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Author Topic: Vertical with dumby MMDS antenna attached at top  (Read 1005 times)
KD7YHP
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Posts: 3




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« on: January 14, 2004, 09:07:29 PM »

I am in a restrictive area that allows MMDS antennas with mast lengths up to 12' long.  I would like to move to general class in the next few months and move into HF.  I would like to know if anyone has insulated a MMDS (Yagi type) directional and mounted it on top of an HF vertical?  

Would the yagi disrupt the signal even if it was insulated from the main antenna.  I have read a little theory looking for a good response and have found none.  

I am trying to play the game and look like a MMDS (which requires no approval from the HOA), but still get to have an outside HF on the roof line.


(I guess I am luckier than most, I have received permission to have a ~12" antenna in the back yard which is not perfect but I could push it and get away with ~18.  From the street my rear yard looks lower so unless they jumped the fence and found away around my dog they would assume it was 12'.)

Thank you
73s
KD7YHP
John
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KC8VWM
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Posts: 3119




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« Reply #1 on: January 14, 2004, 11:02:18 PM »

You could just put up your HF vertical "mast pipe"

Then construct a "make believe plastic" dummy antenna for the top.

If the dummy antenna is all plastic construction it will be lightweight and have no RF conductive properties.

Use thin plastic straws for the elements. Glue the elements to a "cut" bottom section of a plastic coathanger to "act" as the support boom.

You could drill a small hole through the top of the HF antenna for the "coathanger" boom.  Use a glue gun to seal it tight. There may be people here with other ideas for the "boom mounting" part.

You can space the elements for a particular band if you want the practice.

Paint the whole thing with "aluminum grey" color paint to "resemble" a real antenna.

SWR will be 1:1.5 across the entire radio spectrum. No need for coax, this is a "passive" type of antenna. (hihi)


Good Luck

73

Charles - KC8VWM
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KD7YHP
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Posts: 3




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« Reply #2 on: January 15, 2004, 12:07:26 AM »

Thank you for the tip in the plastic.  I was planning on using a factory antenna as the mast so I will contact the manufacturer and double check to see if the antenna can hold the minimal weight.


Thank you
KD7YHP
John
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N3ZKP
Member

Posts: 2008




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« Reply #3 on: January 15, 2004, 11:17:35 AM »

What vertical antenna are you referring to?

Attaching ANYTHING metal to the top of a properly functioning vertical antenna will affect that functioning, most likely adversly. At the very least there will be some considerable detuning.

Lon
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KI4BUM
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Posts: 59


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« Reply #4 on: January 15, 2004, 03:07:59 PM »

I have a similar restriction but what I was thinking of doing was putting the wind measuring portion of my weather station at the top of a hollow plastic tube (PVC?) and slip the vertical antenna inside.  That way it looked like I had a weather station at the top. There's no rules about weather stations Smiley

However the wind direction portion of the station does have a tiny bit of metal in it and a wire that connects to a transmiter that would be mounted below the antenna. Im just afraid I'd fry something in the weather transmitter even if I placed the transmitter portion below the antenna. (this would be for 2meter)

thoughts?
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KC8VWM
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Posts: 3119




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« Reply #5 on: January 16, 2004, 11:19:33 AM »


>>>Attaching ANYTHING metal to the top of a properly functioning vertical antenna will affect that function<<<


Who said anything about attaching metal to the top of a vertical antenna?


73

Charles - KC8VWM
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N3ZKP
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Posts: 2008




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« Reply #6 on: January 16, 2004, 01:05:40 PM »

Chuck:

Reread the original post:

<< I would like to know if anyone has insulated a MMDS (Yagi type) directional and mounted it on top of an HF vertical? >>

In addition to the detuning, I am unaware of any over-the-counter HF vertical that would actually support any kind of antenna attached to the top without failing (and falling) in even a modest breeze.

Lon
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KC8VWM
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« Reply #7 on: January 16, 2004, 03:22:56 PM »

oh ok Lon, sorry for the misunderstanding.

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WX7G
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Posts: 6055




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« Reply #8 on: January 21, 2004, 03:45:24 PM »

I ran a quick NEC simulation of a 14 MHz vertical with and without an MMDS antenna placed 1 inch above it. There was VERY little detuning. I think you idea is a good one and with a little PVC or other plastic you can mount the MMDS on your vertical. The wind survival will be lessened. I can calculate the before and after wind survival for you when you select a vertical.
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AD7DB
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Posts: 370


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« Reply #9 on: January 21, 2004, 04:43:53 PM »

Maybe you could use a real MMDS antenna and mount it to the top of a metal mast that is insulated from ground. At ground level, hook it to some automatic remote tuner (such as the Icon AH-4 if your radio supports it - there are other brands too) and the ground of the tuner goes to a bunch of radials and counterpoises. The antenna at the top of the mast should be completely connected, all parts of it, to the mast. This might actually help with top loading it, and if it's tall enough might work on all bands 80 through 6 meters.
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NA4FM
Member

Posts: 11




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« Reply #10 on: January 23, 2004, 10:19:54 PM »

Doesn't the pole for MMDS need to be guyed?  You might want to guy it with a couple of inverted Vees.

Just another thought.

I like the above option, stand the pole over a coke bottle and feed it with an antenna tuner.

Buck
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KD7YHP
Member

Posts: 3




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« Reply #11 on: January 28, 2004, 02:24:57 AM »

I was planning on using a Butternut HF6V (or simular) it is 26' long and should rise only about 11 feet over the roof line of the house.  What I am worried about is the impact that the house will have on reception.  I have to make it look like a MMDS antenna so it will be up near the house.  I was not going to wire it down but if the wind survivability is to low than I will have to put a few up (would be thankful to WX7G for an analysis).  I think the Plastic Yagi is the way to go.  I am still learning about antennas so I am open to any advise.  Does anyone have any operating time on a CPK Counterpoise kit?  Will it work as well as radials?


Thank you for the input!!

KD7YHP
73's
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