moonraker under a groundplane??

[ranger6900]

I have a question for the tower antenna guru's

I want to run a ground plane for local tx/rx on top of the Moon raker 4 ....extend the pole up above it for the solarcon
any ideas or feed back i

all is appreciated


Ranger

[drdx]

Been there and done that. It will make the vertical above directional, in the same direction as the beam. It won't be AS directional, but it will be. The vertical elements on the moonraker radiate as part of the ground. -drdx

[gun runner]

How far do you need to keep your stick from your beams ?

[drdx]

Preferably a wavelength away, but as long as it's on its own pole with its own ground you'd lose the directional problem. That, or just go with a flat beam and the stick on top and you're fine. Its the vertical part of the beam that causes that. -drdx

[ranger6900]

dr dx

have any idea how much loss there is ....or another way of asking is to what degree will the ground plane become directional %

And would you say don't do this at all or its ok and wont hurt anything just lose a % of omnidirectional on the ground plane



also i have been told that the GP needs to be at least 3' above the tips of the elements on the raker4 or more but use 3' increments
wave length ratios were the reason


any comments ??


the reason i ask about this set up is i have a lot of trees and very limited to where i could add a second pole for the ground plane


thanks for the insight and sharing your experience


RANGER

[linx]

Ranger,

As I said in your PM to me a couple of days ago, when you put that much pipe above your tower you are looking at major troubles. Think about this. You need to get your bottom vertical elements away from your tower. That's at LEAST 10 ft of pipe without the vertical above it. To get the omni antenna above the moonraker, you will have to get it away from the top vertical elements. That's at least 10 more ft of pipe.

With the weight of a beam, you do not want 20 ft of pipe above your tower. The first wind storm you get, and the pipe is gonna bend double. That's way way way too much stress on a piece of pipe.

Have I see it done? Yes, but usually the person is using a flat side beam sitting right on top of the tower with about 5 ft of pipe above the flat side beam with a vertical omni antenna.

drdx is right as usual. It will pick up some of the characteristics of the beam.

Let me say this, I used my Imax2000 at 50 ft for a couple years. That Imax2000 is now sitting on a 15 ft piece of pipe, that is just slid inside the corner post of my chain link fence (I removed the cap on top of the post). I can TX an RX just as good with that Imax as I did at 50 ft. No jokes about it. Once you get used to using that beam, you will probably phase your vertical out as most folks do.

[drdx]

Great point there by linx on the load issue. You get a big beam, and a vertical above, the leverage there does become apparent. They do make special masts for that purpose but they are heavy and expensive. Think about all that weight and length that, once it clears your tower, thrust bearing, or whatever you have for a top, it is on its own. Speaking of thrust bearings, USE ONE.

On the directional topic, my experience with one was noticeable close up and even more so far away. You would be better off putting the vertical on a 20 ft pole or whatever you could instead of up on the tower, as it would operate better for an omni antenna. Depending on your style of operation, with a beam and a vertical, you'll probably use the vertical as a casual local and "spotting" antenna any then go to the beam unless you're right in the middle of your usual contacts. If you have to spin the beam around to make a contact on the vertical, you're defeating the reason for having it.


-drdx

[Buckshot]

Listen to good advise, It pays & saves headaches & money Good luck!

Buckshot

[drdx]

Hey, just another lump of thought for this talk soup: Your location, west of me, is still kinda out of town. I mentioned using just a flat beam with a vertical on top, but you're probably gonna want to have a vertical beam FOR SURE based on your location. Unless you're surrounded by stations, based on your outlying area location, why not scratch the vertical on top and run a 6 or 8 element beam to get you into town better? It would be money well spent and give a good return on both tx and rx. Then, just do the low vertical antenna for close-up, local, testing, etc.

Another word of advice. When you go to buy your coax, get good Times Microwave LMR400 or equivalent. Ony buy the one run to the top of the tower. Then get a remote coax switch, like an Ameritron 4 position one, that uses the coax for a control cable, and it will pay for itself in coax savings if your coax run is anything over about 100 feet. The switch is like 129 and will take a good amount of power and saves on install hassle and when the coax does get old, or contaminated, you're only buying one run. And.... nothing says more cb fun like another box on the bench with lights and switches.

-drdx

[721HACKSAW]

I have lusted over a beam for some time now. I currently have 50' tower with the Imax 5' above on a 10' mast pole. (5' in the tower 5' above) Lately I have seen several setups with the flat 3 or 4 element Yagi just above the tower, with the omni-type antenna above it. I questioned the possibility of interference/ reflection problems, but all I have read it seems to be a non-issue. With a verticle type beam though I have to agree way too much mast length to be feasible. Just my two cents.

[drdx]

The flat beam setup is great if you talk skip only or talk to other locals on flat antennas, but if you have the flat beam, don't plan on it helping you in a local power war with vertical mobiles and bases, as the drop in signal from horizontal to vertical, or vice versa is 20 db or more, so that flat beam will be weak to the other vertical stations locally. When the skip rolls the signals are random in polarity, or more plainly, in their horizontal vs. vertical orientation, so it does not come into play. Others will chime in and "correct" me on this I'm sure. Lonesome500, where are ya? -drdx

[ranger6900]

Experience is the voice to good advice.

I am taking the advise and have decided to scratch the two in one set up.

Many thanks Linx and Dr DX for the input.

I appreciate your willingness to share from your past experiences.

FYI i already have the moonraker and tower just need to relocate get it ready to raise it here.

Ranger

[linx]

Good choice on putting the imax seperate from the beam.

If it were something like a dipole or wire antenna, then I'd say use the same tower.

I tell ya, get that moonraker 10 ft above the top of the tower, and you'll be praying to someone in the first wind storm!

My mast pipe is 15 ft. It is 1 1/4" schedule 80 pipe. about 6 ft in the tower, and maybe 9 ft out of the tower. At 40+ MPH winds, the mast pipe bends like a drinking strawl.

Good point is I've survived 85mph winds with no guy wires. I have it guyed off now, which I need to post pictures of.

Drdx is a mud duck.