Hi all, I am currently building a new 2 meter beam for SSB. I am using the DL6WU design on a 6 meter boom. While working on the antenna last night a thought struck me "why not interlace a 70 cm beam on the same boom"?
so here is the question, does any one have any data on interaced beams in particular the degredation of performance of the equivelent monoband yagis.
There are a number of reasons that this interlaced beam idea is appealing to me (mostly mechanical) but I am not sure how badly the gain may be effected. Does anyone have real data on the issue?
many thanks
Mike
VK3XL

"VK3XL" wrote in message
...

Hi all, I am currently building a new 2 meter beam for SSB. I am using
the DL6WU design on a 6 meter boom. While working on the antenna last
night a thought struck me "why not interlace a 70 cm beam on the same
boom"?
so here is the question, does any one have any data on interaced beams
in particular the degredation of performance of the equivelent monoband
yagis.
There are a number of reasons that this interlaced beam idea is
appealing to me (mostly mechanical) but I am not sure how badly the
gain may be effected. Does anyone have real data on the issue?
many thanks
Mike
VK3XL

Some help: I saw one for sale at HRO a few years ago. Might have been this
one:

http://www.eham.net/reviews/detail/3297

Note also that many VHF TV antennas are this way; the low-band elements for
55 - 88 MHz share the boom with the high band elements for 172 - 216 MHz.

These two bands are approximately in a 1 : 3 ratio, as are 2M & 70cm.

Thanks for the reply. All very interesting, but I am thinking of something a bit bigger ie 12 elements on 2 meters on a 6 meter long boom and up to 27 elements on 70 cm on the same boom. I fear that because 70 cm is almost exactly the 3 rd harmonic of 2 that the 2meter elements will act as unwanted directors in the 70 cm beam, any thoughts welcome.....
Mike
VK3XL

"VK3XL" wrote:
Thanks for the reply. All very interesting, but I am thinking of
something a bit bigger ie 12 elements on 2 meters on a 6 meter long
boom and up to 27 elements on 70 cm on the same boom. I fear that
because 70 cm is almost exactly the 3 rd harmonic of 2 that the 2meter
elements will act as unwanted directors in the 70 cm beam, any thoughts
welcome.....

One method of solving that problem is to orient the 2m elements
at right angles to the 70cm elements. Of course, if you don't
rotate the antenna by 90 degrees between bands, you would
lose 3 dB on both bands (assuming you want horizontal
polarization on both bands).
--
73, Cecil http://www.qsl.net/w5dxp

I think that you'll not really know what happens unless you model the
whole thing.

You might be able to tweak the whole thing for best performance in
software then. There are likely too many things you'd have to change
to do a manual optimization with the number of elements you're talking
about, but at least you'll know what the pattern is.

I did this for a 2m/432 combo where I hung the 432 4 element off the
nose of the 2m 5 element, but, admittedly, this was a MUCH easier
situation, as the 432 beam by itself had 20dB F/B. The pattern was
changed by proximity to the 2m antenna, but it was an improvement.

I adjusted the spacing of the 432 beam for the best F/B and the 2m beam
ignored the 432 entirely.

73,
Dan
N3OX
www.n3ox.net

VK3XL wrote:

Hi all, I am currently building a new 2 meter beam for SSB. I am using
the DL6WU design on a 6 meter boom. While working on the antenna last
night a thought struck me "why not interlace a 70 cm beam on the same
boom"?
so here is the question, does any one have any data on interaced beams
in particular the degredation of performance of the equivelent monoband
yagis.
There are a number of reasons that this interlaced beam idea is
appealing to me (mostly mechanical) but I am not sure how badly the
gain may be effected. Does anyone have real data on the issue?
many thanks
Mike
VK3XL



First, I would suggest you skip the DL6WU design. While it is good, the
K1FO design has much better charactistics overall, better gain, better
noise temperature, better pattern, better bandwidth.

And the answer, from a long series of 2m/70cm band interlaced
optimizatations I did 15 years ago is, don't bother.

That being said, there is another way to do the dual band that does
work. If you'd like to know, drop me an email, and I'll sewe if the guy
who thought it up agrees to let me tell you. I did a bunch of modeling
for him on the idea last year, and it should work.

To tantalize, it let you put 6, 2 and 432 on one boom. And they all
work well with good bandwidth and pattern.

Any NLRS members reading (there's at least one) who were at Aurora 2005
know who came up with this neat idea.

tom
K0TAR

Thanks for the replies, as yet I hav'nt done any antenna modeling, but that sounds like a good project for these cold winter nights. Any suggestions on what software to use?
Thanks
Mike
VK3XL

Tom thanks for the offer, if it is ok with the originator, can you send me the details of the multi band vhf/uhf antenna.
sent it to vk3xl(at)yahoo.com
thanks
Mike