NI4L fan dipole

[N2DTS]

I had got one of these for 80 to 10 meters (4 fans) and put it up today.
I normally make my own antenna's but sometimes try pre made ones.

They do not include anything to keep the dipoles separated.
Its not made badly, but its not great.
I made some seperators, likely too close at about 4 inches from each other and put it up.
Its a bit long (the 80 meter section) so it sags a bit in the center,
Very low swr on 80, way off everywhere else but 10 meters is ok.
40 meters has a low swr at 7580, 20 meters 15.250 MHz, 15 is 22.15 and 10 is 29.6.

40, 20 and 15 are way high???

[Pete, WA2CWA]

Did you add a choke balun to keep the RF from flowing down the outside of the coaxial shield? Looking at antenna prices, I think I'm in the wrong business 

[N2DTS]

No, I never use them.
I have had fan dipoles before that worked much better without a balun.

Did you add a choke balun to keep the RF from flowing down the outside of the coaxial shield? Looking at antenna prices, I think I'm in the wrong business 

[WB5IRI]

My experience with fan dipoles (and I am using one right now as my station HF antenna) is that they are extremely sensitive to placement. Nearby objects will interact. So, if the 40 meter element is resonating high, try adding some length to each end, but be aware that another characteristic of fans is that all the elements interact to some extent. Resonate the 40, and you may find the 80 is now off or the 10 is no longer where it should be. You can get them to work, but sometimes it is a real PITA to do so. I usually get the elements close and then use a tuner.


Doug

[N2DTS]

I may just end up making a nice one for 80 and 40 and that should not be that hard.
The thing about the NI4L was it was supposed to be cut so it would be very close to the frequencies you pick.
I can see some interaction, but over 300 KHz off on 40 and 1 MHz off on some bands is just crazy.

Glad I did not mess up the old 80 meter antenna, I can just add a 40 meter dipole and put it back up.
It's made out of #10 solid copper wire.

[N2DTS]

Anyone got any good idea's for spreaders?
Light, UV proof, will stay in place?

I suppose the more separation the better, so say about a foot long?

[Pete, WA2CWA]

Anyone got any good idea's for spreaders?
Light, UV proof, will stay in place?

I suppose the more separation the better, so say about a foot long?

The supplier doesn't give any recommendations  In order for him to cut the lengths to some resonant point as part of the design, he should have some rough idea what spacings are required.

[W1RKW]

my first dipole was a fan dipole 100% homebrew.  I cut plexiglass for the separators.  They lasted for over 10 years without any replacement.

[N2DTS]

Maybe those fiberglass rods they use to mark things for the snow?
I will have to check that out, although they may be sold out now!

[WB5IRI]

I used 1/2" schedule 40 PVC because it's what I had on hand. Been up about 8 years now, no problems. Cut it to length, drill holes, good to go.

[W9ZSL]

I put up a 75/40 fan three years ago.  The 75 was cut for 3885 and the 40 for the center of the CW band.  I used 3/4" PVC pipe 6" long for spreaders with clamps to hold them vertical.  Each end is 20 feet high as is the center.  I have a 1:1 balun at the center feed point with a pair of spreaders on either side.  The top wire is copper weld and the bottom some #14 insulated soft-drawn I had on hand.  I fed it with RG-58.

This fall one of those tree limbs came down just left of the center support bending the front mast and center support.  I straightened the front, replaced one 10' section of the center and removed the 40 meter.

This antenna surprised the heck out of me.  At the resonant freqs I was getting so close to 1:1 SWR that any reflected power wasn't enough to measure effectively.  Of course, trying to use it on 80 meters CW I was getting something like 1.8 to 1.   -Mike-

[N2DTS]

Thanks guys.
I will pick up some small PVC pipe and drill it.

On 80 its got no swr at all around 3880, 40 has 3 to 1 everywhere, but it might be twisted or just too close to the 80 meter antenna.

The best bet for me would be to add 40 to the old 80 meter antenna, and maybe 10 meters since that is so easy, but I think I will try and separate the NI4L thing and see what happens.

[N2DTS]

The weather was not bad so I took down the NI4L and added a 40 meter leg to the original 80 meter dipole, using thin pvc spreaders, 3 each side 3 feet long.
I made the 40 meter add on 36 foot each side so I could reduce it to get the swr low.
1st test had a very nice dip at about 7200, cut 9 inches off and had a nice dip at 7240, cut 6 more inches off and had no dip anyplace and a 3-1 swr, just like the NI4L setup.
80 meters is still fine.

There must be some strange interaction between the two sections, one dips at 3900 and is very broad banded, the other will dip nicely till I get close to 7300.

Next chance I get I might add a foot to each side and get it to have a dip, lower then I want, but a dip.
Even the RX is about 10 Db down if I go past the point of no return, when the dip was on the low side the RX was just as strong as the normal 40 meter antenna.

Its up about 50 feet, coax comes down directly into the shack, coax length seems to not matter.

[N2DTS]

I added about a foot to each side of the 80-40 meter dipole on the 40 meter part, and the swr is 1.4-1 at 7285 an goes up very slowly from there.
80 meters still has an swr of 1.2-1 at 3885.

I notice the old 40 meter dipole swr has gone up to 2-1 over time, maybe the coax is wet or something?

[N2DTS]

What a great thing.
Switch between 80 and 40 meters, nothing to tune, nothing to change, very low swr on both bands, I should have done this years ago.

[W3TDH]

For spreaders you may want to try PVC Electrical conduit.  It has the advantage of being sunlight resistant.  the schedule 40 stuff is plenty strong but you would do well to apply couplings to each end of your spreaders and drill your holes through the couplings.  The thicker material of the couplings will resist the abrasion of the antenna wire shifting in the wind.  PVC conduit is grey in color so it stands out less than PVC piping against the sky and is therefore less visibly obtrusive. 

--
Tom Horne W3TDH 

[Steve - K4HX]

I used black plastic open wire line spacers for my 80/40 meter dipole. I had this antenna up for several years at a previous location. Worked FB.

[N2DTS]

I have some very thin tubing, the stuff they use for the snap on connection stuff I think.
Its rigid, sort of like small thin walled pvc pipe.
I drilled holes in it to pass the wire through, but could not pass it past the top dipole coils.
The 80 meter antenna is made out of #12 stranded copper wire, but it was just a bit too long to fit between the trees I have so 3/4 the way out I put coils, about 5 turns of #12 on a 1.5 inch form, that gets me down to 110 feet.
So the tubing is wire tied to the top antenna in the center parts, and on the ends through the tubing.
The lower part (40 meter) goes through the holes and is wire tied in place.
Very temp setup.
When it warms up, I plan on lowering it and using stainless safety wire to hold the spreaders in place.