75 / 40 meter fan dipole

[WB4AM]

Hello All,

I installed a 75/40 meter Fan Dipole over the weekend.  A good friend suggested to use those Ladder Snaps that are used to make 600 ohm ladder-line.  So I did and for the most part I am happy that I did.

But I am having an issue with 40 meters.  I installed the Apex around 42 feet in a tree.  Then I installed one leg in another tree while the other leg dangled below the Apex of the middle of the Dipole.  Just for kicks I went into the shack to see what the SWR would be even though the one leg of the 75 and the 40 meter was just dangling below and not yet installed.

On 40 meters the SWR was around 1.3 to 1.5.  On 75 meters I could not get the antenna in resonates.  No big deal I thought because the antenna wasn't completely installed.  I then installed the other leg of the Dipole and checked the SWR.

On 75 meter the SWR was perfectly matched on the desire frequency, great! (That never happens!)

Then I went to 40 meters and the best I can get is 3.0 pretty much on the entire band.  And if I go above 40 meters or down below 40 meters to find resonates, it doesn't resonate anywhere.  

How come I found it to resonate when it was half installed and now fully installed it will not resonate?

I really don't expect anyone to have a complete answer due to not having all the facts in front of them, but I am hoping for some ideas so I can go back to the antenna and see what I might be able to do to make it right.

I am using that special strained steel copper clad wire at 13 gauge (No.13 Poly Stealth) with the hard shell insulation.  The Apex is around 42 feet in the tree while one leg is about the same height and the other leg slopes down to about 30 feet.  I am not using any balun and it is being fed with RG213 coax cable.

Any thoughts would be a great help.

Thank you,
Ken

[K1JJ]

Hi Ken,

Seems strange that the 40M has no 50 ohm J0 spot..

How are you measuring the swr, with an MFJ-259B or a transmitter / swr bridge?

As an experiment, try using some clip leads and add a foot or two to each end of the 40M dipole and see what happens. The clip leads can hang down vertically.

Maybe there is a strange interaction to the 75M dipole.  By lowering the leg of the 40M dipole you probably made it resonate lower in freq, so maybe adding some length will help.

Sometimes these fan dipoles need tweaking in the real whirl, and it is usually the higher band legs needing the tweak..

T

[N2DTS]

I had great results with my fan dipole and love it.
I am a bit short for 80 meters, so had to add coils to save about 4 feet each side, at first the 40 meter dipole hung 2 feet below the 80 but last time it was down I made it 1 foot.
I replaced the plastic tubing with thin fiberglass rods used for edge markers, sold at Lowes with reflectors on top.
I drilled holes in the ends after cutting to one foot lengths and used wire to tie them on the antenna's.
If you do not get low in swr, the antenna is unbalanced and one side is longer, lower, or closer to something then the other.
The last time (after replacing the tubing) I got the swr below 1.5 to 1 on both bands at the usual frequencies.
Before that I had a 2 to 1 on 40, I shortened one side 2 inches and that got it down to 1.4 to 1.

The antenna's interact some but adjust as normal to get the swr down.
That is, once you hang it, small adjustments on one antenna do not change the other antenna.

I got lucky, shortening the one side (the easy to get to side) did the trick. 

I use no tuner or balun, works great.

[John K5PRO]

My first antenna as WN4PRO decades ago was a three band dipole like this, 80/40/15 meters. Course I was only cruising on the novice bands then at 75 watts with a hotwater 16.

[WA2SQQ]

If you have an SWR analyzer see where it is resonating. Adjust accordingly.

[WD8BIL]

Separate the elements by at least a foot. I just use nylon cord tied and taped to support the 40 meter elements of my fan.

[steve_qix]

I've used fan dipoles for many years.... both at home (75/160) and rattlesnake island (40/75/160).  I have found that element separation is important.  In my setup, the 40 meter antenna is more of an inverted V, while the 75 is pretty much a flat top dipole (this is at Rattlesnake island). The 40 meter ant hangs below the 75 meter ant.  The center is up at around 60 feet.

The elements are not too close together, except where they join at the center insulator.  The ends are probably 10 to 15 feet from the 75 meter dipole - maybe more.  I get a very good match on all 3 bands.  It can be done!

Regards,   Steve

[WB4AM]

Hello,

Thank you to all who chimed in.  I originally was just using a rice box to test the SWR's.  Then when you Tom, K1JJ asked how was I measuring the SWR's, I thought yea maybe I should used the analyzer.  The analyzer is an AEA model for HF only.  Anyway I had discovered that maybe the antenna might be a bit long because I could see the swr get slightly lower as I went down in frequency.  However the best that the analyzer could calculate was 2.79 swr.  I have now taken off 12 inches on both sides.  I find all this is doing is moving the swr curve up in frequency.

Also what I didn't mention, I am using a ceramic egg insulator at the Apex but it is inserted in a very small plastic electric "T" box that is just enough for the insulator to fit into as far as the thickness of the insulator.  The box is more less a T-Shape box for electrical plastic pipe to connect to.  I have wrapped both 75 and 40 meter wire around this insulator about two in half times before soldering the ends to a pigtail of the RG213.  The 213 pigtail is only about 6 inches long.  The pigtail comes out of the bottom section of the "T" shaped box.  The other end of the pigtail is fitted with a pl259 and then joined with a barrel connector then joined with the run of the full length of the rg213 coax going to the shack.

I think separating the two wires farther apart might be what is needed as mentioned.  I also did some more research and it seems there is a lot of fan dipoles that are spread out in the fashion that has been mentioned.

I could not add a wire clip to one end to make it longer for testing because the one leg of the dipole goes through tree limbs that keeps it from reaching the ground when lowering it through the pulley system.  (40 meter is to short for this operation)  I actually have to pull the one leg back through all the branches until it reaches the point of where the Apex is located.  If I was to do so, when pulling it back through the alligator clipped wire would just simply fall off.  But I am able to trim the wire by pulling it back through the branches to the Apex.  But then I have to climb back down and pull it back in the opposite direction to raise it back into the air.  ( A lot of work I can tell you! )

I might just give up and install an 160 meter dipole and feed it with 600 ohm ladder line and call it a day.  I now went through an OCF Dipole and a Fan Dipole and I am not having much luck.  I am used to home brew mono-band vertical antennas.

If I try to separate the two wires farther apart as far as the one leg going through the branches, I think it will end up getting tangled in the branches.  The reason for the branches on the one leg is due to the tree having two trunks coming up from the bottom.  I have the apex of the dipole installed in the opposite trunk of the one leg that goes through the branches of the other trunk. I hope I said that clear enough to understand.

Any other comments or ideas is appreciated.

Thank you,
Ken




  

 

[N2DTS]

Seems overly complex.
I use an end insulator about 4 inches wide and loop the coax over it then solder to the antenna wires.
I then cover it with coax seal, the loop prevents water getting in, no connectors to fail.
I use rg8x to come down from the antenna as its light weight.

To adjust the antenna length, I make it long, and then fold back the ends to shorten.
I do not cut it off, just fold it back and wrap it around the antenna after tying it off.

I am not sure you will ever get a good match if the antenna is in the trees, and it will change a lot when it rains.

[W2NBC]

"Seems overly complex"..

Yes indeed.. and when you're getting those interactive results with standing wave it can get a bit confusing :

http://amfone.net/Amforum/index.php/topic,37729.0/.html

What comes round.. 

[N2DTS]

I think it would be very hard to do more then 2 bands, lots of up and down and interacting.
Nice when you get it working though.

[KB5MD]

Check the feedline for shorts or loose connection.  Check for corrosion in the barrel connector.  I had pretty much the same thing happen
and it turned out to be a bad barrel connector.

[IN3IEX]

The shorter dipole, 40m here, must be longer than half wave by a consistent amount, depending on angle to the 80 m dipole. Search for actual resonance at 7.5 - 8 MHz...

[N2DTS]

The one I have up now is not far off in length from a standard one band dipole, but it has to be balanced to get a low swr.
If one side is longer/lower/closer it will never get low.
And it takes very little, 3 inches one side of the 40 meter leg will have you at 2 to 1 or more.

[WB4AM]

Okay I am taking in all the comments and suggestions.

For starters I think I will replace the coax.  The reason here is I had trouble with an OCF Dipole dipole as well that I had given up on.  I have plenty of cable so why not give that try.  If this does not change anything I think I will try to change the feed point so that the dipole wires are not coiled around the egg shape insulator.  And while I have it down, I will attempt to make longer spreaders for separation purposes as several have stated.

It will be hard for me to twist the one leg of the dipole through the tree branches, I know that is for sure, but I am willing to give it a try!

I have been listening to everyone's advice here. (Thank you)  My thoughts are, if I just scrap the idea and move directly to a single 160 meter wire fed with 600 ohm ladder line and then use a tuner for other bands, what will I have learned from this experience.  I have experimented with more then several antennas over the years, but never a fan or an OCF dipole until lately.  I have used mono-band fan dipoles for more bandwidth that had always worked with ease, but not multiable band dipoles.

So next will be the coax replacement.  A simple change out.  However I will be busy within the next couple of days, so I will not be able to get to it right away.

Again I appreciate any comments or ideas along the way.  I wish I had at lease a working antenna on 75 while working on this project.  I enjoy listening which I can do on another antenna design for 20 meters and up but as everyone knows transmitting on this antenna is out of the question.  So its slowly driving me more anxious as I anticipate getting this fan dipole up and working!

I will post my findings on the coax replacement.

And again thank you all for your continuing help.


Ken

[KB2WIG]

I run a fan dipole here. It started out as a dog leg 80m dipole at around 20 feet.  Its now up at around 30~35 feet, still in a dog leg configuration. I cut a 40m dipole to around 65 feet long, and married it to the 80m dipole. I had the ends of the 40m dipole fan out to a separate trees; kinda like an "X" with a serif on one leg.  Imagine my surprise when it was resonate at 7250. Happy days. Then came the wind, and I have the 40m part of the fan in an inverted u configuration. One end is at 40', the other end is around 7'. So I'm still piss weak, but at least I can also load this thing on 80,40,15 and 10m. If you can use different end supports, you may find your system easier to trim.


klc

[WB4AM]

Hi Ken,

Seems strange that the 40M has no 50 ohm J0 spot..

T

Okay,first let me say "Stupid is as Stupid Does" !

I thought it was odd as well that I could not find a dip along the 40 meter band.

After reading all post and searching the Net on Fan Dipoles, I thought maybe I alt to change how I am feeding the Fan Dipole.  I saw a lot of what I thought was a crude designs on how to separate the two dipole wires, but at the same time I thought it would be quick and easy to mimic.

So I made up the feed point using a bread cutting board and used 3/4 copper pipe for the buss bars by flatten them.  I also used stainless steel bolts and nuts to bring it all together.

I figured on spreading out the two dipole wires after I change out the feed point assembly.  Well when taking the cover off the gray "T" electric box housing that had the Egg Shape Insulator inside, it appeared that I had soldered the left leg of the 75 meter dipole to the center conductor of the coax but also soldered the right leg of the 40 meter dipole to the center conductor of the coax instead of the left leg of the 40 meter.

This in turn caused the shield to be solder opposite as well.  How the 75 meter even worked or how the 40 meter worked when it was dangling toward the ground before it was fully installed is beyond my thinking.

Anyway I was in the tree at the Apex of the dipole at 42 feet as I was taking this apart. Although I found what I had done I still continued to install the new Feed Point assembly, thinking that I still have to spread the wires out anyway.  Well when I finished changing out the assembly I thought I should at lease check out the SWR before spreading the two dipoles apart; just in case.

To my surprise I still had a 1.1 SWR on 75 meter and I thought I had a 1.3 SWR on 40 using the rice box's swr meter.  It turned out using the AEA Analyzer it was 1.79 swr.  But the good news is I had a dip or a SWR curve on 40 that I did not really have before.

And this 1.79 swr could still be from the close proximity of the two wires like most everyone had said.  I still have not replace the coax, so I don't want to rule that out just yet.  It will be easier for me to replace the coax then to spread the two dipole wires on both sides and rerouting it through the tree limbs.

In the back of my mind I keep telling myself I should change out the coax with 600 ohm ladder-line. 
For one it is very low loss as we all know, and I can use a tuner since it will be used with a tube rig/boat anchor.

I appreciate everyone's comments, thoughts, and ideas.  If anything it helps drive me towards making the dipole better by listening to what is being said and knowing there must be hope around the corner so to speak!

Can someone give me their thoughts on using 600 ohm ladder-line with a tuner verses using coax directly without a tuner?

I was always told that the tuner just protects the rig or/and fools the rig in believing the antenna has a 50 ohm load.  Which I still believe and I understand that indeed is the case.  But what I am getting at is the efficiency of the ladder-line that efficient that its better to go with the ladder-line and a tuner verse the coax?  I also read somewhere that 1.1 SWR isn't the golden rule of having an efficient antenna.

Any comments would be helpful.

Thank you,
Ken

[WB4AM]

Another pic of the right leg of the fan dipole....

They are hard to see and they are twisted.  I think I used to many spacers and they had gotten to heavy.

[Steve - K4HX]

http://amfone.net/Amforum/index.php?topic=37871.0

Spacers should work FB.

If you only plan to use the fan on 80 and 40 meters, there is little advantage in going to 600 Ohm line and a tuner. The main advantage would be on 80 and 75 meters where you could span the entire range. If you want other bands, then 600 Ohm line and a tuner will be a BIG advantage.

Given that you put so much effort into the current configuration, I'd go ahead and use if for a while. If it doesn't meet your frequency/band coverage requirements, then consider switching to open wire line.

[N2DTS]

Overly complex, all you need to do is connect the coax to the antenna legs, all you need is a normal antenna insulator at the center and some solder.

If the swr is low, the loss in the coax will be very low on 80 and 40 meters.
One of the advantages of the fan dipole is no tuning needed.
With coax, weather does not impact things much.

[WB4AM]

http://amfone.net/Amforum/index.php?topic=37871.0

Spacers should work FB.

If you only plan to use the fan on 80 and 40 meters, there is little advantage in going to 600 Ohm line and a tuner. The main advantage would be on 80 and 75 meters where you could span the entire range. If you want other bands, then 600 Ohm line and a tuner will be a BIG advantage.

Given that you put so much effort into the current configuration, I'd go ahead and use if for a while. If it doesn't meet your frequency/band coverage requirements, then consider switching to open wire line.

Hello Steve,

I think that's great advice.  It has been an ordeal for me to get this antenna working.  Its more of the climbing up and down to the Apex of the antenna more then anything!

Thanks Steve,
Ken

Overly complex, all you need to do is connect the coax to the antenna legs, all you need is a normal antenna insulator at the center and some solder.

If the swr is low, the loss in the coax will be very low on 80 and 40 meters.
One of the advantages of the fan dipole is no tuning needed.
With coax, weather does not impact things much.

Hello Brett,

Yea I seem to do that from time to time.  Sometimes it pays off immediately with good results and other times it takes awhile due to the learning I get from finding out I shouldn't had done it this way or that way!
But that is how I learn.

Thanks for your input Brett, maybe I'll get to work you on 75 or 40 now.

Ken

[Steve - K4HX]

Ken: Your energy and enthusiasm is inspiring.

If you are willing to purchase, the Budwig HQ-1 is strong but light as a feather. Many vendors sell them.

http://www.universal-radio.com/catalog/antsup/1782.html



I used to climb, them I learned about slingshots and bows.  

[N2DTS]

Why have a connector up there at all, just solder the coax to the antenna.

I am not fond of connectors outside.
They always seem to get nasty no matter how well water proofed.

[W3GMS]

Ken: Your energy and enthusiasm is inspiring.

If you are willing to purchase, the Budwig HQ-1 is strong but light as a feather. Many vendors sell them.

http://www.universal-radio.com/catalog/antsup/1782.html



I used to climb, them I learned about slingshots and bows.  

Here is another one that I have had great luck with.  The SO-239 is somewhat recessed and works very well. 

Its the model 801

https://thewireman.com/prodpix.html

See photo's attached

Joe-GMS

[K1JJ]

Nice mechanical connections. Looks strong.

I would add some sealant for the PL-259 connector and coax.  Water can quickly wick its way down the coax and contaminate the braid and inner conductor and turn them brown. If so, the efficiency of the coax drops way off.  

I once did a poor sealing job and within a year the braid was wet and green all the way to the ground.


There's a few ways to seal it:  

1) Cover with clay that is sold for sealing feed lines.  Then wrap some wide 2" electrical tape around it pulled tight as it wraps. (Or tape first and then add the clay)

2) Spray with a Krylon-type  lacquer spray, let dry, tape it with 2" tape, spray again, tape and spray again.

3) Wrap with 2" wide electrical tape and paste on a covering of RTV silicon. Let dry and tape over again.   RTV silicon alone will peal off in the wind within 5 years.

I would also be sure that that gray dipole connector was well sealed inside so that the three eye bolts did not leak. (Or add some RTV to the outside entryways)


* Another good idea is to loop the coax up before it starts its run down to discourage gravity fed water from potential connection leaks. Especially when hung on a tower or other center support this can be an easy thing to do.

And, as already said in a previous post, the first thing to suspect when there is antenna trouble is the coax connector used outside. The worst situation is using one out on a beam antenna that fails and needs to be taken down.  All of my outside antenna connections make hard wired connections to the driven elements and are sealed as described above. I have yet to have one leak. However, I have a quite a few S0-239 barrel connectors that terminate in the dog houses outside. Some of these, even though well sealed, develop moisture inside and the pins get a gooey green paste that cause an intermittent connection after a few years. I try not to use connectors that I cannot service easily.

The tape will stick better if applied above 50 F degrees or so. Also, it is not a good idea to seal coax connectors when the humidity is high. I suspect that when it turns cool, the trapped moisture may condense. A dry day may be the best time for sealing antennas connections. This may be the reason some of my connector center pins developed a blue/green goo, I dunno... :-)

In general, electrical and mechanical splices of all kinds are the biggest failure points of most installations.

T