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Author Topic: multiple antenna/ single feedline....  (Read 4077 times)

Posts: 20

« on: June 14, 2013, 06:30:41 PM »

Here is what I am l looking for...

I want a multiband dipole(ish) antenna system that is for a confined space.  I have a 2 bedroom townhouse that allows for no external antennas (perm installs anyway..).  I have no access to an attic space so I am pretty much limited as to what I can fit into the upstairs bedroom diagonally across the ceiling with planter hangers...

My shack is downstairs in my living room/ harmonics playroom/ xyl's hangout and other purposes...

With that said my question is, I like single band dipoles for tuning ease, but I want a multiband where I don't have to swap feedlines or retune ... so I was looking at the fan dipoles and kind of like that idea but price on the commercial ones are beyond what I wanna pay so I had a thought, I know I can get a couple hamsticks, a MFJ-347 and have an instant dipole with a little tuning.... but here is where my twisted mind gets to thinking.. can I get multiple MFJ347's and tie them together fairly close together (vert spacing of 6in or so and connected with tee connectors) and it work ok? I already know it would not be the most efficient but would it not function similar to a fan dipole?  though with the cost of the hamsticks and 347's maybe I could get a decent something else that would work better?

I have thought about outting a dipole in the gutters and running the feedline up the inside of a downspout lol..

Posts: 1789

« Reply #1 on: June 14, 2013, 06:52:50 PM »

I would suggest you keep it simple.  Put up, even if you have to bend it into a "U" or "Z" shape, the longest center fed "dipole" you can and feed it with ladderline or
300 ohm line to a decent tuner or tuner and balun.  The larger/longer wire will have considerably more capture area and most likely better efficiency than a buddipole or hamstick. You could also try a closed or open loop around the perimeter of the ceiling of the room(s). My last choice would be one of the small inductively wound commercial antennas.

If your gutters are metal, laying an antenna in them would be pointless; no way that would work.  If they are plastic it may be OK.

Very respectfully, and I mean this to help you, not to be condescending: The best thing you could do at this point is pick up a good antenna book such as the
ARRL Antenna Book and put in some study time to get a better understanding of basic antenna theory. There are a number of things you likely can do for an
antenna that would be better than some short commercial wound whip, but you need to understand what and how it might be matched and fed. Again, very
respectfully, the more challenging your QTH and antenna situation, the more important it is to understand theory as it will definitely give you more options.
Difficult antenna situation usually lend themselves to homebrew antennas. The antenna books contain other antennas that you may see and find an easy way to modify
it to fit your situation. Your situation is unique and a few comments or suggestion from on here may not be enough to give you a good result. Knowledge is your best friend in this situation.

  73,  K0ZN

Posts: 14452

« Reply #2 on: June 14, 2013, 06:59:16 PM »

I think I'd try to get a dipole setup for a single band first and see how that works out. That would at least give you a reference performance to judge other antennas against. Working with an inside antenna, being able to get out okay and not getting RFI into everything is a challange. Multiband antennas are more complex and the chances of you just hanging something from the ceiling and having it all work 100% with no RFI without a lot of experimenting are not good.

How much space to you have? A 20M dipole will be about 33 feet long. Do you have that much space corner to corner? If not then you'll need some type of loaded antenna like a pair of Hamsticks. They would be about 15 feet long. Shortening a dipole to 50% is about the best you can do and still maintain a reasonably good efficiency. As you go lower in frequency (40M and 75M) the antenna will need more loading coil to keep it physically short and that will make it less efficient. My experience has been that the lower in frequency you go the more RFI gets coupled into home wiring and the more problems you have getting into things like smoke detectors, GFI breakers, etc.

Bob  AA4PB
Garrisonville, VA

Posts: 1003

« Reply #3 on: June 14, 2013, 09:49:50 PM »

If you have space for a 17 foot span, try this:
get a hamstick dipole bracket, two Hustler 54" masts, two VP1 brackets to allow three resonators on the end of the mast,
and get a pair of resonators for each of the three bands you want to use. you can feed this with coax, and a tuner built into a rig will work fine. cost, not including coax for this will be about $200, depending on what bands you buy resonators for.
 If you want to verify that you can radiate from your attic, first run the coax up there - RG58 or RG8X will do fine - and make a wire dipole for whatever band that's likely to be open, that you can fit in the attic.  15 or 17 meters would be a good bet. If that works, you could make a wire fan dipole for a couple of other bands, on the same feedpoint. If the space issue is a killer, then the dipole using mobile components will give you the least grief.  If you have a big budget ($500 or so), one of the MFJ Magnetic Loops could be a good choice if you don't have any metal ducting in the attic.
BTW - a hamstick dipole can work on 40m - I have one, along with a hustler mobile vertical that's on a metal roof - I can switch polarity on that band, and it does make a difference, depending on the propagation and the polarity of the other station.

Posts: 17418

« Reply #4 on: June 14, 2013, 09:50:33 PM »

The Hamstick-style antennas are just shortened antennas with a loading coil.  You can make
your own using wire if you are willing to wind a coil on a piece of PVC pipe (or even a toilet
paper core.)

As AA4PB suggested, I'd start with one or two bands to see how it works, then add more
bands as you go along.

Probably the best approach would be to put the feedpoint in the middle of the ceiling and
run the wires towards the corners then down the walls as far as they will go, or until you
run out of wire.  (This probably will take a bit more wire than the formula for a straight
dipole.)  On the bands where you are still short of length, put a loading coil in at a
convenient spot, such as the junction between the wall and ceiling.  Adjust the number
of turns on the loading coil for resonance.  Rather than putting the wires close together,
I'd spread them out as much as you can:  put the longer wires (probably 20m and 40m)
into the corners and the shorter ones in between.  There will be some interaction when
you try to add 17m and 12m along with 20, 15 and 10m, but at least the adjustments
are convenient to reach.

Posts: 67

« Reply #5 on: June 15, 2013, 04:55:56 AM »

For about $138, why not just buy an Alpha Delta DX-EE multiband antenna?  It will work 40, 20, 15 & 10M and is only 40 feet in length and is a fan dipole.  Not sure if your room will accommodate that, but I'm sure you could make it work.

John - KD8TZC

Posts: 20

« Reply #6 on: June 15, 2013, 10:14:31 PM »

I know that I mentioned that it would not be the most efficient antenna.  I also have the Practical guide to Antenna as an ebook on my tablet that I have been reading so I am studying theory a little deeper.  I have also built my own antenna that work quite well on 40 meter that I built out of some pvc and a bit of romex so I am experimenting with that but I was looking for something to use that is semi tuned to actually use the radio vs the analyzer and not have wire strung all over the place as I have curious toddlers that would try to find a way to swing from it as they have already torn one down on me...

As far as the DX-EE I am reading the reviews on it and most seem favorable so that may be an option. but again I don't have 40ft to properly mount one in a straight line... but I may sneak it out into the trees... But if I do that I may as well get a rigid antenna and a portable mast

my FT-857D dosen;t have a built in tuner and I have yet to buy one

Posts: 71

« Reply #7 on: June 17, 2013, 04:21:54 AM »

The OP has a bit of a challenging set up, not ideal but it is what he has. Why anyone would suggest that he spends $138 on a commercial antenna that would be a real PITA to make work I have no idea.

As others have said, keep it simple.

If you can route ladder line then put up the longest dipole that you can and match it with a tuner. Ladder line might be tricky indoors.
Or start with a single band dipole. You can get it to work on other bands with a tuner. The coax loss is easy to work out using one of the on-line calculators.

Once you have a base to work with you can experiment with extra elements and/or loading. As the antenna is indoors it would be easy to pop upstairs and change bands if needed.

A mag loop may also be a good choice.

Posts: 20

« Reply #8 on: June 17, 2013, 06:29:50 PM »

other challenges that I have are that I can't hang anything out my back upstairs window as there is a power line lurking right out the window that if the antenna was to fall could hit the lines which would be a fairly bad thing. and the front upstairs would be too obvious and would not fly with the management.  I have thought of using some Plexiglas isolators and hanging the antenna out the back off the gutters but the cable distribution box is right out there and I am sure that would cause some issue with the neighbors. 


Posts: 20

« Reply #9 on: June 23, 2013, 10:33:54 AM »

So I managed to construct a 1/2 wave dipole for 40m but had to dogleg it around to 2 bedroom ceilings to get it up off the floor and as high as possible, works fairly well though it is taking up more space than the wife would like and I am not really keen on it traveling through the bedrooms as well as having almost 70 ft of coax running to the feedpoint. THIS is what I was trying to avoid when I asked my original question.


Posts: 9930

« Reply #10 on: June 23, 2013, 11:29:06 AM »

do a google on Fan Dipole, or search here for same.. eaasy to make for a couple of bucks of  cheep wire.

Posts: 593

« Reply #11 on: June 23, 2013, 12:52:27 PM »

What are the dimensions of the bedroom?  Is it rectangular?  What is it's height?  How much power do you want to run?  How are you getting the feedline from the first floor to the second?

Posts: 20

« Reply #12 on: June 23, 2013, 03:31:55 PM »

It is roughly a 12ft x 15ft ceiling height it roughly 8ft I can measure and post an exact measurement later if needed, there is a utility closet that has the water heater in it that has a hole cut to allow for pipes to pass through that leads to another utility closet where the HVAC is at downstairs.  I can easily get a cable through there as I have done it with Ethernet before.

I do have a window in the room however the catch here is there is a powerline that is coming from the service pole that mounts in between my apartment and the one next to me and its a little too close for my liking.

I built my center isolator out of some plexiglass, an SO-239 and a handful of #6 x  1/2" bolts and a couple plexiglass endpoint isolators.  for each leg I used some 12 gauge insulated romex that I had left over from when I used the bare wire for a loading coil and a tuning coil that is part of another project in the works

Adding to what I have made would be fairly easy but again its the space that is the issue at hand.  If I can get a fanned dipole to work where I am just taking up space in a single room instead of 2 and a hall/stairwell then I am all for that as well.

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