Nesting of multiband stacked Yagis

The following is a summary of answers as result of an inquiry posted by Roger Rehr to the Moon-Net reflector regarding possible inconvenients of nesting multiband stacked Yagis. I found the subject so interesting that I decided to publish the summary here.

On 7 October 2000 Roger Rehr wrote:
Thanks to all who responded to the question on "Nesting" of yagis.
I got over 20 responses.  The gist of things as I interpret the results was nicely summarized by CT1DMK, and his comment makes understandable my observation that avid Tropo Weak-Signal types
and satellite guys almost to a man said nesting would be NO problem (that's how I almost made the mistake of nesting; I almost didn't ask the EME guys even though that is what I plan to do!!), but the EME guys almost uniformly say it won't work well, because every dB counts.

I have posted this to VHF, EME, and TOWER lists as I had a significant number of requests for the results from each of these.

SUMMARIES OF COMMENTS

CT1DMK summarized things very nicely, when he noted: "Final comment. For tropo, sat, etc, you wont notice the diffrence. for EME you will eat your nails in every QSO."

Ian White G3SEK has a very nice web page (URL     http://www.ifwtech.demon.co.uk/g3sek ) that explains stacking interactions and a lot more.

Jeff Bishop W7ID discusses his personal experience, which I take as a demonstation of CT1DMK's comments.

Alaistair Beaton has a "middle of the road" approach, again implying a difference between the requirements of EME and Tropo, etc., but noting that some EME'ers "Do It", i.e., nest their stacks.

Lionel Edwards VE7BQH makes the very good point that any metal that falls within the pattern of an array must affect it adversely.

Bob K4MRW has run NEC simulations which show only a small degradation when the arrays are not symmetrically placed, and has not noticed an effect in operation.  I didn't find him in the EME
database I have, so I am guessing he does other weak signal work and would then fit the paradigm outlined by Luis, CT1DMK. (If this assumption is wrong, I apologize, Bob).

Dave Collins K2LME had numerous comments that were very helpful to me personally, recommended polarization switching and referred me to perhaps the most technically interesting ham site I have EVER seen:

http://ham.te.hik.se/homepage/sm5bsz/index.htm  .

BERT, NS4W, gave me the solution to my dilemma; parallel vertical stacks for 2M and 432, placed on opposite sides of the boom, with 1296 placed above 432.  A mechanical challenge, but electrically correct.  This is what I plan to do.  THANKS, BERT!!

I considered the alternative of 2 x 2 stacks with 432 and 1296 on top of 144, with 144 below the boom and the high bands above, but worried that at low elevations near the horizon the tower would fall within the pattern of the 2 meter array and distort it.  As I would like to continue to use "flip mode" reversing the stacking would not provide a solution. With the vertical stacks, the tower can be kept out of the capture area of each array if the boom is at least 6.2 feet long each side of center.  An offset boom could be used to make up for the difference in weight between the high and low band sides, I believe.  (Please tell me if I am wrong on this point!!).

Mike Crawford, WA2VUN, who will be constructing the frame for the array, tells me getting non metallic supports that will support this is not a problem.  I want everything except the yagis non metallic
as I want to use the new M2 2MXP18 22 foot, 18 el dual polarity yagis so I can switch polarity.  These are HOT off the press, not yet even on M2's web page...but M2 does have data sheets on them...

Finally, I included Mike Stahl's comments on Polarity Switching, circular polarity, etc for satellites.  I agree with him entirely now (I didn't when he wrote it).  Have you noticed that many of the excellent European stations you work on the birds have lots of metal in the air, but linearly polarized? Ever wonder why?? I did; now I know...

THANKS to all of the above, and to THOSE who were VERY helpful but that I didn't include...these comments were either echoes of the above, or of personal help to me but not in my opinion of more general interest.

BELOW ARE SOME OF THE ORIGINAL COMMENTS, with email addresses so those of you with a lot more technical wherewithal than I can communicate directly with each other.


From:   cupido@mail.ua.pt
Sent:   Tuesday, March 03, 1998 8:21 PM
To:     rrehr@EPIX.NET
Subject:        Re: Nesting of multiband stacked yagis

Hello,

I used 4x11el on 2m and nested 4x23el on 70cm. While The 2m remained with the same performance with the 70cm inside or not, The fact is that the 70cm array exibithed lower gain than expected.

What is normally a reasonable setup for 70cm EME (4 yagis 5m boom) proved to be very marginal, and comparable to a 2 yagi station. As many stations reported to me "you are weeker than EA3DXU" a 2 yagi station. (also same 1.5KW)

I took them out of the array, but verified  what was the SUN noise increase with the 2m array out (for maintenance). I measured 1.9 dB more.

That was my experience.

Final comment. For tropo, sat, etc, you wont notice the diffrence. for EME you will eat your nails in every QSO.

Cross talk and desensing is not a problem, if good high IP and selective preamplifiers are used.

Have Fun.

73 de CT1DMK
(Luis Cupido)


-----Original Message-----
From: Ian White [mailto:G3SEK@ifwtech.demon.co.uk]
Sent: Thursday, March 05, 1998 3:36 AM
To: Roger Rehr
Subject: Re: Nesting

Take a look at my web pages, which contain an "FAQ" on this subject.

The closest distance for stacking of mixed antennas depends on the capture area of each antenna, which you can estimate from the manufacturer's recommended stacking distances for two of the same antenna.

I don't have the information from M2 so I can't comment further, but you can judge the interactions by drawing the capture areas as ellipses on squared paper or in a CAD program, and seeing how they overlap. For a definitive answer, you have to model the whole nested stack using NEC-2.

Also, W1JR wrote about this problem in his VHF column in the old Ham Radio (can anybody supply a reference or a reprint?).

As anecdotal evidence, I don't recall any truly successful 432MHz EME station that is using nested stacking with 2m.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.demon.co.uk/g3sek


-----Original Message-----
From: Jeff Bishop [mailto:jbishop@2online.com]
Sent: Thursday, March 05, 1998 12:01 PM
To: Roger Rehr
Subject: Re: Nesting of multiband stacked yagis

Roger,  I have used interlaced antennas for all of the bands that you are looking at for 10 years or so. I started out in the early 80's with four home made 8 element crossed polarized antennas for 2 meters. I used these mainly on the Oscar satellites but also worked EME with them. I replaced them with four KLM 17LBXs mounted on a 12 foot by 13 foot H frome at 55 feet on 25G tower. After a year with those antennas I mounted 4 x 31 element KLM 432 yagis inside the four 2 meter yagis.  Later I added two 44 element KLM 23 cm yagis stacked vertically inside the 432 H frame. Then I added the 2x3 foot 2400 MHZ dish on the other horizontal member inside of the 432 H frame. They all worked well. I used them for satellite work, tropo and EME. The only problem I noticed was that the 2 meter array didn't hear as well as it did when it was up there by it's self. The sidelobes were definately bigger resulting in a decrease in the received signal to noise ratio. The gain remained the same, as many stations told me that my EME signals were still excellent. But I did have a harder time hearing the weaker stations. The 432
array played very well. I did not notice any ill effects when I mounted the other antennas inside them but I am sure that there must have been some pattern distortion as there was with the 2 meter array. What I found though was that if you do not have the space for separate towers for these arrays that you can interlace them and make lots of contacts. It is not the best solution but it does work.  On the circular vs linear question. For the satellites, after I took my home made circular antennas down and went to the
linear antennas I felt that it was nice to have the circular array in that the fading is much lower with them. But the gain of the much longer linear antennas more than made up for it. The satellites signal faded up and down 10 or 15 db as it tumbled, but because the signals were so far above the noise, it did not seem to matter much. By the way, my 432 array worked so well that I had to turn my transmitt power all the way down to 1 watt to not overload the Oscar 13 mode B transponder. Of course the more gain your array has the more accurate your antenna pointing has to be.
Good luck with your project and I would love to be included in hearing the results of your questions on this matter. 73 - Jeff Bishop W7ID

-----Original Message-----
From: Alastair Beaton [mailto:beaton@wintermute.co.uk]
Sent: Tuesday, March 03, 1998 7:45 PM
To: Roger Rehr
Subject: Re: [TowerTalk] Nesting of multiband stacked yagis


Hi Roger,

You're obviously right in your assumption that a "box within a box within a box" would degrade the performance of each array. By just how much would be difficult to gauge without some fairly sophisticated modelling.

Lots of people do it, though. There's a picture of AA0L's two-band boxed array in the ARRL Operating Manual (4th Ed, p12-8), and OH5IYs 4x17(2m) and 8x15 (70cm) on p 12-17. If memory serves, one of the top JA EME'ers has something like this too. It would appear, therefor, that it's not a catastrophic problem:-)

I've used a pair of stacked 70cm Yagis in between a pair of stacked 2m Yagis with a 23cm loop Yagi for MS/Tropo work. During times when one pair or the other was missing for contests or repair I didn't notice any improvement. EMEs a different ball game, though, where every .1dB matters.

I was deeply impressed with the M2 OR-2800 rotator. It's head and shoulders above any Telex or Yaesu device. It's effectively a prop pitch device with its worm drive and torque plates. I haven't seen their EL rotor close to, but from the published specification it appeared equally well engineered.

I'd be very interested to hear what others have to say on the subject. Please post a summary on TowerTalk or fwd to me.

73
Al, GM4BAP


-----Original Message-----
From: Lionel Edwards
Sent: Wednesday, March 04, 1998 2:46 AM
To: Roger Rehr
Subject: Re: Nesting of multiband stacked yagis


Roger:

The optimum stacking for 4 x M^2 12 el is E Plane = 11.41' H Plane = 10.53' You can go to 90% of these spacing with a minimum of degredation.

You will be subject to interaction between antennas if you nest them inside.
Remember anything inside (or out) the 2 meter array stacked as above will be within the pattern of the array. While it will work, be prepared to give up performance on ALL bands. The 2 x 3 slotted dish will be an equal problem.

I cannot give you the specific dimensions for the other antennas as I do not have the 432 or 1296 antennas in my computer files.

However, optimum stacking is based on the following formula. Do not be swayed into believing narrower stacking is correct.

DL6WU STACKING FORMULA:

   Dopt =   WAVELENGTH / 2 SIN (beamwidth/2)

   GOOD RESULTS CAN BE OBTAINED DOWN TO 90 PERCENT OF THE ABOVE FORMULA IF A SMALLER STACKING FRAME IS DESIRED.CLOSER STACKING THAN 90 PERCENT OF DL6WU'S  FORMULA WILL RESULT IN A DEGRADATION OF G/T.


From:   owner-vhf@w6yx.stanford.edu on behalf of RWHam [RWHam@aol.com]
Sent:   Tuesday, March 03, 1998 11:21 PM
To:     ns4w@qsl.net
Cc:     vhf@w6yx.stanford.edu
Subject:        Re: [TowerTalk] Nesting of multiband stacked yagis

I have run numerous NEC simulation with quad and six stacks of 35 el 23cm inside and above quad stacks of 25el 70cm yagis. I saw very little interaction on gain and only small pattern degradation when the arrays were not symmetrically placed. When the 23cm array is placed above the 70cm stack, the
results showed almost no degradation in gain and only slight elevation plane pattern degradation. The setup I decided upon has the 6X35el 23cm stack above the 4X25el 70cm quad. I have noticed no degradation in operation.

Robert
K4MRW

From:   RWHam [RWHam@aol.com]
Sent:   Tuesday, March 03, 1998 11:14 PM
To:     rrehr@epix.net
Subject:        Re: Nesting of multiband stacked yagis

The 23cm array (if not symmetrically stacked) within the 70cm array may experience some pattern (and gain) degradation (there are those that would say that even a symmetrically placed 23cm array inside a 70cm array is no good).

I have found very little interaction for the 23cm inside the 70cm. The same comment on the 70cm inside the 2m. If you were using a nonharmonically related array, there would be no problems at all. Keep the arrays apart if you want no pattern interaction, otherwise you may have slightly higher sidelobes and
slightly lower gain.

Robert
K4MRW

Bert
From:   owner-towertalk@contesting.com on behalf of Bert [ns4w@qsl.net]
Sent:   Tuesday, March 03, 1998 7:13 PM
To:     Roger Rehr; mgef@brownell.com; vhf@w6yx.stanford.edu;
towertalk@contesting.com; MOON-NET@VM.STLAWU.EDU
Subject:        Re: [TowerTalk] Nesting of multiband stacked yagis

I am currently installing Six m2 432-9wl, and 4 - K5GW-10 yagis (quite similar to m2 12 ele.  I was originally going to do exactly as you proposed, (with 4 432 instead of six).  After *lengthy* conversations with Mike Stahl & Gerald Williamson, both gentlemen thoroughly convinced me not to stack box style.

1.      432 pattern on the 9wls will be destroyed.

2.      144 array will be degraded.

3.      432 beam width too tight for terestrial (sat too ?) vs vertical stacking.

They convinced me to stack vertical on both bands (ie - 4 high) one band on each side of frame(Yes - 30 to 32' riser). Put 144 on side one, & 432 on side two with 1296 above or below 432.

Mine are set about 10 feet horizontal separation.  remember, you need ~ 16 feet to clear roof line. Install lower antennas , raise tower, rotate 180, lower tower, install upper (now lower) antennas.   Pull frame over to tower to work on antennas, then pull over to other side to repeat with other side antennas.  You use your gin pole to put leverage on the far end, then the horizontal boom will slide from
side to side.

Bert - NS4W

Polarization Switching (re:satellites):

----------
From:   K6myc@aol.com[SMTP:K6myc@aol.com]
Sent:   Tuesday, September 09, 1997 1:00 AM
To:     rrehr@epix.net
Subject:        Re: Polarization Switching

In a message dated 97-09-06 18:04:11 EDT, you write:

<< I am WA3JYM and have been using on of your 435CP30's for satellite work
 for 6 months now.  I like the antenna but have the following comments

 1.     I have done polarization switching experiments with several stations
        that use the KLM with switching (I realize you are the "M" in KLM)
        when they switch polarization during the fades there has been a
        consistent improvement with
        both the Fuji Oscars and AO-10; from
        unreadable to S6-9 and back again!   I NEVER SAW MORE THAN ABOUT 6 DB
IMPROVMENT  AND THE BIG THIS WAS THAT IT NEVER PREVENTED A CONTACT.  I HAVE ANOTHER WHOLE MENTALITY WHICH I WILL DISCUSS IN A MOMENT.

 2.     I am convinced enough so that when I place new antennas, which
        I will do as soon as I get clearance for my new antenna structure,
        I will not consider anything that can't be switched from R to L polarization
        and back, remotely.

 3.     Thus,
        a).     Can I use one of the other manufacturer's switches on M2 antennas
 NOT EASILY NOR WOULD I RECOMMEND THEM SINCE THEY ARE UNRELIABLE AND LOSSY.
        or, preferably,

        b).     Will you come out with (1) add on switching for existing antennas and
                /or a new line with polarization switching?  WE HAVE DEVELOPED A VERY
NICE DIODE SWITCHED SYSTEM BUT I THINK IT IS ALL A BIG WASTE OF TIME AND MONEY.
 HERE ARE MY THOUGHTS.  IF YOU WERE TO TAKE APART THE CP ANTENNAS AND PUT THEM BOTH IN THE SAME POLARITY, YOUR NET GAIN/LOSS TO A CP SIGNAL COMING IN WOULD BE 0.  NO SWITCHING IS REQUIRED AND YOU ARE ALWAYS GOING TO HEAR THE BIRD REGARDLESS WHETHER IT IS RH OR LH.  NO LOSSY, UNRELIABLE SWITCHES, OR EXTRA COST.  SECOND AND HERE IS THE BIGGY, YOUR TERRESTRIAL SIGNAL WILL BE IMPROVED BY 6 DB OVER THE CP ANTENNA!  YOU MAY HAVE NOTED THAT MANY IN EUROPE AND OTHER PLACES HAVE FIGURED THIS OUT.  A SMALL SYSTEM USING A PAIR OF 2M9'S ON ONE SIDE AND A PAIR OF 440-18'S OR PREFERABLE A PAIR OF OUR NEW 440ATV21'S WOULD BE OVERALL A FAR SUPERIOR SYSTEM TO A PAIR OF CP YAGIS AND YOU DON'T NEED ANY FIBERGLASS CROSSBOOM, AND YOU DOND HAVE TO BRING THE FEEDLINES OFF
THE REAR OF THE ANTENNAS!  CAN YOU SEE ALL THE ADVANTAGES? 

 UNFORTUNATELY CP HAS BEEN HAMMERED INTO OUR HEADS FOR SO LONG WE ( AS  A GROUP) TOOK IT FOR GRANTED.  IN THE EARLY DAYS, THE SATELLITES WERE LINEAR OR POOR CP AND IT MAY HAVE MADE MORE SENSE BUT NOT ANY MORE.  THINK ABOUT IT AND FEEL FREE TO CALL AND DISCUSS IT FURTHER OR LET ME GIVE YOU OTHER ANTENNA CHOICES WHICH MAY EVEN ALLOW SOME OSCAR -0- CONTACTS!

 4.     What about antennas for those of us optimists wanting to get 1.2G and
2.4G
        ready for Phase 3 D now, as well as for what will eventually follow?  MY
THOUGHTS ARE THE SAME HERE, GO LINEAR WITH TWO EACH ANTENNAS AND ENJOY TERRESTRIAL ALOT MOR IN THE PROCESS.   BY THE WAY LAST I HEARD FROM BILL TYNAN, THEY DIDN'T KNOW WHEN THEY MIGHT GET A RIDE AND ON WHAT.  LETS ALL KEEP OUR FINGERS CROSSED.

73, MIKE


(Note: I'm not showing any E-Mail address here in order to avoid them from being collected by SpamBots. You can possibly find the E-Mail addresses of the above OM at QRZ.COM.)

This discussion is still not closed. If you have any opinions or additional related information you would like to be published here, just send me an E-Mail

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