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Message |
    
Rickinsc
Junior Member
Username: Rickinsc
Post Number: 16
Registered: 6-2003
| | Posted on Saturday, November 19, 2005 - 10:09 am: | 
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I wanted to mount my antron 99 on top of a horizontal 4 element beam that will be on a tower. I have heard that this will allow the beam act as a ground plane for the antron.Is there any truth to this ? What should be the distance from the antron to the beam? Thanks |
Mikefromms
Advanced Member
Username: Mikefromms
Post Number: 806
Registered: 6-2003
| | Posted on Saturday, November 19, 2005 - 10:50 am: |
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My experience has been that a even a groundplane kit does not help the Antron 99. It is self-suffient. Get it up about 9 ft above the beam to prevent getting a directional signal on your Antron. I've seen this happen. Can't really explain it.
Mikefromms |
Allagator
Advanced Member
Username: Allagator
Post Number: 719
Registered: 9-2002
| | Posted on Saturday, November 19, 2005 - 10:02 pm: |
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hey Rick the A99 will work best 6 to 10 inches above the 4 element !
i run a A99 above the M104C and ive got mine set at 6 inches ! but if your useing a imax 2000 move it up to 10 plus inches 11-12 inches work great for the imax 2000 !
hope it helps !!!
Allagator
CEF115
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Thehobo
Junior Member
Username: Thehobo
Post Number: 28
Registered: 2-2004
| | Posted on Sunday, November 20, 2005 - 8:14 am: |
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say hey, flat 4 at 11/2 ft above the rotor, and the i max 11/2 ft above the flat 4!! swrs almost flat and all of this is up on a 60 ft homemade tower..been working for over 2 years now.. hope this gives you another look at what your doing??
thehobo
274150 am
monitor ch. |
Dx431
Senior Member
Username: Dx431
Post Number: 1123
Registered: 2-2002
| | Posted on Sunday, November 20, 2005 - 10:16 am: |
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I ran the A99 and the M103C flat and loved it. Tech833 told me to install the A99 as close to the beam as I could get it. So I did, and it worked great for me.
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Marconi
Intermediate Member
Username: Marconi
Post Number: 493
Registered: 11-2001
| | Posted on Sunday, November 20, 2005 - 1:33 pm: |
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Well if the A99 or Imax did use the beam as a ground plan, then it would be a miracle, and would have to be very close to the feed point in order to even do that. If it did act as a GP, it would not be a very good one, but it should not hurt anything either.
The Imax should not be affected at all by the presence of the beam, because the natural polar isolation between vertical and horizontal fields would surely cover up any directional qualities, if there were any.
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Thehobo
Junior Member
Username: Thehobo
Post Number: 29
Registered: 2-2004
| | Posted on Monday, November 21, 2005 - 6:21 am: |
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marconi, on my setup i put 6 watts of power on the i max, and then drove a circle of about 1 mile distance around the i max over the flat 4 and found this reading on a field streath meter!!! in front of the beam, i set the f/s meter to most sensative and at the max mark on the meter, then made the drive around the mile circle!! at 30 on front, it dipped slighty to 28 on the sides then to 25 on the back of the beam.. it does look as thou the beam slighty makes the wave patteren of the i max a bit directional??? not much but as we tried this at both one mile and 2 mile, the meter showed the same dip in the signal streanth.. as my freind has the same set up as me, his did the same?? also it seems as the hearing and sending is slighty different off the back or front?? this was checked using a station about 25 miles away!! at both ends, there was about an s unit or one and a half differance at each station?? just thought id show what was going on here at our location?? thanks for your input!!
thehobo
274150 am
monitor ch. |
Marconi
Intermediate Member
Username: Marconi
Post Number: 495
Registered: 11-2001
| | Posted on Monday, November 21, 2005 - 10:16 am: |
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That is a remarkable FS meter you have there hobo. I would think you're probably correct, the beam will likely affect the pattern of the vertical to some degree. I was just suggesting that the beam is likely not serving as a ground plane that's all. Just about everything close to an antenna has some affect. At a miles distance you could have a building, a power line, a street light pole, or just some bad earth between you and the antenna that could have some affect on a very sensitive meter. Even the auto moving past another auto can have an effect on a mobile rig.
While driving around what did you do to be sure that the responses you were seeing on your FS meter were from you Imax and not a thousand other signals closer to you? Like maybe the vehicle you were in, AM and FM broadcasting, TV signals, or those from medical or commercial radio?
I've been around this business since the 60's, and I have never seen a field strength meter that was frequency sensitive. How did you know? |
Thehobo
Junior Member
Username: Thehobo
Post Number: 30
Registered: 2-2004
| | Posted on Monday, November 21, 2005 - 1:20 pm: |
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on the field streath meter, what we did was have the guy on base key and unkey the radio a few times to see if what we were seeing just mite be what we were after?? as far as other interfearance
that wood be a thing that a person wood have to take into consideration?? we tried the best we new how and worked with what we had to do this?? agin, i assure you this isnt a 100% thing, probley not even close, but in doing both set ups, like i said, there was a dip on the sides and back of the beam!! how much??? didnt have anything that sensative to do this!! we just played with what we could as the same question was ask local if the beam did affect the streath of the signal?? we could be a million miles off but in our interpertation, it did what it did??/
like you, ive been into this stuff from in the milatary to now, joined in 1955, helped out in the mars station werever i could!! just like doing odd things that most others wood'nt think of!! lol.. agin thanks
thehobo
274150 am
monitor ch. |
Tech833
Moderator
Username: Tech833
Post Number: 1099
Registered: 8-2002
| | Posted on Monday, November 21, 2005 - 5:42 pm: |
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The horizontal beam will serve as a terrific ground plane for your vertical antenna. You should know that it IS true, you will get some directivity on the 'front' of the beam due to the beam antenna re-radiating a small portion of your signal from the vertical. The effect is not very pronounced, however. It does not reduce any signal in any direction, but provides a slight (SLIGHT!) boost in the direction off the front of the beam. It will also very slightly reduce the front-to-back ratio of the beam, but not noticeably.
Either way, it is a win-win because no signals are reduced in any direction. |
Tech291
Moderator
Username: Tech291
Post Number: 296
Registered: 11-2004
| | Posted on Monday, November 21, 2005 - 6:49 pm: |
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Hobo,
what you might try different is to have the fs meter stationary at whatever distance and monitor the signal as you have someone turning the base antenna.that would cut down on the variables that driving around would present.
tech291
cef#291
kc8zpj
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Thehobo
Junior Member
Username: Thehobo
Post Number: 31
Registered: 2-2004
| | Posted on Tuesday, November 22, 2005 - 6:32 am: |
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good idea, just mite try that?? huummm.. thanks..
thehobo
274150 am
monitor ch. |
Mikefromms
Advanced Member
Username: Mikefromms
Post Number: 813
Registered: 6-2003
| | Posted on Wednesday, November 23, 2005 - 9:50 am: |
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We had a guy install an imax just above his very long tv antenna and his signal just stuck in certain directions. Maybe the Antron 99 will work better than the imax with the beam under it? Anyway, the bird meter doesn't lie and numberous cber's experiencing same thing does make a statement.
mikefromms |
Tech833
Moderator
Username: Tech833
Post Number: 1101
Registered: 8-2002
| | Posted on Wednesday, November 23, 2005 - 10:09 am: |
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Mike, What would a Bird meter have to do with signal strength in certain directions?
BTW, Bird meters are NOT always right. Unless the load and source are both 50 ohms, the meter will indicate incorrectly. SOme of the professional market Bird meters come with a correction table for frequency and load variations. |
Rickinsc
Junior Member
Username: Rickinsc
Post Number: 17
Registered: 6-2003
| | Posted on Wednesday, November 23, 2005 - 2:25 pm: |
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Thank you for all the replies, I will definately make this happen but now it may be in the spring time. Thanks again. rick |
Marconi
Advanced Member
Username: Marconi
Post Number: 500
Registered: 11-2001
| | Posted on Thursday, November 24, 2005 - 1:02 pm: |
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833, concerning your comments. Would any meter give us a true or accurate reading when the load and source are not both 50 ohms, while using a feed line to connect?
If so, isn't this a situation found when using a coax feed line rather than just the meter being wrong or lying. |
Tech833
Moderator
Username: Tech833
Post Number: 1106
Registered: 8-2002
| | Posted on Thursday, November 24, 2005 - 3:46 pm: |
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There is no 100% perfect wattmeter. You have to correct for frequency and resistance (sometimes reactance) variables.
Of course, odd values of feedlines can be used as transformers and such, but this is not what we are talking about here.
The best way to measure 'SWR' is with a return loss bridge and tracking generator (measuring retunr loss). However, unless 25 grand is in you budget for a fancy SWR meter, stick to the affordable stuff available and just know that its reading is not EXACTLY gospel truth. It will get you close enough for this kind of work though. |
Marconi
Advanced Member
Username: Marconi
Post Number: 501
Registered: 11-2001
| | Posted on Thursday, November 24, 2005 - 11:34 pm: |
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Yeah I know 833, I know we were talking about Richinsc putting an A99 above his horizontal beam, but these discussions just seem to very often trend this way, off to other subjects at times. Still I sometimes find the side issues interesting as well, like in this case.
Mike mentioned the use of a Bird meter like it was always accurate. You advised him, correctly, that the Bird would also reflect thus and such, just like any other inline meter. However your statement did not tell him why. I then popped up and basically said that what we see, under the conditions you site as controls or the lack, was caused by the coax line we use and not because the meters lie or even read incorrectly. I don’t mean lab quality stuff here either. The devices you mentioned are really out of the scope of the discussion.
It is true that the results, any results, shown on an inline meter may not show the true conditions at the feed point. This is mostly true because the inline meter is not at the feed point and/or for sure something in the system or the load is not equal to 50 ohms resistive. I guess, as you suggest, if things were otherwise an inline meter would more than likely show a correct reading of the true condition at the feed point in SWR, right?
So, I believe all of this is not because the meter lies or is incorrect. It is because this is the nature of a coax line, a coax line that terminates at an impedance load that is different from the source and/or the characteristic impedance of the connecting line, to show us a condition that only exists at the specific point in the line where the meter happens to sit for the moment.
Most guys seem to have taken this, lack of matching at line termination, to say this is the reason their meters are lying to them, just as Mike implied. So, maybe a run of coax is a transformer if the control conditions you site are not met.
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Tech833
Moderator
Username: Tech833
Post Number: 1108
Registered: 8-2002
| | Posted on Friday, November 25, 2005 - 12:17 pm: |
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I think you have it.
All except a pice of coax being a transformer. In the case where your load is expected to be 50 ohms and you use 50 ohm cable (but all is not perfect), the coax does not act like a transformer, it just further amplifies any mismatch one end sees of the other. Of course, this all depends on where in the coax you take your measurements. Move up or down the coax a few feet and your reading will change. |
