Stacking antennas, placing a 70cm Yagi between a 2M stack or not?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by VA6DX, May 9, 2019.

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  1. VA6DX

    VA6DX Ham Member QRZ Page

    Getting ready to mount some antennas on a 120' tower (near the shack) so have some questions about my 2M5WL stack. All antennas will be horizontally polarized.

    Putting a large 11el 6M yagi (with a 50' boom) on the lowest position on the mast (just a few inches above the tower top). Then was going to mount one of the 2M yagis 5 feet above the 6M yagi. The optimum stacking distance between the two 2M5WL yagis is 10' according to the specs. I had also wanted to put a 70cm long boom up there too. So if I wanted to keep the 2 meter stack pattern clean, I probably should not mount anything between the two 2M yagis and then mount the 70cm yagi about 5 feet above the top 2M yagi. But the mast is starting to get pretty long at this point. It's getting to be about 21 to 22 feet above the tower. Getting a bit long even though most of that is a steel pipe.

    Wondering if I should just be mounting the 70cm yagi between the two 2M yagis so 5' between each yagi all the way up. Even if I attempted to keep the pattern clean on the 2M stack by not mounting anything between them, I doubt my pattern is all that clean with a 50 foot yagi just 5' below the stack and another 70cm yagi 5' above the stack. So is it really worth the extra mast length by not putting anything between the two stacked yagis? I have no problem with the extra mast if its much better, but do you think it's really worth it or will my pattern be distorted enough as it is with the other yagis on the tower that mounting the 70cm between the two won't make a big difference anyway. Any thoughts?

    It would have been better to increase the distance between the 6M yagi and 2M stack and also the same with increasing the distance from the 70cm yagi but the mast would be crazy long and would really bounce around lots in the wind increasing the chance of some kind of failure. Or better yet putting only the 2M stack up there by it's self, but it's hard not to take advantage of a 120' tower near the shack for the other bands.
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If you're discussing the M2 2M5WL, recommended stacking distance is 14 feet as far as I know, and the data on their website indicates same.

    If you separate the two by 14' then you'd have 7' between the 70cm beam and each of the 2m beams and that should work very well. I stack higher frequency yagis "inside" lower frequency stacked yagis all the time and have done so for 35 years. Attached is an old photo (it really is old! - from 1987 and was a print from film that I scanned to make a .pdf) of what I had up for 135-70-33-23cm all on one mast at that time, with higher frequency stacks inside lower frequency stacks and all performed admirably with great, tight patterns and nearly perfect Z matching created.

    Attached to that is another photo of my (at the same time) 20L stacked system for 50 MHz (4 x 5L) on a separate tower.
     

    Attached Files:

  3. VA6DX

    VA6DX Ham Member QRZ Page

    Yes you're right, 14', not 10. Was thinking of a different antenna with the 10' distance. Very good, TNX for the reply.
     
  4. VA6DX

    VA6DX Ham Member QRZ Page

    With the extra distances, I may have to rethink this. Mast it getting way too long if I want the 2M5WL stack.
     
  5. WA7F

    WA7F Premium Subscriber QRZ Page

    DXE has mast loading calculator that you may find useful. Not sure if it’s Ok to post links to vendor sites so I won’t. It should be easy to find.
     
  6. ZL1TKL

    ZL1TKL Ham Member QRZ Page

    well heres a kiwi way of doing it , stand all antennas on their reflectors pointing into the air at the distance you reckon is best for you then check the swr of each and a receiver on the rest , this gives you any rf injection to any other antenna if you get some thing move it to suit if you dont get a swr alteration or a rf desensing its in the rite place and so on you will be surprised how easy it is then mount them on the tower job done
     

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