Antenna Interactions

[VK3QI]

Tim,

Ham Radio Magazine was an American based publication that ran for many years from the late 1960's to 1990 and was published principally as an alternative technical magazine to what was available with QST, 73, CQ magazines and a variety of other smaller publications.

In its time, it was seen as a somewhat superior technical publication, as it was able to devote all the space to technical articles rather than the other magazines, which had to cater for more "social" aspects as well.

Some of the famous names in Ham Radio (and in professional circles) contributed articles, such as Joe Reisert W1JR, Ted Rappaport N9NB, Ulrich Rohde DJ2LR, Bill Orr W6SAI, Bob Locher W9KNI, Brian Beezley K6STI of Yagi Optimiser fame, etc..

W1JR ran a VHF/UHF column in the magazine for some time in the 1980's and his two part article on stacking yagis in April and May 1985, is considered by many to be the best "graphical" summary of what goes on with stacking, prior to the general availability of computer programs such as EZNEC and YO as powerful personal computers became generally available.

In the May 1985 edition, Steve Powlishen K1FO (well known in EME circles) with the collaboration of WA1RWU and K1WHS (from Cushcraft Antennas) wrote an extensive article on his experiments with stacked yagi arrays for EME, using an adjustable H frame, allowing him to vary the vertical and horizontal spacing within the array.

The key finding there was that narrower spacing actually contributed to a better S/N ratio on receive, with minimal loss of transmission gain.

++++++++++++++++

As has happened in most publishing circles, the magazine fell on hard times and was subsumed into 73 mgazine around 1990.

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I have seen reference to the whole of the magazine series being available as an archive, but have not tested it.

see: http://archive.org/details/ham-radio-magazine

Copies of the particular articles I was referring to, I have snail-mailed to Leigh for his perusal.


It might be worth trying out the archive site, or perhaps ask around at the next Ham Flea market - usually the magazines go for next to nothing!

Cheers

Peter VK3QI

[VK3QI]

Yes,

I agree - an excellent article on stacking of different frequency antennas on the same mast and some information on aperture requirements for multiple single frequency arrays.

And if you note the author at the bottom of the page - it is none other than Dave K1WHS (of Cushcraft fame), who contributed to the K1FO article of HR May 1985 and already mentioned!

Cheers

Peter VK3QI

[VK2XAX]

Hi all,

Thanks to Peter for pointing me in the right direction.

I found the article in question can be downloaded from here....

http://www.qsl.net/tri-atv/HR_05_1985.pdf

regards

Tim

[VK3QI]

Excellent Tim

Presumably the W1JR articles in the April 1985 (pages 129-135) and May 1985 (pages 95-1040 editions are also available .

Cheers

Peter VK3QI

[VK3QI]

Tim,

Jim W6PQL (of 1.2 and 2.4 Ghz amplifier fame - many Aussies have used his boards etc. ) did an excellent slide show presentation on stacking of yagis a few years back and it is available from his website.

www.w6pql.com/misc/pnwvhf/Stacking%20Antennas.ppsx

Jim summarises the work done by W1JR, DL6WU and VK2ZAB and presents two EXCELLENT graphical slides.

slides 22 and 24 where he compares the patterns at Dopt and 0.9 Dopt - this is essentially the question that Leigh has been asking - comparing the stacking distances at the recommended and optimum gain distances. For reception this can be quite critical.

Well worth the look.

Cheers

Peter VK3QI

[VK2KRR]

Peter

I am unable to open that file. It opens a zip folder and Ive extracted that but cant view any of the files, perhaps I dont have the correct program ? Did it work for anyone else ?

[VK2GOM]

Leigh, it's a MS Powerpoint file with XML extensions.

You can get a viewer for it here:

http://www.fileinfo.com/extension/ppsx

73 - Rob VK2GOM / G0MOH

[VK3QI]

Leigh, Rob's link should help if you don't have Microsoft Powerpoint installe on your machine.
Cheers Peter VK3QI

[VK2KRR]

I have Powerpoint program, but it doesn't like the files.

Peter, I wasn't aware of the Cushcraft history and didn't know they had been around for so long, so its been interesting hearing about all this information.

[VK2GOM]

Leigh, sound like you have an old Powerpoint, before the XML extensions came along.

73 - Rob VK2GOM / G0MOH

[VK3QI]

Leigh,

Cushcraft has been around since the mid 1950's.

They were probably the leaders in amateur VHF/UHF antenna stacks from the mid 1960's onwards. Certainly on the USA east coast.

I remember my first 2mx beam was a A144-11 in 1968!

Cheers

Peter VK3QI

[VK3AUU]

Leigh, I did an EZNEC model of your proposed array with similar yagis to those you have, with the actual spacings you had in your diagram. It turned ot that there was virtually no reduction in the gain of the 70 cm array, but there was substantial loss of gain for the 2 metre array.

By itself, the 2M array spacing is slightly too wide in the sense that the first side lobes are only about 11 db down, but the gain is good at around 20.2 dbd. This dropped to only 16.5 dbd with the addition of the 70 cm elements. Not a good result.

I still have the file, so I will perhaps have a look at the effect of reducing the size of the 70 cm array, but for the moment I would suggest that separate installations are needed.

David

[VK3QI]

David,

That is pretty much what W1JR and K1FO were saying back in 1985.

At first glance it is anti-intuitive that the lower frequency array would be affected more than the higher frequency, until you think about capture areas and the fact that the aperture area of the 70cm antenna is less than the dimensions of the 2 mx array, whereas the 70cm array is smack bang in the middle of the capture area of the 2mx array!

As Leigh has intimated, when he used the smaller (recommended) spacings on his 2mx array, his reception (i.e. his S/N ratio front on) was better than with the wider spacing, due to the lower 1st secondary lobe.

It's good to see that EZNEC hits the mark!

Cheers

Peter VK3QI

[VK2KRR]

Thanks for your efforts David/Peter,

I will run both the arrays seperately. Am quite happy to use the smaller spacing as mentioned, as its much easier to work with

[VK2KRR]

Peter, the info you sent arrived today thanks again, will have a read.