20M Struggle

[K5UJ]

Okay that's cool--thanks for all the replies--this started as a problem for Fred and I feel like I wound up getting the benefit 

Fred, if the dual dipole setup has been done already and proven to work then go for it. 

Very interesting about losses and dielectric.  I have tried modeling once or twice with EzNEC but it was simply too time consuming--it took hours just to model a simple antenna.  I wanted to model my horiz. loop and I realized that would take hours over days and I had too much else to do so I gave up on it.  I have never heard of these other programs.  I'll have to check them out.

[K9ACT]

Take a look at the bottom image - the 3D pattern. Now you are seeing everything. Look at all those crazy lobes and nulls. This makes it clear why adding a 20-meter dipole (or similar) might be a good idea.

You sure know how to spoil my day. I was feeling pretty good about how well my 80 m dipole was working on 20.

Yuch!

js

[Steve - WB3HUZ]

Doesn't mean it won't work. It may mean another antenna will work better. You won't know until another is tried.

Take a look at the bottom image - the 3D pattern. Now you are seeing everything. Look at all those crazy lobes and nulls. This makes it clear why adding a 20-meter dipole (or similar) might be a good idea.

You sure know how to spoil my day. I was feeling pretty good about how well my 80 m dipole was working on 20.

Yuch!

js

[flintstone mop]

Jack,
You're doing pretty good on the air with your system. I heard you 10 over the other night in Western Pa. on 14.286.  As Steve says, a shorter dipole connected along with your 80M wire might be a little better. My problem using a 180 foot dipole on 20M creates a lot of ugly lobes. Less lobes are better.

And Rob, I know the frustration of computers and getting things like EZNEC and plugging in numbers and interpreting what the computer is trying to tell you. That's why I lean on the group here to feed me with info. They know my shortcommings....hi
And don't feel that you "hijacked" the thread. It got the grey matter working for all who have been reading and responding.
Sometimes there are nice neat shortcuts to get RF to work for you.

Fred

[K3ZS]

This has been an interesting discussion.   It seems that with parallel dipoles, the one that dominates with the antenna current is the one doing the most radiating.   As Rob has stated, I am not sure if the one having the best match will dominate or the one with the lowest impedance will.    The free software seems to do a good job of modeling the patterns in any case.    My antenna is a 135 ft in parallel with a 16 ft dipole.    It did change the tuner settings mostly on the bands from 20M to 10M.     The operation on 10M is much improved as far as I can tell after adding the dipole, just as EZNEC has shown.   Tom, my QRZ picture is getting dated, it was at my son's wedding before I ever had a digital camera.

[K3ZS]

I have been fooling around with EZNEC today.   According to it, the above described antenna will have about 3.5 times the antenna current in the 16 ft dipole as compared to the 135 ft dipole at 28.4 MHz.   I replotted the azimuth patterns at the maximum gain elevation angle.  Except for off the end, the dual antenna has less than 5 dB variation in the azimuth directions on 28.4 MHz.   Without the added 16 ft section, the nulls are many and go down to 20 to 25 db below the maximum points.   The best gain is about 10 dBi at the main lobes about 35 deg from the end of the antenna.    With the added 16 ft section the best gain is around 13.4 dBi pretty close to 90 degrees from the antenna wire.   Both azimuth patterns are best at a 16 deg elevation angle at the antenna height that I used, which was 30 ft.

[K3ZS]

I just plotted Fred's antenna with two 16 ft legs added to it.     The result is not as good as in my antenna.    The nulls are filled in but they are still about 10 db below the max, however the max gain is 12 dBi.   Off the end it is also about 10 db below max.   This all is at a peak elevation angle of 14 degrees and a frequency of 14.2 MHz.

[flintstone mop]

Hmmmm I'm getting curious with this EZNEC. I was looking at the W7EL website and will try to find the free version. I thought someone here said it was free.
I promise I won't get frustrated if it doesn't work OR I don't understand what the computer is spitting out.

And thanks for the results Bob. I'll be adding the other element once this rain thing quits.

Fred

[K3ZS]

The first time I tried EZNEC, I didn't want to spend the time learning what it was about.    The free version has a limited number of segments so the results are not that accurate, but it still gives a good idea what is going on.   If you have time, using the sample files that come with it, you can eventually make sense out of it.   
If I was to be an antenna hobbyist I would purchase the program.    I don't intend on making any changes now to my one and only antenna.

[K1JJ]

Fred,

Try EZNec and you will be able to try any old antenna you have dreamed about over the last 40 years without leaving your chair. It's like being able to climb any tower height and have perfect antennas... or model the limited conditions we all have.

After a week of playing with it, you will soon see how easy it is to anticipate patterns, mistakes, proper phasing and the like. It's really an education in antennas.


*** BTW, I finally got around to modeling the 160' flat top for 160-40M and second 22' flat top for 10-20M.  As a combined antenna with common openwire feed, I was very disappointed.  The 160-40M portion looks OK, but the 20-10M bands were not so good. 20M was barely acceptable, but 10-15M looked terrible.

The two antennas should be erected as two separate flattops fed with their own openwire and they willl perform beautifully, pattern-wise.     ie, ONE feedline feeding three bands (160-40M)  and a second feedline feeding three bands. (10-20M)


Personally, I like separate antennas fed with coax, but one needs the room to separate them to quench interaction.

My rule with FIXED mono-band Yagis is to have NOTHING in front of them, nothing on the sides, but I load up the field behind them with other Yagis looking the other way. A Yagi sees nearly nothing behind it due to the reflector.  However, a dipole is sensitive to front and rear, so actually takes more room to isolate it.

The good thing about dipoles is you can hang them at right angles to each other, using the same support, You CANNOT do this with Yagis or the interaction is severe.  (This assumes the same band antennas)


So, bottom line is to MODEL every antenna before trying it. Some patterns seem logical (like my 160', 22' idea) but turn out to be real garage.

Fred, I would STILL recommend using a separate coax fed 33' flat top at 35'-40' high  for 20M. Wind up 6 turns of coax on a 4" ABS pipe at the feedpoint  from Home Despot and you have a balun and clean pattern.  Use the ABS pipe as the center insulator to secure the leg wires, too. Use a rope to hang the abs pipe on a side-arm on your pole that hangs out horizontally a foot or so..  Instant band switching - leave your openwire antenna tuned up on 160-40M. Compared to the openwire version with the common legs, it is superior in pattern by 6db in spots. It is smoother and predicable.  It is down only 4-5db from a full-size 3el Yagi at the same height. Put it up as I described and I guarantee you will start making lots of contacts on 20M, reliably, or your money back...

T

[K5UJ]

The EzNEC I got was on a CD that came with either the ARRL Handbook or the ARRL Antenna book, probably the latter.  Maybe it  is easier to use now.  What I got had a few samples and I tried to model a dipole on 20 M and it took hours.   So I decided I had to be retired to use it    But maybe I should save it for a cold winter holiday.  Now that I think about it, I believe what I got had to run on windows and I now use mac and linux machines.   Are any of the other packages out there written for linux?  Probably not for macs.   I'd love to model my loop.  It's sort of a rectangle (or more trapezoidal) with two 80' sides and the other two about 40' to fit on my 50 x 100 foot lot.   It's up about 25 - 30 feet and fed in the middle of one side, the south side (one of the long sides) with 600 ohm ladder line.  I wanted to model it but after finding out the dipole took forever, I figured the loop would never happen.  I want to try to raise the loop another 15 feet or so to try to reduce capacitive loss.  You'd think this is trivial but it involves four man-made supports that can't be guyed because they're very close to the property line.   City ordinances prohibit lattice towers.  I'm looking at some aluminum tubing ($$$). 

Fred, so T says you should use separate feedlines.  heh heh heh...(can't resist gloating  ).  K3ZS ur photo looks Mahvelous.
Has anyone seen this weird video of people on towers in wedding clothes singing?  I saw it at Dayton a few years ago.  Never did figure out what it was about.

73

Rob K5UJ

[Steve - WB3HUZ]

Not sure what program you were using. Any of the spreadsheet entry type programs out there would take about a minute to model a dipole. Just enter the two end points in X,Y,Z coordinates, specify wire size and type, frequency and ground type and hit run. Some programs even allow you to draw the antenna, which can be easier for loops and sloping wires, etc.

Dunno about Linux but CocoaNec is available at no charge for the Mac.

[K1JJ]

Fred, so T says you should use separate feedlines.  heh heh heh...(can't resist gloating  ). 
Rob K5UJ

Rob,

   Don't gloat until you've looked at your OWN pattern...

Your loop fed with openwire probably has a similar "octopus"  look as on Fred's 10-20M dipole.


His exisiting dipole for 160-40M with an additional coax fed dipole for 20M would be a good compromise.

I also like the idea of using one openwire feeder to feed a 160' flat top for 160-40M.  Then a second feeder to feed a second 22' flat top for 10-20M. The resulting patterns are beautiful figure-8's on all bands.   Yes, more effort, but cleaner results.

The interesting thing is you can place the 160M-40M dipole higher than the 10-20M dipole to fine-tune the take off angles.
Model those when you can and see what they look like.  There is a way to model your own loop and then compare the pattern against other antennas - slick and revealing.


Tell ya what - since you're not set up with EZNec yet, I'll model your loop as described and let ya know what it looks like on the various bands. Maybe later tonight -

T

[K5UJ]

Steve and T:  cocoaNEC that is fantastic!  I must find out about it.  Modeling my antenna THANX!! I can't wait to see it.  I'm sure there are crazy lobes on the high bands but a net I check into from time to time on 14.340 always works better with everyone especially the guys in the south and southwest when I'm on the loop.  But the other 20 m. antenna is a Gap Titan, so it isn't much to compare the loop to.   the Gap vertical is mainly being used now to hold up part of the 160 m. inverted L.

I was just listening to W0HRO on 3880 with my 12 KHz passband rx feeding the heathkit EA-2 from the product detector and did he ever sound fantastic on a big speaker! 

73

Rob K5UJ

[flintstone mop]

WOW yous guys caught me as I was going out the door to start measuring and planning the 20M add-on.
This adds a little twitch by having to run another ladderline for 10-20M. Can I run it along with the existing ladderline? Does there have to be separation from the two runs?
If there has to be any kind of separators to keep them apart, then this will be a bad problem during Winter as we get a lot of steady to heavy winds for days blowing from the West. The ladderline system runs along the back of the house from the shack, then hooks on the back side and goes up to the feed point on the utility pole.
I was able to dig up some old pics for the install of the utility pole and the feedline runs and the dipole and the broken DAM Yagi.
And the quest continues. THanks for the input

fred


ROB, I used to have an EA-3 Heath amp. That was my very first electronic kit.

[K1JJ]

Fred,

In your case, wouldn't it be far better to fix the triband Yagi instead?

If not, if you plan to use 10-20M, then the second 22' flattop with another separate feedline will work FB.  Keep the two sets of openwires at least 2-3 feet apart from each other and the isolation shud be fine. Add a slow twist to one or both of them and the coupling will be even less. You don't want the same two wires looking at each other for too long of the run.

If you build a second tuner dedicated to 10-20M, that wud be pretty slick and cornvienient.


If you desire adding ONLY 20M, then the 20M dedicated coax dipole is by far the easiest solution.



Rob, my modeling doesn't have downloadable pics like Steve's, but I can describe the patterns I see on the screen. Maybe Steve will also model your loop and show the pics.

T

[K5UJ]

Rob, my modeling doesn't have downloadable pics like Steve's, but I can describe the patterns I see on the screen. Maybe Steve will also model your loop and show the pics.

T

Okay, that's fine--what do you see?

Rob

[W2VW]

How about juggling the lengths of the 160 footer and or resonant 20 meter parallel dipoles so that they have different impedance characteristics as possible on 14 mhz. I would think the 20 dipole would show more of a classic dipole pattern if the 160 footer's load was in a different neighborhood on the Smith chart. The job would be probably be easier if one loses the resonant idea for the 20 radiator.    

[flintstone mop]

That's an interesting apporach, Dave. Change the ingredients around a little to get some different results.
I don't have EZNEC so, I'll impose on some who does, if juggling some antenna lengths around, would make the 160M antenna work with a second radiator on the same feedline. I have heard that the free version won't display what I think we're trying to do here.

A little re-cap of present system: Ladderline is approx 130 feet, 160M antenna is 180 feet, want to add a 20M element using same feedline.

BTW, Dave the modified TS-440 is still a happy radio.

Fred

[W2VW]

Hi Fred,

     Step one would be to see if 180 feet is OK for a broadside pattern on 40 meters. You may want to take 15 or so feet from that length. Stay under 5/4 wavelength for that wire. Then try what I said in my last post. Unless I'm missing something that system properly configured should exhibit 2 different patterns on 20 depending on which system resonance you adjust the coupler for. We could call it the TFPD Tunable Fred Parallel Dipole.
   
     Glad the TS-440 is doing well.

73,
Dave.

[K1JJ]

Rob, my modeling doesn't have downloadable pics like Steve's, but I can describe the patterns I see on the screen. Maybe Steve will also model your loop and show the pics.

T

Okay, that's fine--what do you see?
Rob

Will do, Rob -

Got busy last night but will get it done for you today - and post it tonight.

T

[K5UJ]

Rob, my modeling doesn't have downloadable pics like Steve's, but I can describe the patterns I see on the screen. Maybe Steve will also model your loop and show the pics.

T

Okay, that's fine--what do you see?
Rob

Thanks so much; I hope there is enough general information there so that is is useful for others besides me, i.e. anyone with a small lot rectangular 1 lamda loop on 80 that's a cloud burner.  I'm fairly sure I'm not the only one with that sort of antenna except others may be feeding it at a corner instead of the middle of one of the long sides.  My feed location is due to it starting out as an 88' center fed dipole.  I'm pondering some sort of coax fed fan dipole for 10 - 20 now.  Looking at baluns at balundesigns.com


Will do, Rob -

Got busy last night but will get it done for you today - and post it tonight.

T

[K1JJ]

Hi Rob,

I modeled your loop as a rectangular 80' X 40' X 80' X 40'  loop, and fed it in the center of one of the 80' legs. The height is at 27' high.

Generally, it IS a high angle antenna for 160-40M and the angle gets lower on 20-10M. 

On 160M the peak take-off angle is 90 degrees and almost ominidirectional. However the efficency is only about 13%, being too short for 160M as you'd expect.

On 75M, this is probably your best looking pattern and for local work. It's a broad figure eight, with TO angle at about 88 degrees, 95% efficient. Good cloud burner for general use.  Max radiation off the front and rear. (front and rear being the 80' legs)

On 40M, the maximum radiation switches to the sides and the front is down -6db while the rear is down -2db.  TO angle at 70 degrees.

20M, broadside best, (front/rear) big butterfly pattern. TO at 30 degrees, which is good for USA work and maybe Eu. A 1/2 wave dipole would be better for general use.

15M  Big butterfly with lots of nulls. -10db down in the front and rear. Poor pattern, pot luck.

10M: VERY useless octopus pattern with many deep nulls - pot luck.

All in all, 80M is probably your best band followed by 40M for local work.  20M has a decent take off angle, but has a "nully" butterfly pattern horizontal.  160, 15 and 10M look poor.

Bottom line:  If you're serious about 10-20M, I'd put up a 22' flat top fed with openwire and you will get a nice sharp figure 8 pattern on all three bands, even better looking than the loop has on 75M.

I imagine this is pretty much what you expected.  It agrees with the idea that it takes several specialized antennas to get optimum patterns across many bands. One will not do it all.   You will still be heard and make contacts on the higher bands, of course, but in many cases you will be 6-10db weaker than when running a simple 1/2 wave dipole dedicated to the band.

Hope this helps, OM.

Tom, K1JJ

[K5UJ]

Wow Tom this is fantastic information; I can't thank you enough!   I was going to try dipoles on 20 15 and 10 but one fed with ladderline will be much easier.  I have everything to make one and put it up right away! 

This gives me some incentive to get the loop higher up.  I have an inverted L on 160 because the loop was much too small and low for that band.  This explains why with the loop I'm good on 20 out to N.M. and So. Cal.  yes, it's the bomb on 75 for local work and I often get 20 to 40 over 9 reports from hams within 200 miles.  the 40 report was a bit of a surprise. 

>On 40M, the maximum radiation switches to the sides and the front is down -6db while the rear is down -2db.  TO angle at 70 degrees.

TO angle is a little lower than I expected but not complaining.  Can you say which long side is the front and which is the rear?

I have been thinking about co-locating a 75 m. inverted L with the 160, use the same ground system and feedline, LDF4-50, and switch it out at the feedpoint.  Hopefully I'd get some low angle on 75 to the east coast. 

Anyway, it's starting to sound like it's time to say goodbye to the Gap Titan, it got me back on in 2001 and seemed like a pretty good antenna until I put up the 88' ladderline fed dipole and compared the two.  I gained 15 dB right then and there, as if I had fired up a 10 kw amp.  the loop extension added another 10 dB. (this was all on 40 with close in hams.)

tnx again & 73

Rob K5UJ

[ke7trp]

For the sake of conversation. Here is my current antenna modeled on EZnec by Joe.  The only real change is that I went to 600 ohm open wire line.

This antenna works very well on 80.. SUPER on 40 and pretty nice on 20m.  I have made alot of contacts on 20 with it but its the only 20 m antenna I have owned so its hard to compare.

Clark