only drive one or other sets of elements at a time - normally.
In certain special cases they may drive both elements sets simultaneously using lengths of coax calculated to cause a signal that rotates as it travels - commonly called circular polarization, but that is a whole new can of worms.
Simon
Tech237
KD7IEB
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Tech833
Moderator
Username: Tech833
Post Number: 1681
Registered: 8-2002
| | Posted on Sunday, May 13, 2007 - 11:42 am: |
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You are also forgetting that on receive, if the omni and horizontal yagi are fed at the same time, the signal from each is shared between the radio and the opposite antenna. Then, you introduce phase loss. UNLESS they are phased properly (a 90 degree coax section would do it). |
Allagator
Advanced Member
Username: Allagator
Post Number: 762
Registered: 9-2002
| | Posted on Friday, June 08, 2007 - 7:38 pm: |
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now tell me why a A99 sitting 8 inches above a M104c has better recive and little better transmit but if you move it 3' above it the recive is not the same and the trans is not as good ! but you can stick a imax 2000 up 3' above a M104c and it works good but if you move it down ! to 8" above the M104c the recive drops and the trans realy drops ! any one tell me why this is ! (and the M104c is on the flat side ! to make things clear)
Thanks if anyone can answer it !
Allagator
CEF 115 |
